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Old Jan 28, 2011, 09:20 PM
Learning is worth the effort
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Originally Posted by barzaun View Post
Have you tried the tachometer in your meter? Is it really an optical tachometer?
No, I have not tried the Tac function yet. I just received the meter this week and have only used the Battery Checker function and the Internal Resistance function. Yes, the manual says it is an optical tach and suggests to make the reading in the shade from a distance of 4 to 8 inches.
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Old Feb 02, 2011, 05:57 PM
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Originally Posted by Wayne Giles View Post
Scott,

Anytime really. Slightly surprisingly, the IR of a lipo pack is almost independant of charge state until the charge is virtually depleted. Obviously if the cell has no stored energy left then any load will collapse the voltage, but until that point is reached the IR seems to be virtually constant.
Provided you are careful to measure IR at a fixed temperature, it is the best guide to what is a good or bad lipo and correlates with best performance in practical flying, ie in the ability to deliver max power to the motor with minimum temperature rise.

Wayne
Hi Wayne,
just got notice of this thread

I use a hyperion charger and I never discharge my lipo's more then 80%,
i asked hyperion this question about their total pack IR measurement:
why changes the internal resistance from 15mOhm when starting the charge slowly to 4mOhm at end of charge , is that normal ?

i got this answer from Hyperion:
IR changing with charge level, higher when a pack is empty (thats why a pack get hot if you discharge too much)

you are saying: IR of a lipo pack is almost independant of charge state

Is the answer of hyperion wrong?

Wayne i've sent you a PM.

Cell resistance measurement is a good thing but to interpret these results
is another thing.
So is there a summary anywhere what could help me to decide if a lipo pack cell is bad or end of life when measuring IR per cell ?

With the hyperion charger EOS0615iDuo3 and hyperion software i make statistics out of the database, and this
is a result of a report i generate out of the database. I use the software only during charging my lipo's.
The IR value is taken from the database at end of charge. ( not the value at the beginning because at charge start IR is higher then at end of charge)

this is one of my reports of my lipo's, do i have healthy lipo's??
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Old Feb 03, 2011, 08:51 AM
Southern Pride
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Haralson County GA. USA
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Snip from one of Wayne's post ,post #14 this thread.

Quote:
The only Charger I have which reads IR is a Hyperion EOS0610iNET which is a great charger but not very good at measuring IR. It reads between 150 and 250% of the IR I measure, varying with pack size and other factors which I cannot quantify. So much so that I quickly gave it up as a measurement source.
IMO sadly most chargers do a very poor job of reading IR and even the ones which do a decent job of this ,provide numbers without supplying the necessary education on how to interpret and apply these numbers.

FYI Some of the statements made concerning IR ( Ri ) by some of the LiPoly vendors ,chargers and IR reading devices are so lame that they are funny.


A recnt post of mine comparing some IR readings

http://www.rcgroups.com/forums/showp...4&postcount=94
Charles
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Old Feb 03, 2011, 09:44 AM
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Originally Posted by jaccies View Post
So is there a summary anywhere what could help me to decide if a lipo pack cell is bad or end of life when measuring IR per cell ?
Quote:
Originally Posted by jaccies View Post
this is one of my reports of my lipo's, do i have healthy lipo's??
Only you can make this assessment. Don't get too hung up on IR numbers. Does the lipoly still perform well in your particular application? Is the lipoly undamaged and still stay in balance when charged? End of life for one application may be perfectly suitable for another application. As an example, I have some lipolys that are 6 years old that work poorly in my high performance planes but perform wonderfully in my trainer planes. They are undamaged, stay in perfect balance when charging, and still provide great utility. As such, it'd be foolish for me to discard them.

Mark
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Old Feb 03, 2011, 01:54 PM
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Jac,

It am not sure which method chargers use to measure IR. I suspect that they measure the voltage step when the charging current is turned on. If so there is likely to be an error in that there is some hysterisis in the first application of current. If you used this method with a NiCad/NiMH cell then the results would be garbage.
Other measurement methods are applying a 1000Hz AC load and measuring the ripple on the cell, but this measures impedance rather than resistance.
As users we are only interested in resistance as that is the parameter which determines the voltage drop when we apply a load (a motor) and hence the power we can get from the pack.
My post saying that IR appears to be independent of charge state is only based on various odd measurements
I will run a test on a pack measuring the IR during a low rate charge and discharge cycle, taking spot measurements and produce a plot of the IR over the whole cycle. It has to be very low rate as high discharge heats the pack and reduces IR whilst charging is endothermic and would increase the IR.
It will take a few days to do and I will postpone analysis about Hyperion's comments until the plot is complete other than to say a heavily discharged lipo will be hotter because more total heat has been generated and it takes some time to get to the surface of the pack.
I agree with Mark's comment about choosing the applications for your lowest IR packs; all lipos seem to increase their IR with age and a rapid rise indicates end of life.
I also agree with Charles' assertion that many suppliers information is useless. Twice recently I have come across the confusion between Impedance and Resistance written into the instructions of IR measuring devices.

