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Old Oct 28, 2012, 10:43 PM
Frankenstein recycled packs
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USA, AZ, Gilbert
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New terrority here for me at this discharge rate...
I am testing a 2200 4S 65C pack for a buddy and after 6 easy cycles I went for around a 45C discharge and pulled 102 amps from it tonight; twice.
It was holding 3.5x and eventually down to around 3.43 when I cut power. Amps dropped too, from 102 down to around the mid 80's. Pack temp was under 130F even after a 5 mn warm up/cool down persiod.

My PL8 IR is reading 3.2 to 3.0 on all cells around 70F ambient. Using the calculator it should be around a 30C pack but the numbers on my wattmeter suggest a higher C.
What should I be expecting for cell voltages during a ~50C discharge?

Rick
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Old Nov 01, 2012, 01:13 AM
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Quote:
Originally Posted by mrforsyth View Post
It's generally easiest to track performance over time by being as absolutely consistent as possible with respect to measurement temperature. iCharger will be more than sufficient to tell you this, unless your packs are huge (>5000mAh).

Mark
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Originally Posted by H2SO4 View Post
That would give them a FOM of 4.53, a max current rating of 126A, and a 48 'true' C. A record, I believe.

What are you using to measure IR?
Hello Gentlemen; I've been reading your discussions about IR. I have the i Charger 208B and recently started to keep a closer eye on my batteries. I have moved up to more expensive Planes.
I also have just one quick question;
At what point say on a 2700mah 4s 35c would IR be considered too high per cell? I'm just looking for a rule of thumb. Over 20 mOhm per cell? Thanks Bill
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Old Nov 01, 2012, 02:37 AM
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Quote:
Originally Posted by bonner View Post
Hello Gentlemen; I've been reading your discussions about IR. I have the i Charger 208B and recently started to keep a closer eye on my batteries. I have moved up to more expensive Planes.
I also have just one quick question;
At what point say on a 2700mah 4s 35c would IR be considered too high per cell? I'm just looking for a rule of thumb. Over 20 mOhm per cell? Thanks Bill
Bill,

Thats a bit how long is piece of string but in practical terms you are probably about right.
If you put 20 milliohms and 2700mAh into the calculator. (http://www.jj604.com/LiPoTool/)
You will see that it gives a real C of 11 and a max current of 28A

This probably means that the pack is ok if you want to use it in a lazy model to just putter round. It would be overstressed if delivering more than 400W.
As it is a mid sized pack which should be capable of 20 or 25C, we would expect it to deliver about 900W powering a mid sized model in which its performance now would be disappointing.

If all the other cells are lower in IR and just one cell is 20 milliohms, then that is telling you that the pack is dying.

Wayne
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Old Nov 01, 2012, 05:12 PM
That's a funny word
NE Ohio
Joined Apr 2003
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Quote:
Originally Posted by rampman View Post
New terrority here for me at this discharge rate...
I am testing a 2200 4S 65C pack for a buddy and after 6 easy cycles I went for around a 45C discharge and pulled 102 amps from it tonight; twice.
It was holding 3.5x and eventually down to around 3.43 when I cut power. Amps dropped too, from 102 down to around the mid 80's. Pack temp was under 130F even after a 5 mn warm up/cool down persiod.

My PL8 IR is reading 3.2 to 3.0 on all cells around 70F ambient. Using the calculator it should be around a 30C pack but the numbers on my wattmeter suggest a higher C.
What should I be expecting for cell voltages during a ~50C discharge?

Rick
3.4 volts would be expected (unless it finally falls on it's face. Are you picking the voltage from the same (discharge) lead OR from the balance taps?
At 130 and 3.5 volts they have just a bit more to give. (probably not much)
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Old Nov 02, 2012, 02:18 AM
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alex va.
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Originally Posted by Wayne Giles View Post
Bill,

Thats a bit how long is piece of string but in practical terms you are probably about right.
If you put 20 milliohms and 2700mAh into the calculator. (http://www.jj604.com/LiPoTool/)
You will see that it gives a real C of 11 and a max current of 28A

This probably means that the pack is ok if you want to use it in a lazy model to just putter round. It would be overstressed if delivering more than 400W.
As it is a mid sized pack which should be capable of 20 or 25C, we would expect it to deliver about 900W powering a mid sized model in which its performance now would be disappointing.

