Partially discharge Lifepo4 with fully charged sister packs?

[Ditcha]

30A is fine. But what if it's 300A?

I've fried jump leads before. Not a good experience. And I'm still not completely sure why it happened. And lead acid and lithium batteries have very different internal resistance profiles. I'm not sure you'd get the same sag you do on lead acid.

Just let him try it and he can comeback with his own feedback proof is in the pudding so they say think his mind was made up from the start anyway

 

[Boldly]

Can you fit some sort of diode so the current doesn't flow?
I know nothing about electrics so feel free to mock.

 

[Raul]

30A is fine. But what if it's 300A?

I've fried jump leads before. Not a good experience. And I'm still not completely sure why it happened. And lead acid and lithium batteries have very different internal resistance profiles. I'm not sure you'd get the same sag you do on lead acid.

I believe you, but, you are forgetting few things.
Like I said, the analogy of jump starting is similar. However on your jump lids you did not have a BMS. A bms detects inrush current and the short circuit protection kicks in even when you connect a inverter, 15 milliseconds; then is the over current protection usually max bms amps. You can't have a 300a inrush from a 100ah battery, unless you rip the bms out, bypass it and then dead short it. Now you can have a inrush greater than the bms allows.

 

[Ditcha]

I believe you, but, you are forgetting few things.
Like I said, the analogy of jump starting is similar. However on your jump lids you did not have a BMS. A bms detects inrush current and the short circuit protection kicks in even when you connect a inverter, 15 milliseconds; then is the over current protection usually max bms amps. You can't have a 300a inrush from a 100ah battery, unless you rip the bms out, bypass it and then dead short it. Now you can have a inrush greater than the bms allows.

Let's hope his BMS never gives up the ghost not good practice in my view but everyone to their own.

 

[Guigsy]

I believe you, but, you are forgetting few things.
Like I said, the analogy of jump starting is similar. However on your jump lids you did not have a BMS. A bms detects inrush current and the short circuit protection kicks in even when you connect a inverter, 15 milliseconds; then is the over current protection usually max bms amps. You can't have a 300a inrush from a 100ah battery, unless you rip the bms out, bypass it and then dead short it. Now you can have a inrush greater than the bms allows.

It is like relying on the rev limiter on your engine when you're bouncing off the redline. Sure, it's there, but you should avoid using it if you can.

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[Raul]

Let's hope his BMS never gives up the ghost not good practice in my view but everyone to their own.

If thats the case the bms is not fit for purpose, it will fail to disconnect on overcharge or overload, even on normal operation. A 100ah will have set a max 0.5C charging, 50a.

 

[Carpmart]

Let's hope his BMS never gives up the ghost not good practice in my view but everyone to their own.

I agree that my use case is not ‘a typical’ and 99% of people should follow the method you suggest. However bad practice it is or is not, if it enables what I want to do with low (ish) risk, then jobs a good un!

That fact the Raul and others have done similar aids my confidence from the approach in the original post!