Category Archives: Caravan Fault Finding

Vehicle Wiring Projects… Some Thoughts.

01 Wednesday Jan 2020

Posted by in Accessories, Campervan Wiring, Caravan Electrical Fault Finding, Caravan Electrics, Caravan Fault Finding, Maintenance, Modifications, Motor Home, Projects, Technical, Tips, Vehicle Wiring Projects

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My email box tends to get a wide variety of questions covering all sorts of subjects. The most frequent one is to do with wiring and electrically related problems. Sometimes trying to diagnose issues via email and a few photos is a bit of a challenge, but hey who doesn’t like a challenge! One thing that I do see a lot of is electrical work that is…. well, quite frankly not up to scratch in my opinion. So here is my attempt at a basic guide.

(c) Image from http://gus-stories.org/march_1942.htm

You have to have a plan.

So many projects start by adding one or two things… extra 12 volt outlet here… maybe another light and then something else comes along that needs adding in. Before you know it you have a mess of spaghetti that the local Italian restaurant would be ashamed of. It is all too easy to fall into the trap of adding circuits to existing fuses…. or installing a new fuse and a few weeks later adding another circuit to it as it’s easier than installing another fuse.

Wiring diagram for basic overland vehicle or camper van.
Start with a plan…

You can download these and other drawings from the Electrical Drawings page in the drop down menu under “Document Library”

You need to draw out how the major elements are going to connect together – leisure batteries, solar charger, DC to DC charger, inverter and include all the big fuses, buss bars and fuse box. Don’t think about where any of this goes for the moment just get the basic layout and how everything interconnects worked out. It might take a few goes but paper is usually cheaper and less frustrating than sorting out the mess afterwards.

Once you have all that figured out you can start working on the details… just how many fuses will be needed… and what ever number you come up with add half as many again as a minimum. Having a few spare fuse positions that maybe never used is way cheaper than in twelve months time having to install an additional fuse box. A this point you can start adding details…. what size cable is needed for each link, what sort of fuse box do you need.

You can also now start to think about specific facilities you might need. For example, many overlander vehicles will have a button on the dash that when pressed and held down activates a high current relay that links the house batteries to the engine cranking battery. Very handy to have… jump leads are not much use if you are 200Km from the nearest vehicle. If your only trip ‘off road’ however is the muddy car park at the local car boot sale than maybe not a priority.

Don’t use the vehicle chassis as a ground.

Modern vehicles are constructed using different materials and quite often panels and sub frames are glued together. Back when virtually all the panels were spot or seam welded steel, using the body and chassis as a ‘ground’…. which really isn’t a ground but the neutral return path… this was acceptable. However now, sections can be glued together and are often sub assemblies of aluminium and other light weight materials bonded together. Just because you see a neutral bonding point (earth terminal) don’t assume this is is capable of being a suitable point to bond the neutral side of a circuit or accessory you are installing. Modern vehicles often have small bonding straps between sections that can carry the current that the vehicle manufacturer rated the bonding point for. Adding additional equipment and accessories might exceed the original design spec.

I did see a spectacular failure due to a 3000W inverter having it’s neutral lead ‘grounded’ in the rear of a vehicle. Running at about 2000W the neutral side was trying to ‘return’ a current of about 170 amps through the body of the vehicle, which lead to serious damage to some of the vehicles wiring and a number of vehicle components… and a ‘repair’ bill of nearly £1500. Putting a riv-nut in a body panel that is mastic bonded to the body is not a suitable negative bonding point!

Additionally a number of vehicle circuits are now negative switching or operation and installing additional equipment or accessories could have unforeseen issues. Always from any accessory or piece of equipment you install, add the neutral return path back to a suitable single common point or buss bar you install for the purpose and connect this directly back to the leisure battery.

Ideally all the ancillary leisure circuits should never rely on any of the vehicle wiring and the negative side of the leisure wiring should only ever connect to the negative side of the leisure battery.

Don’t use battery terminals as a junction post.

Both the leisure battery and engine battery should only have connections that lead to either in the case of the positive terminal a master fuse /circuit breaker and isolator switch. The negative terminal should only have the connection to a master negative terminal point or buss bar.

Nope…..Not OK…. it’s a terminal not a junction post
(image from the Internet)

If you want to install any sort of battery monitoring, it is convention to install the shunt on the negative return to the battery between the negative buss bar and the negative battery terminal. If you have multiple circuits terminated on the battery terminal it makes future changes and upgrades, including installing a battery monitor very difficult.

Just NO!
(image from the Internet)

Using the battery terminals as connection points for multiple services also makes fault finding very difficult. Each circuit may or may not have it’s own fuse and it’s difficult to isolate circuits….. plus I’ve had enough sparks flying round when trying to disconnect a battery because someone did not install an isolator to know that it’s only a matter of time before one goes ‘pop’.

Just because it’s shiny…. NO!!! Not OK
(image from the Internet)

Please, just don’t do it.

Have a think on this. If you had to go to an auto electrician to get a fault traced and corrected, they would immediately put at least an hours time on the invoice just to figure out what was going on with all the cables on the battery. Also, If you don’t have a battery master isolator installed, get one installed now. It’s a safety item that must not be missed out. Having the ability to quickly turn off all the leisure circuits in an emergency might just save you from the unthinkable happening.

Cable Termination

Every cable should be terminated. Period. There shouldn’t be any cables in an installation that don’t have a crimped (or soldered) termination. Even if it’s a screw terminal such as those found in joining blocks or 13 pin plugs.

If you are embarking on a wiring project, its always best to start building up your stock of terminals. I usually buy selection boxes of terminals on line and supplement these with bags of single type connectors for the more commonly used ones. To keep everything organised tote organiser boxes are my preferred option.

A few of the 20+ of my storage boxes with wiring components

There is nothing more annoying than running out of the something and its always just as you want to finish a project off so you end up cutting corners.

