Battery SOC minimum %

[denmendez65]

Like I said, lab tests are done with constant current.

Yes but cycles matter also for Lithium based batteries. If you want to max it out then the above recommendations still matter. Just depends on whether the ROI is worth it.

 

[wingnut771]

Yes but cycles matter also for Lithium based batteries. If you want to max it out then the above recommendations still matter. Just depends on whether the ROI is worth it.

Yes, with the 25c 0.5C constant current lab tests from 3.65V to 2.5V back to 3.65V, the cycle life count is 6000 cycles to 80% SOH or 10000 cycles to 70% SOH.

 

[cavedog]

Yes, with the 25c 0.5C constant current lab tests from 3.65V to 2.5V back to 3.65V, the cycle life count is 6000 cycles to 80% SOH or 10000 cycles to 70% SOH.

So what damage do you need to do to a battery with a bms to get like 40% SOH? I though BMS protects the batteries from damage?

As it stands my Ecco battery bms is reporting 8 cycles which seems correct from when my system went live so that is 1 a day. At the 6000 rated cycles that is 16 years at least. Thats crazy. I guess if I finally switch to SBU mainly trying to be off grid the cycles will increase especially in bad weather where it might cycle a few times a day.

 

[denmendez65]

Yes, with the 25c 0.5C constant current lab tests from 3.65V to 2.5V back to 3.65V, the cycle life count is 6000 cycles to 80% SOH or 10000 cycles to 70% SOH.

With the 30 to 80 you get considerably much more. But it’s a ROI thing now as you don’t use most of the capacity.

 

[wingnut771]

So what damage do you need to do to a battery with a bms to get like 40% SOH? I though BMS protects the batteries from damage?

As it stands my Ecco battery bms is reporting 8 cycles which seems correct from when my system went live so that is 1 a day. At the 6000 rated cycles that is 16 years at least. Thats crazy. I guess if I finally switch to SBU mainly trying to be off grid the cycles will increase especially in bad weather where it might cycle a few times a day.

Charge it to 4.2V or let it sit in 60c temps .

 

[wingnut771]

So what damage do you need to do to a battery with a bms to get like 40% SOH? I though BMS protects the batteries from damage?

As it stands my Ecco battery bms is reporting 8 cycles which seems correct from when my system went live so that is 1 a day. At the 6000 rated cycles that is 16 years at least. Thats crazy. I guess if I finally switch to SBU mainly trying to be off grid the cycles will increase especially in bad weather where it might cycle a few times a day.

1 cycle = 100% -> 0% -> 100% or 2 rounds of 50% DOD or 4 rounds of 25% DOD and so on.

 

[wingnut771]

With the 30 to 80 you get considerably much more. But it’s a ROI thing now as you don’t use most of the capacity.

Is 20 years too short for you by using 100% capacity or do you want it to last longer?

 

[cavedog]

Is 20 years too short for you by using 100% capacity or do you want it to last longer?

I'm using it quite extensively. 10% SOC cutoff. 95% cutoff at the top. I think the battery even at this will outlive the setup. I have the charging max current set to 40A also. The 20A recommended is a bit slow so that might age the battery also a bit but still. It will last years and years.

 

[wingnut771]

I'm using it quite extensively. 10% SOC cutoff. 95% cutoff at the top. I think the battery even at this will outlive the setup.

Make it 100% absorption voltage of 55.2V at the top, BMS needs to top balance the cells, and there is no way to gauge 95% SOC using voltage or BMS (don't trust the BMS SOC count) with LFP.

How do you know its 95%?

but yes, you're good to go and hand it down to your children.

 

[cavedog]

Make it 100% absorption voltage of 55.2V at the top, BMS needs to top balance the cells, and there is no way to gauge 95% SOC using voltage or BMS (don't trust the BMS SOC count) with LFP.

How do you know its 95%?

On AC at least. I checked the stop charging when grid is available stops around 93-95% The issue is with Solar charging. This inverter doesn't have a solar cutoff unless it can communicate with the battery BMS which it doesn't. I can't get that working so it charges to 100% SOC and I see the battery BMS already have 178 OVP warnings in 8 days.

 

[wingnut771]

On AC at least. I checked the stop charging when grid is available stops around 93-95% The issue is with Solar charging. This inverter doesn't have a solar cutoff unless it can communicate with the battery BMS which it doesn't. I can't get that working so it charges to 100% SOC and I see the battery BMS already have 178 OVP warnings in 8 days.

Try AGM USER mode, set bulk/absorb to 55.2V, low cut off to 45V, FLOAT 53.6V.

 

[cavedog]

Try AGM USER mode, set bulk/absorb to 55.2V, low cut off to 45V.

I tested today. I have the low cut off at 48V which is the highest it can set. At 1.6kW load the inverter cut off at 6% SOC with Grid and PV switched off.

 

[wingnut771]

I tested today. I have the low cut off at 48V which is the highest it can set. At 1.6kW load the inverter cut off at 6% SOC with Grid and PV switched off.

Thats okay, you just wont get all 90% if you have a huge load pulling voltage down. Set float to 53.6V.

 

[wingnut771]

I tested today. I have the low cut off at 48V which is the highest it can set. At 1.6kW load the inverter cut off at 6% SOC with Grid and PV switched off.

IS this lead acid mode? 48V is a half full battery with lead acid? Surely it goes to 40V?

 

[cavedog]

IS this lead acid mode? 48V is a half full battery with lead acid?

No its on Lithium LI setting.

I wanted to test the cutoff just to make sure if I end on battery that the inverter cuts off the load and I don't overshoot so the BMS must cutoff.

 

[wingnut771]

No its on Lithium LI setting.

Change to lead acid.

 

[denmendez65]

That s

Is 20 years too short for you by using 100% capacity or do you want it to last longer

That’s why I said ROI. And I am pretty sure over half the LFP batteries in the market will never cross even 10 years.

There’s a ton of people that have failures around 3 to 5. Your battery is only as good as its BMS.

 

[wingnut771]

That s

That’s why I said ROI. And I am pretty sure over half the LFP batteries in the market will never cross even 10 years.

There’s a ton of people that have failures around 3 to 5. Your battery is only as good as its BMS.

Exactly, so make hay while the sun shines. Also why you should build DIY version so one can replace components if need be.

 

[wingnut771]

16kWh fixable battery for R30k:

 

[denmendez65]

Exactly, so make hay while the sun shines. Also why you should build DIY version so one can replace components if need be.

And also where do you get 20 years from? Every battery I see online, even Freedom won, says 2000 cycles at 100% DOD.

Thats 5 years only. A person with 20kWh of battery would have only 16kWh. And it’s a downward spiral from there.

I do see others saying 3000 cycles. But on average I see 2000.

Keep in mind this is in ideal situations at 25 degrees. For every 10 degrees over you shorten the life even more. So the 2000 cycles will be some 1800 or so.

Then there is C rates. Is the person using it at the recommended C rate? So that can go even as low as 1500 cycles.

I think Lupus said his boss was running his batteries down to 0 all the time and his boss had to replace them in 3 years.