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.

You can just answer the questions above and I will be very grateful or you can read on below and perhaps get more confused.


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:
http://www.tayna.co.uk/Numax-CXV31MF-P3694.html
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

 

 

Attachments:

File comment: What seems to be the connection to the existing lighting system from the two batteries under the seat. Can I connect this to my leisure batteries? 20130825_185617.jpg [ 263.85 KiB | Viewed 223 times ]

File comment: The mystery box in the back of the van. Is this an inverter? 20130825_192935.jpg [ 175.76 KiB | Viewed 235 times ]

Wow sounds complicated...

So you have a 24V inverter that you want to run off a 12V vehicle? Well it ain't going to work... You just can't hook it up like that... If you hook your 2 lesiure batteries in series and then in parallel to charge them at the same time that's a massive short circuit... You can't connect one under seat battery across one leisure battery and the second across the second leisure battery with the leisure batteries in series because that's a short circuit too...

Both those under seat batteries look factory installed judging by what is clearly ford wiring under there and the hold down plates and that... In saying that only one is a genuine ford battery... Can't tell from what wiring you can see, they may just be hooked in parallel all the time? The right hand one but has massive cables coming off it so that has to be the starter one... But if both are connected in parallel then they're both starter batteries...

If your inverter is going out on low volts and you have two batteries in series, but only had the charge across one of those batteries than one is flat and this why you are only getting 20V at the inverter...

If you have a 12V vehicle and need to charge a 24V system for the inverter you need a charger like this:

http://www.redarc.com.au/products/produ ... arger-40a/

It will accept 12V in and step it up to 24V to charge those 2 big 12V batteries in series hooked to that inverter...

The wiring for the charger can be seen here:

http://www.redarc.com.au/handy-hints/-/ ... tallations

And the instructions can be downloaded... I have the 20Amp model in my work ranger charging the second 80AH battery which runs the 1500W inverter... The 20amp is a touch on the small side in my opinion but I survive by doing such long drives... For that size inverter and that sort of battery capacity I'd think you'd want the 40A model...

This is going to be the easiest way to charge your 24V system without forever having to break the series connections to make parallel connections to charge while driving... That'd be a bastard...

No idea on the silver box... looks home made... Maybe just a fuse panel with a couple of ciggy sockets on board?

If that were mine I'd be pulling the whole lot out and starting fresh... Some auto sparkies are as rough as bags and looking at what yours showing it looks rough... Cheap nasty inline crimps, no solder connections, fuse in both positive and negative wires, cut off wire dangling in the breeze, the two dodgy looking fuses mounted on an insulating panel instead of using good fuses or circuit breakers...

Hate to say it but I wouldn't be taking that anywhere until I was sure it wasn't going to burn to the ground on me...

Cheers,
Tim

Hi Tim,

Thanks for such a great reply. The device you have suggested I'm sure is great but is very expensive.

Regarding the short circuits, didn't I already have the same set-up when I had my starter battery wired to one leisure battery in series?

Also, if the starter battery and leisure battery were wired up in series, doesn't that make them into one big battery? In which case if one is getting charged then the other is getting charged as well? Any suggestions for how I could make it so the leisure battery is getting charged as it is is now currently wired up in series to the starter battery?

Best,

Paul
P.s. As you can maybe tell, this is all pretty new to me..

Yeah I don't think you understand why it won't work... I'll draw some pictures tonight and attach them in here...

Put simply without something to step 12v up to 24v it won't work.... You have two options... Either buy some form of 12v in 24v out charger or sell the 24v inverter and buy a 12...

You're right, what you had hooked up seemed to work... But now your inverter is going out on low volts isn't it?

I'll explain it tonight after work...

Cheers,
Tim

Hi Tim,

Well, I had wondered about the 12v to 24v issue and hoped it might charge but just more slowly.

The setup I had working for a while doesn't work now, correct, as the inverter shows a voltage drop, so it looks like I hadn't connected it properly, or perhaps to the wrong one of the two batteries. I had it connected to the Ford battery on the right. You can see the long thin red cable trailing away. Perhaps it would charge if I connected to the positive terminal on the other battery?

In any case, I have considered your advice so far and the massive difficulties this has posed me and decided that I need to just get hold of a 12V inverter and then just wire the two leisure batteries to it. I am trying to get an exchange off they guy who sole me the 24v inverter.

So, once I connect the two leisure batteries in parallel, positive to positive and negative to negative, I intend to connect one of the starter battery's positive terminals (I suppose it should not be the Ford battery's positive terminal as that wasn't charging the leisure battery before?) to my 12v voltage sensitive relay ( I will earth the relay) and then the 12v voltage sensitive relay to the positive terminal of one of the leisure batteries. (Does it matter which leisure battery terminal I connect to?) I will then connect one of the leisure battery's positive terminals (Does it matter which one?) to the positive terminal of the inverter and earth the negative terminal of the inverter.

