Battery Management System for LifePO4...is it necessary?

[Spacelander 1946]

Is the BMS really necessary for LifePO4........
My smart charger tells me when battery is fully charged an should not "over charge" and my controller regulates the Amps & power from battery to the motor.
Why need the BMS.... and could this be the source of many no-go's and cutouts....I think many of these boards are of poor design and suspect quality.
ALSO I have been warned that in Regen mode my controller may damage the mosfets or other componants in the BMS board.
Any comments please........Thanks in advance.

[biohazardman]

I do not have a BMS on my batteries, 600-700miles on the kit, but I do have the cell balancing charger.  I was paranoid at first and measured the voltages on the individual batteries all the time for near a month as well as checked them for heating.  I found them to be very well balanced and cool to the touch every time so I don't worry so much now.  If you don't have the BMS system on-board then your controller will do the basic protection for you if it is set up for proper voltage cut off.  There is always the chance that something might happen though as the BMS looks at individual cells and the controller looks at the full pack. Still I doubt I will bother with one unless something new comes to light.  That's my two cents hope it helps. Pic shows the system but I have cleaned up the wiring and added a battery switch and 20 amp fuse.

[ahend]

I think the main point of an onboard BMS, as biohazardman points out, is that the monitoring and protection of the battery is carried out at the cell level.  Using one could well mean that your system may cut out earlier and perhaps more often than it would by relying on the controller alone. I think it boils down to how much risk you are willing to assume with your investment.

I recently purchased a BMS[/acronym]%2DKit]BMS kit from TPpacks.com. This is the project that was cooking in a thread over at Endless Sphere. The design is completely transparent and open to scrutiny, and the quality of the final product is in your own hands.

[sigpaw]

"By the time you get a series of 12 cells, there is always a possibility of overdraining a single weak cell before the overall pack voltage drops before the controller LVC"

Very, very true. It does appear that some of the cells in these packs can be "fragile" and subject to failure. TPPaks has a very nice LVC circuit for sale that will monitor up to a 16 cell pack and apply a brake signal to your controller to shut things down if any cell drops below 2.1 volts. I would sttrongly recommend obtaining one of these. You can then obtain a spare 15 pin connector and conmnect this board externally to the charging connector. Makes for a slick setup all in all...

These appear to be very robust, lightweight packs. But a bit of care and cauttion is recommended...

[biohazardman]

I think the main point of an onboard BMS, as biohazardman points out, is that the monitoring and protection of the battery is carried out at the cell level.  Using one could well mean that your system may cut out earlier and perhaps more often than it would by relying on the controller alone. I think it boils down to how much risk you are willing to assume with your investment.

I recently purchased a BMS[/acronym]%2DKit]BMS kit from TPpacks.com. This is the project that was cooking in a thread over at Endless Sphere. The design is completely transparent and open to scrutiny, and the quality of the final product is in your own hands.

Thanks for that.  I had been watching but evidently not close enough.  I am pretty sure you got mine cuz when I looked they was gone with the rest. ;^) Looks like I was a bit slow on the draw but will get one when they are available again for the newest build as it looks to be a very good safeguard and will allow me to carry a lighter/cheaper charger.  Need the batteries that go with them also.  Guess I will be waiting till the Olympics are over for the batts.  Waiting for spokes to come from Miami, FL. and a couple more wheels too.

[ahend]

I am pretty sure you got mine cuz when I looked they was gone with the rest. ;^)

Early bird and all, I knew I would have to act fast.
I was hawking that discussion at endless sphere for a good while. The BMS design is pretty solid and fairly innovative in its handling of charging current from almost anything. Those guys did a great job. Unfortunately, I will not have a full contingent of cells to get up and running anytime soon. I'm still waiting on a replacement.