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Battery Isolator question.


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I'm new to motorhoming. I bought a 2006 VW LWB Crafter conversion so that I can stick a large motorbike in the back.

On the electrical side it has 2 x 110 ah leisure batteries, a CBE PC100 controler, with a CBE 516 battery charger and a Duritc voltage relay switch. I have since also fitted a 120 w solar panel wired via a solar reg. into the controller. Everything works fine - EXCEPT all my 3 batteries show the same voltage - this was the case before I fitted the SP.

I found that the van battery would not start the van after about 3 or 4 days on my drive (this was before I fitted the SP). My understanding was that when plugged into the mains that the split charger and relay switch should charge the van battery and then switch to the leisure batteries, which may be the case - but why then do all batteries show a reduced charge after 3 or 4 days. I would have thought that the van battery would retain it's charge. My 2006 Fiat Scudo panel van can sit there for 2 months unused and still start 1st time.


I know that VWs have canbus computers and alarms etc. but would have thought that these would have little drain on the battery. Now I have the solar panel, the batteries are always charged up, but it would be good to know what is draining the batteries - as far as I am aware everything is switched off. I'm more concerned about the van not starting when away than not having enough juice for the tv, lights etc.

The green status windows on the leisure batteries say they are ok.

Are van batteries usually connected to the the leisure batteries or completely isolated - except for the charger link?


Would fitting an isolator switch into the van battery +ve cable solve my problems?

I have already replaced the van battery with a brand new one but same issue occurs.


Do other people have similar problems with van battery running flat.?

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Sounds like there's 2 problems here. All three batteries are connected in parallel, and something is draining them. If you buy or borrow a DC clamp meter you can quickly go round the wires and see where the current is flowing, it must be quite a drain for it to flatten 3 batteries in 3 days.
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We have had issues with the Durite Voltage sensing relay 'sticking closed' so permanently linking all three batteries. Usually following Jump starts.

What we think happens is that the 'donor' vehicle is connected to the 'dead' vehicle and the engine ran for about 10 minutes to put some juice into the dead battery. Standard Jump Start procedure.

However, during this process the 14.4v from the donor vehicles Alternator causes the voltage sensing relay to trigger linking the habitation batteries and dead starter battery together.

When the Starter on the 'dead' vehicle is operated enough power is drawn from the Habitation batteries, through the Voltage sensing relay fusing it in the closed position.


One we cut open after a jump start had the contacts welded together.


Try disconnecting the wire from the Starter battery to the Voltage sensing relay and see if the battery then holds a charge?


I suspect you have a duff habitation battery which is dragging down them all?

110Ah batteries (assuming they are the same size as a normal Motorhome Exide G80 style battery) will most likely be right at the budget end of the market, as the sturdier batteries in that size are lower capacity, like the G80 being only 80Ah.

Capacity is generally sacrificed to produce a sturdier battery, so a 110Ah is likely to be 'limited life' construction?

It may be that you have either one or both habitation batteries past their best as the budgets often don't make it to their second birthday and still retain any real power?


Try and isolate the Solar panel and isolate each battery.

An isolated good battery will still be at 12.8v/12.9v after 4 weeks, so test after 2 weeks and see what the results are. Important the test is done with the batteries isolated.








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Thanks for the input - I'll have to investigate each at a time - look for drains when off, disconnect the durit and see what happens, disconnect each battery in turn etc. etc.


I thought that I may have to do all this. There is rarely a silver bullet!


Thanks folks.

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