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Old Oct 29, 2010, 01:42 AM
Reduce the drama...
rick.benjamin's Avatar
USA, OR, Damascus
Joined Apr 2004
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Quote:
Originally Posted by Wayne Giles View Post
Rick,

Second thoughts on this; don't know why, my brain probably wasn't engaged in first reply! These are obviously cell readings, but they look very high and too close for reality. The "Cell" range is only specified for 0 - 30 milliohms, although the meter will read up to nearly 40milliohms. If you do not plug the search wire into the balance connector (so that it is monitoring one cell), then the meter will read it as over-range, in which case it will read the highest it can, which could be any value between 35 and 40 milliohms.
This suggests that the search wire was not connected or the balance leads on the pack are open circuit. Does the meter read 'Cell' Voltage before you press the 'Operate' button??
What size pack is it in mAh??

Wayne
Polyquest 2200mAh 3S, Oct 2005
Search wire inserted
Pack voltage 12.00
cell voltage 4.02 37.12megohms
cell voltage 4.00 37.12
cell voltage 3.98 37.08
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Old Oct 29, 2010, 02:38 PM
Registered User
Rugby, UK
Joined Feb 2007
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Quote:
Originally Posted by rick.benjamin View Post
Polyquest 2200mAh 3S, Oct 2005
Search wire inserted
Pack voltage 12.00
cell voltage 4.02 37.12megohms
cell voltage 4.00 37.12
cell voltage 3.98 37.08
Rick,

Those cell IRs still look suspicious. They look high for a pack of that size at normal temperatures and unusually well matched. I see it is an old pack so would expect the IRs to be drifting apart, even if they were well matched to start with. If you flew a pack with those figure it would be pretty weak; with a total of 110milliohms, 20A would drop the volts by 2.2v until it heated up which would give very poor performance.
Could you post a few results from other packs and also the IR of the pack as well as the cells as this gives a cross reference check. There should be a difference of 6 -8 milliohms between the sum of the "Cell" readings and the "Pack" reading.
This difference is the resistance of the connector + leads + terminations.

Wayne
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Old Nov 05, 2010, 07:13 AM
Rocky Mountain High
Colorado
Joined Nov 2006
195 Posts
Wayne, received my meter Thursday. Appreciate your prompt shipping
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Old Nov 06, 2010, 06:58 AM
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Rugby, UK
Joined Feb 2007
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Quote:
Originally Posted by mtnflyer44 View Post
Wayne, received my meter Thursday. Appreciate your prompt shipping
Thanks, Marvin.
If you have any results from various lipos you feel happy to post it would be most interesting.
Provided they are taken at the same temperatures they are comparable.
The are several reasons that your results from chargers are so unreliable.
(a) Many don't use Kelvin connections, so connectors are included which used to be insignificant but not now with such low cell IRs.
(b) They are measuring charging IR at low currents not discharging IR at high currents.
(c) Charging itself is endothermic so the cell cools and IR rises. At low currents the I2R heating is insignificant but as this is a square law and the cooling is, I believe, linear with current, the I2R becomes dominant at higher charging currents. This heats the cells and drops the IR reading.

Wayne
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Old Nov 06, 2010, 07:14 AM
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Melbourne
Joined Aug 2010
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Wayne,

Awaiting delivery of my unit

When should I be taking readings ?

Before charging, after charging, when stored at storage voltage ?

Cheers
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Old Nov 06, 2010, 05:28 PM
Registered User
Rugby, UK
Joined Feb 2007
831 Posts
Quote:
Originally Posted by crusey_aus View Post
Wayne,

Awaiting delivery of my unit

When should I be taking readings ?

Before charging, after charging, when stored at storage voltage ?

Cheers
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
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Old Nov 11, 2010, 08:11 AM
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Fort Worth, Texas
Joined Nov 2002
185 Posts
Wayne,

I received my meter and all was well until I dumb thumbed it... lol. I just picked up a plane with some 5s batts run in series for 10s, and wasn't even thinking when I plugged it in... so, I replaced the fuse, and looked for any signs of other damage, but did not see any. It still just melts the fuse when 4s pack plugged in. Do you have any advice for troubleshooting?

