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Old Feb 11, 2013, 04:02 PM
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Rugby, UK
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Jim,

Thanks for the endorsement.
Re the variation of "C" rating with temperature, The short answer is yes it does vary. The IR can increase by 50% for a 20degC fall at low temperatures so that affects the heat dissipated within the cells and effectively reduces the C rating.
We have all seen models take off in winter and cut out on LV limit within half a minute because the IR of the pack is so much higher than it would be at summer temperatures. A 50% increase in IR suggests a decrease in C rating of about 20% because a square law is involved.
The reverse is true but it depends on the rate at which the IR decreases with temperature and, of course, we have the limitation of maximum operating temperature. As you raise the starting temperature, you are decreasing the heat dissipated within the lipo, but you are starting closer to the max operating temperature so that the acceptable rise is less.

I always start any discharge testing from a nominal 25deg.C to ensure that all lipos are compared on a "flat field" basis, ie they all start from an equal point.

The 'battery load test comparison' thread is a different approach but will almost certainly come up with the same general conclusions as it is measuring and comparing the voltage drops from different packs under the same conditions.

Wayne
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Old Feb 12, 2013, 05:20 AM
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United Kingdom, England, Ware
Joined Aug 2012
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We have all seen models take off in winter and cut out on LV limit within half a minute because the IR of the pack is so much higher than it would be at summer temperatures

Would this be because the pack was cold initially and not installed relatively warm or the resultant internal generated heat was not sufficient to maintain the starting IR .?





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Originally Posted by Wayne Giles View Post
Jim,

Thanks for the endorsement.
Re the variation of "C" rating with temperature, The short answer is yes it does vary. The IR can increase by 50% for a 20degC fall at low temperatures so that affects the heat dissipated within the cells and effectively reduces the C rating.
We have all seen models take off in winter and cut out on LV limit within half a minute because the IR of the pack is so much higher than it would be at summer temperatures. A 50% increase in IR suggests a decrease in C rating of about 20% because a square law is involved.
The reverse is true but it depends on the rate at which the IR decreases with temperature and, of course, we have the limitation of maximum operating temperature. As you raise the starting temperature, you are decreasing the heat dissipated within the lipo, but you are starting closer to the max operating temperature so that the acceptable rise is less.

I always start any discharge testing from a nominal 25deg.C to ensure that all lipos are compared on a "flat field" basis, ie they all start from an equal point.

The 'battery load test comparison' thread is a different approach but will almost certainly come up with the same general conclusions as it is measuring and comparing the voltage drops from different packs under the same conditions.

Wayne
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Old Feb 12, 2013, 03:35 PM
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Rugby, UK
Joined Feb 2007
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Jim,

This is because the pack is cold to start with so the IR is high and therefore the heat dissipation at a given current in the lipo is higher. This generates heat which lowers the IR so that the voltage then rises. There is a delay involved, so that the first flight fails but the second attempt is often successful because the heat generated in the first attempt has now spread through the pack and the IR is much lower.
The plot below which I did some years back demonstrates the problem.
Look at the low temperature (yellow) discharge plot.

http://static.rcgroups.net/forums/at...emps.Irfan.jpg

Wayne
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Last edited by Wayne Giles; Feb 12, 2013 at 03:37 PM. Reason: Wrong link
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Old Feb 13, 2013, 02:57 AM
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United Kingdom, England, Ware
Joined Aug 2012
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Thanks Wayne and interesting to see the cold pack does start to sort itself out after a relatively short period .
Bit like warming up an engine before expecting to get max power supply

Jim



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Originally Posted by Wayne Giles View Post
Jim,

This is because the pack is cold to start with so the IR is high and therefore the heat dissipation at a given current in the lipo is higher. This generates heat which lowers the IR so that the voltage then rises. There is a delay involved, so that the first flight fails but the second attempt is often successful because the heat generated in the first attempt has now spread through the pack and the IR is much lower.
The plot below which I did some years back demonstrates the problem.
Look at the low temperature (yellow) discharge plot.

http://static.rcgroups.net/forums/at...emps.Irfan.jpg

Wayne
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Old Feb 13, 2013, 10:40 PM
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Ontario - CANADA
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Hello Wayne. I read about your device in the Model Aviation - Canada publication.
Can you e-mail shipping details? Thanks. esadok@rogers.com
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Old Feb 13, 2013, 10:46 PM
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Originally Posted by Edward64 View Post
Hello Wayne. I read about your device in the Model Aviation - Canada publication.
Can you e-mail shipping details? Thanks. esadok@rogers.com
It's also sold in the u.s. which might save you a little and help us, too!

http://www.progressiverc.com/tools-a...electric-tools
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Old Feb 14, 2013, 09:20 AM
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Ontario - CANADA
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LiPo Internal Resistance

Thank you, JohnathanSwift, for your link to Progressive RC.

Also, Mr. Wayne Giles has e-mailed me, as well. I appreciate this help.

The LiPo battery internal resistance meter is a very useful device for assessing the "real" capacity of a LiPo battery.
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Old Feb 14, 2013, 09:32 AM
Stop scaring my donkey!
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Originally Posted by Edward64 View Post
Thank you, JohnathanSwift, for your link to Progressive RC.