For some of the larger cables, if you don’t feel up to making your own terminations there is usually a local auto electrician available that will terminate them for you for a small charge. However, a crimping tool that will terminate up to 50mm cable is not that expensive – around £27 and will probably work out cheaper in the long run. I’ve a link to the one I bought via Amazon and regularly use in the SHOP page.

Get the size right…

Selecting the right size or gauge of cable is critical. There are two factors that determine what gauge of cable to use for a installing any particular circuit. The maximum current that’s going to be drawn and the length of the cable. Once you have selected the right size cable then means you can select the right size fuse for the circuit. Never fuse a circuit greater than the current capacity of the cable.

Handy wall chart of cable size and terminal sizes.

You can download these and other drawings from the Electrical Drawings page in the drop down menu under “Document Library”

I generally tend to list what is going to be installed, then work out all the gauge for the cables for the circuits. From there it’s easy to see which is going to be the most popular gauge and rather than buy several different gauges of cable try to select a limited selection of gauges.

Always go for the safe option of over specifying the gauge of cable for any particular circuit. If it’s a 10 amp circuit and you have used cable suitable for a 16 amp circuit, it doesn’t mean however you need to use a fuse greater than the 10 Amp circuit requires.

Something else to consider too. Most 12 volt cables are copper, however if you are installing them in a less than ideal environment, such as a boat, you may want to opt for tinned copper cables. These are far less susceptible to cable corrosion. Even in the best marine installations I’ve seen copper cables corrode through in less than a couple of years.

Cardinal Sin! – Never ever use two smaller cables to make up the equivalent of one larger capacity cable. You would be surprised how many times I’ve seen this… sometimes done by “professional” tow-bar installers when reported poor leisure battery charing or poor fridge performance is reported and the voltage drop is too great.

Wiring Looms – wrapping it up properly!

Dressing cables into looms is not difficult nowadays. There are many options available on the market to help you produce a professional looking finished product. I personally like for looms within the vehicle using a felt finished looming tape. You don’t wrap it so it overlaps but at a sharp enough angle so as it spirals round the cable bunch it leaves some of the cables exposed.

Felt is good as not only does it keep the loom together, it allows quite a bit of flexibility and prevents cables from rubbing or banging on flat surfaces making a noise.

For any cables outside the vehicle body there are two options depending on use. In the main I’d go for split tube conduit. It’s available in various sizes and can be bought in either cut lengths or rolls. The other option is to use self amalgamating tape. It looks like ordinary PVC tape but as you wrap it round you stretch it and it releases a chemical which when overlapped onto its self becomes a permanent bond, effectively making a sealed tube. It is generally however fairly inflexible. Both have their place.

Anything in the engine bay or underneath the vehicle I use split tube and generally only resort to self amalgamating tape to seal inline joints.

Relays….. yes or no?

For me its Yes. I much prefer locating all the relays in one place therefore minimising the amount of heavy cable. By using relays to do the heavy switching you can use smaller and sometimes more attractive switches. I have in the past used 7 core trailer cable to connect 4 switches including LED indicators back to a relay bank rather than make up a custom wrapped loom.

Handy wall chart of relay types

You can download these and other drawings from the Electrical Drawings page in the drop down menu under “Document Library”

It also makes tracing faults easier, as it’s simple to test if a switch is working, you can hear or sometimes feel the relay operating as you operate the switch. Its unusual to have a fault with a relay but quite simple to test… just unplug and swop over with a known working relay. If all the relays are located together it makes this task and testing the feed to the relays so much simpler. From that point all you need to check are the two wires going out to the device and the device itself.

Obviously some circuits don’t require a relay or if it’s designed to be turned on for a long period… such as a diesel heater, then adding a relay will just increase current draw, albeit small, on the leisure battery. A bit of common sense can easily determine if you should opt for a relay or not.

Grommet?…(no not Wallace’s friend!)

Whenever a cable or cables pass through anything solid you should use a grommet. You would be surprised at the amount of damage I’ve seen to cables due to either not installing a grommet to an insufficiently sized (too small usually) grommet.

When ever I pass either a cable or loom through a bulkhead for example I like to supplement a grommet with a bit of heat shrink sleeving over the cable as well. Even passing a cable through an existing grommet from the engine compartment to the interior, adding a length of heat shrink sleeve won’t do any harm.

There’s a link to these in the SHOP… only about £7 for the full box.

Having a handy selection of grommets available before you start threading wires through is far better than trying to install protection afterwards. You’d also be surprised at how many cables I come across that have been damaged while pulling through holes in metal and wood panels. Always better to start with a grommet or two! Where a cable or loom passes through a grommet, it’s aways best practice to try and anchor the cable or loom either side of the grommet to something solid using “P” clips. This will reduce the chances of ‘fretting’ with the movement of the vehicle.

While we are on grommets…. a quick note about cable-ties (zip-ties). Stop doing them up so tight! I’ve come across cables cable-tied to a chassis rail so tight that the cable-tie has cut into the insulation and is fretting the conductor inside. Cable-ties are generally made out of a harder plastic than the cable insulation so will over time wear away at the insulation.

Get yourself a cable-tie tool that not only allows you to precisely control how much tension you put on the tie but also cut the end off so that there isn’t a wrist slashing booby trap lying in wait for some unsuspecting person. I use a fairly cheap pair (left). I think they were around £8. So not really expensive. But they make a nice neat job of installing multiple cable ties with the correct tension and the ends cut cleanly off level with the lock tab. You can buy ones that have a tension dial built in so you can set them to a pre-tension, but I find after a bit you know just how much to squeeze the handles to get the correct tension.

So what is the correct tension… well if you are doing them up so tight an elephant could dangle on the cables then that is too tight. They should be tight enough so as not to slip but you should be able to spin them round the cable(s).

Cable-ties really should not be used to make looms or anchor cables or looms to anything solid. If you want to make a loom, wrap it in specialist loom tape. If you want to anchor cable or a loom to something solid use a “P” clip. If required… use a length of heat shrink to make the loom a tighter fit in the ‘P’ clip.

