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LiPo IR and why it's important

PostPosted: Tue Jun 12, 2012 8:13 am
by beca

I would like an explanation on Internal Resistance (IR) in LiPo.s and why it is important to measure. I've been looking on the internat for information on this and I can't find any good answers, just that high IR is bad and has a close relationship with the performance in a pack.

What I would like to see:
What is a LiPo made of.
How do you measure volts, amps, IR.
When to measure, for accurate readings, i.e. fully charged, at storade charge, warm/cold? or what.
How to determin when a pack is good or bad, is there indications beforhand to see when a pack is about to go bad.
How to maintain/charge a pack to maximize performance and battery life.

I subscribe to the youtube channel I think your reviws are great, Good comon sense and great tecnical skill. It's a good combination!

Heli pilot. Sweden

Re: LiPo IR and why it's important

PostPosted: Tue Jun 12, 2012 8:26 am
by cynr100
Hi BR,

A good quality charger and a good quality analyser, will go a long way to prolonging battery life. (A Turnigy Accucell 6 and a HK-010 for me)

Have a read of for some tips and clues.

Cheers Dennis

Re: LiPo IR and why it's important

PostPosted: Tue Jun 12, 2012 9:36 am
by RCModelReviews
Measuring the internal resistance of a high-current battery is not a trivial task if you don't have the correct equipment.

In short, the lower the IR of a battery, the more of the battery's energy will go into the load (motor/ESC) than into heating the battery itself.

Generally, the IR is directly related to the C-rating of the pack.

A low-C pack will have a higher IR than a high-C pack.

Try to draw a high current from a pack with a high IR (low-C) and two things will happen:

1. the output voltage will drop so the amount of power delivered will be limited
2. the battery itself will start to get hot.

Power is delivered according to the formula I^2 * R where I is the current and R is the total resistance in the circuit.

If you have a battery with (for instance) an IR of 1 ohm and it's delivering its power into a load (motor/ESC) with a resistance of (say) 9 ohms then 90% of the battery's energy will go into the load and 10% will be wasted heating the battery.

A lower IR battery (say 0.5 ohm) will result in only 5% of the power being wasted by heating the battery and 95% being delivered to the load.

You can soon tell if your battery pack has too much IR for the application it's used in because it will get too hot and the performance of the model will be lacking.

The IR of a pack tends to increase as the battery gets older and when that happens you'll notice lower performance, shorter flight-times (because less power is going into the motor) and a warmer pack after each flight (because more energy is being wasted heating the battery due to its own internal resistance).

That's a pretty basic overview anyway.

Re: LiPo IR and why it's important

PostPosted: Sat Jun 16, 2012 4:26 pm
by beca
Thanks for the replyes.

The formula and information provided above is great, will be using it from now on. Thanks

As I own a ICharger 208B I can use it to measure the IR accuratly.
So why did I post this for a rewiev, Well as stated in my first post above there is no real hands on information about this on the internet and the discussion is all over about what is and is not the bottom line when it comes to IR. So it seems that many pople is aware about IR but don't realy know the meaning or why it's important.

And thanks for the Link above, very useful information there. If your on the lookout for Lipo information follow the link Dennis posted.

And now to my most desired question: When do you measure IR? (What state shuld the battery be in?) And I get that the IR shuld only be measured in that state every time, to get a comparable reading.

// Bengt

Re: LiPo IR and why it's important

PostPosted: Thu Jun 28, 2012 7:37 am
by S-rob
Would batt internal resistance make any real world differnce to foamy parkflyers ??
ie, if you cant tell the difference , when flying, its not going to matter.

You arnt going to chuck a usable 20c batt out, just because it's 'R' is higher than the latest new range of 60c batts.
And wont R actually increase(heat) once its in the air & being used, making a simple bench test more worthless?
Im not sure how the charge state of the batt affects R either. Id imaging R would change as the batt looses charge ??
Ive got an Icharger as well, I never bothered with the internal resistance test.

rant almost finished :-)
heres what hyperion say about there high 'C' lipos , you simply cant run lipos at the claimed discharge rates
"NOTE: High C-Rate Cell Ratings for CONTINUOUS operation refer to the CELL'S ability to pass current. ..... Note that NO CONNECTOR SYSTEM in use for RC Cars matches these rates, nor do RC cars draw such high continuous currents. Therefore if you intend to do CELL testing at max C rates continuously, hard case must be disassembled and appropriate cell connections made, by expert users only."

