Looking for a IR lipo meter up to 6S

[john stones 1 - Moderator]

You seem set on the lecky route Adrian, models/motors etc you go for ain't cheap, you umming n arrring, over the price seems out of character.

Do you think you need one, if yes, get one bought.

[Adrian Smith 1]

Ouch, John!! That was below the belt!

Well I know I go for high-endish stuff, but no point in duplicating what I have got already which seems to be the case here. I am just trying to educate myself as to what these things mean. Something I enjoy, as is all the feedback received here.

[Dickw]

Posted by Adrian Smith 1 on 23/11/2018 12:48:53:

.......

. I am just trying to educate myself as to what these things mean. Something I enjoy, as is all the feedback received here.

Put your IR figures into this little calculator to find out how good your battery is.

Dick

[john stones 1 - Moderator]

Posted by Adrian Smith 1 on 23/11/2018 12:48:53:

Ouch, John!! That was below the belt!

Well I know I go for high-endish stuff, but no point in duplicating what I have got already which seems to be the case here. I am just trying to educate myself as to what these things mean. Something I enjoy, as is all the feedback received here.

It wasn't meant to be, if you feel you need one, this item is the best one from all I've read, other makes don't seem to do what this kit do's nor have it's accuracy.

[Gary Manuel]

Interesting that your Turnigy appears to be better than the Hacker and Overlander (assuming capacities were the same).

[Attilio Rausse]

I have a WG as well, what it taught me was to warm the pack up to 25c + and then test. Besides the IR test (which is just an indicator to us) it gives a reading of the max current you can draw. The lesson learnt is warm the packs up quite a bit before use this will reduce the IR and allow you to draw more current. If the IR is high then heat is internally generated and this will shorten the battery life.

[Attilio Rausse]

I don't for one minute regret purchasing the WG.

[Martin Harris - Moderator]

I understand that the level of accuracy in IR measurement built into chargers is fairly arbitrary so beware of taking these values as absolutes. What they should provide is comparative readings that can be monitored over the life of the batteries - a failing cell should show up clearly as significantly different to the others especially if you've kept a record. There seems to be an encouraging pattern (or rather lack of pattern) to your examples which suggests that individual cell measurements may be fairly accurate compared (at least) to each other.

Typically, there will be a steady increase in IR as the cells age - I'd retire them when power delivery or duration became a concern if the meter didn't show a failing cell or two in advance of the others, which would prompt me to discard them at that point.

Edited By Martin Harris on 23/11/2018 16:02:14

[Adrian Smith 1]

Yes Martin, I agree with what you say. For the moment I want just establish a trend in readings at this point, so the arbitrary nature is less important for now.

Gary.

Yes they were all 5000 mAh lipos. All roughIy the same age too. I expected more degradation with the Overlander given the dropping to lowish voltages at the end of flight on a windy day a couple of times.

The batteries tested had been at room temperature (20degC +) for some time, but I accept that probably is not sufficient warmth and I need to run them for a while before retesting. Anyway all this has been a first step on a longer path.

DickW

Thanks for the calculator - something for me to play with!

[Mark Howard 1]

I'm not sure how old or how well used your packs are but those IR figures look a bit high to me for the size of pack. My 4000 to 500mAh packs tend to have IR's around 1.6 to 2.2 milliohms (measured on Powerlab PL8 chargers). Even my tired small packs (6S 1200mAh) have IR's nearer 3 or 4 milliohms. Your figures indicate the packs are only capable of 10-12 C or 50-60Amps.

I understand that most chargers only measure IR properly during a charge cycle (the figures change with charge state and temperature) so it may be worth reading up to see how best to get accurate figures. As all of yours seem very high I suspect that either the charger is not accurate or the readings are not being taken at the correct point in the charge cycle. Of course it may be that the packs are pretty tired but as all of them are high, I suspect the common denominator is the charger or measurement process.

[Adrian Smith 1]

I read your post with interest, Mark. So if you will humour me because given my level of ignorance I need some clarification here. Referring to Mike Freeman's Puffed Out piece in February's RCME and I quote "Generally speaking the larger the pack the lower the initial IR". He then goes on to say " a typical 2200 mAh cell (pack?) in good condition might have an IR of around 10-20 milliohms". He then goes on to identify puffed lipos showing a reading of 35 milliohms per cell. All of this I understand.

