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I have a 48V battery bank made up of 4 deep cycle 12V batteries in series. My charger only has 12V and 24V options.

I've considered using relays to put the batteries in parallel and charging at 12V. I'm assuming there has to be a better way. Ideally, one that allows all 4 batteries to remain in series.

Is there a common method to do this? What effect would charging one 12V battery have on the other three in series?

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The common solution, unfortunately, is to use a 48V charger.

I can think of two potential problems with charging the batteries in circuit. First, you want the batteries to have the same charge since they are in series. If you charge them one at a time, while there is a load on the bank, they may become out of sync, some charged, some less charged. If you remove the load while charging, this would not be much of a problem, I guess, but charging them in series would still be better in terms of keeping them synced up.

Second, there could be some kind of grounding issue. Does your charger ground the battery negative terminal to earth ground? Does it have an isolation voltage rating? Does your 48V bank, or the inverter connect 48V ground to earth? Just to be explicit, imagine this. Your charger negative is earth grounded. When you charge the bottom battery, no problem. When you charge the next battery up, you would actually be shorting battery 1 + directly to battery 1 - by way of earth ground. That would be bad.

Good luck!

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In my opinion, the better way to charge those batteries is to use individual 12V chargers for each battery so that they all charge at the same time. However, you MUST ensure that each charger's output is completely floating with respect to earth ground. Most charges DO have floating outputs but some have the negative lead connected to the AM Mains earth terminal. You have to check.

Obviously, all 4 chargers should be identical.

The reason I suggest charging the batteries individually is you lessen the chance of one or more of the batteries of becoming either under-charged or over-charged.

It's probably also less expensive than purchasing a dedicated 48V charger - good-quality 12V chargers often go on sale at decent prices.

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Charging the 12 volt batteries individually would be a Bad Thing, as you want alll the batteries in the 48 volt bank to be in the same state of charge.

Ideally, you should use a 48 volt charger, but I think it would be acceptable to use two 24 volt chargers, one on each half of the bank.

Note that many marine or RV chargers claim to charge two or more battery banks - however their outputs all have a common ground, so cannot be used in your situation.

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  • \$\begingroup\$ Why is charging the 12 volt batteries a Bad Thing, but splitting them into two banks and using 24V chargers acceptable? \$\endgroup\$ – Johnny Feb 3 '15 at 21:57
  • \$\begingroup\$ In my first paragraph, I was thinking of taking the four batteries out of the circuit, then charging them separately. I think it would be OK to leave the batteries connected in series, then using four separate chargers, one connected to each battery. In this case, the outputs of the chargers must not be grounded, or otherwise connected together, except by your connections to the batteries. \$\endgroup\$ – Peter Bennett Feb 3 '15 at 22:11
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I have a 48v bank made up of 24 2v 500Ah cells. for simplicity and faster recovery after a power failure, I use 4 Noco Genius 12v smart chargers. if you have access to the individual cells then you can use a hydrometer and check the charge state per cell and if you have a difficult cell then you can deal with it.

It is very important that whatever chargers you use have floating leads. This is because if as others have stated, charger 1 has a negitiv lead to ground connection and you add charger 2 to battery 2 the charger 2 negitive lead being also grounded is now also attached to the positve lead of battery 1. this creates a circuit through the ground and shorts out battery 1.

Bank chargers in general share the same sources so are not good for series banks. There are some with the proper protection built in but are still not effective due to the low charge rates. eg 12v 4battery bank charger food for series applications with 24A capacity. take the total capacity an divide by number of batteries: 6A ea. a 240Ah bank will take approx 48hrs to completely recharge. this adds the extra time for absorbtion and top-up. now if using 4 individual 24A chargers it will take 12hrs to recharge.

Using smart 5 or more stage chargers will ensure that the batteries are always in sync and always fully charged with the least amount of fluid loss. Just make sure you do not load split these batteries as that will cause issues with bank availability. load splitting is taking a 12 or 24v load and tapping the bank for it. this of setts the bank by that load current and will cause uneven discharge rates and thus can (and usually does) damage that battery. this is easily seen as the 36v bank trying to push current through a dead 12v battery. it tries to charg that battery as it supplys the load and this boils the dead battery.

in summary: use good quality smart chargers that have floating leads and make sure you have at least 10% of your banks Ah rating in charger capacity. Using 4 individual chargers does not add together for capacity. use on chargers capacity as total charging capacity. and dont mix and match chargers. use 4 of the exact same chargers. that way all specs and calcs are the same.

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can charge 4 nos 12v battery in 24v charging system but the battery capacity (AH) must same,otherwise charging time varries also low capacity (AH) Battery will charge Early.You must check the chager capacity minimum 24v/10A ,you didnot mentioned battry capacity & Chager capacity.But 12v/80AH or 13 Plate Battery ,4 Nos can charge in this charger. Please very careful connect TWO Battery Series so this is one set also connect another set ,so each set have one end +ve Terminal & other end have -ve Terminal then connect Two Sets as Parallel ,switch on charger select 24v & set current rate .dont use in invertor & Ups. Indian.

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Listen they are batteries and yes you need to be very careful not to cross wire as this will short the battery. However you can charge 48v with a 12v charger it will just take a lot longer also the slower you charge your battery the more life you will get out of it charging at a high rate does damage battery faster less life on battery. I have a scooter that i wired in a series battery bank I use a 12v charger to charge battery which is 36v it takes about 10-12 hours to charge but it does ive had the scooter for 3 years and the batteries run and charge great fluid is still pretty much full I could take the batteries back now and they wouldnt even know they were used. Be careful buy the correct charger if you want a faster charge time but if you have a weekend event planned well plug it in on thursday everybody wants to be more tech savy than the next a pos is pos neg is neg a wire is a wire blah blah. Oh no make sure your series 1-9 dv data base port control model synth connects to the switch 5 route mega ac computer mother media hdmi yeah yeah get a charger read instructions everything you buy tells you how to use. Stick to that and everything will work stop trying to rig things or hope there is a secret way to do it and get the tools for the job.

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  • \$\begingroup\$ Why don't I want to short the battery? Is it dangerous? \$\endgroup\$ – curtis Sep 9 '15 at 0:26

protected by W5VO Nov 15 '15 at 17:44

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