Also, Mr. Wayne Giles has e-mailed me, as well. I appreciate this help.

The LiPo battery internal resistance meter is a very useful device for assessing the "real" capacity of a LiPo battery.
Anything for you Canadian dudes! Also, it will either corroborate or show false your chargers data on ir.
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Old Feb 14, 2013, 11:32 AM
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Hello Wayne. I read about your device in the Model Aviation - Canada publication.
Can you e-mail shipping details? Thanks. esadok@rogers.com
I bought mine from here. Charged me $7 for shipping at the time. Love the tool!!!! Pull it out at the field and in less then 5 minutes you have a crowd around you. Best bet is school someone on the simple instructions and go fly, either that or you will be testing batteries all day.

http://www.f3aunlimited.com/webstore...roducts_id=572
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Old Feb 19, 2013, 09:33 PM
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Wayne
That all falls in line with something's I have read elsewhere where there is an inhibitor within the cell chemistry to pre-long shelf life .
In your initial cycles what voltage are you terminating at ?
After the 5C cycle do you consider that the pack is now ready for proper field use or should there be further breaking in cycles
I have seen suggestions elsewhere that 10C sustained load be considered as part of the 'break-in' so in my case of 5000 Ma that equates to 50A which I fell could be a bit extreme !

Cheers Jim




Jim,

In most lipos I have noticed that the first cycle reduces the IR.
I think it depends on the electrochemical makeup and this varies from one type to another.
I always run them through at least one 1C cycle before any testing and then go to a2C cycle, a 5C cycle and then to serious testing. The fact that the IR changes suggests to me that the cell goes through a "forming" process on the lines of an electrolytic capacitor.
As an example the GensAce lipos I tested dropped in IR by 25% on first cycle which is the most I have seen but then remained constant. The Haiyin I recently tested which was 20C dropped about 15% and then remained constant.
Other people say the IR falls for several cycles but I have never seen that; it just seems to be the first cycle.
It is certainly worth doing so measure it with your new pack, being very careful you do so at the same temperature and see if you see a fall.

Wayne
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Old Feb 20, 2013, 02:07 PM
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Rugby, UK
Joined Feb 2007
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Originally Posted by Jimob23 View Post
Wayne
That all falls in line with something's I have read elsewhere where there is an inhibitor within the cell chemistry to pre-long shelf life .
In your initial cycles what voltage are you terminating at ?
After the 5C cycle do you consider that the pack is now ready for proper field use or should there be further breaking in cycles
I have seen suggestions elsewhere that 10C sustained load be considered as part of the 'break-in' so in my case of 5000 Ma that equates to 50A which I fell could be a bit extreme !

Cheers Jim




Jim,

I terminate the cycles at 3V, but that is the loaded voltage.
After a cycle I think that a lipo is ready to use as I do not see any change in IR after that point, so that presumably, any forming process is complete.
I only run further low C cycles when testing in case that theory is wrong and to remove any excuse for failure or poor performance.

Wayne
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Old Feb 20, 2013, 03:59 PM
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United Kingdom, England, Ware
Joined Aug 2012
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Thanks Wayne
I will follow your suggestions and let you know where the final C rating ends up.
Cheers Jim



Quote:
Originally Posted by Wayne Giles View Post
Jim,

I terminate the cycles at 3V, but that is the loaded voltage.
After a cycle I think that a lipo is ready to use as I do not see any change in IR after that point, so that presumably, any forming process is complete.
I only run further low C cycles when testing in case that theory is wrong and to remove any excuse for failure or poor performance.

Wayne
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Old Apr 18, 2013, 04:44 PM
r/c addict
USA, LA, DeRidder
Joined Jul 2004
202 Posts
hi wayne

i own this meter and what a great piece of equipment it is and was wandering is there any way possible to use this meter to test the esr of electrolytic capacitor's? as i also work on tv's and electronics as a hobby but my $220 esr meter bit the dust. so i thought if i could use this one i could save a few bucks. thanks
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Old Apr 18, 2013, 06:53 PM
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Melbourne, Australia
Joined Jul 2005
6,628 Posts
Nitro, I'm sure Wayne will provide a proper explanation but the answer is no.

The ESR in the meter name stands for the Effective DC Series Resistance internal to the pack and is not the same as capacitor ESR which is an AC parameter. The ESR/IR meter needs the LiPo pack to power it and supply the voltage for the measurement.

John
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Originally Posted by nitrodude71 View Post
i own this meter and what a great piece of equipment it is and was wandering is there any way possible to use this meter to test the esr of electrolytic capacitor's? as i also work on tv's and electronics as a hobby but my $220 esr meter bit the dust. so i thought if i could use this one i could save a few bucks. thanks
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Old Apr 19, 2013, 05:10 PM
Registered User
Rugby, UK
Joined Feb 2007
876 Posts
Yes, sorry Nitro, but John is correct.
The two types of meter are quite different in operation so my meter cannot read a capacitor and a capacitor ESR meter cannot read the IR of a lipo pack.

Glad you like the meter; thanks for the endorsement.

Wayne
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