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Capacity Test on a BB 12v 100aH Battery

guidecca

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I did a capacity test on one BB 12v 100ah battery over night. I set the dummy load to 5A and the battery is at 12.8V this morning. The test has gone over 12 hours. Does this look right or could the battery be defective? Multimeter shows 13.05v. The battery was at 13.56v last night. How low should the BB battery voltage go? Thank you in advance.

Did I tell you about Samlex Customer Support sending me the new EVO User Manual? They sent 108 pages out of over 200 pages (two pages per sheet of paper on one side), then they argued with me that they had sent the whole manual. Then, consulted with their office who somehow knew they only printed on one side of the paper. Battle Born is sure good at selling batteries.

Capacity Test.jpg
 
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It looks like you are right on track. Assuming the battery hits 100Ah capacity, the test would take 20 hours at 5a. You should have another ~5 hours to go. Once it hits around 12V (per multimeter), it will start dropping quick. What is your setting for low voltage cutt off on the capacity tester? 10V would be typical for these batteries. Some will set it lower due to voltage drop, so setting capacity tester at 9.x would mean 10v at the battery. There is so little capacity remaining once you get that low, it's not going to make a big difference either way.
 
I didn't set the low voltage cut-off on the tester. It was late when I started so I just ran the test. I was thinking that the batteries might have low voltage protection, but I'm not sure. There seems to be a discrepancy between the multimeter and the tester but maybe I should shut the tester off before testing with the multimeter. Maybe that is the "voltage drop" I heard about. When the two batteries were connected to the system in series for 24v it seemed like the MT-50 showed a sudden drop. Maybe my system setup is not working right.
 
Did I tell you about Samlex Customer Support sending me the new EVO User Manual? They sent 108 pages out of over 200 pages (two pages per sheet of paper on one side), then they argued with me that they had sent the whole manual. Then, consulted with their office who somehow knew they only printed on one side of the paper.
What new EVO? You can probably download the manual.

Maybe that is the "voltage drop" I heard about.
Voltage drop is normal and anyone doing DIY needs to have an understanding of it. If you google "voltage drop calculator" you will find what you need.

I didn't set the low voltage cut-off on the tester. It was late when I started so I just ran the test. I was thinking that the batteries might have low voltage protection, but I'm not sure.
Did you read the manual for your battery? All Battle Born batteries have a BMS built in and the information is in the manual.
 
What new EVO? You can probably download the manual.


Voltage drop is normal and anyone doing DIY needs to have an understanding of it. If you google "voltage drop calculator" you will find what you need.


Did you read the manual for your battery? All Battle Born batteries have a BMS built in and the information is in the manual.
BB did not send a manual but the flyer is good enough to answer my question and explain the warranty. You are correct; low voltage < 10v. If an individual cell falls below a prescribed threshold, the BMS will prevent further discharge . . . " Like this voltage drop calculator, https://www.calculator.net/voltage-drop-calculator.html ?
 
Since you have the battery BMS protecting the cells, the low voltage setting on the capacity tester should just be set low enough to make sure it's doesn't end the test too early. You should be able to see the setting by just clicking through the different pages using the single button on the tester (the display is something like "V < 10.0" or something like that). If you set it at 9v, it should never fire. If you set it at 12v, it's going to shut down the test too early. If you set it to 10v, you have an extra layer of protection if your BMS fails to shut down, but I wouldn't worry about that personally.
 
Thanks for that. I disconnected the first battery after 17 hours and the battery was at 12.6v on a 5A load. The second battery tested at 13.2V before the test and is now, 15 minutes later, with a 10A load reading 12.6V. I have a charger coming in a couple days and will charge the batteries before I test them. The multimeter is reading 13.1V so it must be voltage drop; maybe voltage drops more when current is higher.
 
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Why did you disconnect the battery at 17 hours? There is plenty of capacity remaining at 12.6v, especially if that was the voltage showing at the capacity tester (which will be lower than actual battery voltage). Just run the capacity test until the BMS shuts the battery off. The battery charger is a good idea if you don't have another good way to top off the batteries before the test.

If you are not already aware, the voltage for these cells is a terrible indication of state of charge. It barely moves at all for 90% of the cell capacity and then quickly rises and falls at either end.
 
I am in the process of finishing this DIY Solar project. I'm not sure if all components are set up correctly; I noticed the batteries did not last very long and the MT-50 indicated that. So, I attributed their short discharge time to the batteries themselves. Now, I'm not so sure what the problem is and I'm working on it. Might be good to change the small wires that came with the load tester with larger wire to eliminate resistance, heat, and voltage drop in the load tester. Testing at 5A is too slow but the temperature stayed at 40C; at a 10A load it is running at 60C.
 
Here is the 2nd capacity test on the 2nd battery. Voltage went down to 0.37v in 11 hours 21 minutes with a dummy load of 10A. The BMS shut down the test some time in the night.

Capacity Test 2.jpg

I went back to the first battery which was at 12.6A when I disconnected and restarted the test. I reset the dummy load to 5A; the discharge time had been about 17 hours 30 minutes.

Capacity Test 1 at over 20 hours.jpg
 
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