Blake
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Old Nov 11, 2010, 10:34 AM
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Rugby, UK
Joined Feb 2007
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Quote:
Originally Posted by DBA-FW View Post
Wayne,

I received my meter and all was well until I dumb thumbed it... lol. I just picked up a plane with some 5s batts run in series for 10s, and wasn't even thinking when I plugged it in... so, I replaced the fuse, and looked for any signs of other damage, but did not see any. It still just melts the fuse when 4s pack plugged in. Do you have any advice for troubleshooting?

Blake,



Blake
If you have put 10S on it the chances are that it has blown up most of the circuitry as the reference regulator is only rated for 30V and if that blows then it will have put the input voltage of about 40V onto everything including the PIC. If the fuse blows then the FET is definitely gone. It is a Fairchild FQP85N06 which are easily available. It is possible that it may have saved the other circuitry so worth a try changing it.
You need to unsolder the pushbutton tags in the PCB and unscrew the toggle switch to remove the assembly. It is then easy to change the Fet, a TO220 marked "TR1A"
Retry it with just a 2 cell pack afterwards.
If no good I will repair it free providing the PCB is recoverable as you 'bared your chest' in public and admitted the error!! (nice change; most people would claim it failed and blame me!)
If you do need to return it, let me know and I will PM my address.
Best of luck; take care not to damage the PCB unsoldering the push button - use a solder sucker or solder removing wick.

Wayne
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Old Nov 11, 2010, 11:37 AM
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Fort Worth, Texas
Joined Nov 2002
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Thank you. Before my post I had already desoldered and resoldered the push button to get a look at the front side of the board. I will look for the Fet and let everyone know how it goes!
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Old Nov 13, 2010, 11:52 AM
who dares wins
like2fly!'s Avatar
London,England
Joined Apr 2005
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Mine arrived promptly. Thanks for fitting 4mm gold bullets Wayne, i wish i could solder connectors so neatly!
Just checked the ir on the cells of two packs, both are 4s 2650mAh Thunder Power Pro Power 45C, which have about 90 cycles on each, both bought early this summer on the same day and used in a 3dhs Aspera and 3dhs 51" A J Slick.
At ~21 deg c (~70 f) rounding to 1dp one pack cells are 5.8, 5.8, 5.8, 5.8
The other is 6.2, 6.2, 6.2, 6.2

Neither pack has been used for 3 weeks, both were storage charged to 3.95v on a hyperion duo and cool stored. voltage today is very well matched for the cells in both packs

Alex
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Old Nov 13, 2010, 01:01 PM
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Rugby, UK
Joined Feb 2007
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Quote:
Originally Posted by like2fly! View Post
Mine arrived promptly. Thanks for fitting 4mm gold bullets Wayne, i wish i could solder connectors so neatly!
Just checked the ir on the cells of two packs, both are 4s 2650mAh Thunder Power Pro Power 45C, which have about 90 cycles on each, both bought early this summer on the same day and used in a 3dhs Aspera and 3dhs 51" A J Slick.
At ~21 deg c (~70 f) rounding to 1dp one pack cells are 5.8, 5.8, 5.8, 5.8
The other is 6.2, 6.2, 6.2, 6.2

Neither pack has been used for 3 weeks, both were storage charged to 3.95v on a hyperion duo and cool stored. voltage today is very well matched for the cells in both packs

Alex
That's impressive for packs which are 90 cycles old, depending on how hard you cane them of course. Perhaps TP do actually match cells on assembly. Presumably the two packs have been soaked at the same temperature for some time. A dodge I do is to rubber band them together overnight if I am comparing packs and measure again next day. Temperature is so important.
I have a pair of 6S5000 20c Turnigys which are unused and are equally perfectly matched, but they are, as yet, unused. I also have two 5S3000 20C Turnigys which are fairly unmatched in IR terms and were not matched when new.
It's interesting to look at a pack which is showing signs of deterioration; generally you find a cell which higher than the rest - a sign it is on the way out.

Wayne
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Old Nov 13, 2010, 01:27 PM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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Quote:
It's interesting to look at a pack which is showing signs of deterioration; generally you find a cell which higher than the rest - a sign it is on the way out.

