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

 

[ahtyrrell]

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

That description doesn't fill me with confidence!

Our PCB Board is manufactured by machines, not by hand !This is extraordinary
clean and it gives no cable tangle !

Our Material is First Hand Material!
We do not use "Second Hand Material" like many other supplier !

 

[sean_ork]

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

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

what utter nonsense .....

 

[ahtyrrell]

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

what utter nonsense .....

What your saying that you think its correct to fuse both live and neutral off a battery?

Also to the OP the red cover that is stuffed between the batteries should be attached to protect the terminal on live side of the left hand battery.

 

[sean_ork]

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

What your saying that you think its correct to fuse both live and neutral off a battery?

indeed - you have to remember that there may well be multiple live connections off the battery

 

[DieselShunter]

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

Batteries are DC devices. The terminals are usually referred to as Positive and Negative, and yes, in some circumstances it would be good practice to fuse both.

 

[Guest111]

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

the set up looks something similar to that used in rac vans, Firstly you cannot charge a 24v set up from a 12v alternator well you can but you need a lot of heavy relays and it all gets very complicated, second remember that an alternator on a vehicle must run at a minimum or 1500 rpm to put out charge so it isn't going to charge on tickover and finally there is no need to fuse the negative side of the supply as most negatives are in contact with the chassis anyway ( negative earth) as others have said either use a small genny or go to an auto electrician,if you have a go and it catches fire you may find your car insurance not paying out.

 

[ahtyrrell]

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

indeed - you have to remember that there may well be multiple live connections off the battery

Yes but in this instance there seems to be a single circuit added where both live and neutral are fused which is not required all live connections from the battery should be fused normally the terminal clamp also has several large fuses built in so that all circuits are protected as close to the source as possible. Also its very rarely necessary to connect back to the batteries negative as the vehicle chassis should be used,

 

[DieselShunter]

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

Phil,

When extra alternators are added to vehicles to run auxilliary devices, such as freezers in an ice-cream van or RF amplifiers in TV satellite uplink trucks, they are usually fitted with pully ratios that ensure the alternator will run at a suitable speed to provide rated output whilst the engine is at tickover.

There is most definitely a need to fuse both negative and positive connections in certain circumstances, for the very reason Sean explained. And the example in the picture that ahtyrrell commented on is ironically a perfect example of exactly when it is necessary and has been correctly done.

 

[sean_ork]

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

for what it's worth I think those pictures generally show an installation that has been carried out by someone who does know what they are doing, the invertor is of poor quality and there's a fuse cover and battery terminal cover missing, but the mounting of the fuses, the containment of the wiring and the general layout looks very good - nothing is perfect in this world