Bms ratings

[Timm0]

How do i calculate the pulse and continuous current for the bms I want to use?

i really need this!

 

[snoobler]

Power / voltage = Amps

3000W/12V = 250A

 

[RCinFLA]

As to BMS rating, most of the BMS's current rating are relatively short term loading. They are under competitive pressure to show the most optimistic numbers. At advertised spec current it will take only a few minutes before they get too hot.

For continuous current cut the advertised spec by half or more.

If you are expecting high inverter surge current for motor starting derate BMS even more as the greater the voltage drop across BMS during startup surge the more current is going to be required by inverter degrading the inverter's surge capability. This also applied to battery cables gauge. Very important for 12v inverters, less so for 48v inverters.

 

[pjones]

That's such a nice way of saying Ebay listing lie.

Buy the most amps you can fit into your project or budget.

 

[snoobler]

FWIW:

10 year old solar needs battery bank upgrade

I have (2) magnum ms4448pae with an outback flex 80 with 18 panel solar array im needing to upgrade my battery bank (currently 2 banks of 8 - full river agm dc400-6) i dont have issue with building out batteries from raw cell but i wonder if the warranty exchange is worth the cost comparison...

diysolarforum.com

 

[HRTKD]

A 280Ah battery does not need a 280 amp BMS unless your loads are really going to need 280 amps. Most folks with a 280Ah battery are getting by just fine with a 100 amp BMS. It all depends on your loads. You need to define your loads for your situation.

 

[RCinFLA]

The Chargery DCC 'HB' series contactor boxes are MOSFET switches and they have listed in their specs what the switch voltage drop is at 100 amps of pass current.

This allows me to make some calculations to predict what their continuous current rating and maximum current rating have for voltage drop and heating wattage loss.

Keep in mind these DCC switches have a heat sink with fan cooling so they will tolerate a lot of heating that a regular BMS with no fan and poor heat sink will tolerate.

 

[Rocketman]

Another way is to disconnect the switching job from the bms and assign it to a relay that can handle the job. The bms can drive the relay but the bms electronics do not handle the massive current.

 

[schmism]

while OP's question is specifically continuous current the BMS will pass, the other job it has is to keep the cells in balance. Inexpensive BMS may just use a resistor and burn off extra voltage from the high cell. This process generates heat and needs to be dissipated. (the other option is to connect the high cell to the low cell or to discharge the high cell to a cap, then charge the low cell with the energy stored in the cap)