I know you are dying to ask…. when do I use cable-ties? Well generally at the installation stage to get things to stay in place before installing P clips or if I have to run a new loom along the same path as an existing loom, I generally opt for cable-ties to hold them both together (as long as the original is suitably anchored to support both)

While we are talking abut cable-ties… I have seen the worst kind of mistakes in the use of them. It is not OK to cable-tie anything to brake lines, fuel lines, vacuum lines, hydraulic hoses, coolant hoses or steering components (yep one bright spark cable-tied his front LED light bar wires to some of the steering components!)

Heat Shrink Tubing

An absolute must have in my opinion. There are two main types – plain and pre glued. The plain are the main one you would use, while the pre glued are great if you have to over sleeve a connection to make it waterproof. As you heat up the pre-glued type, the glue softens as the tube strings and bonds to the cable as everything cools. They can be a little more rigid when installed, so make a service loop in the cable. The finished covering is usually waterproof enough for brief submersion if done correctly.

Having a selection of sizes and colours is handy and assortment boxes of multiple sizes and colours can be bought on line cheaply enough. In the workshop I use an old paint stripper heat gun on low power as I find that is more controllable than a flame.

Bridging the gap… something in the future?

Although not so common in the UK, in Australia and the USA wild camping (boon docking) is probably as popular as campsites. To this end trailers and caravans usually have much larger battery capacities than anything found in Europe. It’s not uncommon to find outfits with 600 to 800Ah battery banks recharged mainly be solar, buy increasingly (especially in Australia) an additional bridge between tow vehicle and trailer is made using heavy duty “Anderson” connectors and cables capable of supplying upwards of 60 Amps from the vehicle to the leisure battery bank.

With the cost of lithium batteries reducing almost daily, I can foresee very soon that light weight lithium batteries will be installed in caravans. The down side of this currently and trying to retrofit Lithium is the existing charging setup of current European vans is not really suitable for looking after these type of batteries. We have a Sterling Power Wildside unit installed in our caravan which allows us to charge any type of battery chemistry, including lithium when connected to the tow vehicle. The draw back is the caravan’s inbuilt charger is only capable of wet lead acid or AGM. I think that a high capacity DC to DC charger installed in the vehicle and an additional cable to supply the caravans battery banks may not be too far away. It’s something you might want to keep in mind for the future. It’s something I’m looking into currently.

Well, that’s a bit longer than I anticipated and there is still a few things to cover. If you made it this far…. take a toffee out of the jar… well done! If you think I missed something or would like me to cover something specific, drop me a comment below.

Something For Your Toolbox…

03 Wednesday Apr 2019

Posted by in Caravan Electrical Fault Finding, Caravan Electrics, Caravan Fault Finding, Electrical, Maintenance, Technical

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A few weeks ago I posted a blog post called “A Quick Fault Finding Tip…” and that  generated quite a few emails regarding electrical testing and how to trace faults.  In fact a lot of the other electrical posts I’ve done over the years still generate emails and comments (it’s always worth checkingback on some of th eolder posts to read the comments) I’m going to try to explain a technique that’s really handy to have in your tool box for general fault-finding.

Earth Side Testing

Most people who perform general maintenance on their vehicle, motor home or caravan will be familiar with checking the voltage of the vehicle or leisure battery using a multimeter. Great little things to have and personally I think everyone should be able to do the basics with one.  So as a bit of a refresher I’ll go through this scenario with you. Checking the lights on your tow vehicle you notice one of the brake lights is a lot dimmer than the other. Let’s find out why. I’m going to simplify the circuit a bit it should give you the idea behind the principle.

Depending on the device you re reading this on the drawings might be small. If you want to see the drawing full size just click on it to open it up full size.

Earth Side Testing 1-0

In the drawing above you can see the basic circuit. The positive lead from the battery goes through the ignition switch and on to a fuse. From there through a connector to the brake pedal switch and on to another wiring loom connector to the back of the vehicle. It passes through another connector before arriving at the brake bulb holder. The holder is connected to the vehicle chassis via another wiring loom connector. The vehicle chassis is connected back to the battery in the engine bay. You can see we’ve checked the battery voltage with out meter and it reads 12.68 volts… so not a flat battery. We’ll make a note of the battery voltage.

OK… so the problem is this bulb  is not at full brightness.. so it’s got to be a loss of voltage supplying it somewhere in the circuit. We need to check the voltage along the circuit with the bulb lit (circuit live) and the black negative lead of our multimeter attached the battery negative terminal. (I’ll explain how to do this later).

Earth Side Testing 1-1

Probably the next place to check it would be the fuse… 12.66 volts, not too bad only 0.02 or 20 mV loss… lets keep going….

Earth Side Testing 1-2

..next is a wiring loom connector, back probing it gives a 10 Mv drop (loss) normally these modern connectors are pretty good.

Earth Side Testing 1-3

Brake light switch… Hmm a bit more of a drop… maybe a quick spritz with contact cleaner will sort that…

Earth Side Testing 1-4

Back probing the next connector gives a bit more of a loss… I’ll come back and check the brake light switch connector.

Earth Side Testing 1-5

OK, now at the back of the vehicle and a bit more of a drop at that connector but nothing too much…

Earth Side Testing 1-6

Well 12.13 volts on the bulb contact… so between the battery and bulb positive tip a total loss of 0.55 V or 550 mV…. that’s about within limits as I would not expect to see much more than a 500 mV… half a volt drop on a typical circuit like that. So what’s going on? A 500 mV drop can’t account for the dim bulb?

However, if we keep going and measure the voltage on the earth side of the bulb holder….

Earth Side Testing 1-7

Hang on we see a reading of 2.67 volts. How can that be? We are connected to ground at both ends of the meters test leads? A circuit has two sides, the positive side to the load – in this case the bulb and the return or negative side back to the battery.

Just because the negative wire on the bulb holder is only short and goes to a bolt securing it and maybe many others to the chassis doesn’t mean we can assume it is the same as being clamped to the negative battery terminal.

