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[yetiking]

im having a hard time finding bms that can handle 400 amps that dont cost $400-700.
what is everyone else using?

is the contractor the main reason high amperage bms are expensive?- in which case could i just use the contractor on the bms in the activation circuit for the main contractor?

i've seen some without contractors also- unless im missing something, doesn't that defeat the purpose of having a bms?

btw im using a123 26650 cells- about 23 in series.

thanks for the help-

[frodus]

need more information on the system

total pack size and configuration

controller size and type


Getting under $500 is going to be a problem.

[yetiking]

i guessed as much- tentatively its a a123 26650 battery pack- around 200-250 cells 23 in series. operating voltage- 72
continuous discharge- 240 amps  peak-400 amps

I think i've seen some bms without contractors. unless they tie into the main contractor, i dont understand how this could work.

i guess i shouldn't be surprised but it just seams 500 bucks is quite expensive for such a simple device.

[frodus]

why 23 in series? Thats a really weird number. They usually go together in groups of 4, so you should do 24s if you plan on being able to find a charger, BMS and controller suitable for that setup.

Its not a simple device. A BMS balances the cells, looks for overvoltage, undervoltage and in some cases, overcurrent. Some provide extra monitoring so you can see what your cells are doing. Maybe you don't understand what a BMS does.

You could use 3 manzanita micro BMS boards (each do 8 cells), or try a miniBMS.

What systems have you found?

[yetiking]

i have a 72 volt system. 23X3.2 = 73.6 thats were i get 23 i guess im running 24 then.

i'm starting to understand why they could be so expensive, though compared to a controller they seam rather simple.

i looked into mini bms but read that the max amperage was around 90- did I read this wrong?

i was also looking into the lithiumind, which i read was only good for 125amps for 10 seconds.

the lithiumate just seams like more then i need for a bike, through the 600 amps was impressive.

until late night i was under the impression that bms had their own contactor for disconnecting the controller or charger.

what other companies are out there?

is 400 peak amps really that uncommon?

[yetiking]

mini bms would cost me about 300 bucks, is this system just not adequate for high performance needs?

not sure if it would work for my cells though- a123 26650 are normally 3.3v, while the bms is designed for 3.6 or 3.8 i'm assuming this is a big problem.

are there any others out there?

Thanks for the help

[Harlan]

Email Dimitri, he is CleanPowerAuto, the designer of the MiniBMS.  He can setup the MiniBMS with whatever voltage limits you want.  Just send him the battery specs.

[frodus]

You still haven't mentioned what motor and controller.

Minibms sounds like a good fit. It doesn't limit the current nor does it measure it. I don't like the BMS that current limit. The BMS should look at the voltage and decide if that is too high or two low. When its too high, the Minibms cuts off the charger. When its too low, it reduces throttle and starts to sound the buzzer.

The Lithiumate only uses the current sensor to calculate state of charge. The Lithiumind does sense current and would not be a good choice for your system.

One thing....

how are you going to assemble the A123 batteries? do you have a welder? Thats a lot of cells to put together if you don't have the right tools.

[yetiking]

yes, i have a few welders, not a spot welder though, so i would probably just solder them (we all know how well that works) i do have a tig welder if that would work?
im running a agni 95r
and a kelly kdc 72601- 72v 600amp regen.

you guys are scarring me here- someone said betting a bms under 500 would be tricky. i beleve the mini bms will cost me around 320 bucks.

well sounds like the mini bms is a good system- anything i should watch out for or know?

Thanks for the help