Battery internal resistance

[Outlaw]

Quick Question. Should the Battery internal resistance be measured when it is fully charge , at storage charge, or does it make any difference? I haven't been able to find this anywhere. Pat R or Ty if you could chime in here.. Also, what about battery temperature?

Thanks

 

[PatR]

IR will change with charge state and temperature. A cold battery should show a slightly lower IR than a hot battery. There's usually a slight decrease in IR when a battery is charged the first time.

As for when IR measurements should be taken, there is a correct time but I don't recall what that point is. Personally, I record IR in several states. When a battery is first obtained prior to the first charge. That also lets me know the voltage state when the manufacturer shipped the battery. 30 inutes after charging a battery to full state. The 30 minute period is for cool down from the charging process. I also like to check IR after the battery has been subjected to normal current loads for a couple minutes. In a way that one is the most important as it's reflective of what the system is experiencing. One way to do this is to take a fully charged battery and connect it to a charger with a Discharge function. Set the discharge load at 1C (not 1Amp) and let it run for a minute or two. Terminate the discharge cycle and as quickly as you can check IR.

Battery temperature is a pretty loose question in and of itself. What are you concerned about in that regard?

 

[Outlaw]

[QUOTE=Battery temperature is a pretty loose question in and of itself. What are you concerned about in that regard?



I've always heard batteries are most efficient around 90 degrees F. but not sure if that is because the IR in the pack is lower at a higher temp. I know cold is suppose to slow down chemical reactions, so it would make sense, (cold bad, warm good.)

Thanks for your help, you have answered most of my questions.

 

[PatR]

IRRC, best lipo performance is obtained between 10C and 30C. Ideal storage is around 20C. High temps screw them up too.

 

[Phaedrus]

When I was racing electric RC boats (capable of 70 to 100+ mph) we found that 110 degrees F (43 C) was ideal for max performance. Lipo performance falls off sharply with temperature.

 

[PatR]

Thanks Phaedrus[emoji4]

 

[Phaedrus]

I'll add that for our application I would not worry about warming the pack to a particular temperature. Just don't use them when they are cold to the touch. I typically place my packs on the dashboard of my car when it is really cold out. That keeps them warm enough. Just holding them in your hands for several minutes helps.

 

[PatR]

I agree. If the cab temp is comfortable for the occupants it’s good enough for the batteries. Of course there’s always the masochist that enjoys dripping sweat or shivering in the cold but we can pretty much ignore those few.

 

[Phaedrus]

Basically I don't run a pack that is cool to the touch. 75 degrees or more is a good number to use.