A few things to ponder…. vehicles are made of steel… steel is not as good conductor of electricity as copper… nether is aluminium that some vehicles have in their construction. At one time steel panels were all spot welded together… now a lot are bonded on with specialist adhesives. The earth point may well be in the boot or under the floor and will be subject to corrosion as will the main battery neutral cable in the engine bay. All this can compromise an electrical path back to the battery.

If we look at the voltage drop on both sides of the circuit we have 0.55 volts on the supply added to 2.67 volts on the neutral side…. 3.22 volts in total, so we are trying to light our bulb with only 9.46 volts.

Could we have got there quicker?

One of the checks I always do first with the ignition on is the battery voltage check to get a reference to work with and then simply move my red positive test lead over to some main point on the engine block….

Earth Side Testing 1-8

If I get a reading of more than 0.4 volts (400 mV) obviously my negative return path from the vehicle chassis is compromised. Time to turn everything off and undo the main earth cables to the chassis and engine and give them and the mounting points a good clean with scotch bright or fine emery and a dab of specialist grease (see “Shopping” below) to protect them from further corrosion.

In the scenario we have just gone through, I’ll bet a wet weekend in Blackpool that cleaning both the earth terminal at the back of the vehicle and the battery earth to the chassis would have sorted the problem. I’d also have a look at the brake pedal switch as there is a bit more of a voltage drop than I’d like. Most likely it’s the connector rather than the switch itself.

For those that tow…

Nearly all tow bar wiring looms will ground to the same point in the back of the vehicle with some of the other assorted vehicle earth cables…. installers take the easy route and if there are already cables earthed there … then another couple won’t make a difference.

This can and will have an effect on the performance of your caravan electrics. Both the leisure battery charging circuit and fridge circuit will probably be earthed at that point.. So in the case of the fault above, each of those circuits will have a voltage drop of 2.67 volts. Therefore if you have leisure battery charing or fridge issues its possibly not the wiring in the caravan,  it could be the wiring in the vehicle. Check the ground path first.

One quick check is with lights and ignition turned on, do a volt drop test between the battery negative terminal and one of the cable secured under the earth point at the rear of the vehicle where the tow pack electrics are terminated. If it’s above 0.5 V (500 mV) then give the earth points a clean.

One bit of advice I’ve given to people in the past is to run a 4mm or 6mm cable directly from the negative battery terminal to the back of the vehicle and terminate it at the earth point where all the rear lights and tow electrics terminate. Makes a heck of a difference.

Back Probing…

Frankie-Howerd

Right…. Franky Howard fans stop it now! Back Probing, you might have heard of it and really it’s nothing special. It’s a simple technique used when fault-finding and involves using a fine probe to get into the back of the connector where the cable enters to test the voltage without disconnecting the connector. Sometimes you can get away with a straightened paperclip wound round the tip of the multimeter test lead. You can buy test lead accessory packs that have various attachments or ‘caps’ that fit on the end of your test leads to make the task easier.

Screenshot 2019-04-03 at 11.11.25

How do I test between the battery and some other point on the vehicle or caravan?

I have made a few of these over the years… basically it’s a long length of wire, about 20 feet with a battery terminal sized crocodile clip at one end and a small crocodile clip at the other… and I don’t know how many I’ve given away to people. I have a couple, one long enough to get tot he back of the vehicle and one long enough to get to the back of the caravan when its hooked up to the vehicle. SImply clip one end to the battery negative terminal and the other to the negative lead on your multimeter. Often its an idea to tie a loose knot in the two leads to stop them coming apart. Caution though, this lead is connected to the ground side of the battery – don’t let it dangle where it might touch something… put a bit of tape for protection around the connection if required.

Shopping…

Multimeters…. a person can never have enough multimeters…. and since the demise of Maplin a couple of great places to keep an eye on is Aldi and Lidl. I got a couple of great general purpose multimeters from Aldi for £9 each. Not always available as they generally come up as special buy’s. However if you are an Amazon shopper then this https://amzn.to/2I91q91 seems like a great little multimeter with a lot of positive reviews for £12

I use Liqui Moli 3140 Battery Clamp Grease – https://amzn.to/2Vn0qSo for battery and chassis terminals. It’s a small tube but does last a while.

If you want to make your own long test lead this box of crocodile clips https://amzn.to/2VedU32 for about £4.50 is always handy.

A dream test tool…

If you are into testing or it’s part of your job then there has been something on the market for a while called “Power Probe” Now while the original is obscenely expensive and there are a number of copies out there. The Auto Power scan PS100 is priced at about £80 and does the job in one simple instrument – https://amzn.to/2OJHYAW (Any sponsors out there… hello….hello…) This is on my “I really want one of those” list!

Finally…

"Oscar" our senior safety cat.

As always when working on anything electrical think safety. Oscar our Health & Safety Cat would like to remind you that working on vehicle electrics can be just as dangerous as working on house electrics. If you are unsure then DON’T…. get in touch with someone who is qualified. Find the right person and they will usually help you to do it safely. Be like Oscar – Be Safe.

A Request…

09 Sunday Dec 2018

Posted by in Blog updates, Caravan Electrical Fault Finding, Caravan Electrics, Caravan Fault Finding, Caravan Servicing, Electrical, General, Help Guides, Maintenance, Motor Home, Technical

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Ok, not one of my usual blog posts. I get a lot of email asking about various electrical items related to caravans and motorhomes and a few things seem to keep cropping up on a regular basis. One is to do with 12 volt relays… what types are there and what are the pin connections.

Another is to do with cable size relating to load and its relation to the length of cable…. “I have a 40 Amp load and its 3 metres from the battery… what size cable do I need?” type questions.

In the past I’ve emailed back with answers, but one caravan engineer asked me if I know of any information sheets that had this type of info that he could put above his workbench.

So I’ve produced a couple of A3 size PDF information sheets (they will print A4) that can be downloaded printed out and pinned up, shoved in your notebook, glued to the lid of your tool box or used to wrap that must have tool present for your beloved caravan or motorhome DIY enthusiast in your life (seasonal eh!)

