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Sammus
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04.29.2008, 03:25 AM

Why don't manufacturers just give their cell internal resistance. Wouldn't that solve all these under rate over rate, no standard for C rating nonsense? I always though a cells internal resistance would ultimately determine its discharge capabilities. Could you say anything about the temperature of a pack in given conditions from the packs resistance?

Even better, why not use a charger (hyperion duo and fma 10s are two that I know of) that will tell you the batteries internal resistance, I think that would have to give you a good indication of cell quality.

edit: just notice in the pdf's above that the impedance @1khz is listed. I always thought a packs resistance would be say the average of the resistance during a discharge using V = IR. Is there some other method of testing? I also realised that those chargers measure it during charge, and say that the figure gets more accurate the longer it is charging for. any light on this?

Last edited by Sammus; 04.29.2008 at 03:27 AM.
   
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lutach
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04.29.2008, 08:06 AM

Max Amps should get one of those CBA and run some cycles through the packs at 10C, 15C and 20C to see what they really are. I know normal guys that has a CBA and MA as big as they are should have one too. I know they won't know how to explain why they post 20C ratings on a 15C rated cell. Maybe they can just apologize and say they got money hungry. It looks too much like a "Sponge Bob Square Pants" cartoon where they Sponge Bob and Patrick were selling chocolate. They were having trouble, but they saw a advertisement for some chips and got an idea of elaborating the truth. I like the one where he says, "Chocolate will make you younger."

P.S.: I'm forced to watch it .
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kulangflow
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04.29.2008, 09:16 AM

Quote:
Originally Posted by BrianG View Post
I like bench testing better - much better controlled environment without the added variables of track conditions, the driver taking corners a tad differently, etc. Just need some time, dummy loads, and measuring equipment...
I agree that bench testing would be better, but unfortunately I don't have the dummy loads.

My unedumakated theory thus far was that it didn't matter so much what kind of driving or vehicle got the load, so long as they got the same load. 90A is 90A, right? Like, within the first 1000mAh of a run, if pack 1 hits a max of 90A seven times and drops the voltage to less than 6.1V each time. Then pack 2 hits a max of 90A twelve times in its first 1000mAh but only drops voltage to a min of 7.1V, isn't that proof enough between those two packs? Do the variables really matter at that point?

I like the idea of drag race style testing like John mentioned in the NK thread. I could just draw a line on two ends of my street and do 10 straight runs back and forth on each pack, fresh off the charger in the same vehicle.

I certainly won't claim to know more about this than you guys do, so please correct me when I'm wrong. I'm here to learn just like everybody else. The only reason this all started for me is because I can't use these $100 packs in my Revo. These packs should be a perfect fit for my Revo based on the advertised C rates.

Thoughts?
   
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glassdoctor
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04.29.2008, 09:36 AM

I have done similar basic tests using a datalogger.

All you have to do is get the amps up.... to see how low the voltage drops at those points.

Keep track of the temp of the packs being tested too. Cool lipos don't perform nearly as well as a nice warm pack. My tests showed a big difference between say 60s* and 90s*


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skellyo
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04.29.2008, 09:42 AM

If I had the batteries and some spare time, I'm sure I could run some very accurate discharge tests on any of these batteries. One of my more recent programs here at work had 2 - 6kW programmable load boxes ( http://nhresearch.com/Products/4700-...onic-load.html ) that could be set up for a constant current load so that you could verify voltage under a specific load. It could also be programmed such that you can cycle through current spikes at various intervals. Add a data recorder to that and it would be real easy to plot the current versus voltage in a very controlled situation. I may have to look a little further into where all the equipment is now to see if it's something that would be feasible to come in and do on a weekend. Is this something you guys would be interested in seeing if I could do it?
   
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DrKnow65
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04.29.2008, 09:56 AM

Skellyo, absolutley! I'd love to see graphs of MaxAmps, Neu Energy, FlightPower, TrueRC, Zippy Lipo, and those cheapy no name ebay packs.

I think knowing the voltage drop at the rated "continuous" and "burst" amperages would be a good indicator of what works and what doesn't. How much the cells heat up at the "continuous" amp draw would also be an indicator of potential life span.


If I could only draw what I see in my head, then afford to build it, and finaly get to play with it...
   
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Sammus
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04.29.2008, 09:57 AM

I'm guessing you would end up with something like the graphs of the enerland testing posted earlier. It would also be good to have them compared with similar voltage/mah A123 packs, and to have the temperature logged all the while.
   
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johnrobholmes
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04.29.2008, 10:04 AM

Maxamps does have a CBA, Jason posted up about it a while back on RCC. Still no data from them....


I feel like getting one just to play around with. New revo, or CBA? Tough choice.
   
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lutach
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04.29.2008, 10:09 AM

Quote:
Originally Posted by johnrobholmes View Post
Maxamps does have a CBA, Jason posted up about it a while back on RCC. Still no data from them....


I feel like getting one just to play around with. New revo, or CBA? Tough choice.
I woder why he doesn't post real graphs from using the CBA . If I had a CBA, I would be having fun with it .
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johnrobholmes
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04.29.2008, 10:13 AM

I don't know why. He is passing anything I say as just "hating" at this point. Jason has directly stated that good news is "truth" and bad new is "claims" in that thread.

I have a feeling I could post up 10 graphs and he would give me 10 reasons why they didn't say anything about the packs. Really disappointing to see somebody in our industry so unwilling to accept anything but what he wants to hear.
   
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lutach
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04.29.2008, 10:28 AM

Quote:
Originally Posted by johnrobholmes View Post
I don't know why. He is passing anything I say as just "hating" at this point. Jason has directly stated that good news is "truth" and bad new is "claims" in that thread.

I have a feeling I could post up 10 graphs and he would give me 10 reasons why they didn't say anything about the packs. Really disappointing to see somebody in our industry so unwilling to accept anything but what he wants to hear.
Wow. He actually said that?
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skellyo
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04.29.2008, 10:29 AM

Quote:
Originally Posted by johnrobholmes View Post
I feel like getting one just to play around with. New revo, or CBA? Tough choice.
I did some looking at the CBA you guys were talking about. It looks like it would be around $1500 + shipping for everything needed to test 2S packs. That would be the CBA, 2 - 500W amplifiers and a 1000W harness kit.
   
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kulangflow
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04.29.2008, 10:43 AM

Sorry John, but it looks like Jason booted you and erased all your posts from NK because of your "hating".

I keep wanting to defend your good name there, but I don't want it to compromise my ability to get answers from them. I'm sure I would immediately be booted like you were.
   
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lincpimp
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04.29.2008, 10:59 AM

Quote:
Originally Posted by lutach View Post
I woder why he doesn't post real graphs from using the CBA . If I had a CBA, I would be having fun with it .
Hmm, I wonder why too
   
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lutach
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04.29.2008, 11:03 AM

That's not a good sign from MA at all. Are Austin and Jason relatives or maybe best friends, but if they are none of the above, I would seriously start restructuring the company ASAP. Get better products and qualified people to handle issues with the out most professionalism so their actions won't make the company look even worst. I bashed a little in rctech regarding the Speed Passion GT controller, but those guys handled that well. Jason has also shown us that he doesn't know how to deal with pressure at all. Good point was when lincpimp posted in the MA thread.
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