Currently I have two banks of lifepo4 24v each with 300AH with respective BMS connected in parallel. It is running fine at 24v. Now I want to run 48v system using same battery banks and connect them in series. Is there any problem with the connection as each battry bank has its own BMS?. Appreciates any comment and recommendations.
Connecting two battery banks for 48v in series
- Thread starter Daham
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Yes, this can be done. The Ah will not change since the connection is in series. Only the volts change. Some battery manufacturers say it's OK to series connect their batteries, some don't give that approval.
If these are DIY batteries that you created, my preference is to take the cells apart and make a 16s battery with a single BMS.
If these are DIY batteries that you created, my preference is to take the cells apart and make a 16s battery with a single BMS.
GXMnow
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There are two possible problems when you series separate BMS units. The first one is that the 2 separate BMS units can't balance between the two strings. This could cause a situation where one bank is fully charged into the upper knee while the other is still in the flat voltage area. That can cause one BMS to overvoltage disconnect while the other string is not fully charged. The same could also happen on the bottom end. The second problem is when one BMS does disconnect. The possible voltage across the open BMS during a shut down is now double. Many cheaper BMS units are not able to handle that much voltage and components could fail. I agree with HRTKD, you should replace the 2 8S BMS units with a single 16S BMS. That fixes both issues.
One of the battery banks is connected as 2parallel and connected in 8 series making it 24v 300AH while the other bank is 8, 280 AH cells connected in series. The two banks are connected in parallel. Can the same configuration be connected in series with single 16S BMS.
GXMnow
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That would be a bit of a problem. 280 to 300 may sound close, but it is not close enough, that will cause a problem. What I would suggest is getting 8 more of the 280 AH cells, then parallel a 280 and a 150 cell in each positions, and series those 16 pairs. Then you have 280 + 150 = 430 AH 16S. Then you can use one 16S BMS. But this is also assuming the existing 280's have not aged much. They should be good for 3,000 cycles, so a year of daily cycling is not too bad.
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