Split Charger for leisure battery

[TONYT25T25]

Hi, Am about to install a leisure battery on my 84 VWT25. Having read previous forums and some usefull info on Wiki, I still have a few queries if somebody could answer. I intend to use 15 amp cable with 10amp fuses and a 30 amp relay. The diagrams show a straight forward connection, my questions are why does the relay have to be connected to the no charge light, is this the light that comes on with the oil pressure light, and where is the best place to connect to it, I have looked in the Haynes and I think it is the blue wire but not sure where this is located. I only intend to use the interior lighting, the water pump and the radio which will have to be connected separately. Any advice would be welcome. Tks Tony

[marlinowner]

The connection to the ignition light is so that the leisure battery is only connected to the main battery and hence charging circuit when the alternator is charging. Its to avoid draining the starter motor by accidently leaving the ignition on. A simpler method is to use a "smart relay" which monitors the voltage on the starter battery to tell if the alternator is charging or not and doesn't need extra wiring.

[Hacksawbob]

Like this...

http://www.vehicleelectricsshop.co.uk/p ... _AMPS.html

Various kits are available on ebay with wiring and fuses etc, but you could probably put one together for less.

[TONYT25T25]

Tks, the relay I am using has four connections and is numbered as per the diagram in the wiki diagram, is this a smart relay or the standard type.

[TONYT25T25]

Just seen the link so question answered mine is the standard relay. Still unsure about the wire to the charge light, I thought the connections 87 and 30 on the relay when energised transferred this ?? Tks to all for assistance.

[MidLifeCrisis]

Have you looked at the information in the Wiki about Split Charge setups?
https://club8090.co.uk/wiki/Ca ... it_charger

The purpose of the 'split charge' system is to connect the starter battery to the leisure battery so that the alternator charges the starter battery and the leisure battery. But it only connects the leisure battery to the starter battery when the engine is running (and therefore the alternator is turning) otherwise the leisure battery might draw power out of the starter battery which would be a bad thing.

On your relay - pin 30 and pin 87 will be connected together when the relay is energised (as you have noted) - so the starter battery is connected to pin 30 and the leisure battery is connected to pin 87 - so when the relay is energised the two batteries are connected together and thus the alternator can charge both.

So, how is the relay energised? On your relay - pin 85 needs a positive connection and pin 86 needs a negative connection for the relay to energise. The negative connection on pin 86 is permanent (i.e. its just wired to ground) - so the only question remains how does the relay get its positive connection on pin 85 (but only when the engine is running) - this is where the connection to the charge light is used.
By connecting the relay pin 85 to the 'negative' side of the charge light (which in turn is connected to a terminal on the alternator) - then this is negative when the engine is not running but positive when the engine is running - hence driving the relay when the engine is running.

Hope that all makes some sense - read the Wiki a few times and it should all fall into place

[CJH]

I connected my pin 85 to the charge light by tapping into a connector behind the fuse box. I preferred this over disturbing the wiring on the dashboard connector. The wire I added is the one marked with the arrow in this photo:



I removed the blade terminal from that white plastic connector and then crimped and soldered both wires into a new 'male blade with latch' from here, but you could equally well solder your relay trigger wire to the original blade.

[TONYT25T25]

Tks again all, good information above which I needed as not used to electrical issues, however looking at the wiring diagram on wiki, connection 85 is connected to earth and 86 to the no charge light which contradicts above unless I am having a bad day, last problem was renewing a water pump etc. Rgds Tony.

[CovKid]

I tried in vain to get the feed that way and ended up running a new wire from the same connector on the alternator all the way to the split charge relay. I've never worked out why it would only work that way but apparently its not uncommon to have to run another wire.

[CJH]

...however looking at the wiring diagram on wiki, connection 85 is connected to earth and 86 to the no charge light which contradicts above...

You're right - the diagram in the wiki is correct and shows 85 connected to earth - that's actually the way I wired mine. I believe that most relays will still work with these two switched over, but I'm no expert.

[Oldiebut goodie]

All it is is a coil that generates magnetism so it will work either way round. (Unless there is a diode included inside for some reason)

[TONYT25T25]

Tks for getting back to me, possibly it works as both described either way, will connect as per wiki. Thanks again for help. Rgds Tony

[TONYT25T25]

Update on connections, installed the system today using the wiring diagram as per the wiki guide, and thought was all ok, however I noticed that after switching the engine off power was still being fed to the leisure battery from the main battery, I tested this by connecting a meter to the leisure battery and noticed that the voltage was the same as the main battery, on disconnecting the leads from the relay the connection was broken and the true voltage was shown on the leisure battery. (ps I am using a normal battery att as a leisure battery until I get the system sorted.) Any advice on why the connection is still there would be welcome.

[MidLifeCrisis]

Where/how did you connect to the charge/battery light??

[TONYT25T25]

Hi, underneath the dash above the steering column, identified the blue wire, cut it to determine it was the generator light and then spliced the connection from relay no 86 into it.