One thing about being retired… you have way too much time to think about things. One thing that has been wandering round my grey cells for the last few months relates to an email I had September last year and it was from someone who was fitting out a van and had a few electrical issues, which I managed to help him remotely sort out the problems.

Something that struck me was an off the cuff remark about being able to separate the vehicle side electrical system and the habitation electrical system but still have them work together.

So here is my thoughts and a bit of a sketch (you all know I like sketches) on a possible but workable solution…

Taking a bit of inspiration from the world of aviation and how systems are split into individual bus systems and master bus system that can be combined and isolated as safety procedures require, I thought about how the current wiring on conversions could be improved.

Installing two fuses, one on each pole between the vehicle and habitation, would limit the maximum current between the two systems… the habitation system and the vehicle system. I’ve called these the “Habitation System Isolation Fuses”

In my sketch, the DC to DC charger is a 50 Amp unit, so I have sized the fuses at 50 Amps… (I’d actually install Tyco W23 thermal switch circuit breakers… more about that later) Fusing the positive (live) is normal, but adding a fuse in the Negative / Neutral line is not normally considered. However I have a sound rational for doing this.

Looking at the right hand side – the Habitation Side, we can see that there are two LiPo batteries located some distance apart and connected by a battery bank interlink cable. The feed from the battery bank goes from one battery via an isolation switch and 200Amp fuse to power the habitation equipment and the return is via shunt to monitor the battery bank to the opposite battery. The interlink Positive cable is fused at each end with a 200 Amp rated fuse. All that is pretty normal.

However there is the possibility that the battery interlink cable could be routed through bulkheads or the cable from the battery bank via the battery isolation switch could be routed through vehicle bodywork bulkheads to a distribution point. If this cable was to chafe, there is the potential for a direct short or intermittent / low resistance short to the vehicle ground. As this battery bank is fused at 200 Amps, you could end up warming up a bit of vehicle cabling to the point of PVC fumes filling the van or a full blown fire. Remember you can stick weld steel with 150 Amps!

By inserting a fuse in the Neutral /Negative line – the Habitation System Isolation Fuses, you have effectively fused any potential short to ground from the habitation side battery pack to 50 Amps which if a direct short will blow the fuse before any of the 200 Amp fuses have started to even warm up! Note… if your DC to DC charger is only 30 Amps then these two fuses would be rated at 30 Amps.

Could This Be Improved?

Well yes, everything can be improved. Upgrading the Vehicle Charging Isolation Switch to a double pole would mean when you are parked up, turn the switch off and the habitation electrical system is completely isolated from the vehicle electrical system… down side is some solar chargers have a trickle facility for the vehicle battery (normally connects to the vehicle side of an isolation switch to work and relies on negative continuity between the two systems)… and one day you will forget to turn it on when you are going to do a days driving.

Load sensing on the Neutral / Negative at the Habitation System Isolation Fuse would show if you had a drain from the live side of the habitation system to vehicle ground.

Prerequisite …

The big prerequisite to doing this is of course you haven’t been a cheapskate and only used one wire to supply equipment on the habitation side and used the vehicle body as the Negative / Neutral path.

Short story… someone contacts me, can’t get a device working properly. Tracing the power side, no issues, tracing the return path… some resistance. Turns out the body panel is bonded on to the vehicle and there is no electrical continuity between the body panel and vehicle neutral… so in order for the 5 watt interior light to work, the vehicle manufacturer installed a 75mm long flat beaded strap between the body panel and the section of chassis it is glued to. I recon this strap was good for about 2 or 3 amps… so when the fridge was running and the 5 amp accessory powered up the combined negative wires that were screwed to this body panel slowly heated up the bit of flat braided bonding strap installed by the manufacturer.

Morel of the story…. if you are supplying electrons to something…. also install a route for them to go home! Don’t rely on others to have done it for you. They don’t know what you were planning to do when they designed the thing!. (OK Physics majors will now be sitting upright, drawing their keyboards close and about to compose a long winded essay on why I’m wrong… Yep I got it… I know electrons, negatively charged, move the other way).

Not using the body as a conductor has been known about for a long time by the Professional Audio Boys… you know the ones on You Tube… stereo bass kicks in and the girls….. hair…. that’s a better word… jiggles about with the sound pressure driven by speakers that consume enough energy that even Doc Emmitt Brown would raise his eyebrows at ( I wonder if that where he got Jigga Watts from?)

Tyco W23 Circuit Breakers

On aircraft anything that is powered by electricity goes through circuit breakers and nearly all fall into two types… W23 / W31 or W58.

W58 are pop out breakers that you push in to reset, but W23 and W31 are switch breakers. W31 look like a toggle switch while W23 have a button that can be pulled out to turn it off. I like W23 style breakers….

They are made for 240 volts AC, 50 volts DC and have been around for 40+ years. I’ve flown planes built in the 60’s that still use the original CB’s in them. Now they are mostly made in Mexico or China but are all to a very well established spec and testing standard. You can get them in 1, 2, 3, 4, 5, 7.5, 10, 15, 20, 30, 40 and 50 Amp ratings so you can best match them to your system. The spec sheet even tells you what to torque the cable screws to when installing. Personally I’d replace all fuses with these things…… oh yesssss…. I do like a good CB panel… pat on the back if you guess the aircraft type.

Conclusion…

Well I’m not an expert in 12 volt systems and although I have designed and worked on aircraft electrical systems, that really means nothing in this context. These are my thoughts on something that may or may not be needed but it’s how I’d probably go about doing things.

P.S.

If anyone from INEOS is reading…. I love the new Grenadier and especially the aircraft style panels…. quite happy to do some tow testing for you…. hello…. anyone there?