Split Charge Relay kits - warning!

[g8dhe]

Can I make people aware of a common problem with some of the Split Charge Relay kits that are currently on the market.

Be aware that some kits only fuse the Starter battery side of the circuit, they don't have a fuse on the Leisure battery side.

The fuses are there to protect the cable from a power source, either Starter Battery or Lesiure Battery and also these days Solar Panel systems however most solar controllers have protection built in.

One kit of note relies on the fact that neither an exposed +ve terminal clamp or a 12" (approx) length of cable to the relay nor the other side of the relay will ever be damaged in a small front end collision where either the radiator or bonnet are pushed back or down onto the battery itself.

The simple inclusion of a battery terminal mounted fuse such as these

and a protective insulating cap for the terminal is all that is needed.

[Northern Bongolow]

thats a good little gadget geoff, especially when peeps are tending to fit the biggest physical sized battery they can in both the starter and leisure battery positions this is even more important as the battery terminals are raised up to nearly touching the underside of the bonnet.

[Bob]

Good call.

Could this be included in a Fact Sheet or Sticky?

[g8dhe]

Also people seem to buy batteries with the +ve terminal situated at the front rather than at the back, which means the bonnet is even closer to the terminal

[timhowes]

Well spotted, describes my kit perfectly, and thanks for sharing.

On my LB +ve terminal the split charge kit sends 3 wires converging onto 1 ring connector. Can't tell what current they are rated to but guests somewhere between 20-30A. Presumably then I should pick a fuse rating appropriate to the rating of one individual wire. Can someone correct me if I'm wrong please? Ta

[g8dhe]

Really each wire should be individually fused. Best practice would be only two wires, one the charging connection to the SCR rated at about 40Amps, the second would lead to a fuse block where you would break down to smaller fuses, the fuse feeding the block again would rarely need to be above 40Amps both cables would be rated at or above the fuse rating.

[timhowes]

Apologies for confusion, I was actually talking about the loom wiring which runs ultimately to my fuse panel in the cockpit. Now this actually has a multi-fuse box after a shortish (?12 inch) run from the +ve terminal. So there are fuses, but they are not as close to the battery as they might Is this unwise?

I'll stick a cube fuse on the high-rated cable from +ve to relay. This is thick, battery-type cable. What rating fuse should I choose for this run?

[g8dhe]

There is no regulation to advise about length so its down to best practice, what you need to think about is is it likely that the cable from the terminal to the fuse, could it be trapped and cut by anything metal in the event of a collision. Bear in mind that there is very little to absorb the impact behind the radiator being pushed backwards, likewise the bonnet crumpling. Another aspect is the battery clamp's, could a wire be squashed behind the clamp if the battery gets pushed backwards, in several layouts I've seen people push the fuse block down the back of the battery with the live side cables running past the clamp - ideal for them to be trapped by the threaded clamp rods which are nicely earthed! In practice a couple of inches should give you enough room to put a decent waterproof in-line fuse holder in position so why have more unprotected cable ? The cube fuses above are an even better solution and don't have to be that much more expensive if you shop around, covers for the terminals are often sub £1 as well.

On my own vehicle I use the quick release battery terminals with the fuse block and relays mounted direct to the clamps



Oh and before someone says I don't have a battery clamp - I do, its the type that fits at the bottom of the battery and holds the lower rubber lip in place!

[mikeonb4c]

Where do you buy these wonderful items on ebay etc geoff. Couldn't find that fused battery terminal and haven't yet tried sesrching yet for quick release battery terminals and lip retaining battery clamps but all sound like good ideas.

[g8dhe]

There termed "Battery terminal fuse" or "Cube fuse";
https://encrypted.google.com/search?q=c ... utf-8&aq=t

The battery clamp is built into the tray itself, basically a hole at the rear of the try with a captive bolt, then a triangular section of metal with a hole at the apex of the triangle, which goes over the bolt, the base of the triangle clamps the battery lip and a nut is screwed down to hold it all in place. I can't take a photo as the van is being tended to for its rust problems at the moment so isn't here!

[Alan2016]

OK time to embarrass myself Soooo..if the leisure battery side isn't fused and you have said collision, what actually happens that would be avoided by the fuse? Is it the battery shorting out to the chassis or more than that? Sorry for the lack of basic understanding ... feeling a bit like this Looking at my system it seems to have a fuse between the starter battery and the relay (close to the relay after a longish run from the starter) but nothing on the leisure battery side.

Thanks

Alan

[g8dhe]

Yes the danger is that an un-fused cable will be damaged and short to earth, where currents exceeding 200-500 Amps can be expected.
In one design, no names mentioned, there is only one fuse, on the basis that the Split Charge Relay is mounted very to the battery terminal, and the length of cable is sufficiently short that the danger of it being damaged is very low - however that ignores the point that the SCR is most likely to be operated at the point of a collision and the cable the other side of the relay is hence LIVE and un-fused from the second battery ..... the relay will quite happily handle several 100's of Amps before it melts, either way there will be the equivalent of a free flying arc welder (arc welders use currents of 50+ Amps) under your bonnet

[Alan2016]

Ah thanks for the clarification. So in my Bongo I seem to have a bunch of wires heading off from my leisure battery +ve. Along with the SC relay I have another 3 going to a fuse box stuck to what I think is the air intake cover about 12 inches from the battery and a Karl Chadwick loom heading off to another small fuse box for swapping the lights/blinds over to the LB. I assume these would also be safer if they were fused at the battery terminal..? If so then how do I size the fuse needed or would the 150A one shown in your original image be suitable? Also what consideration needs to be take with the starter battery (if any) as the runs from it to the fuse before the relay are longer than the run from the leisure battery to the relay.

Thanks again

Alan

[g8dhe]

I would have thought a 50Amp fuse on the LB terminal would be more than adequate.
Most of the systems do fuse the starter battery, but there are a lot of custom systems out there! Karl's kits are normally well designed, given what I have seen of them.
The main problem is the wires from the terminal itself, provided each one is fused within a few inches of the terminal then that's fine.
Its when the charging cable has no fuse in it that you need to get concerned, even if the relay is within a few inches.

[mikeonb4c]

There termed "Battery terminal fuse" or "Cube fuse";
https://encrypted.google.com/search?q=c ... utf-8&aq=t

The battery clamp is built into the tray itself, basically a hole at the rear of the try with a captive bolt, then a triangular section of metal with a hole at the apex of the triangle, which goes over the bolt, the base of the triangle clamps the battery lip and a nut is screwed down to hold it all in place. I can't take a photo as the van is being tended to for its rust problems at the moment so isn't here!

Thanks Geoff, a great help as ever.