Re: LiPo IR and why it's important

PostPosted: Sun Jul 01, 2012 12:13 pm
by beca
Hi S-rob

I do agree that for low current planes like most park fliers IR does not matter unless you notice degraded performance while flying. And I will not discard any LiPo unless I'm confident it is all used up. :)

The R value is not constant it varys depending on the amount of volts in the pack at the time of measuring, from what I have seen so far a fully charged pack has less IR than a pack at storage charge 3,83V and an even greater IR at 3,70V. That is valid for the packs I used and that have about 80 cycles on them

The reason IR is important to me is that I have a couple of 3s Lipo that have 1 degraded cell and 2 ok that I'm planning to rebuild in to fully working 3s packs to use in my less power hungry park flier.
But I still like to get the most out of the rebuilt packs, and there is where the importance of IR comes in.

I currently investigating 3 Zippy 6s packs and will post the results here when they have got a few more cycles.
Started the measuring at storage out of the box and then again at full charge to see the difference, so stay tuned for the results.

// Beca

Re: LiPo IR and why it's important

PostPosted: Mon Aug 06, 2012 7:24 pm
by beca
Hi again

Due to really poor sumer wether in Sweden (or atleast where i live) the 10 charges mark took some time to achive. But here are the results.
You shuld be aware that these Zippy's were bought from H-king and I choose to break them in a bit so they have never been below 3.8V after a flight (Yet).
All flights was done with a Protos 500 FBL. So now to the results.

Zippy 6S 3000 40C
Cell Pack 1 Pack 2 Pack 3 O
Volts milli Ω O Volts milli Ω O Volts milli Ω New uncharged
1 3,83 3 3,83 4 3,83 3
2 3,83 3 3,83 3 3,83 3
3 3,83 8 3,83 8 3,83 8
4 3,83 8 3,83 8 3,83 8
5 3,83 7 3,83 7 3,83 7
6 3,83 7 3,83 7 3,83 7

Cell Pack 1 Pack 2 Pack 3
Volts milli Ω O Volts milli Ω O Volts milli Ω After 1st Charge
1 4,2 3 4,2 3 4,2 3
2 4,2 3 4,2 3 4,2 3
3 4,2 9 4,2 9 4,2 8
4 4,2 8 4,2 8 4,2 7
5 4,2 6 4,2 8 4,2 7
6 4,2 6 4,2 6 4,2 6

Cell Pack 1 Pack 2 Pack 3
Volts milli Ω O Volts milli Ω O Volts milli Ω After 10 Charges @storage
1 3,83 4 3,83 4 3,83 4
2 3,83 4 3,83 4 3,83 4
3 3,83 13 3,83 11 3,83 11
4 3,82 12 3,82 12 3,82 10
5 3,82 9 3,82 9 3,82 10
6 3,82 11 3,82 8 3,82 10

Cell Pack 1 Pack 2 Pack 3
Volts milli Ω O Volts milli Ω O Volts milli Ω After 10 Charges @full
1 4,2 3 4,2 3 4,2 4
2 4,2 3 4,2 4 4,2 3
3 4,2 10 4,2 9 4,2 10
4 4,2 10 4,2 9 4,2 10
5 4,2 9 4,2 8 4,2 7
6 4,2 7 4,2 6 4,2 7

Thanks for you reply I converted the text to rich format and pasted it, dosent look as nice as in word but I was not allowed to upload with extention doc.
So there we are, I will follow up the testing after another 10 charges, but the wether is not in my favor so it might take some time before next update. Still raining :(
Just looked at the preveiw, looks like crap I'll try to get it right later.

// Bengt "Frustrated" with rain pouring outside.

Re: LiPo IR and why it's important

PostPosted: Tue Aug 07, 2012 12:15 am
by cynr100
Can you cut and paste to a new Word Doc then add the Word Doc file to the post :?: :?: or can you convert the html to Rich Text then copy and paste to the post. :D