How to hook up onboard 12V charger to 4 batteries in series?

[northernmike]

Guys. I was wondering. I have a 12V AC Delco digital pulse charger I want to use for my moped conversion project, I'd like to mount it onboard - but my batteries are going to be hooked up in series. 4x 12V 7AH for 48V.

So.

Is there a simple way, with relays, or a switch, or something, to do this?

 

[Patriot]

Unless you had disconnects to physically seperate your 48v pack into 4 seperate 12v packs...

you're out of luck.

At least as far as I know.

If one was to try and split the leads into 4 paralleled sets in order to charge it in 4 seperate sections, the negative would essentially short itself to the positive, which means very bad things will happen.

I would advise just finding yourself a 48 volt charger.

I found some real cheap ones on ebay for only $25 shipped. HOwever, they claim they are for SLA only.

I plan on gutting one to see if I can adjust the voltage output for LiFePO4 balancing.

 

[northernmike]

Diodes?

 

[Roy Von Rogers]

I'm running in to the same problem. The simplest way I was able to do it was to use Anderson power poles. Put a power pole beween each 12v pack, you will need three sets, and jumper them to put pack in series. When you want to charge with your 12v charger, remove the jumpers, this way you can charge the batteries seperatly with one charger. Just put 4 black and four red power pole conectors on your charger, and plug in to the respective colors. And of course match those colors on the battery packs, so you cant get confused what belongs to which.

You also will need two extra connectors on the end of the 48v pack, and use those to connect to your system.

Have fun.

Roy

 

[northernmike]

Roy, what rated capacity Powerpoles are you using?

They are the natural solution, aren't they?

 

[bobmcree]

Diodes?

no. there is no number of diodes you could use that would let you do this. you can, as suggested, disconnect the batteries and charge them separately, and this is actually a good idea though it can be a pain. when you charge batteries in series, even sla, they may not all charge equally. there are devices like the powercheq that can be placed on each sla battery to make them share the load, and lots of people swear by them.

when you overcharge sla they bubble but are not damaged terribly if the overcharge is not too prolonged. when you overcharge ni-cd or ni-mh they get warm and if they do not get too hot they are not damaged. this effect makes it fairly easy to charge these batteries in series and you just keep charging until the last one catches up. if you do this with lifepo4 there is no mechanism to get rid of the extra charge and your expensive batteries may be damaged.

btw most 7 ah sla batteries are really not very good for high current. i would really try to use 12 ah if you are sticking with sla. you will likely only get about 4 ah out of your 7 ah batteries unless you drain them down so far their life is shortened radically.

 

[Roy Von Rogers]

Roy, what rated capacity Powerpoles are you using?

They are the natural solution, aren't they?

Use whatever amps that your pulling, Anderson has different inserts to match what amperage your needing.

Actually havent completed it yet, but was my answer to the same dillema. I put it on paper to get a visual, and thats how I came up with that answer. Its the only way, without going through a relay, which could be problematic due to amperage and vibration. As was mentioned it could be a pita to do it that way, but if done right would be the safest way of doing it.

I just bought a bms board from Gary, so I have a better way of charging/balancing. But will make up more packs which I will put in parallel, and the same problem will pop up, and I will use the system I reccomended to you.

I realy dont trust putting A123 cells in parallel, those cells cost way too much to take a chance on improper charge/discharge. So even if I use a bulk 42.2v charger, I want at least to be able to put a balancer on each 12s pack to keep in balance.

Roy