Wayne
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Old Feb 03, 2011, 03:22 PM
Southern Pride
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Quote:
I will run a test on a pack measuring the IR during a low rate charge and discharge cycle, taking spot measurements and produce a plot of the IR over the whole cycle. It has to be very low rate as high discharge heats the pack and reduces IR whilst charging is endothermic and would increase the IR.
Wayne FYI Charging at increased rates causes slight warming and thus lower IR reading using FMA CellPro10 / POWERLAB8. FMA advises charging at 1C and using IR obtained at EOC.

Charles
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Old Feb 03, 2011, 04:55 PM
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Originally Posted by everydayflyer View Post
Wayne FYI Charging at increased rates causes slight warming and thus lower IR reading using FMA CellPro10 / POWERLAB8. FMA advises charging at 1C and using IR obtained at EOC.

Charles
Charles,
I am just trying to hold the pack at a steady temperature and will do the test in a temp controlled environment. Although the charging process is endothermic, the effect is swamped by the I2R heat if the pack is charged at high rate. Probably about 1C is the best rate for both charge and discharge.
Presumably the result at the end of charge is the composite result of many measurements and should nullify any odd values from the initial reading.

Wayne
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Old Feb 05, 2011, 09:01 AM
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Jaccies,
I have carried out the IR v Charge state measurements and the plot is attached. I chose a well used Loong Max 3S1000 20C pack which shows a nominal cell IR of about 15 milliohms at 25deg.C.
The pack was charged and left to settle in a temperature controlled chamber at 25C for several hours and then discharged at 1C (ie 1A) with measurements of the IR of Cell 1 being taken at 50mAh intervals.
The pack was discharged down to 3V/cell ie fully discharged.
The process was then reversed with the pack being charged at 1.2A (no 1A setting on charger) with readings again taken at 50mAh intervals, this time of Cell 2 so as not to confuse the graph.
Note that at about 2/3 charged I thought that the charge rate was too high and heating the pack causing the IR to fall so I reduced it to 0.7A. This caused the IR to start rising slightly which you can see on the lower plot, which confirmed my suspicions; I should have used a lower charge rate throughout.

You can see that allowing for the slight heating caused by the charge and discharge currents that the IR of the pack is essential independant of state of charge, certainly in the area where you are working ie between fully charged and 80% discharged.

So in answer to your question, and confirming what Charles has said in his post above, yes, whoever from Hyperion told you it varies is quite wrong. The reason a fully discharged pack gets hotter at the end of discharge is that the extra total heat produced has got to the surface of the pack.

The problem with getting technical information from suppliers (apart from their prejudice) is that invariably you are talking to a salesman who has no technical understanding and is therefore talking through the wrong orifice.
If only we could get to the engineers at Hyperion et al, we might get some sense!

BTW you should get your IR Meter next week; perhaps you would be good enough to measure some of the lipos you have listed in you original table. If you could post the results it would be helpful to us all. (You MUST use the same temperature when comparing packs.)

Wayne
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Old Feb 05, 2011, 04:03 PM
ancora imparo
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Wayne, thanks for taking the time to do that. If only the careful work of this kind wasn't totally swamped by the loudly held opinions of the very large number who have no idea of what "controlled variables" are.

On your note below, I have to say good luck. Mainly because for many manufacturers it involves speaking through a pleasant but technically ignorant person whose English is just comprehensible to an Engineer who speaks only Chinese. Both communication paths are fraught! I speak from experience. Not a criticism of them of course, just a fact of life for those of us who are inadequately monolingual.

John
Quote:
Originally Posted by Wayne Giles View Post
The problem with getting technical information from suppliers (apart from their prejudice) is that invariably you are talking to a salesman who has no technical understanding and is therefore talking through the wrong orifice.
If only we could get to the engineers at Hyperion et al, we might get some sense!
Wayne
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Old Feb 06, 2011, 04:42 AM
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Quote:
Originally Posted by Wayne Giles View Post
Jaccies,
I have carried out the IR v Charge state measurements and the plot is attached. I chose a well used Loong Max 3S1000 20C pack which shows a nominal cell IR of about 15 milliohms at 25deg.C.
The pack was charged and left to settle in a temperature controlled chamber at 25C for several hours and then discharged at 1C (ie 1A) with measurements of the IR of Cell 1 being taken at 50mAh intervals.
The pack was discharged down to 3V/cell ie fully discharged.
The process was then reversed with the pack being charged at 1.2A (no 1A setting on charger) with readings again taken at 50mAh intervals, this time of Cell 2 so as not to confuse the graph.
Note that at about 2/3 charged I thought that the charge rate was too high and heating the pack causing the IR to fall so I reduced it to 0.7A. This caused the IR to start rising slightly which you can see on the lower plot, which confirmed my suspicions; I should have used a lower charge rate throughout.