Wayne

Like this Pro Power 45 as per POWERLAB 8 cells at 80F 4.7 / 4.2 /4.2

and at 70 F 6.9 / 5.6 / 5.6

http://www.rcgroups.com/forums/showp...19&postcount=1

but being a year old 303 bench cycles and 16 flights plus always being stored at room temerature not bad.
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Old Nov 13, 2010, 02:16 PM
who dares wins
like2fly!'s Avatar
London,England
Joined Apr 2005
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Quote:
Originally Posted by Wayne Giles View Post
That's impressive for packs which are 90 cycles old, depending on how hard you cane them of course. Perhaps TP do actually match cells on assembly. Presumably the two packs have been soaked at the same temperature for some time. A dodge I do is to rubber band them together overnight if I am comparing packs and measure again next day. Temperature is so important.
I have a pair of 6S5000 20c Turnigys which are unused and are equally perfectly matched, but they are, as yet, unused. I also have two 5S3000 20C Turnigys which are fairly unmatched in IR terms and were not matched when new.
It's interesting to look at a pack which is showing signs of deterioration; generally you find a cell which higher than the rest - a sign it is on the way out.

Wayne
Hi Wayne,

Iím quite fastidious about looking after my packs, i never discharge more than 80% and always ziplock (with crystals to absorb moisture) cool storage whilst not in use, basically I go with Charles recommendations across the board

The Slick set up is the more demanding of the two, drawing about 50 amps at wot on the ground. Relative to the rating they get a pretty easy life

http://www.rcgroups.com/forums/showp...ostcount=12925
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Old Nov 13, 2010, 02:43 PM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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Compared to the trashing mine has been put thru

http://www.rcgroups.com/forums/attac...mentid=2697622

I advocate taking care of them but my test packs get hammered.

Charles
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Old Jan 27, 2011, 03:21 PM
Learning is worth the effort
United States, MI, Grand Rapids
Joined Jan 2009
240 Posts
After reading this forum and others on IR, I wanted to see what my LiPos measured. So, I purchased one of these meters because of its versatility, knowing it wouldn't be near as accurate as Wayne's meters. http://www.hobby-lobby.com/i_meter_7...34262_prd1.htm

I just received it and measured all my LiPos. I also realize the exact numbers don't mean much because it's the relationship of the numbers that count.

With that understanding here are some IR numbers (all in mohms) of individual cells (it doesn't measure total battery IR):
Two brand new (just received, never charged) 3S, Zippy 2200, 25C batteries from Hobby City. One reads 26, 27, 26. The other battery reads 23, 24, 23.

Three one-year old (about 15 cycles each) Turnigy, 2200, 3S, 25C batts read as follows:
33, 32, 33;
35, 32, 32;
37, 38, 33.
These readings came as no surprise in comparison to the two new batteries above.

I used to keep my batteries charged all the time, before I knew better. Here are some readings of those batteries:

A four-year old ABF 3S, 2200, 20C (about 20 cycles) reads: 90, 105, 95.

A three-year old Rhino, 3S, 1350, 25C (about 25 cycles): 96, 107, 104.

A two-year old HobbyZone 3S, 1300, 15C (about 10 cycles): 115, 57, 68.

Other similar 3S batteries had similar readings. The relationship of these readings come as no surprise given what has been said on these IR forums.

A two-year old ThunderPower 3S, 4200, 15C (about 2 cycles but kept charged for over a year): 64, 88, 66.

I find that my 4S batteries are holding up better. They have less cycles but I wonder if that's the only reason. I think I read that larger batteries hold up better. Some 4S readings:

My four-year old 4S HexTronix, 3250, 20C from Hobby City: 33, 32, 39, 38.

Two PolyQuest (several years old) 4S, 3300, 25C:
32, 30, 36, 38;
32, 34, 30, 32.

My two worst 4S batteries (Rhino, 3700, 20C) are only about two-years old and have only about five cycles on them. But again, they were kept fully charged for about one year:
137, 107, 95, 107.
40, 68, 93, 63.

Now I have a good idea what are my best and worst batteries. Okay, so what do I do with that info? I ask because my worst batteries still seem to work okay. Maybe not as long flight times but that's about all I can detect. I don't fly my batteries hard, maybe that's why I don't see much weakness. I'm sure not ready to cut off the leads and throw them away. I guess I just need to be aware of the weak ones and keep a keen eye on them when flying.

Any thoughts or observations?
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