I have been receiving a lot of emails over the last two or three months from people reporting issues around charging their leisure batteries after changing tow vehicles and a similar number from people who are having problems with performance of the installation of the electrical harness on their new vehicle tow bar.
I’ve spent quite a bit of time answering emails and thought I’d try to sum up what is happening. A lot of this is also going to apply to Motor Homes, especially if they have a new Euro 6 engine.
When we bought our VW Amarok last year (2016) It took me a few days of research and an exchanging of emails with the technical people at Wolfsburg to make sure I had the correct VW approved OEM electrical tow package for the vehicle installed. (Read about it here: Choosing A New Tow Vehicle Pt3…) As the Amarok has a smart alternator with regenerative braking and stop start technology I started to do a bit of research on what this would mean for us towing. While looking in to it I started see a couple of things that I thought as potential issues not only for us but for anyone that tows a caravan or for motorhomes when it comes to charging the leisure batteries.
What exactly are ‘smart alternators’?
Well they are not really smart. They do what they have always done and that is convert mechanical energy into electrical energy. What is smart now is a central control unit (ECU, EMS) which controls them.
In order for vehicle manufacturers to produce more efficient engines with more power and fewer emissions they looked at ways of reducing other loads on the engine and one way is to control the alternator. When you put your foot down for acceleration, the Control unit senses this and reduces the field coil voltage and hence the mechanical load the alternator puts on the engine to maximise power available. Like wise when cruising along to reduce emissions the load on the alternator is reduced. However to make up for all this the energy to charge the vehicle battery has to be found from somewhere and its done by using something called regenerative braking. When you take you foot off the accelerator and start to brake, the control units senses this and ramps up the field voltage to get the maximum output from the alternator using the excess energy from the braking action of the engine being driven by the road wheels.
That is a very quick and simplistic view but for me to sit and type a detailed explanation of what’s actually happening would probably take me a couple of days (with one finger typing and editing) and they say a picture… well in this case a video, is worth a thousand words.
If you are a regular reader to the blog, you will know I have been pointing people in the direction of Sterling Power products for a while for inverters and battery to battery charging and recently Sterling’s MD, Charles Sterling produced a video in which he explains some of the issues with smart alternators….
Other issues…
All vehicles now use a central control unit to manage systems, everything from engine tuning to controlling lights. Now when you turn on the heated rear window for example all you re doing is pushing a button that requests the central control unit to turn on the heating element. Like wise, when you connect your caravan electrics, the control unit detects this and changes a number of things, the abs and traction control systems, maybe the shift points in the automatic gearbox and it turns on power to pins 9 and 10 on the 13 pin towing socket. Traditionally a relay has turned on power to pin 10 (the fridge circuit) which in turn activates the habitation relay in the caravan allowing pin 9 to charge the leisure battery.
Now, the operation of pin 10 and pin 9 are controlled by the central control unit, so if it detects that the vehicle systems require more electrical power due to low alternator output, it can turn off both pin 9 and pin 10. Something else I have recently discovered is that with some vehicles, pin 10 becomes live as soon as the key is inserted without the engine running, powering up the caravan and activating the habitation relay, therefore putting a drain on the vehicle starter battery. This may or may not be an issue, but I don’t know if there is protection within the vehicle to stop any engine starting procedure from drawing current from the caravan leisure battery. This is particularly important for engines with stop start features.
Something else this now leads to. If the central control unit can turn off power to these pins at will, then turn it back on again if this happened while driving this could have implications for caravans fitted with the ALCO ATS system. One function of the ATS is when first powered up it goes through a self test procedure which involves operating the caravan brakes and releasing them before confirming everything is OK by turning the indicator light to green. If the vehicle turns off the power then restores it, this could lead to the ATS applying the brakes while the vehicle is underway. I really don’t know if this is a possibility?
