Initial Battery Capacity Tests

[pdarlingks]

Newbie here. These are the 2 first tests of a LiTime 12V 100Ah battery recently purchased using a basic CBA 5. The capacity increased about 2% between the first and second test. Is this real? and if so, what is a likely reason? In each case, the battery was fully charged using 10A (0.1C) and then discharged at 0.1C for the test. Or are the test results variable enough so I might get a 3rd distinctly different number next time I test it?

Thanks in advance for your comments or suggestions.

 

[sunshine_eggo]

Common for new batteries to arrive with cell imbalance. 2nd charge might have reduced it.

Did you keep the same charge termination criteria for both charges?

 

[fnnwizard]

Newbie here. These are the 2 first tests of a LiTime 12V 100Ah battery recently purchased using a basic CBA 5. The capacity increased about 2% between the first and second test. Is this real? and if so, what is a likely reason? In each case, the battery was fully charged using 10A (0.1C) and then discharged at 0.1C for the test. Or are the test results variable enough so I might get a 3rd distinctly different number next time I test it?

Thanks in advance for your comments or suggestions.

Common for new batteries to arrive with cell imbalance. 2nd charge might have reduced it.

Did you keep the same charge termination criteria for both charges?

Most likely this. You can see in your graph a higher starting V that takes longer to draw down.
Temp would play a part as well as your dis/charging gear. Lab says 30 minutes on time before tests.

But I recon it won't change your results by that much at that rate.

 

[frankrudis65]

I had this with ONE new cell.Seems like they sort of fall asleep and need some time to wake upSecond charge/discharge was keeping more capacity....Best regards Frank

 

[pdarlingks]

Common for new batteries to arrive with cell imbalance. 2nd charge might have reduced it.

Did you keep the same charge termination criteria for both charges?

Common for new batteries to arrive with cell imbalance. 2nd charge might have reduced it.

Did you keep the same charge termination criteria for both charges?

Yes, the cutoff voltage was set to 10V in each case.

I did not that the app indicated the BMS was balancing cells for several hours after the 2nd charge.

Thanks!

 

[pdarlingks]

Most likely this. You can see in your graph a higher starting V that takes longer to draw down.
Temp would play a part as well as your dis/charging gear. Lab says 30 minutes on time before tests.

But I recon it won't change your results by that much at that rate.

Thanks!

 

[pdarlingks]

I had this with ONE new cell.Seems like they sort of fall asleep and need some time to wake upSecond charge/discharge was keeping more capacity....Best regards Frank

I'll probably try one more time to see if it now stable.

 

[pdarlingks]

Common for new batteries to arrive with cell imbalance. 2nd charge might have reduced it.

Did you keep the same charge termination criteria for both charges?

I guess I was testing the BMS. Low voltage cutoff in the BMS is 10.8.

 

[sunshine_eggo]

Yes, the cutoff voltage was set to 10V in each case.

Not what I asked. I asked if the charge cutoff criteria were the same. If you didn't use the same charge termination criteria, you could have easily input more charge.

I did not that the app indicated the BMS was balancing cells for several hours after the 2nd charge.

Normally without input or holding at constant voltage, balancing can pull the cell voltages down relatively quickly to the point they stop balancing, so balancing for "several hours" strongly implies you held at a voltage the battery could still accept charge, and you input more the second charge.

 

[pdarlingks]

Not what I asked. I asked if the charge cutoff criteria were the same. If you didn't use the same charge termination criteria, you could have easily input more charge.



Normally without input or holding at constant voltage, balancing can pull the cell voltages down relatively quickly to the point they stop balancing, so balancing for "several hours" strongly implies you held at a voltage the battery could still accept charge, and you input more the second charge.

Thanks for clarifying. I don't know. Charge was done with a Millertech Lithium Charger 10A which flashes red while charging, green when finished. I assumed (yes, I know...) that there was no charge input after the green light came on. Then I let reset (disconnected from everything) fork 1/2 day before starting the second charge.

