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Understanding battery IR

Understanding battery IR

Old 10-07-2019, 11:01 AM
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Default Understanding battery IR

I picked up some LiHV (Reedy Zapper 4s 5200s) and used them for the first time this weekend. I charged at 1c and noticed the IR was typically in the 2-3mΩ during the charge process and 1.xmΩ after the run. I'd like to keep the batteries in good condition for as long as possible and noticed that some people recommended charging them at much higher rates (40a) and discharging them at higher rates as well (my iCharger X6 only discharges at 2a). I have no use for the performance advantage this offers after a five year layoff from racing but I'd like to keep the batteries working to their potential for as long as possible (Reedy recommended max charge rates of 2c (10.4a) so it doesn't look like I can take advantage of that anyways).

What is a normal mΩ range for the batteries to be?
Is there a specific mΩ range I should look at replacing them?

Last edited by madweazl; 10-07-2019 at 11:28 AM.
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Old 10-07-2019, 11:22 AM
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2 to 3 ohm seems unlikely, it shall be in the range of 2 to 3 milli Ohm and that is normal for normal cells.

The guys discharging and chaging their batteries with 40A only do that to heat the cell from te inside, a heated cell will give a lower IR but the question is if you are that good to notice it. With a 20A discharge you will notice a longer stable voltage when charging the battery and driving it so it is wise to check how to build a resistor bank with your X6. No need to go to the max but a 15 to 20A discharge can do wonders w/o shortening the life of your battery.
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Old 10-07-2019, 11:29 AM
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Originally Posted by Roelof View Post
2 to 3 ohm seems unlikely, it shall be in the range of 2 to 3 milli Ohm and that is normal for normal cells.

The guys discharging and chaging their batteries with 40A only do that to heat the cell from te inside, a heated cell will give a lower IR but the question is if you are that good to notice it. With a 20A discharge you will notice a longer stable voltage when charging the battery and driving it so it is wise to check how to build a resistor bank with your X6. No need to go to the max but a 15 to 20A discharge can do wonders w/o shortening the life of your battery.
Right, milli-ohm (fixed the original post). I'll look into a resistor bank.
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Old 10-07-2019, 12:34 PM
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Originally Posted by madweazl View Post
Right, milli-ohm (fixed the original post). I'll look into a resistor bank.
Here is a nice stand-alone discharger. I've heard discharging at high amps is hard on your charger so I picked one of these up. Note: they don't balance though.

https://www.progressiverc.com/skyrc-...SABEgKZ1PD_BwE
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Old 10-08-2019, 06:28 AM
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2-3mΩ is pretty much standard for most packs I have tested when new, the higher the C rating the lower the initial mΩ with some cells as low as 1mΩ... most of my packs tend to lose performance around 6 months to a year and I'm measuring 8mΩ+ at that point which I swap out that pack from a "race" to "practice/qualifier" pack... typically pack swelling starts to occur around 15mΩ+ and that's about the time I retire the pack for good.

For 4S use in 1/8 buggy, I don't think it's necessary to cycle those packs, some brands of batteries do tend to last longer than others. I would encourage you to give Trinity White Carbon a try when the time comes to replace your current packs.

Also be sure to check the IR of your connector too, that will increase your IR readings significantly if you are not using a high quality charge lead.
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