What's this? - electrical query

[Umbongo]

I'm having trouble with my leisure battery blowing fuses. I've a blown one at the moment but the battery seems to be fully charged if I've used my test meter correctly. I've also tried a trickle charger which registers the battery as charged.

Anyway, this is under the bonnet; the positive lead from the leisure battery leads to the yellow connector via the inline fuse. You can see that one connector is not attached, and I'm not sure if it ever has been. It's not likely to slip off and may have been removed when the internal lights etc were changed to run off of the L. battery.

Can anyone tell me what it is and if it should be connected?

Thanks

Iain

[g8dhe]

Well its a standard 40 Amp relay.
Exactly what it controls is anyone's guess
But given that one connection is to the L/B via fuse it could be your charging relay, in which case one of the other THREE connections will go to the S/B via fuse. The other two connections, one is most likely to go to earth/chassis and the other to 12 volts via the ignition switch, so that when your running the relay operates and the two batteries are connected in parallel to be charged from the alternator.

Looking closely at the picture I think I can actually just make out 4 wires going to the relay, in which case the spare one is not needed but the one at the back nearest the bulkhead is difficult to make out so it might have come from there.

When does the L/B fuse blow ? Is it when you start the engine up ? Is it when you turn on devices that run from the L/B ? What size fuse is it to the L/B ?

[duncsuk]

I had a problem with my split-relay charging system, such that if the leisure battery was 'more' charged than the main battery, current was drawn from the leisure battery during starting (needs many many amps) as well as from the main battery and this blew the in-line fuse between the split-charge relay and the leisure battery. I solved the problem by adding a diode to prevent the reverse current (though actually I would have expected the split-cherge relay system to prevent this).
PS : My Bongo came with two 'standard' batteries (the 'cold-start' pack) and I now use the scond as my 'leisure' battery having separated the two circuits.

[g8dhe]

It sounds like the relay is being operated either all the time or during the time the Ignition switch is operating the Starter motor itself. It should be connected ONLY to the ACC position of the Ignition switch as this turns OFF during actual Starting and OFF when the Ignition switch is at OFF. This is perfectly OK provided you don't spend much time with the Ignition in the ACC position but without the engine running (I use the method myself), its probably best to pickup the switched 12 volts from Fuse 8 as its very easy to get to! If you make sure it is connected that way then you can remove the diode and provided both fuses (one near Starter battery and other near leisure battery) are 30 Amps and the wiring can handle MORE than 30 Amps then all will be OK - do make sure you have one fuse between each battery and the relay a total of two fuses, and that the fuses are close to each battery !

Oh, one point if the L/B is really flat then you might blow a fuse if you race the engine just after starting.

[duncsuk]

Thanks for the tips. I actually fitted a SMARTCOM relay system which should only 'open' the relay to the L/B once the main battery is 'full' ... and I assumed NOT during starting ... but it did seem to have a 'fault' when the L/B had a voltage higher than the main battery. I believe the unit was possibly faulty, but as I had completed the installation (after soak-testing for a few days) .. neat wiring, waterproof box etc etc, I decided not to pull it all apart again. Been working fine for the past year (with the diode) .. fingers crossed it stays that way.

Coming back to the original thread (Umbongo), which fuses are actually blowing ?

[Umbongo]

The fuse seems fine when using all that is powered from it but blows upon start up - but not all the time. It can be fine for a while, but blows if left for a few days, which would seem to fit with it being discharged, but it's not.

I've got a 35A fuse in it at present.

[scarlet]

Is the relay in your pic the split charge relay? It could be that your split relay has welded close so your 2 batteries are staying connected as one and your starting battery could be dropping its charge if left for to long, so the drain is been taken from the leisure on start up of the engine which will blow the fuse. in my opinion a split relay should be either a 80 or 100 amp relay at least as high current can be drawn if the leisure battery has been used onsite for a few days with out running the engine.

[g8dhe]

The fuse seems fine when using all that is powered from it but blows upon start up - but not all the time. It can be fine for a while, but blows if left for a few days, which would seem to fit with it being discharged, but it's not.

I've got a 35A fuse in it at present.

If the fuse blows after a few days standing idle it suggests that he L/B is being discharged, have you measured the current being drawn when the ignition is OFF ? If you have moved the radio and similar across to the leisure battery completely then you will often find that it is drawing a ridiculous "off" current quite often above 0.5 amps and that will be the problem.

Given the size of the wiring and the 40Amp limit on the relay I would suggest no more than a 30 Amp fuse at max.

[Umbongo]

The radio, blinds, interior lights & central locking are all off the leisure battery. If the relay is an issue, do I just buy another higher rated one?

If it's down to the draw from the radio etc, what can I do about that?

We're off on holiday in a couple of weeks so I'd like to get it sorted by then.

Thanks for the responses and I appreciate the help.

[g8dhe]

If the central locking is also on the L/B then it sounds like they have diverted all of Fuse 1, in which case there is a good chance that the Radio will be drawing an excess of current, it can only be proved by using a multi-meter and mesuring the current being drawn - my own is the same way but the current is just about OK the L/B will last about 9-10 days without a charge - but many radio's will draw a lot more. If this is the case then there are really only three choices;
1. Change the radio for one that draws less - expensive and the spec's don't tell you what the drain is
2. Switch the radio (unswitched +12volt line) alone back to the S/B - this needs someone who understands vehicle wiring.
3. Add an extra switch to isolate the radio - this also needs some knowledge and DIY skills.