BMS sizing question

gray webber

Solar Enthusiast
Joined
Feb 4, 2022
Messages
189
I am going to assemble my first lithium iron phosphate battery. It will be 24volt 280 ah in size. I have a Victron 24-3000 Multiplus inverter. My issue is the BMS. I really liked the straight forward function and test outcomes great simple web site and downloads of the Overkill brand but it offers only 100a charge/discharge model.
Is this enough for my needs or will I overdrive it with heavy loads? Option two is the JK 200amp model.
Input?
Thank you!
 
Joined
Nov 30, 2019
Messages
12,507
I am going to assemble my first lithium iron phosphate battery. It will be 24volt 280 ah in size. I have a Victron 24-3000 Multiplus inverter. My issue is the BMS. I really liked the straight forward function and test outcomes great simple web site and downloads of the Overkill brand but it offers only 100a charge/discharge model.
Is this enough for my needs or will I overdrive it with heavy loads? Option two is the JK 200amp model.
Input?
Thank you!
3000 volt amps ~= 2400 watts
2400 ac watts / .85 inverter efficiency / 24 volts low cutoff = 117.647058824 service amps

The Overkill BMS is slightly undersized.
If have any pure dc loads then its even worse.
 

gray webber

Solar Enthusiast
Joined
Feb 4, 2022
Messages
189
3000 volt amps ~= 2400 watts
2400 ac watts / .85 inverter efficiency / 24 volts low cutoff = 117.647058824 service amps

The Overkill BMS is slightly undersized.
If have any pure dc loads then its even worse.
That’s what I thought:(. Pushing it too much. Yes, and there should be some head room.
I think Will has paralleled BMS to double Amps. Is this recommended? Wish they offered a 150a model:(.
If not then I guess the JK is in my future.
I looked at the JBD ones but did not like them with separate relays and Solar Garage ran tests that showed they will still charge somewhat at below cold temp cut off???
No good.
 
Joined
Nov 30, 2019
Messages
12,507
I think I have read others recommend to keep max draw at @75% of max BMS output so as to not overtax the FETs?
Prevailing wisdom is to de-rate by some factor for vendor's exaggerated ratings.

The forum has enough experience with the Overkill BMS to say that these BMS's pass their rated current.
Still its a good idea not push things to the limit.
 
Last edited:
Joined
Nov 30, 2019
Messages
12,507
That’s what I thought:(. Pushing it too much. Yes, and there should be some head room.
I think Will has paralleled BMS to double Amps. Is this recommended?
I've not done it but with some care I think it can be done.
There are a bunch of little details to consider.
I think it would be much simpler to go with the JK.
Do you have a product link for the JK?
 

DerpsyDoodler

Photon Sorcerer
Joined
Jan 10, 2021
Messages
2,281
That’s what I thought:(. Pushing it too much. Yes, and there should be some head room.
I think Will has paralleled BMS to double Amps. Is this recommended? Wish they offered a 150a model:(.
If not then I guess the JK is in my future.
I looked at the JBD ones but did not like them with separate relays and Solar Garage ran tests that showed they will still charge somewhat at below cold temp cut off???
No good.
victron makes a BMS that marries well with their inverters and other components. It might be worth looking into. Electrodakus is another BMS worth considering, though YMMV. Seplos BMS seem to be the new mainstream of the DIY community. These are a few options that should help get you moving.
 
Top