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Old Feb 02, 2013, 03:54 AM
The Engineer
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Measuring IR of a LiPo

I am making a series of investigation into selecting the best pack for a project and buying alot.

Have been testing some brands using a method.

A friend pass a SkyRC i-Meter for me to paly around. It is a RC multi meter capable to do one thing i need - measuring the IR of the cell or a pack of cells.

But when measuring 1P vs 4P, the R is almost similar. Parallel the load, resistance is averaged over the 4 cells correct?

Is there a more accurate way to measure them? Some model of packs i have varies too much from the specification by mfg.

Also, during flight, i was collecting data on the max current consumed.
Do you trust the reading from a watt meter or an expensive Fluke current clamp meter?
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Old Feb 02, 2013, 04:44 AM
A man with too many toys
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I have tried thinks like that in the past with mixed results. The only way that I have found to get a good consistent IR measurement is to do it as the pack charges like the Power Lab chargers do. If you are serious about LiPo’s you should own a Power Lab 6 or 8. With the optional PC interface you will get a graph of the IR of each cell as it charges. IR is dependent on the state of charge and cell temperature.




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Old Feb 02, 2013, 05:09 AM
The Engineer
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Yes I heard about PL8. I have Schulze charger and its has that IR function too but I'm not able to get it working. Maybe I need to add resistor to the bal cab connector.. will have to read up on that..

On another note, I have seen some tutorial video using light bulbs.. but those are running 12v. I'm on 6S..
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Old Feb 02, 2013, 06:14 AM
ancora imparo
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You might find these threads useful.

http://www.rcgroups.com/forums/showthread.php?t=1323465

http://www.rcgroups.com/forums/showthread.php?t=1577989

Of the chargers I and a couple of others who are interested in IR have tested, the iChargers and the Hyperions with the latest firmware give very close agreement with an ESR/IR meter and each other, my PL8 is pretty close but tends to give slightly lower values. It is increasingly inaccurate on poorer quality (high IR) packs. Sorry, haven't any data on a Shulze.

The various cheap meters with IR measurement functionality from HobbyKing and others that use only a two wire method (ie only the main battery leads) are a waste of time and money - at least as IR meters.

John
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Old Feb 02, 2013, 07:56 AM
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Originally Posted by jj604 View Post
You might find these threads useful.

http://www.rcgroups.com/forums/showthread.php?t=1323465

http://www.rcgroups.com/forums/showthread.php?t=1577989

Of the chargers I and a couple of others who are interested in IR have tested, the iChargers and the Hyperions with the latest firmware give very close agreement with an ESR/IR meter and each other, my PL8 is pretty close but tends to give slightly lower values. It is increasingly inaccurate on poorer quality (high IR) packs. Sorry, haven't any data on a Shulze.

The various cheap meters with IR measurement functionality from HobbyKing and others that use only a two wire method (ie only the main battery leads) are a waste of time and money - at least as IR meters.

John
so would a iCharger 106B+ be worth getting just for the IR feature because all of my other chargers do not have a IR function or is there something better?
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Old Feb 02, 2013, 10:17 AM
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The 106B+ is fantastic for measuring internal resistance and I keep one of mine in my field kit at all times to help out guys at the field to test their batteries and help them determine a safe maximum current draw.

If you only plan to use the IR function and do not plan to use the 106B+ for charging, Wayne Giles' ESR Meter would be better if you have high performance, high capacity (5000mAh or larger) packs. Wayne's ESR Meter has .04mOhm resolution whereas the 106B+ has 1mOhm resolution. I've found the 106B+ to be perfect for assessing 2500mAh and smaller packs and will bust out my ESR Meter to resolve subtle differences in my larger packs.

Mark
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Old Feb 02, 2013, 11:11 AM
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Originally Posted by mrforsyth View Post
The 106B+ is fantastic for measuring internal resistance and I keep one of mine in my field kit at all times to help out guys at the field to test their batteries and help them determine a safe maximum current draw.

If you only plan to use the IR function and do not plan to use the 106B+ for charging, Wayne Giles' ESR Meter would be better if you have high performance, high capacity (5000mAh or larger) packs. Wayne's ESR Meter has .04mOhm resolution whereas the 106B+ has 1mOhm resolution. I've found the 106B+ to be perfect for assessing 2500mAh and smaller packs and will bust out my ESR Meter to resolve subtle differences in my larger packs.

Mark
Hi i have larger rc packs 3000 to 5400MAH i did look at that ESR meter but it states a limit to 5000MAH capacity does the I charger have a limit also?
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Old Feb 02, 2013, 11:30 AM
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Neither have a theoretical capacity limit on measuring IR. They do have practical limits however. Since high quality 5000mAh cell have IR in the 1mOhm range, resolving an accurate and repeatable measurement can be tricky. That said, there is no better instrument on the planet for measuring IR in this low range than Wayne's ESR Meter.

Mark
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Old Feb 02, 2013, 11:35 AM
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Neither have a theoretical capacity limit on measuring IR. They do have practical limits however. Since high quality 5000mAh cell have IR in the 1mOhm range, resolving an accurate and repeatable measurement can be tricky. That said, there is no better instrument on the planet for measuring IR in this low range than Wayne's ESR Meter.

Mark
Hi then why does it state it good for up to 5000MAH capacity in the info on it?
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Old Feb 02, 2013, 12:48 PM
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Wayne's thread actually states up to 6000mAh but I'm quite certain that this is simply due to the fact that high performance lipoly cells larger than this typically have IR that is on the threshold of repeatable measurement.

He will have to corroborate this. I've sent him a message.

Mark
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Old Feb 02, 2013, 01:19 PM
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Originally Posted by reptileman View Post
Hi then why does it state it good for up to 5000MAH capacity in the info on it?
Hi,

The 5000maH limit is historical because when I first designed the meter,that was the largest lipo available. The unit will measure up to any size but the meauring pulse of 16A was designed to be large enough to load a large cell but not so large at it would damage the smallest cell.
If you are looking at large cells where the IR is likely to be down around 1 - 2 milliohms then the meter is ideal because of it's high resolution of 0.04milliohms.
The other advantage of the meter is that it takes instant readings without going through any charging cycle which can introduce errors due to temperature changes.
On the other hand it is absolutely useless at charging batteries!!

If you want any more details send me a PM?

Wayne
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Old Feb 02, 2013, 01:27 PM
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Is IR naturally higher on smaller cells? I've got two 6s, 2900 mah packs that have about 10 cycles each. Using my 4010Duo the per cell IR reading during charge is always 4 to 5 IR. On some older 2s 5000 mah packs I get ~2 IR per cell.
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Old Feb 02, 2013, 01:30 PM
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Absolutely. Cells of equivalent quality have IR that is linearly dependent of capacity.

Mark
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Old Feb 03, 2013, 03:43 AM
Supersonic Engineering
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Wayne's ESR meter is a great piece of kit, but in order to get results worth having, you do need to be fussy about the battery temperature that you measure at.
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Old Feb 03, 2013, 05:34 PM
The Engineer
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I need it for up to 23.88Ah per cell. Will it work?
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