Is there a better way to terminate charge rather than the LED indicator?

 

[pdarlingks]

Not what I asked. I asked if the charge cutoff criteria were the same. If you didn't use the same charge termination criteria, you could have easily input more charge.



Normally without input or holding at constant voltage, balancing can pull the cell voltages down relatively quickly to the point they stop balancing, so balancing for "several hours" strongly implies you held at a voltage the battery could still accept charge, and you input more the second charge.

Balancing was indicated in the app while the battery was disconnected.

 

[sunshine_eggo]

Thanks for clarifying. I don't know. Charge was done with a Millertech Lithium Charger 10A which flashes red while charging, green when finished. I assumed (yes, I know...) that there was no charge input after the green light came on. Then I let reset (disconnected from everything) fork 1/2 day before starting the second charge.

Is there a better way to terminate charge rather than the LED indicator?

What's the charge termination criteria of the charger?

Yeah. I know. You don't know the answer. Probably because these canned "lithium chargers" don't tell you much about how they work. The only way you can be certain is to ensure all conditions are identical, i.e.,

Charge until green LED
Leave on charger for exactly X minutes
Disconnect from charger and let sit for Y minutes
Discharge test.

X and Y between the two tests need to be identical. The likelihood of you hitting X perfectly is unlikely as it's tedious to exactly catch a green light.

Balancing was indicated in the app while the battery was disconnected.

"several hours" of balancing with the charger disconnected is atypical.

Since you have access to the BMS, the next time you charge it, check the following the moment the green LED turns on (do not disconnect charger until readings are taken):

Voltage at terminals with voltmeter
BMS pack voltage
BMS cell voltages
BMS reporting any protection events?

 

[pdarlingks]

What's the charge termination criteria of the charger?

Yeah. I know. You don't know the answer. Probably because these canned "lithium chargers" don't tell you much about how they work. The only way you can be certain is to ensure all conditions are identical, i.e.,

Charge until green LED
Leave on charger for exactly X minutes
Disconnect from charger and let sit for Y minutes
Discharge test.

X and Y between the two tests need to be identical. The likelihood of you hitting X perfectly is unlikely as it's tedious to exactly catch a green light.



"several hours" of balancing with the charger disconnected is atypical.

Since you have access to the BMS, the next time you charge it, check the following the moment the green LED turns on (do not disconnect charger until readings are taken):

Voltage at terminals with voltmeter
BMS pack voltage
BMS cell voltages
BMS reporting any protection events?

Thanks for your recommendatios on making the tests more uniform and accurate..

I've got a request into Millertech for more detaileled charger characteristics.
I don't have access to the BMS... just a list of parameters and settings that LiTime sent me.

Will try again once I get the Millertech charger data.

Once again, I appeciate the help!

 

[fnnwizard]

Thanks for your recommendatios on making the tests more uniform and accurate..

I've got a request into Millertech for more detaileled charger characteristics.
I don't have access to the BMS... just a list of parameters and settings that LiTime sent me.

Will try again once I get the Millertech charger data.

Once again, I appeciate the help!

I'm assuming you can't see cell V info?
If not, one way to help gauge is to record ( use old phone) the V of the pack and charger as it approaches 13.6V+ and see how long it takes for charger to "turn green". If charger doesn't have a V display you'd need to use a separate meter.

The longer the charge at these higher levels, the more balanced the cells are. If both terminate within minutes of each other after a while, you're good and the delta with be mAh level, if they start to cut off charging abruptly, cells are imbalanced.

 

[pdarlingks]

I'm assuming you can't see cell V info?
If not, one way to help gauge is to record ( use old phone) the V of the pack and charger as it approaches 13.6V+ and see how long it takes for charger to "turn green". If charger doesn't have a V display you'd need to use a separate meter.