How to check if your vehicle has a smart alternator…
If you have any comments or experiences of issues with smart alternators or issues with towing electrics on the latest vehicles, please comment below. If you could include the vehicle manufacturer, model, year and caravan make, model and year it would help others and maybe we can build up a repository of information. I’ll try to answer questions or find out more information for you.
Caravan Chronicles 
we have found running with dipped headlights puts a load on the alternator and so gives sufficient power to power the fridge.
Hi Alan, that does work on some vehicles, unfortunately not on quite a few as the ECU manages this load too and balances the vehicle electrical load with engine output.
Comment from Australian Caravaner:
Hello Simon,
Your explanation regarding ‘smart’ alternator (Isuzu MU-X MY17) affect on charging auxiliary batteries is consistent with my experience; and very enlightening.
I had both an auxiliary and house/van battery damaged due to inconsistent charge voltage until I discovered that a professionally fitted VSR could not function effectively due to the operating voltage range (12.7-13.4v) being above low alternator voltages.
My research directed me to fitting an ignition switched, low voltage DCDC charger which operates between 9-14v and therefore ensures positive charge to auxiliary batteries and fridge.
It astounds me that so much misinformation in this matter continues to be propagated by so many ‘amateurs’!
Hi Peter
You have done exactly what I have done… ignition controlled DC to DC charger.
I have been trying to stop the installation of VSR’s for a while now but it seems that there are ‘experts’ on the internet with thousands of followers that keep the mantra of you have to install a VSR to the point that even tow bar installers don’t install OEM kits for the wiring they just install generic VSR wiring looms that were made cheaply for vehicles of a different era.
Unfortunately the internet and YouTube have produced many “professional amateurs” that see something and think “I could do a video about that” and push out information that they have scraped from the internet as their ‘this is the correct way’ when quite often it is wrong. I have given up on trying to fight the misinformation and just write for my own satisfaction now.
I have a Kia SORENTO 3 diesel 2021, which does not supply sufficient voltage to the fridge when travelling. With the fridge off the supply from the car is 14.1 volts, when fridge is on (170watts), voltage drops to 11.3 volts. I assume this is due to the latest smart electronics on the car. Any suggestions on how to resolve please.
Hi Alan
Take a look at Sterling Power’s “Wildside’ unit. We fitted one a few years ago and it’s been working great.
It basically takes both the leisure battery charging circuit and fridge power circuit and combines them, steps up the voltage for the correct operation of the fridge and it has a smart charger for the leisure battery. You can also set it to charge gel or LiPo batteries.
Yes a voltage sensitive relay and take a 12volt supply through it to power your fridge. You vehicle smart system won’t see this supply.
Hi John
A Voltage Sensitive Relay would not work and today I would never recommend installing one on any vehicle built in the last 15 years.
A VSR senses the alternator voltage and when high enough (i.e. when the engine battery is charged) turn on to power the output connected to the caravan. However with Euro 5 and Euro 6 engines as soon as the vehicle detects the engine battery is charged it drops the alternator output to save fuel to that needed to maintain the vehicles electrical requirements only… and on engines with Euro 5 & 6 with re-gen braking can turn this output off to below 9 volts. So a VSR would never turn on. In fact with re-gen braking the vehicle battery is only ever charged to 80% of full capacity.
The only solution is a DC to DC charger and to get a fridge working properly the Sterling Power Wildside unit does the job.
I’ve written a couple of times about this in the past. VSR’s were great when vehicles had dynamo’s, but since the alternator has improved things so much really they should be only used now for specific applications like stacking batteries.
From my experience, no. If you take the supply voltage directly from the battery, that feeds the load. When the voltage of the battery drops below 14 volts, the alternator sensor switches to recharge the battery. Because the feed is independent of the vehicle smart systems it doesn’t know the the battery is being robbed.
