Battery Capacity Test Update

[Rbertalotto]

Well, done! Charged the 5 year old Renogy battery to 100%. Set the Battery Tester to discharge at 10amps. Went to bed. Woke up at 3am for a BioBreak and checked on battery. Tester reported capacity at 102aH. Not bad for a battery in service in an RV 24/7, never disconnected for five years! Battery was so depleted I had to jump start the BMS with another battery. It is now recharging at 30 amps. Fun little project!

 

[Rbertalotto]

Should the tester be set to terminate the test at a preset minimum voltage or just let the battery bms shut the battery down?

 

[timselectric]

Standard test, is from fully charged and balanced, down to BMS cutoff, at a 0.2C discharge rate.

 

[Rbertalotto]

Standard test, is from fully charged and balanced, down to BMS cutoff, at a 0.2C discharge rate.

Thank you......Others are suggesting to not trust the BMS to shut down the battery at depletion.

 

[timselectric]

Thank you......Others are suggesting to not trust the BMS to shut down the battery at depletion.

That's the only way to know it's true capacity.
If you can't trust the BMS to do it's primary job, you have a major problem.

 

[Rbertalotto]

That's the only way to know it's true capacity.
If you can't trust the BMS to do it's primary job, you have a major problem.

Totally agree! "Trust your parachute!"

 

[Rbertalotto]

Lots of interest in my post on checking battery capacity. Here is a quick "HOW TO" from begining to end on how to use the MakerHawk battery tester. [MAKERHAWK Battery Capacity Tester – RVB Precision](https://rvbprecision.com/.../makerhawk-battery-capacity...)

 

[timselectric]

That tester is fine for capacity of small batteries, or single cells, 85ah or less.
But it can't pull a 0.2C for anything larger.
I should say that it's fine with larger batteries, for comparing two tests, at different times, with the same battery and tester.
But the results aren't comparable with standard testing.

 

[Rbertalotto]

Why do you need to pull a .2C to discharge the battery over time? Using 10a discharge on a 100aH battery should deliver pretty accurate information. At least this is what Will Prowse is now using for capacity testing of batteries over 85aH......

 

[timselectric]

Why do you need to pull a .2C to discharge the battery over time? Using 10a discharge on a 100aH battery should deliver pretty accurate information.

The 0.2C is the standard capacity test.
Anything else will give slightly different results.

At least this is what Will Prowse is now using for capacity testing of batteries over 85aH.....

I'm sure that is old information.
Nobody is testing at 0.1C, if they want to compare it with anyone else's testing.

 

[Rbertalotto]

The 0.2C is the standard capacity test.
Anything else will give slightly different results.


I'm sure that is old information.
Nobody is testing at 0.1C, if they want to compare it with anyone else's testing.

Thanks, you are probably correct....What tester can test at .2c with batteries over 85aH. I just might have to step up my game!

 

[timselectric]

correct....What tester can test at .2c with batteries over 85aH. I just might have to step up my game!

I just use an appropriate load, for the battery I'm testing.
I don't use a specific tester. I don't test batteries for a living, so I can't justify the cost of a tester. But I'm sure that there are many options available.

 

[wpns]

Thanks, you are probably correct....What tester can test at .2c with batteries over 85aH. I just might have to step up my game!

Once you start getting into higher powers, the dedicated testers start getting really expensive. I would either use a low end tester and know that you’re testing it .02C and you should get 10 times the capacity [Doh! RUNTIME!] at a very minimum, or do what everyone else does which is use an inverter and draw kilowatts out of the battery and see how long it lasts.

 

[SolarUKWM]

testing it .02C and you should get 10 times the capacity at a very minimum

Is that true? I know that heavier C rates reduces the nominal cap, and lighter increases the nominal cap, but not in a straight linear way like that ...

 

[wpns]

Is that true? I know that heavier C rates reduces the nominal cap, and lighter increases the nominal cap, but not in a straight linear way like that ...

Who said it was linear? At 0.02C you'll get MORE THAN 10 times the capacity [Edit, I meant RUNTIME] than the 'standard' 0.2C rate, but I have no idea how much more.

 

[Sweet Tatorman]

Who said it was linear? At 0.02C you'll get MORE THAN 10 times the capacity than the 'standard' 0.2C rate, but I have no idea how much more.

Actually, with LiFePO4 you will get a few % more capacity at 0.02C vs 0.2C. Certainly not 10X capacity. With Pb-Acid the differences will run more than 10%, usually on the order of 20%.

 

[jgh]

That should be expressed "10 times the runtime". Not "the capacity".

 

[wpns]

That should be expressed "10 times the runtime". Not "the capacity".

Doh! Of course, sorry for the confusion, I should lock out the keyboard until after my first coffee.

10X the runtime, but only slightly MORE CAPACITY.

I'll shut up now. Oh, no wait, the other thing.

 

[SolarUKWM]

I meant RUNTIME

Ah, now _that_ makes more sense!! (You see why I went ... whut?? ... at the original statement!)