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Lishen 272Ah - Ah measurement way off - Help!

stevenborg

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Sep 17, 2020
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I received a set of 52 Lishen 272Ah batteries, and am running a test of a 12V system as a representative sample to get a solid feeling about the quality of the batteries I received. I'm clearly doing something wrong, as my Ah measurements are coming in very, very low -- less than 1/3 of rated capacity. Can someone help identify what I'm doing wrong?

Here are the details:
- 4 Lishen 272Ah batteries in series for 12.8V nominal
- Charged to 14.18V (over 90%) with cell values as 3.551V, 3.551V, 3.553V, 3.551V (feels very balanced) at around 10 degrees C.
- Connected through a shunt-based capacity measurement device reset to zero
- Connected to a 12V heater (add-on for a car) rated at 150W
- External impedance at 3.2 ohms

Results:
- Immediately on adding load voltage drops to 13.5V (measured both a battery terminals and shunt)
- At 30 minutes voltage had dropped to 13.1V (measured both a battery terminals and shunt), individual battery voltages (under load) at 3.309V, 3.308V, 3.30V and 3.309V.
- Load measured at 3.9A and 51W (which is well below the 150W rating of the 12V DC heater)
- At 8 hours, voltage had dropped to 13.0V
- At 10 hours, voltage dropped to 12.9V (measurements indicated 618Wh, and 47.2 Ah
- At 10 hours, I removed the load to measure battery values without the voltage sag
Immediate readings: 13.08V total with individual readings 3.287, 3.284, 3.286, and 3.288V
After 30 minute rest: 13.12V total with individual readings 3.297, 3.295, 3.296, and 3.293V
- Reconnected load at 10:30 hours
Immediate readings: 13.0 at terminals and shunt

The test is still running, but we've crossed two important boundaries. According to the charts on this site, I have gone from over 90% capacity to under 10% capacity.

Start: 14.18V (over 90% SOC assuming 13.8V = 90%) : Assume 90% to be conservative, measuring at 0Ah starting
Pause: 13.12V (under 10% SOC assuming 13.2V = 10%) : Assume 10% to be conservative, measuring 47.3 Ah at pause, round up to 50Ah for simplicity

That implies I've used 80% of my capacity at 50Ah. That would imply a full capacity of around 60Ah, versus the listed 272Ah.

What am I doing wrong? I'm off by about a factor of 3! Even if I was shipped "bad" cells, I can't imagine they would ever be that bad. I'm likely doing something completely wrong and messed up, but I don't know what.

Should I post a photo? What would help?
 
13.12V is 3.28V per cell.
You can safely discharge to 2.5V per cell.
You still got a lot of capacity in the battery.

Did you connect a BMS? Of not please do so when connecting batteries is series. It's easy to damage your cells if one discharges below 2.5V
 
13.12V is 3.28V per cell.
You can safely discharge to 2.5V per cell.
You still got a lot of capacity in the battery.

Did you connect a BMS? Of not please do so when connecting batteries is series. It's easy to damage your cells if one discharges below 2.5V
Thanks, Banszi! That's good to know. I can safely discharge to 2.5V, but the rule of thumb shows that once my value drops to 3.2V my SOC is already at 5%. So how much more can I expect to get between 3.2V and 2.5V. I can't imagine it's more than I got from the drop from 3.5V to 3.2V given the discharge curves.

In any case, I'll keep running the test. It's only 10 degrees C in the garage. Might that impact my results?

Thanks so much for your response! I really appreciate it!

BTW, I'm measuring the voltage every 15 minutes, and when it drops below 2.8V, I'll measure every 5 minutes. I have a BMS, but it's for a 48 battery system, not 4. :)
 
You mention that the load is 3.9a and 51w for your 150w heater. Is that measurement from your shunt and do you have a way to confirm? That sounds really low for a heater and I'd be suspect of the numbers. If you are at only 3.9 amps, you should be able to confirm that with a multimeter (even if you don't have a clamp style).
 
the rule of thumb shows that once my value drops to 3.2V my SOC is already at 5%.
Im not sure that rule is correct. Due to the linear curve of the voltage drop it is hard to estimate the capacity based on voltage in the 20-80% capacity range. Here is some table I've found, hope this helps.

1612565780753.png
If your not using a BMS non stop monitoring of the cell voltage during discharge is highly recommended.
 
You mention that the load is 3.9a and 51w for your 150w heater. Is that measurement from your shunt and do you have a way to confirm? That sounds really low for a heater and I'd be suspect of the numbers. If you are at only 3.9 amps, you should be able to confirm that with a multimeter (even if you don't have a clamp style).
That's what I'm concerned about. If I'm ACTUALLY running at 150W then my calculations are all off by 300%. And if that's the case, I'm dead on for 272Ah. :) That's what I'm really worried about. I just have one capacity tester. My multimeters both measure current in mA, and have pretty low limits, so I'm not sure how to check that way.

I do plan on testing the capacity tester by using it when I charge the batteries after this test. My charger will let me know the Amps used for charging. If there's a mismatch, I know I have a bad capacity tester.
 
Im not sure that rule is correct. Due to the linear curve of the voltage drop it is hard to estimate the capacity based on voltage in the 20-80% capacity range. Here is some table I've found, hope this helps.

View attachment 36099
If your not using a BMS non stop monitoring of the cell voltage during discharge is highly recommended.
This is really helpful. I'm currently at 12.7V which, by this table still shows substantial amount remaining. The fact that I'm still only 82.5Ah of 272 gives me pause, but I'll let the whole run play out before making a judgment. (Plus testing my current measuring device...)

Thank you again, Banszi!
 
Quick update: Still running.