So you are advocating taking a feed from the vehicle battery to power the VSR and then power the fridge. So when the engine is off it would still power the fridge until the battery voltage dropped…. Also this then has a knock on effect as this circuit is used to operate with the habitation relay in the caravan….. and then if it was still operating and the vehicle was restarted, the habitation relay would still be connecting the leisure battery to the vehicle’s system so starting the engine would draw current from the leisure battery and potentially overloading the capacity of the cables connecting the leisure battery in circuit.
Sorry John, but this is the sort of thing I have spent the last eleven years trying to stop. I have about 30 VSR’s in a box that I have ripped out of vehicles because they simply are installed as a sticking plaster solution.
Hmm, well the VSR seems to work on my 20 Ford Everest just fine. As soon as the engine stops the battery voltage drops below 13.4v and the feed is cut. After startup, once the voltage reaches 13.4v again power to the van (2021 Dethleffs Nomad)
Pingback: Vehicle Wiring Projects… Some Thoughts. | Caravan Chronicles
Pingback: Something For Your Toolbox… | Caravan Chronicles
Pingback: Overland Vehicle Electrics and Other Stuff… | Caravan Chronicles
Pingback: For Anyone Restoring A Vintage Caravan… | Caravan Chronicles
Pingback: Euro 6 Engines, Smart Alternators and Your Leisure Battery… | Caravan Chronicles
Pingback: The problem with information from the internet… | Caravan Chronicles
Quote Having driven a Mercedes Mini bus that the sensor had actually failed on… 3 months later the ECU had to be replaced due to the battery sensor failure causing other issues including reduced output from the alternator Quote.
Unfortunately you probably got the wrong diagnosis, you should have disconnected the sensor as soon as it was found to be faulty then charged the battery, then tested the voltage which should have read around 14.2 continuous, a faulty sensor still connected can cause all manner of problems.
This method works on Merc`s including SLK , Porsche Cayman/Boxster 981, Jeep Cherokee and many other cars with no issues what-so-ever.
Been having problems with KIa Sorento 2015 intermittently operation of Pin 10 fridge circuit. My local Tow Bar specialist informs me he cannot find a solution to it because of the Smart Alternator. This car does not have Stop Start or Regen. Anyone know of anything I can do ?
Eric,
If your car has a smart alternator you will see a small box connected to the Neg clamp of starter battery, disconnect this small plug from the box (sensor), this then turns smart off and standard charging will be initiated, normally around 14.2/4 volts continuous.
Disconnect the sensor on the negative lead of the starter battery ( small connector), as the ECu cannot now read the SOC values it deactivates stop/start and also deactivates smart charging puting the alternator into default standard charging regime, try it, it`s as if the sensor as failed, works fine on my Mercedes.Blueefficiency.
Hi Rob
Having driven a Mercedes Mini bus that the sensor had actually failed on… 3 months later the ECU had to be replaced due to the battery sensor failure causing other issues including reduced output from the alternator – not “standard mode’ as you suggest. Mercedes are the only manufacturer I know use this system and I could not advise anyone to modify any vehicle in such a way. This is not the correct solution.
Would a relay controlled feed directly from the batters circumnavigate these problems? On my 16 Ford Ranger I have perminent battery voltage on pin 9 (AUS-NZ 12 pin) for fridge and relay switched batt voltage pin 8 for habitation relay and batt charging.
Hi John
The issue you have is the wide voltage fluctuations (10.2 to 18.4 volts on some vehicles) and the problem of the engines ECU turning off the alternator for economy…. and if the vehicle has regen braking you will never get full charge on any battery with or without a relay.
DC to DC charging that can take advantage of a wide input voltage and deliver a 3 or 4 stage charge to aux batteries is IMHO the only way to go.
Thanks Simon, gosh I’m learning a lot on this smart controlled electrickery! So I assume a DC to DC charger would handle the voltage fluctuations? Fridge operation would have to be sorted seperately?
Hi John
Yes, a DC to DC charger would sort the battery out by handling the voltage fluctuations.
The fridge is a bit more accepting of voltage fluctuations as it’s just a basic heating element. I have no information though on what range it will accept and at what point the life of the element will be affected.