(I have been told that Office World can print and laminate A3 PDF’s cheaply…. I never knew that!)

Screenshot 2018-12-09 at 10.23.41

Click here to download the  Relay Wall Chart

Screenshot 2018-12-09 at 10.24.11

Click here to download the   Wire Size Wall Chart

Screenshot 2018-10-11 at 16.52.54

Click here to download the Fuse Voltage Drop Table

I have stylised them as technical drawings and I’ve had to watermark them and some of the icons as I found a lot of my drawings were ending up “as is” or edited on various sites and forums without any credit or link back to Caravan Chronicles. You are free to print out and use them for your own personal use, but if you wish to use them (or any of my drawings) for commercial use, inclusion in blog posts or forums please include a credit line back to CaravanChronicles.com and drop me a line to let me know.

We are just back from Chester Fairoaks after doing the Chester Christmas market and a bit of shopping at Cheshire Oaks Designer Outlet Village and will be adding off to York for a bit more Christmas Market action.

I have a couple of more information ‘posters’ in development but if you have any ideas for future offerings, drop a line in the comments below. Of course my legal advisor – Henry has asked me to point out E & OE

(Everything on the internet is improved by a cat apparently… so here’s Henry)

IMG_2176

A Quick Fault Finding Tip…

12 Friday Oct 2018

Posted by in Caravan Electrical Fault Finding, Caravan Electrics, Caravan Fault Finding, Caravan Servicing, Electrical, Technical, Tips

≈ 18 Comments

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Sometimes things you take for granted and have in your toolbox of fault-finding tricks are a dark art to others.

I was talking someone through a bit of fault-finding on their vehicle and asked if they had measured the current in the circuit. “No” came back the answer. I asked what type of fuse and rating it was and asked the person to just put their voltmeter across the fuse and tell me the voltage across the fuse. “Ah… that’s about 3.2 amps then” I said.

“How do you know that?”

Simple really – all fuses have a resistance and if you know that you can work out the current from the voltage drop. Even simpler really – there are tables for various fuses that have it all worked out for you. I have a selection collected over the years stuffed into the lid of my tool box, along with a lot of other junk paperwork!

I created a volt drop table based on PEC (Pacific Engineering Corporation) fuses that are supplied as OEM fuses in most Japanese, Korean and European vehicles however it is pretty accurate for almost all other makes of the same type of fuse. I printed mine out, laminated them and added them to the collection in the top of my toolbox.

Screenshot 2018-10-11 at 16.52.54

It’s quite easy to use. Just set your multimeter to read DC mV and read the voltage displayed. Now select the fuse type, in this case an ATO fuse – the most common used in vehicles, caravans and motorhomes and from the chart look down the left column until you see the voltage measurement that matches the one on your multimeter… lets say 0.011 volts (11mV)

The fuse is a red 10 Amp fuse so follow the 0.011 volt line across until you get to the 10 Amp fuse column and read the current figure… in this case 1.3547 or 1.3 Amps. It’s as easy as that, no need to break the circuit to put your multimeter in as an Ammeter.

fuse-buddy-specialty-meters-esi305m-64_1000
I have a couple of these cheap handy plug-in ammeter’s…  although they do have limitations and only work up to 20 Amps.

Although the table is based on PEC ATO/ATC and MINI fuses (download info below) it is pretty close with most manufacturers fuses and as a general reference for fault-finding will be good enough to 0.1 amp.

If you need to know the actual current through a circuit, you need to use an ammeter and not rely on tables but for general work they are close enough.

These tables also come in handy if you are trying to find out why a battery is draining. Without turning anything on it is easy to run through a fusebox checking to see if any circuits have a current drain on them without having to constantly pull fuses and insert an ammeter, which sometimes can upset or reset the circuit you are working on.

One thing to remember with this test if you’re tracing a fault, is you are only measuring the volt drop across the fuse to determine current. You really need to know how much current you should be drawing. For example, If I was testing the 12 volt fridge circuit fuse and I only got a voltage drop across the fuse that calculates to 6 Amps then I’d know there was an issue somewhere along the circuit as I’d be expecting around 10 Amps or more.

A word from our Safety Officer…

"Oscar" our senior safety cat.

Oscar would like to remind you that working on a live circuit has risks and never attempt to undertake volt drop measurements on mains circuits. Most cheap multimeters do not have the internal protection or fused test leads. Be safe. Be like Oscar.

You can down load the table in PDF format (4 pages) and either print them out or save them to your device from the following link: Fuse Voltage Drop Table

Unfortunately due to a lot of my drawings and text being used elsewhere without credit back to CaravanChronicles.com  I’ve had to start putting watermarks on a lot of things. I hope this doesn’t make the table too difficult to read.

P.S. Someone told me that everything on the internet can be improved by cats and my “likes” would go through the roof!

Getting All Charged Up – Part 3 “The Install”…

30 Tuesday May 2017

Posted by in Accessories, Boondocking, Caravan Electrical Fault Finding, Caravan Electrics, Caravan Fault Finding, Electrical, General, Modifications, Off Grid, Technical

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There has been a bit of a delay since Part 1 and Part 2 due to Sue having a fall and breaking her arm in three places. This required over three hours of surgery to install enough metalwork and screws to keep a blacksmith happy followed up by a lot of trips back and forth to the hospital. However, on with the install of the Sterling Power Wildside unit. I think that this will be the first ever install of a unit in a caravan.

I printed out copies of the wiring diagrams and loaded up the Amarok with everything  I’d need and set off for the storage site. Arriving at the caravan everything was cleared out to give me some space to work.

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I’d planned to install the unit somewhere close to the Sargent control box as all the connections I’d need could be found here and it was close to the fuse box that connected the lead from the 13 pin plug to the caravan services.

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The fuse connection point for the lead from the 13 pin plug is in our caravan, located right at the front next to the centre chest of draws against the gas locker wall.