- At 18 hours, voltage dropped to 12.7V (measurements indicated 1,020 Wh, and 78.6 Ah) with cell values as 3.203, 3.186, 3.204, 3.202 volts

I've ordered a 12V BMS to arrive tomorrow so I don't have to watch the batteries so closely, as well as an additional capacity tester (also with shunt) to verify my testing setup.

I realize I have a non-professional setup for testing these batteries. I don't need to get anywhere near 272 Ah out of them, but I do need them to be more than 100 Ah! :)

Again, I'll keep you posted! Thank you all so much for your wonderful help!
 
Don't freak out until the test is finished. :)
Got pictures of your setup?
Spludgey, thanks for the works of encouragement!

Here's a photo of my crazy test rig, plus a photo of the rest of the batteries. I have 48 for a sailboat repower and 4 for testing purposes.BatteryTestSetup.jpgFreshBatteries.jpg
 
Have you verified the shunts rating is the same as the meter calls for? For example a 50mv 300A shunt will have the same voltage drop at 300A as a 100A 50mv shunt at 100A. If the meter isn't programmed correctly you will have a measurement error due to the different resistance.
 
Have you verified the shunts rating is the same as the meter calls for? For example a 50mv 300A shunt will have the same voltage drop at 300A as a 100A 50mv shunt at 100A. If the meter isn't programmed correctly you will have a measurement error due to the different resistance.
I'm using the shunt that came with the measuring device, but that's no guarantee! I'll see about measuring the shunt resistance when I'm done with this run.

Here's my plan for checking the shunt / measuring device when this first test is complete.

1) I've ordered another shunt based meter from Amazon that will arrive tomorrow. That can be a second check.
2) Tonight I'll charge the battery through the shunt. Since my small charger displays it's amperage I can compare it with the shunt.

I wasn't planning on testing all 52 batteries, just these 4. The others I'll hook up to my 144V system (153.6 nominal), with the full CAN-enabled BMS and charger. Then I can measure the battery input at least. (I don't have the motor hooked up to anything that will cause sufficient draw to draw all the batteries down in a 43kW system.) Then I have to finish all the mechanical work to get the electric motor into the boat. But that's the next step.
 
Have you verified the shunts rating is the same as the meter calls for? For example a 50mv 300A shunt will have the same voltage drop at 300A as a 100A 50mv shunt at 100A. If the meter isn't programmed correctly you will have a measurement error due to the different resistance.
THANK YOU!! You were spot on! Despite the fact it's the shunt that came with the unit (and I can't adjust the unit), it appears to be off by nearly exactly 300%. It drove me crazy that the 150W heater was registering only 50W pull, and now I know why. This is why the right tools are so important. But now I know I can just multiply by 3. :)

To verify, I put a 1.5A charger on the battery and used the charger as the source and battery as the load. And... the measurement read around 500 mA.
BadShuntArrow.jpg

My final readings were as follows:

- Total run 22.5 hours,
Readings: 11.5V total with individual readings 2.886, 2.813, 2.938, 2.898
After 30 minute rest: 12.35V total with individual readings 3.059, 3.084, 3.084, 3.100V
Metered capacity: 91.4 Ah and 1,180 Wh (with bad shunt)
Calculated capacity: 274 Ah and 3.5 kW (measured * 3, very approximately)

That's likely over the expected capacity of 272 Ah, given that my starting SOC was under 100%.

Thank you everyone on this forum! There was a moment of panic, but I'm thinking things are looking good! I'm charging again tonight and will run another test once I get my BMS and new capacity meter tomorrow.
 
I'm real new at this myself, but I'm having no problems with the Lishen 272 Ah cells. Here's my ongoing top-balance and capacity test. One thing I see, your leads are terribly small. On mine, the six BMS leads are AWG8. I'm not sure what two going to my capacity tester and Inverter but they are nearly a 1/2" in diameter. I'm pushing 54.4 amps (the recommended 0.2C for this size cells for a capacity test). I'm getting dead on for capacity at 275 Ah and 277 Ah on the second test.

Sorry, read the first post, saw the picture... didn't read the last post till now.
 
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Thanks, Banszi! That's good to know. I can safely discharge to 2.5V, but the rule of thumb shows that once my value drops to 3.2V my SOC is already at 5%. So how much more can I expect to get between 3.2V and 2.5V. I can't imagine it's more than I got from the drop from 3.5V to 3.2V given the discharge curves.

In any case, I'll keep running the test. It's only 10 degrees C in the garage. Might that impact my results?

Thanks so much for your response! I really appreciate it!

BTW, I'm measuring the voltage every 15 minutes, and when it drops below 2.8V, I'll measure every 5 minutes. I have a BMS, but it's for a 48 battery system, not 4. :)
When you charged the batteries, when max volts was reached, was the current draw down to near zero? Like Will's top balance video, the current should drop to zero when fully charged.
 

We just got done doing a capacity test, and I wanted to share what our process is for capacity testing batteries. While the equipment may not be quite like what you have, there are a ton of cross overs and a lot to learn from the video.

The electronic load can be replaced with an an inverter for example, the shunt with a clamp meter, and the data acquisition unit can be replaced with a pen and paper. If you try to get a consistent discharge current going, then you can time how long you run that amperage at, and effectively get a good idea of how close to capacity you are pulling. Keep in mind though, your accuracy wont be to 5 1/2 digits, it may only be within 5-10 amp hours, but it's enough to see if you are getting a TON of capacity less than you are asking for.

I see that you had the wrong voltage shunt paired with your meter, so that makes total sense why you would only see 1/3 the capacity. I've always felt that these meters should have a shunt included, but I also realize how hard it can be to make a "one size fits all" shunt, especially when higher capacity shunts sacrifice accuracy on the lower end, without expensive frontends on the meters...which the cheap meters from amazon almost never have.
 
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