LIFEPO4 Battery discussion thread

denmendez65 said:

I will set the voltage cut off at 3.1V a cell or 49.6V. Maybe 49 to cover for voltage drop. He has some good info @wingnut771.
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I watched that 5 years ago. Why do you only want to discharge 70%?

*glad you got the popcorn out though and the videos aren't too long now, its my fave channel on YT, I've watched every video from day 1 launch day.
 
cavedog said:
That is under a 20amp load. If you have something like 3amp load it might cutoff too soon if you want to use the last bit of capacity. I think that is what I experienced with my 1 x 5.12kw battery. On a small load like 100w through the night at 50v cutoff/switch to grid there was still around 20% give or take left.

Now since I have more batteries I have more aggressive discharge voltages.

View attachment 1912468
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Agree, 3.1V can mean 70%-90%.

Seeing you wont answer my question about BMS cutoff voltages for bat 1, 2, 3, & 4, live life to the fullest, make to grid 45V and shutdown 42V.
 
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wingnut771 said:
No man, seeing you wont answer my question about BMS cutoff voltages for bat 1, 2, 3, & 4, live life to the fullest, make to grid 45V and shutdown 42V.
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I did answer you...

So the pacebms is 2.7v low cell cutoff and the overall is 43.2v. The new battery 2 I don't know but would probably say 44v and the battery 4 the CFE one is 46v overall or 2.5v low cell cutoff. So 45 or 46v is probably the safe area.
 
@cavedog, try this with bat 3, put your clamp meter on cell 8 balancer and see at what amp level balancing stops (does it only balance when charging?), then set power supply slightly higher to 2A or something?
 
cavedog said:
I did answer you...

So the pacebms is 2.7v low cell cutoff and the overall is 43.2v. The new battery 2 I don't know but would probably say 44v and the battery 4 the CFE one is 46v overall or 2.5v low cell cutoff. So 45 or 46v is probably the safe area.
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Oh, sorry, as you were then.
 
wingnut771 said:
Oh, sorry, as you were then.
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The problem is the imbalance issues with battery 2 to 4. Only battery 1 will be able to handle the 4v low dc cutoff because its so well balanced so load might shift if bms of the others cutoff early that is why my numbers are conservative. I don't want a 60amp load shift to battery 1 when I'm getting to that low area. That is literally living on the edge.
 
cavedog said:
The problem is the imbalance issues with battery 2 to 4. Only battery 1 will be able to handle the 4v low dc cutoff because its so well balanced so load might shift if bms of the others cutoff early that is why my numbers are conservative. I don't want a 60amp load shift to battery 1 when I'm getting to that low area. That is literally living on the edge.
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Not sure what 4v cuttoff is but why worry about 60A to one battery, it can handle 100A which is all your inverter can pull anyway?

It can handle it and it wont be for long as the batteries shut down one by one.

Hopefully with all the blaring alarms going off you would have reduced your load before the lights go out and you sit in the dark.
 
cavedog said:
The problem is the imbalance issues with battery 2 to 4. Only battery 1 will be able to handle the 4v low dc cutoff because its so well balanced so load might shift if bms of the others cutoff early that is why my numbers are conservative. I don't want a 60amp load shift to battery 1 when I'm getting to that low area. That is literally living on the edge.
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How are you managing to drain 20kWh overnight everyday?
 
cavedog said:
That is under a 20amp load. If you have something like 3amp load it might cutoff too soon if you want to use the last bit of capacity. I think that is what I experienced with my 1 x 5.12kw battery. On a small load like 100w through the night at 50v cutoff/switch to grid there was still around 20% give or take left.

Now since I have more batteries I have more aggressive discharge voltages.

View attachment 1912468
Click to expand...
Votage dtrop is higher with higher current or am i missing something. Why would it cut off sooner with less load?
 
wingnut771 said:
Agree, 3.1V can mean 70%-90%.

Seeing you wont answer my question about BMS cutoff voltages for bat 1, 2, 3, & 4, live life to the fullest, make to grid 45V and shutdown 42V.
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3.1 is 10% in his video. under 20A. Thats a 1kw load on a 16 cell battery.
 
cavedog said:
The problem is the imbalance issues with battery 2 to 4. Only battery 1 will be able to handle the 4v low dc cutoff because its so well balanced so load might shift if bms of the others cutoff early that is why my numbers are conservative. I don't want a 60amp load shift to battery 1 when I'm getting to that low area. That is literally living on the edge.
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At this point just throw away the pace bms and get jk. This balancing seems to be a nightmare.
 
denmendez65 said:
Votage dtrop is higher with higher current or am i missing something. Why would it cut off sooner with less load?
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This is why imho it better to set cut off in the knee part of the curve, where voltage drop is less of an issue.
 
wingnut771 said:
Yes, with a constant load. We dont live with constant loads. Why sit in the dark when you still have 10-30% battery left?
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I am going of GELs but it is not recommended to pull high current at low SOC.

When I check with Gemini it also confirmed that you should not discharge high currents at low SOC. That is why I suspect even Andy is keeping the current at 20A and not more.

EVs also pull power significantly when the battery drops below a certain SOC to avoid damaging the battery. So there must be something to it.

If my battery is below 20%, I shouldnt be pulling big loads from it anyway.

Screenshot 2026-06-03 120740.jpg
 
denmendez65 said:
I am going of GELs but it is not recommended to pull high current at low SOC.

When I check with Gemini it also confirmed that you should not discharge high currents at low SOC. That is why I suspect even Andy is keeping the current at 20A and not more.

EVs also pull power significantly when the battery drops below a certain SOC to avoid damaging the battery. So there must be something to it.

If my battery is below 20%, I shouldnt be pulling big loads from it anyway.

View attachment 1912507
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Oh, I thought we talking LFP.

No Andy's used 20A because that is 0.2C, his std test parameters.

Refer to post 796 for different C ratings.
 
denmendez65 said:
If he just gets JK wont that sort his issues? He is saying 2 batteries are giving him issues btw. Or am I misunderstanding it.
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The new bat 2 "issue" is the 100mV deviation, time should fix this one. Bat 4 is fixed, bat 3 who knows but to put a jk he will have to remove the whole pack to gain access to the back.
 
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