As you have probably read, I opted for the Sterling Power Wildside unit which has proved extremely effective and I’m now considering when it comes to the point I need to change the leisure battery going for a AGM or even Lithium… if the price is right as I can now charge these battery chemistry correctly. ( I did work out that for the same weight as my 110Ah lead acid battery I can install 400Ah of Lithium and sill save on weight)
12v fridge problems…I have a Jeep Grand Cherokee Overland 2015 and a Lunar Delta TS 2017. Tow bar and dedicated electrics fitted a month ago by reputable company. Tried 3 different cars on the van and all work the fridge. Had the voltage checked at the tow bar company and all appears correct. Plug them together and relay in car and grey box in the click and don’t work the fridge..HELP!!
Hi Phil
Just checking the voltage I’m afraid won’t tell you much. The fridge circuit on the vehicle needs a load on it of around 100 watts and the voltage measuring then. I suspect somewhere on the vehicle fridge circuit there is a bad cable joint so just measuring the voltage it will appear ok… but under load the voltage will drop below what the fridge operates at.
Pingback: Getting All Charged Up – Part 1… | Caravan Chronicles
Thank you for writing such an informative article, I found it most helpful. I’m towing with a 2014 VW Passat Blue Motion and the electronics do react to the caravan being connected, the most obvious effect is the cancelling of the annoying stop/start system.
Recent telephone conversation regarding fitting LEAS system – system is now connected directly to caravan battery, simple solution.
The Volvo XC60 with manufacture’s electrics automatically switches off stop /start and switches on trailer stability assist. ATC is therefore on effected.
Hi Simon. Most enlightening.
I have read and listened most carefully to the two videos;especially the one that really does explain what is what !!
In very simplistic terms and without the benefit of a Masters Degree in advanced Vehicular Electronic Trickology – the whole notion behind the technology is to make the vehicles more efficient in terms of fuel usage and hopefully turn us into more considerate drivers/human beings whilst at the same time exercise an engineered ‘Protect the Product’ policy by making it very near to impossible to get to the route of the invertible electrical issues that will ensue.
This in-turn will theoretically ensure that the various manufacturers dealers-workshops will be gainfully employed in replacing expensive pieces of technological trickery after carrying out equally expensive Diagnostic Tests on the very very latest equipment that just will not be available to the smaller non-dealer workshops for several years and only then after a mind boggling subscription for the software to carry out such work.
Could this continual and inevitable ‘advancement in Protecting the Product’ result in more and more people opting for the fully serviced and maintained personal lease purchasing of vehicles in the future ?
In real terms – only the business users will seemingly benefit from this strategy as inevitably they will off-set it against taxes – whilst they still survive in this ever competitive world.
Being that I am now pushing the door of 72yrs young and totally retired – I will make do with my replacement recently purchased low mileage older cars that can at-least still be serviced and maintained by my two specialist small workshops.
I started to ask some questions about this type of charging last year when we got back from our trip down to Spain. On two or three occasions on long journeys in the heat across France the fridge defrosted. I had both the tow bar circuitry and the caravan circuitry checked. I suspected there was little or no charge when cruising along the motorway. It was an after fit tow bar, not a factory fitted one. So I don’t think the car computer knows the caravan is there. The final conclusion from my caravan dealer was that these fridges are not very efficient on 12v in hot weather.
The car is a 2015 Ford Kuga diesel. The caravan is a 2016 Lunar Quasar. It is a Dometic fridge.
Hi Tony
I have had a number of emails reporting similar problems.
A couple of them, after doing a bit of checking, had voltage sensing relays installed from a ‘generic’ tow bar kit, not an specific vehicle OEM one and it was found when the vehicles control unit dropped the output on the alternator the voltage sensing relay turned off.
The users only noticed a problem when they under took a long trip as short trips the fridge/freezer would not have time to defrost even though the power was off.
