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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Joe Ed Pederson on May 23, 2023, 02:47:51 PM
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HB~>
EDIT: I got two new batteries in the mail today and checked their resistance. One read 58 mohms on cell #1 and 5 & 9 mohms on the other two cells. The second new battery read 4/5/8 mohms. I then noticed that the wires from the balance board going into the charger was not fully pressed in on the left side. I pushed it back in and now the new battery that had read 58 on cell one reads 6 on cell one. I rechecked the two batteries i wrote about below and they read 5 & 6 on cell #1. I'm embarresed that I didn't catch this before I posted the stuff below
However, is there a general rule that says resistance above __ means the battery is worn out?
End of edit.
HB~>I have two Turnigy 3S 1300, 30-40C LIPOs that sat around at storage voltage (3.85 v per cell) for a couple of years. I didn't take an initial internal resistance reading when they were new. But after using them for about three flights each today and yesterday, the charger didn't bring the 3 cells back to the same voltage in storage mode. Cell #1 had considerably higher voltage than cells #2 and #3 when the charger (a Hitec X2 AC purchased about 2017) said the batteries had reached storage voltage and shut off.
So, I checked the internal resistance and Battery A had 58 mili ohms in cell #1, 8 mili ohms in cell #2 and 11 mili ohms in cell #3, and a combined resistance of 77 mili ohms. [or is it micro ohms?]
Battery B had 58 mili ohms in cell #1, 4 mili ohms in cell #2, and 4 mili ohms in cell #3, and a combined resistance of 66 mili ohms.
The model is a modified Sig Akromaster (18 ounces with battery), a Brodak FM-0c timer, a GForce 2212 1250 KV with a max amp rating of 17 amps and an APC 7 x 5E . I've got a Watts Up meter and have taken readings on the ground that yield 13 amps at the speed setting I'm using. Upon recharging the batteries I have never drawn more than 997 mah (about 4 minutes 30 seconds of run time.)
Ok, so what does the internal resistance indicate?
1) That these batteries should be retired and discarded?
2) They are still usable, but are not performing optimally?
3) Do these readings indicate that the #1 cell in each battery is bad/going bad or that the #2 and #3 cells are bad/going bad?
4) The instructions that came with the charger do not say if the resistance readings will vary with the voltage in the battery. So, are the resistance readings meaningful only if they are taken each time with the battery and cells at the same voltage?
I've never checked the internal resistance on any LIPO battery pack I've ever purchased. If I had been checking, I guess I would know some of the answers to my questions. I guess I'll have to start a log on all the battery packs I buy from now on and record their initial internal resistance readings.
Thanks,
Joe Ed Peerson
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Somewhere around 20-25 milli ohms is probably when packs will no longer hold voltage under load (it will feel like a loss of power) or have enough capacity to finish a flight (you might hit low voltage cutoff or the lap times will slow towards the end of the flight). That is if all cells are of the same resistance. This could vary quite a bit if you are on the edge of having enough capacity to start vs having a large reserve in capacity.
The cells with 58 milliohms resistance are on their way out and the battery should be retired. You risk losing a cell during a flight. I find it unusual that the number one cell in three packs have the same 58 millohm resistance. And that there was no difference in performance (at least that you mentioned). It might be worth measuring again or using someone else’s charger to verify.
Mike
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i FIND THIS TOPIC INTERESTING, BUT EXACTLY HOW DO YOU MEASURE IR. i HAVE HAD Batteries that under load will drop voltage very quickly, but seem fine otherwise. however I don't have anything that can measure IR as far as I know.
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My preferred method to measure a pack's internal resistance is via the charger. My charger is a Turnigy Reaktor 120 Duo (https://hobbyking.com/en_us/turnigy-reaktor-us-plug-120-duo-2x120w-240w-balance-charger-ac-dc.html), which has a "BATT RESISTANCE" measurement mode. In this mode, the unit will display the internal resistance of individual cells as well as the total resistance of any connected pack. YMMV -- check your charger's documentation, or find a battery analyzer.