The longer the charge at these higher levels, the more balanced the cells are. If both terminate within minutes of each other after a while, you're good and the delta with be mAh level, if they start to cut off charging abruptly, cells are imbalanced.

Thank you for the suggestion. No, I can't see the cell V. The charger is no frills.

I'm rapidly finding this can be as expensive a hobby as Amateur Radio turned out to be.... 73, KF5LEF

 

[pdarlingks]

What's the charge termination criteria of the charger?

Yeah. I know. You don't know the answer. Probably because these canned "lithium chargers" don't tell you much about how they work. The only way you can be certain is to ensure all conditions are identical, i.e.,

Charge until green LED
Leave on charger for exactly X minutes
Disconnect from charger and let sit for Y minutes
Discharge test.

X and Y between the two tests need to be identical. The likelihood of you hitting X perfectly is unlikely as it's tedious to exactly catch a green light.



"several hours" of balancing with the charger disconnected is atypical.

Since you have access to the BMS, the next time you charge it, check the following the moment the green LED turns on (do not disconnect charger until readings are taken):

Voltage at terminals with voltmeter
BMS pack voltage
BMS cell voltages
BMS reporting any protection events?

So, according to the distributor (and my listening skills):
1) The chargerr charges at 10A until near the end of charge, when the current drops to 1-2A, at wich point the green light comes on and charger maintains voltage at 14.4-14.5
2) At this point, it is trickle charging at a few tenths of an amp until you unplug the charger
3) The charger will kick back in if the battery voltage declines.

I now see why X and Y are important.

 

[sunshine_eggo]

So, according to the distributor (and my listening skills):
1) The chargerr charges at 10A until near the end of charge, when the current drops to 1-2A, at wich point the green light comes on and charger maintains voltage at 14.4-14.5
2) At this point, it is trickle charging at a few tenths of an amp until you unplug the charger
3) The charger will kick back in if the battery voltage declines.

I now see why X and Y are important.

That's not a horrible algorithm. While it would be preferable for it to drop to something lower like 13.6-13.8V, BUT it is useful for balancing, and many aren't.

Very important not to leave it on the charger for extended periods, UNLESS you need balancing.

 

[pdarlingks]

Given I have only the app to rely on for this battery to indicate balancing, any reconmendation for the green light period to continue while balancing is indicated?

For my EG4 server rack battery, I have the BMS Tools which I'm coming up to speed on. Haven't really used the Tools yet.

For a few Millertech batteries, I haven't charged them yet; I'll have to double check their app capabiities, or find other ways to monitor any balancing.

Thanks for the help. I'll try not to think up a bunch more questions!

 

[sunshine_eggo]

Given I have only the app to rely on for this battery to indicate balancing, any reconmendation for the green light period to continue while balancing is indicated?

A battery is "balanced enough" when:

1) you can charge to the specified charge voltage without disruption (charge protection can cause a voltage spike when engaged)
2) you get rated capacity

If either of the above two are impacted by imbalance, you need more balance.

In your case, if the BMS is no longer indicating balancing, then you likely don't need it.

For my EG4 server rack battery, I have the BMS Tools which I'm coming up to speed on. Haven't really used the Tools yet.

That gives you a LOT of visibility. You'll learn a lot more about the inner workings.

For a few Millertech batteries, I haven't charged them yet; I'll have to double check their app capabiities, or find other ways to monitor any balancing.

Thanks for the help. I'll try not to think up a bunch more questions!

Not the point. This is DIY forum!

 

[pdarlingks]

A battery is "balanced enough" when:

1) you can charge to the specified charge voltage without disruption (charge protection can cause a voltage spike when engaged)
2) you get rated capacity

If either of the above two are impacted by imbalance, you need more balance.

In your case, if the BMS is no longer indicating balancing, then you likely don't need it.



That gives you a LOT of visibility. You'll learn a lot more about the inner workings.





Not the point. This is DIY forum!

Thanks!