Stacking 12V Batteries To 48V

[sshaun302]

I posted a similar question in another area and think I should have put it in here. Here is the story, I bought an all-in-one charge system/inverter. The internal charge controller is 48 volts. The inverter is 48 volts. I am looking to save quite a bit of money on the batteries and found that hooking four 12 volt batteries in series is far cheaper than buying one 48 volt battery. The batteries would all be lithium and the brand would be on the cheaper end like a Chin's or similar. The four stacked 12 volt batteries produce the same amount of watt hours as the single 48 volt battery and save $1,000 - $2,000 dollars in the process.

Here is question. Is it ok to charge the four 12V batteries which are tied in a series using the 48V charge controller?

A person who responded to the other post said, "Maximum of 51.2v doesn't make any sense for a 48v system as that would be 12.8v per battery or 3.2v per cell which is not enough to charge the battery. That would be nominal mid state of charge voltage. Max full charge would be 16x 3.65v = 58.4vdc". I am grateful for their response but am very confused by it. Can anyone help me understand what I might be missing?

Thank you all very much for your help!

 

[DerpsyDoodler]

I posted a similar question in another area and think I should have put it in here. Here is the story, I bought an all-in-one charge system/inverter. The internal charge controller is 48 volts. The inverter is 48 volts. I am looking to save quite a bit of money on the batteries and found that hooking four 12 volt batteries in series is far cheaper than buying one 48 volt battery. The batteries would all be lithium and the brand would be on the cheaper end like a Chin's or similar. The four stacked 12 volt batteries produce the same amount of watt hours as the single 48 volt battery and save $1,000 - $2,000 dollars in the process.

Whatever batteries you purchase and plan to put in series need to have a BMS capable of handling 48v nominal throughput (at full state of charge is roughly 58.4v on the high side). It's not just as simple as buying 4 of any 12v battery and slapping them in series.

Here is question. Is it ok to charge the four 12V batteries which are tied in a series using the 48V charge controller?

Yes. You may need to balance them on occasion.

A person who responded to the other post said, "Maximum of 51.2v doesn't make any sense for a 48v system as that would be 12.8v per battery or 3.2v per cell which is not enough to charge the battery. That would be nominal mid state of charge voltage. Max full charge would be 16x 3.65v = 58.4vdc". I am grateful for their response but am very confused by it. Can anyone help me understand what I might be missing?

Thank you all very much for your help!

The charge voltage is always higher than the nominal voltage. For an LFP 48v battery, at full charge, its voltage measures 58.4v. This is also its "charge" voltage (the voltage you set the charger to). As the stored energy is used, the voltage will drop. Depleted stated of charge voltage for an LFP 48v battery is about 40v. Does this clarify?

 

[sshaun302]

Whatever batteries you purchase and plan to put in series need to have a BMS capable of handling 48v nominal throughput (at full state of charge is roughly 58.4v on the high side). It's not just as simple as buying 4 of any 12v battery and slapping them in series.



Yes. You may need to balance them on occasion.


The charge voltage is always higher than the nominal voltage. For an LFP 48v battery, at full charge, its voltage measures 58.4v. This is also its "charge" voltage (the voltage you set the charger to). As the stored energy is used, the voltage will drop. Depleted stated of charge voltage for an LFP 48v battery is about 40v. Does this clarify?

Yes, it does clear things up a bit. Am I understanding correct that maybe the reason to not use the 12v batteries in series is because, when the batteries are running low, I wont be able to use them for my 48 volt system?

 

[rmaddy]

Am I understanding correct that maybe the reason to not use the 12v batteries in series is because, when the batteries are running low, I wont be able to use them for my 48 volt system?

No, this is not a reason. There is no difference (voltage-wise) between 4 12V batteries in series and a single 48V battery. They will be the same when full and when nearly empty and anywhere in between.

The four stacked 12 volt batteries produce the same amount of watt hours as the single 48 volt battery and save $1,000 - $2,000 dollars in the process.

I'd love to see real numbers on this. You can get an EG4 48V 100Ah LiFePO₄ battery for $1500. 4 12V 100Ah low-end LiFePO₄ batteries will cost over $1300. Better quality 12V 100Ah LiFePO₄ batteries will easily cost over $2000 for 4.

 

[time2roll]

Yes, it does clear things up a bit. Am I understanding correct that maybe the reason to not use the 12v batteries in series is because, when the batteries are running low, I wont be able to use them for my 48 volt system?

The issue is such that if one battery trips off for low voltage (or high voltage) it needs to be compatible with shutting off all 48 volts. Some are only designed to control at the 12 volt level. The manufacturer can verify how many in series are allowed. Otherwise in normal use the 48 volt system is exactly 4x a 12v system.

I would also price in a balancer between the four batteries before they seem to be lower cost vs. a 48v battery.

 

[sshaun302]

All makes sense. Thanks everyone! I was looking at 12V 200 AH batteries. The numbers were approximately as follows: one 10KWH 48 volt battery was around $3,400 with shipping (brand was BCS and didn't see much information out there about them...other brands were a bit pricier). .....four 12volt 200AH with 9600 watt hours totaled around $2,500 (Chin's or brands similar)....the numbers did not make sense at all to try to stack 24V batteries, so I eliminated that idea altogether.

 

[rmaddy]

FYI - 1 48V 200Ah battery is 10,240Wh. 4 12V 200Ah batteries is also 10,240Wh. This is why there is no real difference (voltage and power wise) between 4 12V batteries in series and a 48V battery.

Remember, a 12V LiFePO₄ battery is really 12.8V. A 24V LiFePO₄ battery is really 25.6V. A 48V LiFePO₄ battery is really 51.2V.

The EG4 48V 100Ah battery is $1500. Two would of course be $3000. So that's a lot cheaper than the BCS 48V 200Ah but still more than the 4 cheap Chin's 12V 200Ah.