Leisure Battery Charging

[isaune]

Hi Everyone

Quick question - been in the back of my mind since I bought the van 18 months ago but never got round to asking.

There is a switch on the dashboard with an orange light which illuminates when the switch is on. When I bought the van, I was told that this was used to charge the leisure battery ie when the switch is down, the light on the dash is on, and the leisure battery is being charged. When the switch is up, there is no light on the dash and the leisure battery is not being charged.

This is certainly true as I have a little voltmeter I can stick in the cigarette lighter socket (which runs off the leaisure battery) and when the switch is down this reads 13 plus volts and when it is up it drops down to 12ish or whatever the leisure battery currently has in it.

OK - so far so good. Everything working fine.

My question is:-

Does the main starter battery get charged at the same time as the leisure battery when the switch is down and the orange light illuminated? I assume this is the case but, if I am right, why is the switch there at all? Why can't I just leave the switch down all the time? Why would I ever want to be driving along and NOT charging the leisure battery?

The only thing I can think of is that, during times of heavy main battery usage (eg winter, cold, headlights, heaters etc) the switch is there so I can devote ALL of the charging power to the main battery and NONE to the leisure battery.

Now I appreciate you can't be absolutely sure having never seen my van, but I am hoping you will recognise the kind of system I have got from the way I've described it and be able to make an educated guess?

As things stand now, I have that little element of doubt in the back of my mind which makes me want to alternate periods with the switch on and off (eg half an hour on, half an hour off), so I can be absolutely CERTAIN that the main starter battery is getting its fair share of charge.

I'm 99% sure I don't need to do this, and that BOTH batteries are charging when the switch is down, but would like some reassurance please, especially as I'm off to France next week.

Thanks chaps.

Ian

[AdrianC]

My question is:-

Does the main starter battery get charged at the same time as the leisure battery when the switch is down and the orange light illuminated? I assume this is the case

Y'know the test you just did to prove the leisure was being charged...?

This is certainly true as I have a little voltmeter I can stick in the cigarette lighter socket (which runs off the leaisure battery) and when the switch is down this reads 13 plus volts and when it is up it drops down to 12ish or whatever the leisure battery currently has in it.

...that'll work on the starter battery, too. See if that's running at 13-14v with the light on. If it is, then that's being charged.

but, if I am right, why is the switch there at all?

To justify an extra light...

Why can't I just leave the switch down all the time?

Because if you did that, there wouldn't be any point in having an extra switch and light...

Why would I ever want to be driving along and NOT charging the leisure battery?

I think there might be a bit more to it. I _suspect_ that what's happening is that the switch just connects the two, and "driving along" doesn't come into it. So if there wasn't a switch, then the two would constantly be connected. That, of course, would mean that you'd be draining the starter battery when you're camped. Which is kinda defeating the point of having a separate battery.

Think of the switch as being a manual voltage-sensing split-charge relay...

The easiest way to test if that's happening is to disconnect one +ve terminal (CAREFULLY) and switch the switch on. Then see if you've got +12v at that terminal. If that's a no, then maybe repeat it t'other way round in case the other battery's the one providing the relay switching current.

All bets are off as to exactly what weird and wonderful setup somebody might've concocted, but unless the two are connected with the engine off, then you might as well leave it on all the time so both charge all the time whilst the alternator's putting charge out. After all, that's just what a split-charge relay does. But without the fun of having an extra switch and light to play with.

[1664]

On some conversions that is the switch and light for the 12v side of the fridge rather than using a relay

[isaune]

Why can't I just leave the switch down all the time?

Because if you did that, there wouldn't be any point in having an extra switch and light...

but,

if I am right, why is the switch there at all?

To justify an extra light...

The above made me laugh out loud, Adrian - thanks!!

Yes I do see how lucky I am to have a nice switch to flick and a very smart (if I say so myself) orange light illuminated on the dashboard!!

Joking aside though - that is quite a scary thought that if I accidently leave the switch down when I park up for a camp, then I could be draining both batteries!!

I will do a simple test when I get home. Because my flourescent lights and radio both operate from the leisure battery, I will disconnect the leisure battery and flick the switch down.

And hope to goodness, the lights go out and radio goes off!!!

Thanks for clarifying this in my mind, Adrian!!

Cheers

Ian

[AdrianC]

I will do a simple test when I get home. Because my flourescent lights and radio both operate from the leisure battery, I will disconnect the leisure battery and flick the switch down.

And hope to goodness, the lights go out and radio goes off!!!

Be a bit careful, because if they are both connected with the switch on, even with the ignition off, then the +ve terminal from the leisure will be live all the time the switch is on. That could get sparkly.

[isaune]

Test done. As we suspected (hoped) when the leisure battery is disconnected the lights go out even when my switch is on.

And the main battery IS charging when the engine is running and the switch is down.

All good, nothing bad. And let me tell you it really is a very classy, if a little unnecessary, switch!!

One last question - I assume (from common sense rather than knowledge) that when the switch is on and we are driving along, the charge is SHARED between the two batteries so they each take twice as long to charge. So, if I ever was, for whatever reason, concerned about the state of the main battery, then it would be prudent to leave the switch OFF for a bit.

Is that right?

I suppose, thinking about it, it would be ideal if the starter could rely on the strength of BOTH batteries to start the ignition but I imagine that's just pie in the sky. Yes?

Thanks

Ian

[AdrianC]

One last question - I assume (from common sense rather than knowledge) that when the switch is on and we are driving along, the charge is SHARED between the two batteries so they each take twice as long to charge. So, if I ever was, for whatever reason, concerned about the state of the main battery, then it would be prudent to leave the switch OFF for a bit.

If you were ever concerned in that way, I'd be more concerned in trying to fix whatever fault was making you concerned. Or just go for a slightly longer drive.

I suppose, thinking about it, it would be ideal if the starter could rely on the strength of BOTH batteries to start the ignition but I imagine that's just pie in the sky. Yes?

The cable between the two won't be big enough to make any useful contribution. B'sides, again, if it becomes an issue it's only because you're working around a problem.

[Tobyt25]

Ive just gone for an easy option, quick release battery terminals and a plug in battery charger. Wiring is all hidden and leisure battery charges when connected to electric hook up.