Replace LiPo cells with Li-Ion, keep BMS?

Fettoskyffel

1 µW
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I have a eBike (36v 250w) that have 10S 10Ah LiPo battery pack that i want to make ~17Ah instead with Samsung 18650 Li-Ion cells.

Is it safe to keep existing BMS or should I replace with one for Li-Ion?
 
My guess, without sufficient information, is "probably", but can't really know with the provided information.

So these are the questions to answer to find out:

What is the HVC and LVC for the existing BMS? If this isn't available, you can use a voltmeter to measure across each of the ten cell groups when the pack is fully charged, to get approximate HVC (the highest voltage cell), and when it is empty and has turned off the output to get LVC (the lowest voltage cell).

What is the HVC and LVC you wish to (or need to) use for the new cells? This you can get from threads about using those or similar cells, based on the datasheet.

What is the voltage at which the BMS starts balancing? (draining high cells) and what does it drain them down to? This you can get again with the voltmeter by measuring all ten cell group voltages during recharge, when it's almost done charging. Once above around 4-4.1v, one of the groups will probably be slightly higher than the others. Keep measuring that group, and when the charger shuts off the first time, the voltage you get is the HVC. Keep measuring and eventually the voltage will drop and stabilize, and that's the voltage it balances to. It's not exactly the answers for the question, but it'll help you decide.

Are those the appropriate voltages for the cells you will be using?

If the BMS numbers match the new numbers, or are within the margins you are ok with, then you can keep the BMS.

If the BMS numbers are too far from the new numbers, you might want to use a BMS that specifies numbers that match the new cells' numbers.

If you're not sure if they match or not, post the numbers here and we can help you figure it out.
 
amberwolf said:
My guess, without sufficient information, is "probably", but can't really know with the provided information.

So these are the questions to answer to find out:

What is the HVC and LVC for the existing BMS? If this isn't available, you can use a voltmeter to measure across each of the ten cell groups when the pack is fully charged, to get approximate HVC (the highest voltage cell), and when it is empty and has turned off the output to get LVC (the lowest voltage cell).

What is the HVC and LVC you wish to (or need to) use for the new cells? This you can get from threads about using those or similar cells, based on the datasheet.

What is the voltage at which the BMS starts balancing? (draining high cells) and what does it drain them down to? This you can get again with the voltmeter by measuring all ten cell group voltages during recharge, when it's almost done charging. Once above around 4-4.1v, one of the groups will probably be slightly higher than the others. Keep measuring that group, and when the charger shuts off the first time, the voltage you get is the HVC. Keep measuring and eventually the voltage will drop and stabilize, and that's the voltage it balances to. It's not exactly the answers for the question, but it'll help you decide.

Are those the appropriate voltages for the cells you will be using?

If the BMS numbers match the new numbers, or are within the margins you are ok with, then you can keep the BMS.

If the BMS numbers are too far from the new numbers, you might want to use a BMS that specifies numbers that match the new cells' numbers.

If you're not sure if they match or not, post the numbers here and we can help you figure it out.

Thank you very much for the detailed answer!
I´ll try your instructions but I think I will change BMS if it gets too complicated.
 
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