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Batteries & Chargers Discuss Li-P, Li-Ion, NiMh, Nicad battery technology and the chargers that juice 'em up!

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Old 03-19-2015, 11:07 PM   #1
craigrs84
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Default Internal Resistance - Zippy 3 cell 2200 mah lipo

I was wondering if someone could tell me what the internal resistance of a Zippy 3 cell 2200 mah lipo battery should measure when the battery is in good condition?

When I first bought the batteries I didn't own a charger capable of measuring the IR or capable of setting the batteries in storage capacity. So the result is I've let the batteries (two of them) sit in my refrigerator for the last 2 years almost fully charged.

I have a new charger now and I measured the IR:
Battery #1: 8, 8, 11
Battery #2: 11 10 10

Good or bad?
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Old 03-20-2015, 04:04 PM   #2
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It can be difficult to compare battery Ir. For one thing, different chargers come up with very different numbers. Things like room temp can also change the numbers slightly.

Its more important to compare a pack to itself over time. You can watch the Ir go up as the pack ages - or gets abused

If those numbers had been measured on my Hyperion charger, Id say they were pretty good. If they had been measured on my CellPro, Id say they were fantastic for a 2 years old 2200 pack

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Old 03-20-2015, 06:05 PM   #3
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I have a couple of storage charged same packs and numbers are very similar. That's using my Imax mini 6

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Old 03-20-2015, 06:25 PM   #4
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Yeah they are usable, not great by a long stretch, but should be fine for moderate demand applications.
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Old 03-20-2015, 06:48 PM   #5
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Storage voltage is more important than temperature for LiPo longevity.
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Old 03-20-2015, 08:08 PM   #6
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TBH I honest I have packs with much higher figures, but because the models using them are moderate demand, ie Sunday sport models - they perform fine.

I may be wrong but Ir figures give me indication of what model they will perform in. I have some with figures in the 00's ... but in my powered glider are fine. They only have to provide short bursts. My EDF's though demand far more and then I look for best Ir figs packs.

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Old 03-21-2015, 04:28 PM   #7
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You did not say what C-Rate they have but those numbers are OK, not great, but acceptable. I have a few Hyperion CX G3 3S 2100 ma 25C batteries and when new measured 7-7-7 a year ago and now 10-10-10.
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Old 03-22-2015, 04:51 AM   #8
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Originally Posted by dereckbc View Post
You did not say what C-Rate they have but those numbers are OK, not great, but acceptable. I have a few Hyperion CX G3 3S 2100 ma 25C batteries and when new measured 7-7-7 a year ago and now 10-10-10.
Sorry they're 20C. Does higher internal resistance just shorten flight time?
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Old 03-22-2015, 05:25 AM   #9
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Higher Ir does several things.

The higher resistance causes the pack to reach LVC sooner because of the larger voltage drop. That shortens the flight time because it lowers the effective/usable capacity of the pack.

It also causes the packs to run hotter - again due to the larger voltage drop across the packs.

It also lowers your power output because the motor sees a lower voltage and turns at a lower rpm.

Higher Ir is never good

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Old 03-22-2015, 06:01 AM   #10
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Default Double Checking Ri on your batteries

Originally Posted by craigrs84 View Post
I was wondering if someone could tell me what the internal resistance of a Zippy 3 cell 2200 mah lipo battery should measure when the battery is in good condition?

When I first bought the batteries I didn't own a charger capable of measuring the IR or capable of setting the batteries in storage capacity. So the result is I've let the batteries (two of them) sit in my refrigerator for the last 2 years almost fully charged.

I have a new charger now and I measured the IR:
Battery #1: 8, 8, 11
Battery #2: 11 10 10

Good or bad?
It isn't to hard to calculate the exact internal resistance of your battery pack. All it takes is a wattmeter, motor, prop and the battery in question.

Power up the motor, and increase power to around 20% or so. Record Volts and Amps on the wattmeter.

Then run the motor to full power, and again record Volts and Amps on the wattmeter.

The formula for battery resistance is as below:

Ri = (Volts@20% minus Volts@100%)/(Amps@100% minus Amps@20%)

So, if you measure 11.1 Volts and 12 Amps at 20% then 10.3 Volts and 45 Amps at 100% you get:

Ri = (11.1-10.3)/(45-12) which calculates out to 0.024 Ohms for the total of three cells in your battery pack.

You can use that calculated test derived from your setup to compare with the indicated battery resistance shown by your charger. My Cellpro PL8's show individual cell resistance, so you'd have to add them up to get the total cell resistance.

And, yes, you can calculate individual cell resistance by measuring the voltage on each cell during the load test. Gets to be a bit of a problem with the propeller blasting everything though.

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