Ok so I have run into a conundrum, so I need greater than 300a off my battery bank and would like a bms, and I know at those amps you need a Relay bms, but I don't like that you can't have independent charge and discharge on same port (I'm using aios) in this case would it be OK to hook up 2 fet based 250a bmses?
>300a BMS without relay
- Thread starter Herculezz
- Start date
How large is your bank?
How many cells?
How many cells?
400bird
Solar Wizard
Sounds like multiple parallel banks with individual BMS would be the easier (and common) solution.
hwy17
Anti-Solar Enthusiast
Expound on this?
Rednecktek
Solar Wizard
Common misconception there. A battery can either be charged OR discharged but never both at the same time. This is because your array is putting out power and if the array is powering the load and needs help from the battery then the battery is discharging. If the array is producing more than the load then the excess is charging. You're never charging AND discharging at the same time, it's all about where the power being produced is going.
In extremely rare events, where your battery is fully charged AND the array is providing enough power to all the loads, then your battery is neither charging NOR discharging.
hwy17
Anti-Solar Enthusiast
As in, we would agree that the limitation OP is perceiving isn't there right?
There is some quirks with contactor directionality and I find the EV BMS do expect seperate charge and discharge connections but they can be worked around to make one bidirectional.
There is some quirks with contactor directionality and I find the EV BMS do expect seperate charge and discharge connections but they can be worked around to make one bidirectional.
I am trying to solve this problem in my head right now. How do I make a contactor bms into one bidirectional one without giving up protection features?
hwy17
Anti-Solar Enthusiast
Bidirectional was probably the wrong word. I'm still learning as I build. The Orion has a relay that will open for either charge or discharge so it will protect against charge and discharge faults with a nonpolar contactor, but it won't disable discharging and still allow charging without seperate circuits the way that a FET can. It will disconnect the battery entirely for a voltage fault in either direction.
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