You can see that allowing for the slight heating caused by the charge and discharge currents that the IR of the pack is essential independant of state of charge, certainly in the area where you are working ie between fully charged and 80% discharged.

So in answer to your question, and confirming what Charles has said in his post above, yes, whoever from Hyperion told you it varies is quite wrong. The reason a fully discharged pack gets hotter at the end of discharge is that the extra total heat produced has got to the surface of the pack.

The problem with getting technical information from suppliers (apart from their prejudice) is that invariably you are talking to a salesman who has no technical understanding and is therefore talking through the wrong orifice.
If only we could get to the engineers at Hyperion et al, we might get some sense!

BTW you should get your IR Meter next week; perhaps you would be good enough to measure some of the lipos you have listed in you original table. If you could post the results it would be helpful to us all. (You MUST use the same temperature when comparing packs.)

Wayne
Thanks Wayne for the result.
How did you measure every 50mah the IR while charging/discharging ? , can you do it with the ESR/IR meter while charging/discharging ?

" the IR of the pack is essential independant of state of charge" what we can see in your graph.

Software of Hyperion stores every second all measured values in a database during charge/discharge.
So you can see afterwards the charge/discharge results in a graph.
Attached graph is during a 3S 3Amp 35C lipo charge, charged with 3A
TCS = terminal capacity state in % ( 100%= fully charged)
the Lipo was discharged to 34% level before charge.
And Ri dropped from 27 to 13mOhm.

Charging with (1C) 3Amp will the lipo being heated up inside ( i dont feel the pack is getting warm at all) that much so the Ri drops from 27 to 13mOhm ?

Yes I will measure with IR meter my lipo's and compare with my report, and i will report it.

Getting info from Hyperion engineers is very difficult or secret.
i asked for the table where i can see the cell voltage values with indicated rest capacity in %.
They could not give it to me , its secret they told me
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Old Feb 06, 2011, 03:01 PM
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Originally Posted by jaccies View Post
Thanks Wayne for the result.
How did you measure every 50mah the IR while charging/discharging ? , can you do it with the ESR/IR meter while charging/discharging ?


" the IR of the pack is essential independant of state of charge" what we can see in your graph.

Software of Hyperion stores every second all measured values in a database during charge/discharge.
So you can see afterwards the charge/discharge results in a graph.
Attached graph is during a 3S 3Amp 35C lipo charge, charged with 3A
TCS = terminal capacity state in % ( 100%= fully charged)
the Lipo was discharged to 34% level before charge.
And Ri dropped from 27 to 13mOhm.

Charging with (1C) 3Amp will the lipo being heated up inside ( i dont feel the pack is getting warm at all) that much so the Ri drops from 27 to 13mOhm ?

Yes I will measure with IR meter my lipo's and compare with my report, and i will report it.
Jac,

Yes, you can read the IR at any time during the charge or discharge cycle. All you need to do is connect the IR meter in parallel with the charger/discharger and just press the button any time you want to measure the IR; so I connected a Medusa wattmeter in series with the pack and took a reading every 50mAh. The meter takes a reading in 15mS so that it does not interfere with charging or discharging and does not heat the pack.
Thanks for the attached plot from the Hyperion charger. Almost certainly the IR is falling because of internal heating from the charge current through the IR. The dissipation is about 0.25W in your pack which does not sound much, but in my charging of the 3S1000 pack you can see how reducing the charge from 1.2A to 0.7A stopped the IR falling and allowed it to start rising slightly.
In that case the dissipation was only 0.065W, but it was obviously heating the inside of the pack.
The IR of lipos is very sensitive to temperature; if you take a reading with the meter of a cell on the outside of a pack, place your hand on the cell and take another reading only 10 seconds later you will see that the IR has fallen.

It seems very likely that the reason that the Hyperion charger produces such results is twofold; firstly the charging current is heating the pack and secondly, the measuring system is reading the IR at low charging currents, whereas we are interested in the IR at high discharging currents which is not necessarily the same thing.

I assume the pack you are referring to is 16A in your table. Presumably the Av, Min and Max Ri figures refer to cells within a pack?
When you have a set of figures from the IR meter taken at the same temperature, you will really be able to compare your stock of lipos.

