BMS amperage
- Thread starter NMNeil
- Start date
Agreed. We use a JK 200A BMS on a 24v system. 3kw inverter. Our maximum pull is circa 75A through the inverter but the inverter doesn't trip until 115A.
RCinFLA
Solar Wizard
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Most Chinese BMS's current rating specs are based on about 20 watts of series MOSFET heating.
Most BMS's do not have sufficient heat sinking to take 20 watts of heating for a very long period of time (5-15 minutes) before thermal shutdown is triggered. Since many BMS's have poor placement of thermal sensing thermistor they put the MOSFET's at risk of overheating.
Add to that, the MOSFET's are only heat sunk via a thermal sponge pad to the top of their epoxy device case to a flat sheet aluminum BMS case plate and the actual MOSFET die inside the device package gets extremely hot, upwards of 170 degs C, while the BMS aluminum case plate is only at about 50 degs C.
Most BMS's do not have sufficient heat sinking to take 20 watts of heating for a very long period of time (5-15 minutes) before thermal shutdown is triggered. Since many BMS's have poor placement of thermal sensing thermistor they put the MOSFET's at risk of overheating.
Add to that, the MOSFET's are only heat sunk via a thermal sponge pad to the top of their epoxy device case to a flat sheet aluminum BMS case plate and the actual MOSFET die inside the device package gets extremely hot, upwards of 170 degs C, while the BMS aluminum case plate is only at about 50 degs C.
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That’s my plan as well
We do not see any evidence of that. Mosefet temperature is displayed on the BMS. You can programme shut down temperature of the BMS based on Mosfet temperature. Running 80A loads on a 200A JK BMS, we have seen mosefet temperatures at 41DegC with an ambient air temperature of 31degC. Nothing like what you are suggesting.
timselectric
If I can do it, you can do it.
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I Have 280ah diy batteries.
200a BMS's set to 100a limit.
125a over current protection.
Over build, over size, and under utilize = no over heating and long life.
200a BMS's set to 100a limit.
125a over current protection.
Over build, over size, and under utilize = no over heating and long life.
BlueMarblePA
Solar Enthusiast
This is very helpful!
We have a very similar set up.
280A @24v. 8x280Ah Catl cells
200A JK BMS
We run 80A loads with a limit of 115A by virtue of cut out on the inverter.
Built in resilience
Good advice here. Multiple batteries allows the system to "share" the load as well as provide redundancy. A well designed system will allow one to take one or more batteries "off line" for maintenance if needed.
Sharing the load reduces the actual draw from each pack, extending the time they can provide power and ultimately improve their lifespan.
Running them fast and hard will likely quicken the decision to upgrade the batteries due to degradation.
I have three 24v packs. Small in comparison to many. I am finding that the longer they work together, the closer in overall capacity they become. In other words, with usage they have learned to work well together.
We have a back up lead bank, kept charged by a Victron B2B. If we get a failure of the lithium, we can have the lead on line at the turn of a switch. We are on a sailing yacht where a back up to lithium makes sense
