How do I charge 2 12V leisure batteries connected in series from my starter battery?

[Paul Lauener]

Hello electrical sparkly people!

Can anyone tell me I can charge two 12V leisure batteries from my starter battery? The leisure batteries are connected in series to charge a 24V 3000W (6000W peak) inverter. To confuse things, I also have two 12V batteries which came with my Ford Transit Jumbo T350 2L which I discovered under the seat today. I assume one is a starter battery and the other one is a leisure battery but I am not sure. I definitely have bought two leisure batteries. See extra info below for spec on batteries)

I know how to connect the two 12V batteries in series and I know how to connect a car battery to a leisure battery to charge it but I am not sure how to connect a starter battery to two leisure batteries.

The options I see right now are the following:
(In all of these options the two 12V leisure batteries are in series to power the 24v inverter)

1. Have two cables going from the positive terminal of the starter battery. One of them goes to the positive terminal of Leisure Battery 1 and the other goes to the positive terminal of Leisure Battery 2. In my mind this would mean that one 12v starter battery is charging two 12V batteries. My issue with this is that I have only one voltage sensitive relay (to stop the starter battery running flat) and I could only use that on one of the positive to positive connections.

2. Have a cable going from the positive terminal of one of the batteries under the seat to the positive terminal of Leisure Battery 1 and have a cable going from the positive terminal of the other battery under the seat to the positive terminal of Leisure Battery 2. In my mind this means that one 12v battery is charging one 12v leisure battery and the other 12v battery is charging the other 12V battery, which may be more efficient. My issue again is that I only have one voltage sensitive relay stop the starter battery going flat. My assumption in this scenario is that both batteries are getting a charge from the engine and that they can both pass on their charge to my other leisure batteries.



I have attached some pictures and below is some extra information. From the extra information below or the pictures, can you tell which one of the batteries under the seats is the starter battery and if one of them is the starter battery?


For a while I had one of the batteries under the seat (when I thought there was only one there) wired in series to my one leisure battery (before I bought a second) and so I had a 24V supply supplying my 24V inverter and for a night I had a fully working power supply and was running power tools and all sorts off it. For some reason it then stopped working and the inverter now sounds a fault light and shows that it is receiving only 20V and hence doesn't work.


Extra confusing question:

Can I connect the existing light set up in the van to my leisure battery set-up?

The van was previously owned by electricians and they have what seems to be an impossibly complex system of lights wired up to these two batteries under the seat. I use these lights and the cigarette lighter attachments now but I keep running the starter battery dead and having to get jump started. Ideally what I would like to do is connect this existing wiring and lighting set-up to my leisure batteries so they don't keep charging down my starter battery. I am at a bit of a loss of how to do this. One of the pictures shows the two batteries under the seat with all kinds of wires going from them.

There is also a grey metal box in the back (see picture) Do you know what this is for? Is it an inverter?


Thank you or any help. I have been struggling with this for a couple of months now.

Extra information:

One of my leisure batteries is this:
Numax CXV31MF Sealed Leisure Battery 12V 110Ah 1000MCA 500 Cycles XV31MF - Leisure Batteries - Numax Leisure Batteries
Numax CXV31MF
Sealed Leisure Battery
12V 110Ah 1000MCA
500 Cycles XV31MF
The other leisure battery is a
VARTA LFD90 12V 90Ah (C20) 77Ah(C5)
RC174Min CCA (EN)800A MCA1000A

One of the batteries under the seat is a
Ford Finis 1 682 038
Part 8G9N-10655-PA
12V 135RC
Silve Calcium
700cca 80Ah SAE T7
Plant Dsv5A

The other battery under the seat is a


12V CCA SAE 900 amps
Ah (20h) 90 amps

The voltage sensitive relay is
Durite 12V 140 amp
Cut in 13.3 amp
cut-out 12.8 amp
0-727-33

 

[Dizzy_Maskell]

Best advise get an electrician look at it or take to professional outfit

 

[ayjay]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

asking on here is futile, lots of silly boys(not all) or apprentices or 5 week wonders

does it work as is? do the lights illuminate with the engine off?

the batterys maybye past their sell by date check that)
run the engine and check the charging current with a proper meter ect ect ect

 

[Paul Lauener]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

Best advise get an electrician look at it or take to professional outfit

Surely someone can do better than that as a response... What's the point of a forum if I'm going to be told to take it to an electrician?

 

[Paul Lauener]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

asking on here is futile, lots of silly boys or apprentices of 5 week wonders

does it work as is? do the loghts illuminate with the engie off

the batterys maybye past their sell by date
run the engine and check the charging current with a proper meter

The lighting system works because that is an existing system that already works. I want to set up an inverter system as described in the post. The two leisure batteries are brand new.

 

[ayjay]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

hi paul
electricians dont normally get into that kind of system
there are some older fellas on here that migh be of assistance i used to wire vehicles ans have experience whilst working at a new credit card site all dc an battery back up

 

[telectrix]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

if your batteries are in series then you just need to power the inverter across the 24V of both batteries. if they are in parallel, buy a 12/240V inverter. best advice is an auto electrics forum. we have enough problems wrecking houses without buggering with vehicles.:6:

 

[Coach]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

Hi Paul,

Try this link to the MMM mag. and click on Motorhome matters. There are a lot of knowledgable people on this site, including Auto electricians and Mechanics. Copy your post onto here and somebody should be able to help.

