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Aug 03, 2018, 10:02 PM
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Zippy 2100 2s Life Battery Internal Resistance


What is a healthy internal resistance for a Zippy 2100 2s Life battery? What should each cell register? When should I get new batteries because the internal resistance is to high? Thanks
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Aug 05, 2018, 02:54 AM
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A really good 2100 lipo will have a cell IR of about 5m.ohms so a 2S would be about 10. Zippys are not at the top of the tree and I would expect a cell value in the range 7- 12 m.ohms and would give them up at 20+.

It depends what your application is, if it is just a sport plane stooging around at low current, then you can get away with higher figures.
The time to ditch a lipo is when you see a big and increasing difference between the two cells which means one cell is dying.

Make sure you measure IR at about 22*C ie 72*F

Wayne
Aug 05, 2018, 08:40 PM
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vollrathd's Avatar
Is this about LiPo's? Or two cell receiver type Life cells?
Mar 31, 2019, 09:22 AM
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propnator's Avatar
Quote:
Originally Posted by vollrathd
Is this about LiPo's? Or two cell receiver type Life cells?
I'm sure that's NOT LiFe IR answer, since the ohm number is very similar to a Lipo. I'm no expert but I had my friend test my 2S LiFe 1800.
One cell was 72, the other was 46. It still works as rx battery pushing 5 MG servos all afternoon (5 flights).

If I'm taking a risk here, please tell me. I read in another column you explained LiFe batteries would have much higher IR which makes them perfect for the 6.6 volt low C out put, but no good for high C as in motors.

I used to live in Racine 1952 - 1964
Mar 31, 2019, 07:19 PM
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vollrathd's Avatar
Quote:
Originally Posted by propnator
I'm sure that's NOT LiFe IR answer, since the ohm number is very similar to a Lipo. I'm no expert but I had my friend test my 2S LiFe 1800.
One cell was 72, the other was 46. It still works as rx battery pushing 5 MG servos all afternoon (5 flights).

If I'm taking a risk here, please tell me. I read in another column you explained LiFe batteries would have much higher IR which makes them perfect for the 6.6 volt low C out put, but no good for high C as in motors.

I used to live in Racine 1952 - 1964
As a comparison, those 2500 Mah A123 cells measure around 12 milliohms. But, E = IR for the battery voltage drop. And with a peak current of say 10 Amps, E = 10 * 0.072 or a 0.72 Volt drop at full current. That's still far better than what you'd get with a 5 cell "AA" Nih battery pack at the same 10 Amps.

But, IMHO, keep an eye on the IR values on that pack. I've run into four LiFe battery failures in my RC club in the last two years. The failure was a high resistance cell, with two of the battery packs having a completely open cell. Personal guestimate is that perhaps there was a tiny pin hole in the LiFe plastic baggie that eventually allowed the cell to dry out over a long period of time.

The A123's are hermetically sealed inside an aluminum jacket.
Apr 01, 2019, 04:35 PM
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propnator's Avatar
Thanks volrath for the input. I just purchased a Tenergy battery meter that measures IR. The reading I reported was off my buddy's bench unit and he didn't like the read out either but doesn't know anymore than I do about LiFe batteries. We have recently come to appreciate the value of knowing IR readings in our Lipos so I thought to check this LiFe for kicks.

Also going to purchase a new hump back LiFe battery. Would cost a lot less than replacing the plane if it crashed!

I'd go with the 123's but haven't found any same size. Do they charge at 3.3 per cell?

Thanks again
Last edited by propnator; Apr 01, 2019 at 04:39 PM. Reason: more


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