Balanced charger, or BMS.
Posted: Wed Feb 04, 2009 8:19 pm
Reading through the pages on BMS here and elsewhere has got me thinking and I guess what I am going to ask will have a range of answers. Or maybe not...
My battery pack will be built out of 95 HiPower 50Ah LiFePo4 cells, in series, giving a nominal 300V pack. I purchased them with the HiPower charger, which includes balancing, when charging. Seemed a good idea since I figured I was mitigating problems that might ensue re: warranty if I used another charger, and their charging system did balancing.
Of course the balancing system doesn't operate on use/discharge. Moreover, since the system I am building should be capable of regen (DMOC445 controller), any regen won't be controlled by any BMS.
I guess the two most obvious risks are 1) low voltage on a cell, and 2) overvoltage due to regen. I suppose there are other parameters that a BMS would monitor but maybe (?) these are less fundamentally important.
The question is: is it seriously unwise to try and run a pack like this with effectively only half the battery management active (i.e. during charging)?
Given the pack capacity - 15kWh - and my expected daily use - probably 2 to 5 kWh - I expect to keep the battery state to between 30% and 80% charge. (I see that such claims have led to pretty loud exchanges elsewhere but doesn't seem an unreasonable hypothesis to me today). Obviously there will be a pack monitor to give the global state (I have purchased a Link 10). Regen can also be dis-activated by a dashboard switch.
Is that adequate to give a reasonable level of protection concerning low or over voltage? yes, one can screw it up and let everything get too low or regen and overload... but...
If not - what should I be looking to add in in terms of BMS?
Thanks in advance
Simon
My battery pack will be built out of 95 HiPower 50Ah LiFePo4 cells, in series, giving a nominal 300V pack. I purchased them with the HiPower charger, which includes balancing, when charging. Seemed a good idea since I figured I was mitigating problems that might ensue re: warranty if I used another charger, and their charging system did balancing.
Of course the balancing system doesn't operate on use/discharge. Moreover, since the system I am building should be capable of regen (DMOC445 controller), any regen won't be controlled by any BMS.
I guess the two most obvious risks are 1) low voltage on a cell, and 2) overvoltage due to regen. I suppose there are other parameters that a BMS would monitor but maybe (?) these are less fundamentally important.
The question is: is it seriously unwise to try and run a pack like this with effectively only half the battery management active (i.e. during charging)?
Given the pack capacity - 15kWh - and my expected daily use - probably 2 to 5 kWh - I expect to keep the battery state to between 30% and 80% charge. (I see that such claims have led to pretty loud exchanges elsewhere but doesn't seem an unreasonable hypothesis to me today). Obviously there will be a pack monitor to give the global state (I have purchased a Link 10). Regen can also be dis-activated by a dashboard switch.
Is that adequate to give a reasonable level of protection concerning low or over voltage? yes, one can screw it up and let everything get too low or regen and overload... but...
If not - what should I be looking to add in in terms of BMS?
Thanks in advance
Simon