Club 80-90 Forums

Hi, I'm going to tackle my split charge system/hook up this weekend. One question. I have an excellent wiring diagram to follow from http://www.switchpanel.co.uk" onclick="window.open(this.href);return false; . The only thing I'm not sure about is the split charge thingy! When I search on fleabay there seems to be two options a simple relay. cost about £3.99 or another relay type thing which costs anywhere between £30-£50. Do they essentially do the same thing? All I want to do is keep the leisure battery separate from the main system. Cheers

The simple one is the one called 'split charge 3' in the wiki, and the more complicated one is the one called 'split charge 4'. If you can get the alternator trigger wire to where your relay's going to be (it's accessible behind the fuse box - the wire I added is arrowed in the photo below), then the simple one is all you need. The more expensive one saves you having to run this wire because it senses a charging voltage on the starter battery.

I should have said - there's probably some variation in price due to the current rating for the relays. Make sure you get a relay and wiring that are big enough - there's good advice about current rating in the wiki.

Ah! I think I understand. Is the trigger wire just a switched live? i.e from the ignition?

windydubber wrote:Ah! I think I understand. Is the trigger wire just a switched live? i.e from the ignition?

It could be, but if you do that then a) the two batteries are joined during cranking, and b) you could leave them joined by leaving the ignition on without the engine running. The blue alternator wire is better because it doesn't become live until the engine is actually running and the alternator is charging.

Brilliant. Thank you. I now understand!!

More serious than that though...if they were connected during cranking, the starter motor could potentially draw off the leisure (say if the starter battery was flat) .. the starter could 'try' and draw as much as 180amps (on a diesel) through the split charge wiring and relay...

That's why it is important the relay stays separated 'UNTIL' the engine is started.

Martin