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Before starting, I did a quick voltage check on the leisure battery…. 12.81 volts, which isn’t too shabby as we don’t have a solar panel and it had been February 25th when I left the Caravan show at the NEC and the battery was last charged up. Which was   about 13 weeks earlier.

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To gain access to the wiring going into the Sargent unit, I removed the 4 screws holding the top cover on and the lid simply lifted off revealing all the connections and as a bonus, service loops in the cable. This meant it should be possible to install the wild side unit without having to do any cable splicing. I did debate at this stage if it would be possible to install the Wildside unit inside the Sargent box… but I decided as I didn’t know the heat gain of the Wildside unit, it might be prudent not to attempt it.

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The cables inside the Sargent box are basically separated into two looms. One 12 volt and the other 230 volt which keeps things easy and neat. Also the back of the circuit board within the Sargent unit was printed with each of the plug numbers, so doing all the planning paid off as I could simply find the plug number from my diagram and locate the correct cable easily.

I decided I was going to do a pre-install and connect the Wildside unit up and do a few tests, then once I was happy I’d go ahead and do a full more permanent installation.

It was simply now a matter of finding the plug I needed, unplugging it, locating the correct wire, cutting it and terminating it in the Wildside unit.

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I cut the cables about 4 inches away from the circuit board plug. This would give me plenty of length to crimp on a sleeve connector and heat shrink if I needed to remove the Wildside unit. As a backup I have also ordered some replacement pin inserts for the plugs so I could always re-terminate directly into the plug.

The next connections would be the incoming feed from the vehicle. 4 cables, two neutral and one positive fridge supply from pin 10 and one positive charging supply from pin 9.  These arrive from the 13 pin plug via the fuse box mounted on the front wall through two 20 amp fuses and to the Sergeant unit. I had trouble identifying the cables as the colours were not as indicated in the manufacturers drawings. So to double check I removed the fuse box to gain access to the 13 core cable where it terminates.

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It was easy enough now to trace the correct cables and confirm with my multimeter. So all the connections now made, albeit temporary, I could install the 20 Amp main battery fuse and make sure the Wildside unit powered up OK.

Don’t worry about the brass bolt holding together the three cables, it was so I could easily get a clamp meter on the cables to take current readings.

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It started up without any problems and so I could connect up the 13 pin plug to the Amarok and start the engine and take a few measurements.

I checked the vehicles voltage and it was sat at 14.5 with run/stop disabled and the engine ticking over. OK how come I had a voltage of 14.5 volts in the vehicle with a Euro 6 engine ticking over? Well the Wildside unit basically makes the vehicle’s ECU think that the vehicle battery requires charging (remember an Euro 6 engine cranking battery will only ever be charged to 80% of its capacity so that regen will always work).

The first reading I checked was the leisure battery incoming link. I had a reading of 9.96 volts and a current of 8.8 amps. That was quite a big voltage drop.

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I moved on to test the incoming fridge circuit. This was showing 9.99 volts and a current of 13.3 amps. I had a big voltage drop somewhere. I checked the voltage at the point the 13 core cable terminates and got a reading of 12.75 volts. somewhere between the incoming cable and the termination on the Wildside unit I was getting a  big voltage drop.

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Continuing with taking some readings, I checked the fridge output and it was stable at 14.35 volts, 9.9 amps.

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A problem with the fridge…

On the original caravan wiring diagram it showed the fridge heating element connected with just two wires and on the face of it this looked simple enough. However when I first connected the fridge and powered up, the fridge came up with error code 10 – no power. There was definitely a supply voltage there and it was indicating a current draw of just under 10 amps. I wondered if the voltage detect circuit was polarity sensitive so swiped the connections round and this cleared the error code. So double check the polarity of the connection if you get an error code 10 don’t assume there is a connection fault.

Thinking cap on…

I decided to stop at this point. Unless I could eliminate that volt drop between the incoming cable and the Wildside unit it was pointless taking any further readings.

The next thing to do would be to eliminate the existing wiring for the leisure battery charging circuit and fridge circuit between where the incoming cable from the 13 pin plug terminated and the Wildside unit. I decided to replace the existing caravan wiring with some 2.5mm² cable.

First job was to terminate all the previously terminated cables on the Wildside unit correctly with the correct size ferrule crimped on. When ever you terminate a stranded cable in  a terminal block that compresses the wire, you should first crimp a ferrule on to the cable to ensure a secure connection.

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Next I installed the four new 2.5mm² cables from the 13 core cable to the Wildside unit. I opted to use straight through sleeve crimp connectors to join to the cable coming from the 13 pin plug. I kept the length as short a possible – about 900mm, which resulted in not the best cable route option but I wanted to minimise voltage drop. (remember, the more current you draw through a cable and the longer the cable the bigger the voltage drop!)

All that done, and the correct terminal block installed for the battery positive lead rather than my brass bolt, I powered up everything and hooked up the Amarok and started the engine once again. With the engine running the vehicle was showing 14.7 volts and I was now getting 14.1 volts on the incoming charing circuit with a current draw of 8.2 amps. Note: the clamp meter in the picture is actually showing the charging current for the leisure battery… 5.0 amps.

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Checking the incoming fridge feed I was reading 14.2 volts and a current of 8.6 amps. Which was a vast improvement over my previous readings. (Note: the clamp meter in the picture below is still showing the battery charging current)

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The battery charging voltage was showing 15.01 and 4.8 amps which meant I was at least charing the battery with just the engine on idle.

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Doing a little maths – I was pulling 8.2 Amps via the leisure battery charging circuit and 8.6 Amps via the fridge circuit giving a total of 16.8 Amps. I was supplying 9.9 Amps to the fridge and 5.0 Amps to the battery. A total of 14.9 Amps. The difference would be due to the losses due to stepping up the voltage being supplied by the vehicle to the output voltages of the Wildside unit. In terms of watts – the vehicle was supplying 237.74 watts and the wild side units was outputting 224.49 watts.

