Quote:
Originally Posted by Murby
The problem with the cheap BMS's is not JUST that they pass all that current through them, its that they are cheap BMS's to begin with. They use cheap and undersized components, undersized wire, and are built to the bare minimum survival specs.
I can't even count the number of times I've heard of batteries being ruined because a Chinese BMS drained a cell to zero.
I understand its not that big of a deal to lose a cell in a 50 or 100 ah pack, but I've seen people use these cheap BMS's on off-grid packs with 500ah systems.. and loosing a 500ah cell is an expensive problem.
Some folks don't have a lot of choice, and for a golf cart, I can kind of understand.. Just be careful and don't go parking a lithium ion golf cart running a cheap BMS in your garage. When these BMS's fail with phosphate batteries, its just a big smoker.. You open a window, air it out, buy some new batteries. but when they fail with lithium ion packs, things can catch on fire.
I made a chart:
Expensive LiFePO4 + Cheap BMS = Get Smoke, Lose Money
Expensive LiFePO4 + Good BMS = a good investment
Cheap Lithium Ion + Cheap BMS = Fire, Lose Money, Cart, Maybe your house.
Cheap Lithium Ion + Good BMS = a good investment with only slight risk.
I like LiFePO4.. but dang are they super expensive and bulky.. and since most of them are made in China, you never really know what you're getting. They might advertise 2000 cycles but you won't know until years later, if ever.
Lithium Ion is cheap, packs a lot more power than the phosphate cells in the same volume, and since they're used in EV's, they are generally readily available. Problem is, you need a good quality BMS to prevent the guys with long water hoses from showing up.
Good BMS's.:
REC BMS
Batrium
Orion
And I think Elithion Lithumate should be included as I'm hearing good things. They make a Vinci-LV that is field configurable (GUI Interface) , expandable, comes with CAN interface for a charger, and can operate in a master-slave config without special ordering. $350, which isn't a bad price at all if you're spending $1500 or more on a battery. Best of all, made in Colorado..
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Good info and I like your take on the big picture.
I'd add that of course a "good bms" can fail too. A few threads here detailing issues with Chargery and Zeva (which aren't on your list, but many use them as such). Maybe it is less often, I just don't know. I started out intending to build a Leaf pack, bought a "pretty good" BMS and other parts already before deciding for my use It made more sense to me safety and otherwise (new -vs- used cells etc) to go LifePo4 inside a steel box, so sold the parts I'd already bought.
More than one way to skin a cat, that's for sure. Some inventive folks on this forum have come up with great solutions to all kinds of things.