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Hi. I'm trying to understand (in a simple way) how my starter and leisure batteries work together in my Mazda Bongo. The van also has a Zig unit. The main appliances running off DC (when not hooked up) are a 12v/240v fridge, led lights and the radio.
I've had the van for about 7 years, mostly things are fine, but occasionally I seem to manage to drain the starter. I also suspect the leisure battery could do with replacing as it is over 4 years old and gets several months of use each year.
I definitely have some sort of split charger, and the Zig unit is capable of recharging the batteries when hooked up. It can also provide AC power to the fridge.
A couple of things are confusing me:
A few days ago (in 30+ degree heat) the fridge shut down after less than 10 hours (on 12v). But as I write this, it has been running for 14 hours and still going strong. The leisure battery reads about 11.8v
But, the starter battery also reads about the same. It seems like both batteries drain and recharge together, even whilst the van is parked up and not on EHU. Shouldnt the starter battery sit at around 12.4v or more (ie ready to start the van, and then recharges via the alternator). I thought the split charger relay would isolate the leisure battery when the engine is off.
I just disconnected the leisure battery, and the fridge continued to run. This was surprising! Should I be worried? The fridge probably has a voltage based auto cut-off, but isnt that designed to protect a slow discharge leisure battery, not a starter type battery?
The Zig unit has a "Car or Caravan" battery select switch. I've taped this down so it always selects the leisure battery. Why would I want to draw power from the starter? It also has a battery indicator (red or green light) - but it only ever shows green (for good).
Sorry, a long message. Maybe this comes down to me trying to understand why the relay isnt blocking off the starter battery when the engine isnt running (so all appliance can ONLY run off the leisure). Or have I misunderstood what the relay is supposed to do.
Any recommendations for a good Auto Electrical forum where I can ask this sort of stuff or get more info?
Thanks!
Sounds like there's either some dodgy wiring going on and/or a knackered split charge. The fridge definitely shouldn't be running off the starter battery if you've got a leisure battery too.
I've just rewired my van as I ripped out an overly complex electrical system when I removed my camper interior and fitted a more practical kombi interior with lights/USB sockets/12v socket etc. Had some help off a mate who is a sparky but most of the stuff I bought was from 12voltplanet.co.uk. For the money, it might be worth getting a voltage sensitive split charge unit that doesn't need to be hooked into the alternator like this: https://www.12voltplanet.co.uk/voltage-sensitive-relay-12v-140a.html
Theres also a campervan electrics group on facebook which is dead good.
I thought the split charger relay would isolate the leisure battery when the engine is off.
AFAIA it should isolate the starter battery when the engine is off so all power comes from the leisure battery.
This was surprising! Should I be worried?
That doesn't sound right.
Maybe your SCR is borked?
Relays get stuck, especially if switched unDer load. Test the relay.
Any help with how to identify and test the relay? With the engine running, the voltage on both batteries is up over 13v.
You need to find the relay unit and trace and identify the cabling from your starter battery. As others have said nothing should be draining from the starter battery. It may be an old relay unit that needs replacing. If it was me I would find it and assuming its one of the older basic switch types, replace it.
I have a T6 and installed the elctrics but they have a Euro 6 clever Alternator thing which is different than the previous ones. As above it may be that the relay is open and treating as one battery unit, charging and draining as one unit.
Is it possible that the relay could be connected pretty much directly to the starter battery and contain several fuses? Having trouble identifying it!
Or recommendations for a good auto sparky that does call outs in Bristol
Make sure you don't run down the leisure battery
You don't want it going down 12 volts very often.
Even though i have a split charge relay i hook mine up to a ctek intelligent charger which tops it up
i installed a battery voltage indicator in my van so i know the current charge state of the leisure battery
Is it possible that the relay could be connected pretty much directly to the starter battery and contain several fuses? Having trouble identifying it!
Normally looks like a black block like this
It will connect the 2 batteries together with some fuses
Thanks Tricky - yes, I would have hoped that the fridge would auto shut off before reaching those danger levels. Apparently something else that I need to get checked out.
I have a voltage indicator plugged into the cigarette lighter socket, that was actually another question - is it displaying the leisure or starter battery voltage. As they are also pretty much the same in my case, I cant really tell (I guess I could disconnect them in turn to work it out!).
Having trouble identifying it!
Show us what you've got.
It should be (AFAIA) a single unit the size of a small tin of beans with positives from both batteries and the charge cable going to it.
Mine (on a boat but the same thing) has a light on it to show when the batteries are linked.
You can also hear the relay switch when the starter battery has reached the target voltage.
Check the starter battery voltage before starting the engine - unless it's very charged already the relay shouldn't kick in immediately.
My 2 battery's negative terminals are connect by a continuous fused cable. Both positive terminals disappear out of the bonnet area to what seems to be the interior (behind dashboard) area. I've emailed a couple of electricians, I think I need some help!
I just tested the fridge with the starter battery disconnected, and it doesnt work. But it does work off the starter battery with the leisure disconnected - that aint right!
But it does work off the starter battery with the leisure disconnected – that aint right!
Definitely not right.
Have you tried swapping the positive cables on the batteries to see what happens.
For all we know you may have the two swapped!
That definitely hasnt happened as the cables arent long enough to have been swapped
Thanks Tricky – yes, I would have hoped that the fridge would auto shut off before reaching those danger levels. Apparently something else that I need to get checked out.
Mine doesn't do this. I think you have to have something else installed to do this. I think something from victron.
There are 2 types of relay. A split sharge relay and a voltage sensing relay. I'm told the latter is better
Mine doesn’t do this. I think you have to have something else installed to do this. I think something from victron.
This does the same thing and you can wire it yourself.
Dont mean to offend but I would not be disconnecting battery cables etc if you are not confident. If it was me I would strip it back carefully and using my tester troubleshoot a step at a time. If you aren't confident I would get somebody to look at it for you.
A split sharge relay and a voltage sensing relay. I’m told the latter is better
Ahh, yes. Mine is the latter - an ACR (automatic charge relay).
It senses the voltage of the starter battery and does not start charging the house battery until the starter battery has reached a certain level of charge.