This did make me think. As the fridge was now consuming 149.49 watts (its rated at 150 watts) so it in theory should be at it’s max efficiency… did it need to be on all the time? Could the fridge be switched on a duty cycle of say…on for 75% and off for 25%? This would then increase the ability to put more back into the leisure battery, especially useful on short runs.

Speaking to Charles Sterling, I know this unit has been rated on the conservative side and in theory 20 amps can be pulled from each circuit. This would give around 560 watts of power… and in theory about 400 watts available for charging the leisure battery. Will that damage your vehicle? Well as most Euro 6 engines are fitted with 2Kw alternators, there is still plenty of power available.

Finishing up

It was now a matter of tidying up my mess and installing some cable ‘p’ clips to secure everything to the floor. The two sleeves on the cables that come from the 13 core cable are there so I can identify each circuit. Red for leisure battery charging and blue for fridge circuit.

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The yellow fuse you can see is the leisure battery fuse. It’s rated at 20 amps and is in circuit between the leisure battery and the caravan services, so pull that fuse and the caravan will be isolated from the 12 volt system. I’ll probably replace that with a circuit breaker in the near future.

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A couple of things I thought about while doing this install.

The Sargent control box is a lot of wasted space. I recon that it should have been shrunk down to ¼ of it’s current size and probably relocated to somewhere else… maybe under the draw unit at the front of the caravan.

The incoming fuse connection panel too seemed a little flimsy. All it consisted of was a circuit board with multi plug connectors on one side and spade connection soldered on the other for the blades of the fuses to slide into. Some of the soldering looked ‘dry’ and I wondered if this was causing some of the volt drop I was experiencing… that coupled with the multi-plug connections in the loom. I know it makes the build of the caravan easier on a production line and you only need semi skilled labour to install but hey sometimes things like this matter.

Its obvious that caravan wiring is done down to a cost and the minimum standard required. I would have liked to seen some slightly heavier gauge cable for some of the connections. It amazed me that the leads that connect to the battery are 6mm² but drop down to 2.5mm² once outside the battery box and the connection between the two is just a simple male/female spade connection.

The other thing that struck me was how inefficiently the plumbing was done. I’d never really looked at it before, but casting my eye over it I think I could have laid it out a bit better and saved three push-fit connectors.

Who’s this unit designed for?

Well anyone really that has a Euro 6 engine in their tow vehicle or motorhome (if you have a motorhome you need to look at the BB1230 which is a step up again from this) and cares about maintaining their leisure battery.

If you have a motor mover fitted and use it to get your caravan out from its parking spot before you set off and then find sometimes you don’t have quite enough power to position your caravan on your pitch when you arrive or the reverse… your motor mover always seems to run out of steam trying to put your caravan back in its storage area when you return home, the Wildside unit should make sure you always have a fully charged battery and I’m my opinion is something that should be classed as an essential item.

From a lot of emails I have received it would seem that generally people with motor movers seem to be changing their batteries more frequently. A lot of the time when the motor mover stope working or works erratically the advice from the motor mover manufacturer is “you need a new battery” or” its a problem with your battery”. I”m going to throw this out there… I think it may be down to the batteries never really getting a proper charge and sulphating, radically shortening their life.

Alternatively if you do a lot of “Off Grid” (Boon-docking) camping, this will make sure you maximise the charge in your leisure battery to allow you to get the most from it. Especially if you have a Euro 6 engine.

How easy is it to install?

Planning is the key and a modicum of skill in being able to trace cables and terminate correctly. However a lot is going to depend on your caravan, how it is connected and the quality of the original installation. For me it was quite straight forward but the location of the existing components made it easy. Depending on your particular caravan you may end up having to run some additional cabling. Whatever you do, do not cheap-out on cable termination! Buy the right terminals and a good ratchet style crimp tool and make sure any cable you install is a good quality brand of the correct gauge.

Were there any issues?

Nope, it worked straight out of the box.

What next?

Road test! In a few weeks we are travelling down to Glastonbury which is between a 5 and 6 hour tow and I’ll be taking readings during the trip to see how the battery is being charged and the fridge temp. Just for the pure fun of it….. I’m going to try to make ice cubes in the freezer so we have ice for our drinks when we arrive! I’ll let you know how I get on.

Looking forward.

The biggest problem really is the fridge. A three way absorption fridge is probably the single most inefficient way of chilling anything. Whether its powered from 12 volts, 230 volts or gas. Its far more efficient to use a compressor fridge.

Now a 230 volt compressor fridge is relatively cheap when compared to a three way absorption fridge, great for when you are on hook up, but now imagine being able to run it via an inverter while you are driving or off grid from your battery. As they only run short periods and take less power to run. Coupled with the fact they don’t run continuously like an absorption fridge. It would be possible to do away with a 3 way absorption fridge completely.  As we now have a sensible way of charging batteries, and given the fact the price of modern lithium battery technology is dropping all the time I don’t think technically we are far off making the transition. Its just down to the caravan manufactures…. so don’t hold your breath.

Contact:

Sterling Power

Stuff I used:

You can find links to all the crimp terminations and tools that I used in the Caravan Chronicles Shop

 

Flushed With Success….. Eventually!

13 Tuesday Dec 2016

Posted by in Blog updates, Caravan Electrics, Caravan Fault Finding, Caravan Servicing, General

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You know there are times when I think the service industry is going down the pan.

Right… the prologue

We had driven down to Chapel Lane caravan site to do a bit of partaking of the Christmas Markets in Birmingham and to do a bit of filming with the Venerable Andy Harris of motorhome fame (more about that in the next post though!). We had set up and I was pottering round outside sorting the guy ropes for the awning or the Christmas lights, I can’t remember which, when Sue popped her head out of the door and announced with some consternation… “The toilet won’t flush”

I went in and pushed the button… yep it wouldn’t flush, no pump noise, nothing. I emerged from the bathroom and announced “The toilet won’t flush” at which point Sue gave me the “did you think I was pushing the button wrong or something” look.

