Mixing LifePO4 batteries of different capacities.

[Andy_Knowles]

Hi there,

I have a 120ah 48v LifePO4 battery with a BMS, one of the AliExpress style ones that can be rack mounted. (It's about 6 months old)

I'm thinking of expanding, and wondered if rather than getting another identical battery and running in parallel, that maybe I can get a higher capacity battery and still connect it parallel.

In short - Could I add a 200ah 48v to my existing 120ah 48v and make it 320ah 48v?
Or do I have to get an identical one and go for 240ah 48v..

Kind regards,

 

[BentleyJ]

For parallel connections, mismatched Ah batteries can be connected as you have described and will work well. Many of us have systems like that in operation.
You just have to make sure that both batteries are at the same voltage (+ or - 0.1 or 0.2V) when the switch is turned on so there is not a large current rush between them.

 

[Andy_Knowles]

For parallel connections, mismatched Ah batteries can be connected as you have described and will work well. Many of us have systems like that in operation.
You just have to make sure that both batteries are at the same voltage (+ or - 0.1 or 0.2V) when the switch is turned on so there is not a large current rush between them.

Ok that's great. Thankyou for the info.

 

[JoeHam]

See here :

 

[wattmatters]

Make sure they are both using the same operating voltage or cell count, e.g. both use a 16S cell configuration.

There are some server rack batteries which are 15S and can only be operated with other 15S batteries. Do not mix 15S and 16S batteries in parallel.

 

[xuba-Aaron]

容量不一致可以并联，但要注意三点：
1、电池并联时，两块电池之间的电压差不能太大。并联瞬间高压电池会对低压电池充电，充电电流=电压差/所有电池等效内阻。一般健康的电池内阻很小，电压差越大，充电电流越大。电流太大会导致电池爆炸和着火。如果手头没有电压表，可以在电量耗尽时将几块电池并联，然后一起充电；也可以将所有电池充满电然后将它们并联。
2、充放电截止电压一致。这几乎决定了必须使用相同材质的电池，以及正确的充电器、电池保护板。
3、寿命问题：并联运行后电池组的寿命大约等于剩余寿命最短的电池的寿命。电池寿命结束的表现一般是无法省电，自放电较大，电池用完后电压会迅速下降到放电截止电压以下，而其他健康的电池会继续放电至电池电压低，导致过度放电，寿命迅速缩短。当然，如果每块电池都有自己独立的保护板，就没有问题，这样成本就高了，违背了不同容量电池并联的初衷。