However, given your assertion that readings for your 4000-5000 mAh packs are in the very low single digits (1.6-2.2) I do wonder about the decimal point in some pieces of measuring equipment. That is only an observation and I know nothing on that score. I take you point on researching the ideal conditions at which to measure the IR and I accept my effort was done off the cuff and in an environment which was far from ideal. I just don't understand the disparity with what you achieve and what I am finding on a set of lipos less than 18 month old which, by and large, have had conservative treatment other than the instances I have already mentioned above.

You will appreciate I am just trying to separate folklore and fact with something that looks plausible. Interesting discussion is developing here, for me anyway.

[Geoff S]

Posted by Mark Howard 1 on 23/11/2018 17:17:22:

I'm not sure how old or how well used your packs are but those IR figures look a bit high to me for the size of pack. My 4000 to 500mAh packs tend to have IR's around 1.6 to 2.2 milliohms (measured on Powerlab PL8 chargers). Even my tired small packs (6S 1200mAh) have IR's nearer 3 or 4 milliohms. Your figures indicate the packs are only capable of 10-12 C or 50-60Amps.

I understand that most chargers only measure IR properly during a charge cycle (the figures change with charge state and temperature) so it may be worth reading up to see how best to get accurate figures. As all of yours seem very high I suspect that either the charger is not accurate or the readings are not being taken at the correct point in the charge cycle. Of course it may be that the packs are pretty tired but as all of them are high, I suspect the common denominator is the charger or measurement process.

Those figures are incredibly low. A good LiPo will have ESR/cell of around 3 or 4 millohms if you're lucky. As long as they stay below 5 milliohms they're still pretty good but once they reach 10 milliohms they're only good for low current use.

I usually rely on my iCharger but my Wayne Giles meter gives similar results.

Geoff

[Ben B]

"Good" depends on capacity though. When you're at tiny whoop size batteries 70 ohm is good! At 400mah low teens is good. You also need to bear in mind the impact of multiple cells in parralel on voltage sag.

[Mark Howard 1]

Hi Adrian,

As Ben says, good IR's are relative to pack size so smaller packs have higher IR's than large ones.

The calculator that DickW mentions here helps to illustrate the point. If you plug the numbers in and divide the resultant max current number by the capacity of the pack it gives you the 'C' value that the battery is capable of (i.e. the maximum recommended discharge current).

So, the 10 to 20 milliohm value mentioned in the RCME article is probably correct as for a 2200 mAh pack you get a C value of between 12 and 16 C. Most manufacturer C ratings are pretty ambitious (a nice way of saying disgustingly misleading) so 12 to 16 C from a 20 C pack is to be expected although a little low. Most 20C packs seem capable of delivering around 20C whereas a most 60C packs usually manage maybe 25 - 35C if you're lucky. There are of course exceptions but these seem to be the expected ranges.

My pack (5000 mAh 6S) values of 1.6 to 2.2 give C values of 23 to 27 which considering they are variously rated at 45 to 60C is not that great but is in the expected range. My small 1200 mAh packs are pretty good as they are still giving about 35C which is pretty good for a battery rated at 70C.

Your numbers are indicating C values of 10 to 12 which is quite low even for a 20C 5000mAh pack which is why I'm wondering if your charger is telling you the truth.

According to the Powerlab charger manual, IR can only be properly calculated during a charge cycle when charging from somewhere below 75%. Maybe its worth experimenting with your charger at various stages of the charge cycle to see if your numbers change.

 

Edited By Mark Howard 1 on 24/11/2018 07:09:33

[Adrian Smith 1]

Thank you, Mark for spending the time for your explanation and to to reduce my pool of ignorance no end!

It is clear that my initial check was in as far from "laboratory" conditions as could be, making the readings I achieved almost meaningless. I guess using a charger which has a variety of functions including measuring IR is possibly not going to give the most accurate result as a "catch all" piece of equipment. The only common features in my initial test was all lipos had been stored at an ambient temperature of 20degC and almost without exception the separate cells were showing a reading of 3.70-3.75 volts and not on charge. Which sort of takes me back to the initial question of whether I need a IR specific measuring tool to just observe a trend given the cost outlay

On a non-flying day I will run a few experiments on a selection of my batteries which range from 2S to 6S and see what I come up with. Thanks again.