Right… check the fuses first, all OK. Out came the tool bag and the multimeter. Voltage going to the loo OK… check the fuse in the bottom of the loo behind the cassette. That was OK too.

Now I don’t believe in coincidences and it just so happened a couple of weeks before the caravan had been in to Glossop Caravans to have a spot of damp sorted and they had replaced the wall board that the loo backs onto. It’s got to be that I thought and said to Sue “I’ll bet it’s when they did the damp and took the loo out”

“Give them a ring now while they are still open”

I spoke to one of the service centre receptionists and they said they would get the workshop manager to ring me back and in due course he did. After a brief conversation he assured me it was nothing they had done and if the loo was getting voltage and the fuse in the loo was OK it must be the circuit board. While he was on the phone I managed one handed to peel back the Thetford sticker on the top of the loo and extract the circuit board. A quick voltage check of the pins that connect to the motor revealed that it was zero volts when the button was pushed.

“It defiantly the circuit board then” he said.

The old circuit board top, with the new one below.

The old circuit board top, with the new one below.

I thanked him and started thinking about our next move while answering an email from the afore mentioned Andy Harris. I just happened to say “loos not working need a new circuit board” and Andy emailed back “Try Jonathan at CAK Tanks” A quick phone call and they did have one in stock… just one. I asked them to reserve it and would pop over mid morning. CAK Tanks was only about 18 miles away and took us 30 minutes to get there. After some double checking to make sure it was the right board… Thetford had very usefully changed the part number and not told many people about it. Handily the new part number was a lot cheaper and it cost £19.36 including the non voluntary contribution to the Chancellor of the Exchequer.

Now, you remember when I said I don’t believe in coincidences.  For some reason I thought I’d just check the connections that Glossop Caravans service people would have disconnected.

Its easy to extract the connector through the hole in the floor of the cassette compartment and check the connections….

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On checking the connections it was apparent that they had been connected the wrong way…. i.e reverse polarity!

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The plug that was fitted by Thetford is designed to be connected one way, but the wiring harness in the caravan used two spade connectors that could be connected in any orientation and this time the person re-fitting the loo had a 50/50 chance of being right or wrong and in this case got it wrong. I re-connected the two space connectors the right way and went and fitted our old circuit board. It worked!

So the morel of this story is there are no such thing as coincidences and before setting out on a round trip of 36 miles and spending £19.36 on a new circuit board… check the polarity!

I think I’ll go a flush the loo again…. just because I can.

A Readers Puzzle Answered…

04 Wednesday Feb 2015

Posted by in Caravan Electrical Fault Finding, Caravan Electrics, Caravan Fault Finding, Electrical, Technical

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No, I’m not starting an Agony Aunt post..!

A couple of days ago one of Caravan Chronicles readers, Vic, posted in the comments section of “Understanding Caravan and Tow Car Electrics” that he recently flattened his car battery by leaving his caravan connected to his car. Here’s what he posted:

Hi Simon, while travelling across Spain I made an overnight stop and left the caravan connected to the car electrics I also hooked up to mains. The next morning the car battery was flat, I’m sure I’ve done this before with no consequence. All I can think is that european site wiring can be suspect.
brilliant article.

OK, that got me thinking…
Was it the car-off-van switch faulty? Was there another fault of some sort? I asked Vic for the details of his caravan and he replied it was a 2009 Bailey Senator California. I don’t know the exact details for Bailey electrical schematics, but it should not be too difficult to work out what might be happening. I started to think of various failure scenarios that ‘could’ account for Vic’s problem. At this point I have to say I’m indebted to David Rose for sending me information about the electrical services in Bailey Caravans.

Looking closely at the schematic of the control unit, it all hinged around the correct operation of four relays. Here is the schematic I have drawn out in a simplified form:

Bailey Caravan Relays 01

The drawing (above) shows the four relays – R1, R2a & R2b, R3 as they are set when the caravan is not connected to the vehicle and the master switch is off. The red lines show what part of the circuits are live. The master switch controls relay R1 and when energised by turning the Master Switch on allows current to flow to the caravans 12 volt electrical system via the 12 volt fuse board.

Bailey Caravan Relays 02

Above: We have now turned the Master Switch on and can see that relay R1 has energised and is allowing current to flow to the caravans 12 volt services. The caravan is not connected to the tow vehicle.

Bailey Caravan Relays 03Above: The caravan is now connected to the tow vehicle and the engine is running. The caravan master switch is off. With the fridge circuit powered from the running engine, it energises R3, R2a and R2b. Relay R2b disconnects the master switch circuit so that it cannot operate R1. Relay R2a connects the leisure battery to the 12 volt permanent feed from the tow vehicle. R3 energises, but only switches the feed for the master switch from the leisure battery to the permanent 12 volt supply from the tow vehicle. As this stage it cannot be used to supply the master switch due to R2b being energised.

Bailey Caravan Relays 05

Above: The caravan is still connected to the tow vehicle, but the engine is off. Relay R2a and R2b that are controlled by the fridge circuit are now not energised and revert to the default position. However as the caravan is still connected to the tow vehicle, the 12 volt permanent feed keeps relay R3 energised, therefore supplying the Master Switch – not from the leisure battery but from the permanent 12 volt feed from the vehicle.

This now leaves us in the following position:

Bailey Caravan Relays 06Above: The caravan is connected to the tow vehicle but the engine isn’t running. The master switch is on. The caravan now receives it’s 12 volt feed from the tow vehicle to power all the 12 volt services. I have greyed out the live circuits from the leisure battery. Even though the caravan is plugged into a EHU bollard, the 12 volt services will be run from the vehicle battery and not the mains charger/ leisure battery circuit. The fridge will continue to work on 240 volts as will any mains powered equipment.

So, it’s not a ‘fault’… it’s a ‘feature’ ! Leaving the caravan plugged into the car and turning the Master Switch on allows you to power the caravan’s 12 volt services from the car. Disconnect the lead from the car and the caravan will be powered from the leisure battery.

I hope this solves Vic’s puzzle.

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