Cheers, H^^
-Andrey
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Thanks for the info. Since I posted I have done some research. It turns out I have this device
Tenergy 5-in-1 Battery Meter, Intelligent Cell Meter Digital Battery Checker Battery Balancer for LiPo / LiFePO4 / Li-ion/NiCd/NiMH Battery Packs
I never realized it also measured IR. I will try it tonight and see what kind of results I get.
I did read one article that said c rating can effect IR. Low c batteries usually have higher IR than High c batteries. I use batteries typically 35c for sport flying and 65c for competition.
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"C rating" is a result of IR. IR is determined by cell construction and materials. Lower IR results in less voltage drop and less heat created in the cell under load.
IR increases as cells age. Aging is dependent on temperature, storage conditions(voltage), wear from use, etc.
I'm not sure how well IR measurements compare among devices.
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Is it IR or Ri ? Or Rint ? hehe S?P
;)
H^^
-Andrey
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Thanks for the info. Since I posted I have done some research. It turns out I have this device
Tenergy 5-in-1 Battery Meter, Intelligent Cell Meter Digital Battery Checker Battery Balancer for LiPo / LiFePO4 / Li-ion/NiCd/NiMH Battery Packs
I never realized it also measured IR. I will try it tonight and see what kind of results I get.
I did read one article that said c rating can effect IR. Low c batteries usually have higher IR than High c batteries. I use batteries typically 35c for sport flying and 65c for competition.
Oops, my unit is not the tenergy i referenced , it is a GT power. They look identical but the GT does not have all the functions of the Tenergy. So i ordered one, i’ll have it Sat. I’ll let you know the results.
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Somewhere around 20-25 milli ohms is probably when packs will no longer hold voltage under load (it will feel like a loss of power) or have enough capacity to finish a flight (you might hit low voltage cutoff or the lap times will slow towards the end of the flight). That is if all cells are of the same resistance. This could vary quite a bit if you are on the edge of having enough capacity to start vs having a large reserve in capacity.
The cells with 58 milliohms resistance are on their way out and the battery should be retired. You risk losing a cell during a flight. I find it unusual that the number one cell in three packs have the same 58 millohm resistance. And that there was no difference in performance (at least that you mentioned). It might be worth measuring again or using someone else’s charger to verify.
Mike
Thanks for the information, Mike.
I added an edite that explained that the #1 cells reading 58 mOhms was caused by the wires from the balance board not being pushed all the way into the charger.
Joe Ed
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i FIND THIS TOPIC INTERESTING, BUT EXACTLY HOW DO YOU MEASURE IR. i HAVE HAD Batteries that under load will drop voltage very quickly, but seem fine otherwise. however I don't have anything that can measure IR as far as I know.
This is considered by many radio control flyers to be the gold standard for Lipo battery I.R. measurement. I believe its designer, Wayne Giles, used the "Kelvin 4-wire connection" method which I think is able to eliminate measurement inaccuracies due to connecting wiring.
https://www.progressiverc.com/products/lipo-esr-meter-mark-ii
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Chargers use balance leads to read cell voltage, "4 wire" if you plug in your balance lead. Until balance chargers, IR measurements didn't exist except for specialized equipment. A few of the high end chargers back in the NiCd days centered around RC cars had this feature.
I'm sure the Lipo ESR meter is well designed and calibrated. It must be to read 10µΩ with any reliability. Unless you're pushing packs to their limits, it's a substantial investment. The cheapest chargers are questionable in their calibration and accuracy, but even then, a relative reading would be a valid indicator unless you need 75C from your battery.
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I received my Tenergy meter today. It is in the cheap range, $19 postpaid, but seems consistent. I measured 7 batteries, 5 with many flights 2 almost new. The new ones had all cells in the single digits, they were 50c batteries.
The others were two 5s and four 4s. The 5s are 65c and the 4s 35c. All had low single digits except for cell 1 and 4or5. It will be interesting if i see a performance difference.
The meter is easy to use, just plug into the balance port.