Does that sound right?

Thanks a lot for your help.

Paul

Paul,

Yeah sounds like you've saved me drawing pics then... My paint skills ain't so good...

If you hook your one start battery across one leisure battery with the other connected above that in series then only one will charge... The other will die from under charge (keep in mind once a SLA battery gets to 10VDC it is generally cactus...)

Doesn't matter how you connect what you have now... You can't make it work without taking the 12V you have present there across either of your main batteries and then stepping that up to 24V to charge across your two leisure batteries connected in series...

The only way you can do it is to connect all batteries in parallel so they charge at 12 volts... Then when you want to use your inverter disconnect the parallel connections between the leisure batteries (positive to positive and negative to negative...) and make a series connection (positive to negative) and then run your inverter and when they go flat break the series connection and make the parallel connection and then charge tehm from 12 volt again...

And that'd be a real pain in the a**...

Yep sounds good... If that ford battery has 13.8 to 14.5 volts across it with the motor charging then connect it to that battery... That battery is charging fine and will charge your leisure batteries in parallel (check both your leisure batteries to make sure you haven't dropped one under 10V, if you have it may be stuffed)... It didn't charge them before because you were only charging one of the two batteries... So yeah, ford battery to relay, relay to leisure batteries in parallel and then them to the inverter and no doesn't matter which battery post... whichever gives the shortest cable and or looks the neatest and or is most practical as far as bolt length for lugs or the sort...

Cheers,
Tim

Hi Tm,

Thanks for the explanation and advice. Itis very hard to find someone, including car mechanics, who can help with this. I think the first Numax leisure battery may actually be dead for the reasons you mentioned. We tried to charge it with a fancy mains battery charger overnight and it hasn't charged. At least I have the other Varta battery to work with at least.

When I get the inverter tomorrow I'll try and get everything wired up and let you know how it goes.

Cheers,

Paul

Excellent good luck...

Yeah that's no worries... I'm a sparky by trade and auto sparky by hobby... Happy to help and shed some light...

I'd have thought it to be cactus... If you had 20 at the inverter and one would have been charged properly to say 13 volts then your second would be 7V and i'd call that buggered for sure...

Cheers,
Tim

cant remember but check if vehicle is 24 volts - owners handbook specs, or pull an easy to get to globe and check voltage on it(eg.24v 21/5w etc.)

Ted,

You can see it isn't 24V... Both the installed batteries under the seat clearly have the negative posts connected together... The positive posts are a little hard to make out... And the transits we've had at work are all 12V...

Cheers,
Tim

Tim,
unable to open attachments at the moment,have worked on early transit bus that was 24volt,was making sure.
you can charge 24v series connected batteries off 12v system using series/parallel circuit but not practical due to cost of heavy relays when switched to 24volts to run inverter, it would be cheaper to obtain 1 or 2 12volt inverters and use split charging system to charge auxilliary batteries to operate.

Ted,

I agree... It could be done but you need a few relays and there is always then the added complication of the circuitry and on that note heavy circuitry, heavy wire and suitable lugs for termination... And everything is switching on around short circuits... You only need one contractor to fail and not open or close and you could have a big short circuit again... So you need to then add in adequate protection to prevent damaged to the equipment...

Just one big headache... 12V inverters on a 12 volt system are sure as hell easier...

Cheers,
Tim

Hi Tim,

Happy New Year!

I got the battery and inverter set-up working nicely. Here's a good one for you:

I'm going to a trade show in Munich where I only have a 250W plug socket provided and included in the price or I can pay €150 to get a 3000W socket. I want to run four 150W lamps with plugs and not pay the €150.

Here is my possible solution: Use the socket to connect to a battery charger. Connect the battery charger directly to my 3000W inverter and then connect my light to the inverter. Can an inverter be powered like that? If I can do this it will save me a lot of money at trade shows : )

Thoughts appreciated.

Best,

Paul

Hey Paul...

Happy new year to you too... Sounds like an interesting holiday...

You mean they're power points are 250w? What voltage do they run? You sure it's not a typo? 250 is only just enough to run a laptop... Sounds wrong...

3000w output means you need 3000w input plus losses... So 3000/12=250... So your charger will need to supply a continuous 250 Amps plus cabling will need to able to handle that... Even if you load it to 600w as you say that's 50amps... And if you do have a charger that will continuously it must be the dumb type... Those new ctek and similar chargers won't drive a load because the monitor the battery... Although my 15amp ctek does have a "supply" setting where it just pumps out a straight 12v...

Cheers,
Tim