It might be worth checking out your towing electrics. It would also be worth checking to see if the vehicles control unit was updated or not as this will have an effect on your ABS and ESP safety systems.
The fridges fitted in caravans and motorhomes are quite efficient and if they weren’t up to working correctly in temperatures in southern Europe there would be a lot more complaints on the internet.
Al-ko ATC senses when the vehicle is under way and even if power is interupted DOESN’T go through a self test. BPW is less forthcoming regarding their IDC – didn’t give a definative answer (so I suspect will). Hope this helps.
This doesn’t mean that if power is interupted when stationary that it won’t self test – not much fun if the stop/start removes the ‘permanent’ supply – which I have heard of problems with (especially Volvo).
Chris @ Lodge farm Leisure.
Hi Chris
That is interesting what you say about the ATC system. I have received two emails from readers that have said they think their ATC system has activated a few seconds after their engine has restarted after being stopped in traffic. I don’t know the tow vehicles. Do you have any further info from ALCO on how the ATC determines if the caravan is underway. It might be useful to make this available to everyone.
Apparenly the Al-ko ATC uses the same movement sensing technology as is used in your smartphone.
The issue with stop/start is something that is getting better as manufacturers are realising that a permanent 12v supply is meant to be PERMANENT and not just there where the vehicle is moving!
Thanks Chris.
With my VW Amarok there is specific instructions in the handbook to turn off Stop Start when towing, however when using VAGCOM to set up the towing package if the Westfalia OEM kit is fitted which has a switch in the 13 pin socket that picks up when a plug is present the VAGCOM software can be used to recode and automatically disable stop start, which has been done on my vehicle.
Not all tow bar installers are doing this as it involves manually changing the code at a specific hex address ( I was told this by a reputable tow bar installer).
I suspect this may be a similar situation for other manufacturers and I guess it might be possible to turn off/on the supply to pins 9 and 10 independently.
The only experience with recent towbar electrics I’ve had has been with Land Rovers and my D4 has stop/start which works a treat EVEN when towing. You do have to enable towing electrics in diagnostics for it all to work correctly (including Trailer Stability Control), but once done – perfect!
On the D4 (as all Discoverys since D2s) towing electrics just plug-in. Why can’t all manufacturers make it that easy?
Yeah, I have a Disco 4 as well and as said StopStart works fine even when towing. Point to note, however, it stops working if the battery voltage gets at all low. There is a dedicated stop/start battery whose role in life is to power the electrical / ignition functions when stopped (presumably because the main battery is offline). I’d guess other makes have something similar ?
If Stop/Start works when towing (on any vehicle) then the tow bar electrics have not been installed and coded correctly.
All VAG Euro5 and Euro6 cars (this includes the Amerok) have a switched mode voltage regulator to protect all auxiliary circuits from any voltage fluctuation caused by the smart alternator and the stop/start system. This includes the feeds to the towing module (if fitted).
If the towing electrics have been correctly installed and fed from the correct places you will get a stable 14.4 volts on pin 9 and 10 when the engine is running regardless of other parameters.
I can’t speak for other manufacturers, but I would expect this to be the case for them as well, as generally none of a cars systems would like the voltage fluctuations described above.
After market charge regulators are only useful if your towing electrics haven’t been installed correctly
Hi Dave
I have had chance to do a lot more research on the Amarok electrical system (including wading through the 1100 page electrical workshop manual) and indeed you are correct there are voltage regulators for various components of the electrical supply system.
From measurement I get between 14.45 and 14.75 volts on the internal electrical system, even in regen mode with various electrical loads on the vehicle. The readings are based on two different voltmeters – but neither certified. This translates to a stable voltage (albeit with a loss) at the caravan.
However the voltage drop I did discover was entirely down to the wiring within the caravan and its associated terminations. Since I corrected this I am within 0.3 volts (no load) and the voltage drop with current is near enough as expected by calculation.
S