Wayne
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Old Feb 06, 2011, 05:31 PM
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Originally Posted by Wayne Giles View Post
Jac,

Yes, you can read the IR at any time during the charge or discharge cycle. All you need to do is connect the IR meter in parallel with the charger/discharger and just press the button any time you want to measure the IR; so I connected a Medusa wattmeter in series with the pack and took a reading every 50mAh. The meter takes a reading in 15mS so that it does not interfere with charging or discharging and does not heat the pack.
Thanks for the attached plot from the Hyperion charger. Almost certainly the IR is falling because of internal heating from the charge current through the IR. The dissipation is about 0.25W in your pack which does not sound much, but in my charging of the 3S1000 pack you can see how reducing the charge from 1.2A to 0.7A stopped the IR falling and allowed it to start rising slightly.
In that case the dissipation was only 0.065W, but it was obviously heating the inside of the pack.
The IR of lipos is very sensitive to temperature; if you take a reading with the meter of a cell on the outside of a pack, place your hand on the cell and take another reading only 10 seconds later you will see that the IR has fallen.

It seems very likely that the reason that the Hyperion charger produces such results is twofold; firstly the charging current is heating the pack and secondly, the measuring system is reading the IR at low charging currents, whereas we are interested in the IR at high discharging currents which is not necessarily the same thing.

I assume the pack you are referring to is 16A in your table. Presumably the Av, Min and Max Ri figures refer to cells within a pack?
When you have a set of figures from the IR meter taken at the same temperature, you will really be able to compare your stock of lipos.

Wayne
Wayne ,
thanks for info
no it was lipo 16B in my table, and is the total Ri of the pack.
i did not notice that the RI could drop so much from 27 till 13mOhm

But you dont see in my table anything that you can say, well that lipo is suspicious regarding the Ri value ?,
what i find suspicious is 17A and 17B values.

lets wait for the Ri meter, and compare the values.
Jac
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Old Feb 07, 2011, 08:44 AM
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Originally Posted by jaccies View Post
Wayne ,
thanks for info
no it was lipo 16B in my table, and is the total Ri of the pack.
i did not notice that the RI could drop so much from 27 till 13mOhm

But you dont see in my table anything that you can say, well that lipo is suspicious regarding the Ri value ?,
what i find suspicious is 17A and 17B values.

lets wait for the Ri meter, and compare the values.
Jac
Jac,

Not sure what size packs 17A and 17B are but must be >1500mAh as 17A took 1396mAh in.
In that case the IR does look very high.
Also if the figures are total pack, then the Turnigy 4S5000 (pack 7A) looks suspiciously low; they are low IR packs but certainly not as low as 4 milliohms. I think you will get much more consistent and sensible readings from the meter, but then I am prejudiced!

Mark Forsyth suggested that if the IR of a lipo cell is lower than 12000 divided by the cell capacity in mAh, then it is a (very) good lipo. I'm not sure about the 12000 as it's from memory as I cannot find the posting, but I would certainly agree in principle and agree in fact if the 12000 figure is correct.

Wayne
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Old Feb 07, 2011, 02:16 PM
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Originally Posted by Wayne Giles View Post
Jac,

Not sure what size packs 17A and 17B are but must be >1500mAh as 17A took 1396mAh in.
In that case the IR does look very high.
Also if the figures are total pack, then the Turnigy 4S5000 (pack 7A) looks suspiciously low; they are low IR packs but certainly not as low as 4 milliohms. I think you will get much more consistent and sensible readings from the meter, but then I am prejudiced!

Mark Forsyth suggested that if the IR of a lipo cell is lower than 12000 divided by the cell capacity in mAh, then it is a (very) good lipo. I'm not sure about the 12000 as it's from memory as I cannot find the posting, but I would certainly agree in principle and agree in fact if the 12000 figure is correct.

Wayne
Pack 17A and B are Thunder Power RC 5S 3850mAh 25C , i never used them in a plane yet , they are used by another pilot.

lets wait for my IR meter

I found the thread of Mark here he tells:
For a rough indicator of performance, I divide 12000 by cell capacity to get what I consider to be a very good internal resistance number. e.g. - for a 2000mAh cell, any number below 6 (12000/2000) is quite good in my book.

yes it is a rough indicator because if lipo is 20C 30C or higher ,IR is lower.
And there are so many many different brands, what is a good brand.

i found more posts from Mark and you with graphs, interesting stuff,
thanks
Jac
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Old Feb 14, 2011, 03:50 PM
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Wayne,

received the IR meter.

I did some measurements see picture.
The readings taken from my charger is at end of charge,
the measurements with IR meter are at room temperature.

Some values from the charger are strange 9 very low) as you already noticed.

Only thing suprised me and dont understand why is there a difference,
between the Pack IR and the sum of all cells IR?
It's around 10mOhm difference.

I use a Dean connector with 4mm gold plugs soldered directly on the Dean connector to fit the lipo with the 4mm gold connectors, i have more of them and tried them all but did not make any difference in measurements.

From now on , after charging my lipo's i will record the cells IR.

cheers
Jac
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