Scientific Testing of RC Batteries

[davkhow]

Hello everyone. I am fairly new to the forum but I have noticed a lot of questions about batteries. Is this one good? Does that one last?

I am an engineer that has been building testers to test electric vehicle battery packs for almost 10 years now. So most of what I deal with ranges from 6 or 12 cell modules up to 200 cell, 800V battery packs. They are typically anywhere from 50 to 300AH (not mAH).

I have access to equipment that would be able to accurately measure actual capacity, internal resistance, and be able to pull up to 100A from the battery. I could write a program to do all this automatically while recording all cell voltages.

But my question is, how useful would that be to the community? Would it be worth it? I could run tests in my off time, that’s not really a problem. And the initial programming would take maybe 8 hours or so of my time.

The biggest problem I see is getting batteries to test. Obviously I don’t want to buy all the batteries myself. So that would need to be something to figure out.

One thing I’ve been intrigued about is the C rating of the batteries. If a 6000mAh battery says it’s capable of 100C discharge, that would mean it’s capable of discharging at 600 amps. Personally I find that hard to believe, but that’s why I want to test them. If I can get a good measurement of internal resistance, I should be able to calculate the short circuit current and see if those 100C or 150C claims hold any merit.

So does anyone have any input on if this would be beneficial?

Is there another community that may be interested as well? Obviously this is an Arrma forum but what I’m proposing would be applicable to any RC hobby that uses these type of packs.

And does anyone have any suggestions on ways to get batteries to test?

 

[SrC]

Seems the quality control of the Cell matching counts the most, along with the chosen Grade tier of the cells used by the OE. Which usually dictates price.
C ratings are dark specs with no regulatory rules. C ratings are for the most part simply a Marketting tool as it turns out. The higher the adverstised C rating the more you pay. Not ideal way to choose lipos. Most fall way below the C rating. As you know already. There is more to a lipo, like IR's and actual use Capacity.

Getting lipos direct from the Mfr. by paying for them like the next guy is the best way. That costs $$ . And you don't want to test used lipos with no available history with them.
Getting a Mfr to offer them for free, is not the best or fair way to judge them IMHO.
Not sure if you been to RC Groups, but there is much info there in regards.

I commend your interest in sharing your data results.

 

[LibertyMKiii]

Hello everyone. I am fairly new to the forum but I have noticed a lot of questions about batteries. Is this one good? Does that one last?

I am an engineer that has been building testers to test electric vehicle battery packs for almost 10 years now. So most of what I deal with ranges from 6 or 12 cell modules up to 200 cell, 800V battery packs. They are typically anywhere from 50 to 300AH (not mAH).

I have access to equipment that would be able to accurately measure actual capacity, internal resistance, and be able to pull up to 100A from the battery. I could write a program to do all this automatically while recording all cell voltages.

But my question is, how useful would that be to the community? Would it be worth it? I could run tests in my off time, that’s not really a problem. And the initial programming would take maybe 8 hours or so of my time.

The biggest problem I see is getting batteries to test. Obviously I don’t want to buy all the batteries myself. So that would need to be something to figure out.

One thing I’ve been intrigued about is the C rating of the batteries. If a 6000mAh battery says it’s capable of 100C discharge, that would mean it’s capable of discharging at 600 amps. Personally I find that hard to believe, but that’s why I want to test them. If I can get a good measurement of internal resistance, I should be able to calculate the short circuit current and see if those 100C or 150C claims hold any merit.

So does anyone have any input on if this would be beneficial?

Is there another community that may be interested as well? Obviously this is an Arrma forum but what I’m proposing would be applicable to any RC hobby that uses these type of packs.

And does anyone have any suggestions on ways to get batteries to test?

There is quite a few people doing this already actually.
There is a long-running thread on RC groups and another going on at RCTalk forum.
RC Groups thread: https://www.rcgroups.com/forums/showthread.php?1767093-Battery-Load-Test-Comparisons
RC Talk thread: https://www.rctalk.com/forum/threads/lipo-comparison-thread-lipo-and-nimh-aas.136829/

Getting Lipos to test is one obstacle and in my opinion, when testing the high-end lipos you need to put them through their paces at 300+ amps to see how they respond.

Example from the RC groups forum thread (check the REAL C value on the far right)

Top tier high amperage batteries matter to me because I punish them with runs like this:

 

[davkhow]

Awesome

Yeah, I was just looking through some of the stuff MCSGuy has been doing. Looks like it's already been done.

There is quite a few people doing this already actually.
There is a long-running thread on RC groups and another going on at RCTalk forum.
RC Groups thread: https://www.rcgroups.com/forums/showthread.php?1767093-Battery-Load-Test-Comparisons
RC Talk thread: https://www.rctalk.com/forum/threads/lipo-comparison-thread-lipo-and-nimh-aas.136829/

Getting Lipos to test is one obstacle and in my opinion, when testing the high-end lipos you need to put them through their paces at 300+ amps to see how they respond.

Example from the RC groups forum thread (check the REAL C value on the far right)

View attachment 318691


Top tier high amperage batteries matter to me because I punish them with runs like this:

View attachment 318694

Holy cow! I had no idea these were actually ran that high. What are you doing to put it through this? Is this a 15s speed run?

The machine I have access to can do up to 720 amps and 30kW. So I could in theory take that data log file and replicate it to run on any battery.