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Old 10-08-2019, 09:29 PM   #12 (permalink)
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Originally Posted by Daox View Post
Good analysis!

IMO a BMS is pretty much necessary for any chemistry. For my mower which is currently lead acid, it's a simple monitoring system to make sure I don't over-disharge any specific battery. It's not automated, but it is a BMS.

The lipo chemistry I agree would require a much more robust system for safety and battery life. However, lots of the OEMs are using a similar chemistry in their EVs due to the power and every density advantages over the other chemistries. I agree a BMS would add cost, but I also think (don't quote me on this) that there are more and more off the shelf systems you can get that will do what you need. I haven't looked into that yet to verify.
Originally Posted by RedDevil View Post
You will still damage or destroy LiFePO4 cells if you overcharge them. My LiFePO4 packs have BMSs.
Agree, any battery system should have some sort of BMS, especially lithium, and especially non-LiFePO4 lithium chemistries. I mentioned that the lithium Insights don't use an active BMS because the owners carefully monitor voltage and usually have larger-than-OEM packs that don't get drained as much, so the packs don't spend much time near full or what would be worse, empty.

With LiFePO4 you could probably get away with LED balancing modules and some devices to control temperature based charge/discharge, etc, overvoltage/undervolt circuits, and homemade stuff that would suffice. For non-LiFePO4 I would want an actual BMS.

In the Formula SAE electric formula race car team I am on here at college, we are using regular lithium ion cells in addition to the Orion BMS - a ~$1000 unit. Obviously this is a wholly electric race car, so the power demands are much greater than an Insight or lawnmower would demand, so a Orion probably wouldn't be necessary, but a good BMS for a sensitive lithium chemistry probably isn't cheap.
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