Motorhome, Caravan and Camping Forum | Out and About Live

Clive.

 

[mpb]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

You need to install a split charge system to charge the aux batteries. Look on the net for a VSR (voltage sensitive relay) You connect this relay to the starting battery and the aux battery. When the engine is running and the main battery voltage gets to a set level it closes the relay and starts to charge the second battery.

Martin

 

[UNG]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

Surely someone can do better than that as a response... What's the point of a forum if I'm going to be told to take it to an electrician?

We probably could but your description of what you have is not very clear you have a starter battery of what voltage if it is 12v then it won't charge two 12v batteries in series this what bothers me giving any advice on a forum

Working with batteries can be VERY DANGEROUS I know of people who have been injured one guy lost most of his sight just topping a battery up. Batteries can flow many hundreds of amps with one wrong connection causing fire and / or explosion

For your own and other peoples safety get someone who has the experience of working with batteries to take a look at it

Hope this meets with your requirement of a better response and you heed the advice

 

[Dizzy_Maskell]

Surely someone can do better than that as a response... What's the point of a forum if I'm going to be told to take it to an electrician?

We probably could but your description of what you have is not very clear you have a starter battery of what voltage if it is 12v then it won't charge two 12v batteries in series this what bothers me giving any advice on a forum

Working with batteries can be VERY DANGEROUS I know of people who have been injured one guy lost most of his sight just topping a battery up. Batteries can flow many hundreds of amps with one wrong connection causing fire and / or explosion

For your own and other peoples safety get someone who has the experience of working with batteries to take a look at it

Hope this meets with your requirement of a better response and you heed the advice

This is exactly my point there is nothing worse than someone "having a go" to save a few quid if you are not sure what to do please pay someone who does, is it worth risking serious injury for an hour or two of a professionals time ?

 

[DieselShunter]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

Paul,

It looks as if the van already has a 12V leisure battery and associated charging arrangement. You haven't said what that is used for, and if you still need it. But it's of no use to you for the 24V system.

My first observation is that the two new 12V leisure batteries you're trying to add to make a 24V system are two different types of battery, with different capacities. That is VERY unwise. If you're going to add a 24V battery inverter system then the two 12V batteries should be identical.

The inverter you're using is huge. What is it intended to power? Bear in mind that at 3kW it will flatten your batteries in about 30 to 45 minutes. And it is always unwise to deep cycle your batteries, their life expectancy reduces dramatically if you drain them beyond 80%. The only place I've ever seen an inverter of this size was in an ice-cream van, where it was used to power the two chest freezers. In that situation it was designed to be used with the engine running to constantly recharge the batteries. That particular vehicle had a separate 24V 120Amp alternator specifically for that purpose.

There is no possible way you can recharge this new 24V battery/inverter system from the 12V vehicle system, whilst having it wired to power the inverter at the same time.

If you wanted to charge the 24V system from the vehicle system whilst your not using the inverter, then you could design a switching system that would isolate the 2 X 12V leisure batteries and allow them to be charged as 2 X separate 12V batteries. It's a pretty cr@p idea though, I seriously council against it.

My advice is:

- don't attempt to interconnect the existing 12V system with the new 24V system;
- don't use two different 12V batteries for the 24V system;
- add a 24V alternator specifically for the new 24V system;
- and be careful. One silly mistake and you've got a 1,000Amps of fault current!!

 

[ahtyrrell]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

As above, auto electrics can be very dangerous due to the high currents that can flow and the likely hood of chaffed/trapped wiring causing shorts and fire. It is not possible to charge two 12 volt batteries that are series linked form a 12 volt system, your suggestions seem to suggest wiring that will actually result in a dead short across one battery. You need to do allot more research on an appropriate forum and learn how to wire automotive systems properly using the correct installation methods, connectors and convoluted tubing etc. Also the wiring in your picture appears to show a circuit with a fuse on both the live and neutral while this is not dangerous as such un-like domestic systems it shows a complete lack of understanding on the part of who ever did it

 

[ahtyrrell]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

Also depending entirely on what your using the invertor for a generator may be a much more efficient system, as leaving a car engine ticking over to charge batteries up does not do allot of good

 

[DieselShunter]

Re: How do I charge 2 12V leisure batteries connected in series from my starter batte

And just for good luck, the unshuttered 13A sockets on the inverter are illegal.

Dunno where you got the inverter, but I found a differently branded, but identical looking one on Amazon:

6000 Watt Peak 3000 Watt Modified Sine Wave Power: Amazon.co.uk: Electronics

Reading the specifications is a revelation. This inverter that is rated 3000Watt continuous suggests maximum loads of 50Watts for fridge/freezers, and 30Watts for a fluorescent light. And the 6000Watt peak is for 5mS - that'll be, erm, a quarter of a 50Hz cycle then!

At £140 it looks like an expensive firelighter to me.