Confusion about charge controller output current and max battery input current

[klarpsnarkle]

So, what happens if I have a charge controller that puts out 70 amps and I am using it to charge a battery with a 50 amp max input current? Does the over current protection of the BMS prevent the battery from ever charging? Thank you.

 

[mikefitz]

Possibly, depends on the current limit control in the charger and the way the BMS works. But my guess is that something will fail. Why not use the correct charger or lower the current from the 70A unit if this is possible? What charger and what battery?

Mike

 

[klarpsnarkle]

Possibly, depends on the current limit control in the charger and the way the BMS works. But my guess is that something will fail. Why not use the correct charger or lower the current from the 70A unit if this is possible? What charger and what battery?

Mike

Victron SmartSolar MPPT 150/70 to SOK 12V 206Ah LiFePO4 Lithium Iron Phosphate Battery Pack

 

[OffGridInTheCity]

I use Midnite Classic charge controllers - and they let you choose the amps of output current going to the battery - e.g. this feature can be found on some charge controllers and I presume they offer the feature for cases as you describe. I have mine set at 80a because the Classic an do up to 86a and my panels occasionally will spike that hi - which tripped my 80a breakers going into the battery and disabled my charging.

 

[mikefitz]

Victron SmartSolar MPPT 150/70

You have chosen well. When setting up the charge parameters under user settings you can program the maximum current the unit will deliver, irrespective of the panel power. Panel volts and current must be within limits, 150 volts ,70 amps.

form the instructions,

Mike

 

[meetyg]

At first I thought that you may be incorrect about the SOKs specs, but after looking it up you are correct. It can only handle 50 amps.
Isn't it a bit strange that a 206Ah battery can only discharge @0.5C, but even worse charge at only around 0.25C.

Maybe it's a BMS limitation, but I thought that most LFP's could discharge @1C and charge @0.5C. Or are SOK being very conservative here?


In any case, I suppose that if you supply less solar power to the SCC, you could get that 50 amps your looking for, but of course it has its downsides.

 

[mikefitz]

I suppose that if you supply less solar power to the SCC, you could get that 50 amps

No need, you can program the solar controller for desired current output.

Maybe it's a BMS limitation

Yes its a BMS limitation, to get an attractive selling price SOK fit a low cost BMS, not unusual in this market segment.

Mike

 

[klarpsnarkle]

I use Midnite Classic charge controllers - and they let you choose the amps of output current going to the battery - e.g. this feature can be found on some charge controllers and I presume they offer the feature for cases as you describe. I have mine set at 80a because the Classic an do up to 86a and my panels occasionally will spike that hi - which tripped my 80a breakers going into the battery and disabled my charging.
View attachment 69986

May I ask what batteries you are using that will handle an 80 amp charge current?

 

[klarpsnarkle]

No need, you an program the solar controller for desired current output.

Yes its a BMS limitation, to get an attractive selling price SOK fit a low cost BMS, not unusual in this market segment.

Mike

I watched a video by Will Prowse, and he seemed to like these batteries.

 

[mikefitz]

he seemed to like these batteries.

There is nothing wrong with the battery, the designers have chosen to limit the charge current to 50A, this will prolong the service life of the battery. If your application needs a system where its important to charge at higher currents you need a different battery or an additional battery in parallel.

With your solar setup, programming the controller to deliver a maximum of 50 A will not impact too much on your solar yield.

Mike

 

[OffGridInTheCity]

May I ask what batteries you are using that will handle an 80 amp charge current?

DIY 18650 81kwh powerwall - about 9000 cells.

 

[klarpsnarkle]

DIY 18650 81kwh powerwall - about 9000 cells.

Ah. OK.

 

[740GLE]

Sounds like you just need to buy two SOK batteries run them in parallel and soak up all that solar you can ?

 

[HOU_Castle]

Victron SmartSolar MPPT 150/70 to SOK 12V 206Ah LiFePO4 Lithium Iron Phosphate Battery Pack

Many LiFePo4 battery mfgs suggested to charge the battery at 0.2c rate for best result.