If all the other cells are lower in IR and just one cell is 20 milliohms, then that is telling you that the pack is dying.

Wayne
Wayne; Thank you for the easy explanation. I'm too old to get into the technical stuff. I have however started reading this thread from page one. I find it very interesting even through their is a lot I don't understand. I'm not lazy but , I was looking for a value I could use and pass on to my fellow flyers, like typically a new 4s 2500 mah battery one would expect each cell at 72F to read approx 4 to5 m Ohm per cell and, a questionable battery might be reading 20mOhm or more per cell as it nears the end of it's useful life.If a human was measured in this way, I'll probably be reading a IR of 30 m Ohm per cell. LOL
Any way thanks for your answer in layman's terms. Bill
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Old Nov 02, 2012, 07:01 AM
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Bill, for what it's worth, I use mainly 3000mah batteries and my rules of thumb are:
i) Any single digit IR reading is good
ii) 10 - 20 milliohms is still perfectly useable
iii) Over 20milliohms: Whilst there are some who will say that these are useless and should be discarded, I identify strongly with your human analogy so prefer to take the view that they should undertake light duties only and certainly never be subject to any stress or abuse.

I hope that helps
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Old Nov 02, 2012, 08:47 PM
Frankenstein recycled packs
rampman's Avatar
USA, AZ, Gilbert
Joined Jan 2006
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Quote:
Originally Posted by gulio View Post
3.4 volts would be expected (unless it finally falls on it's face. Are you picking the voltage from the same (discharge) lead OR from the balance taps?
At 130 and 3.5 volts they have just a bit more to give. (probably not much)
Thanks for responding. V was from taps.
Testing has stopped as I sucked the esc wires into the fan and grenaded it but the last cycle was still as impressive.
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Old Nov 02, 2012, 09:12 PM
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United States, CA, Placerville
Joined Feb 2006
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Took my new Lipo Tool to the field today and and ran some curiosity tests with my friends on all sorts of packs from 3S 2000mah to 5S 5000mah packs. I asked my friends to arrange their packs of the same capacities in order of their perception of performance (if they had an opinion of that) and then we measured pack and cell IRs. As expected, the packs with good performance (relatively speaking) had cells that had more closely matched IRs. Most were surprised at the mismatch in cells and the effect it had on performance.

As expected some basically felt it was interesting, but felt it was 'too much information' and preferred to just fly and let the chips fall where they may..... ;-)

Don
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Old Nov 02, 2012, 11:58 PM
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alex va.
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Quote:
Originally Posted by Trevorh View Post
Bill, for what it's worth, I use mainly 3000mah batteries and my rules of thumb are:
i) Any single digit IR reading is good
ii) 10 - 20 milliohms is still perfectly useable
iii) Over 20milliohms: Whilst there are some who will say that these are useless and should be discarded, I identify strongly with your human analogy so prefer to take the view that they should undertake light duties only and certainly never be subject to any stress or abuse.

I hope that helps
Another prefect answer for me, Just what I was looking for!!
Thanks much, Bill
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Old Dec 05, 2012, 06:43 PM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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A post on why I like the meter, and some data on 2S 800mAh Turnigy packs.

Another example of "Don't believe the label".

http://www.rcgroups.com/forums/showp...&postcount=416
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Old Dec 09, 2012, 05:12 PM
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Joined Jun 2012
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Hi,

I have made my own LiPo internal resistance tester. It has some inacurancies, but I think it is quite useable. The big advantage is that it is free, the disadvantage is that you have to make your own, I just give every plan I have for it.

http://cseb.hu/lipo_rin

Critical components (except the microcontroller) can be ordered as a free sample from the manufacturer. the microcontroller can be disassembled from a faulty ESC. :-)

Regards,
Csaba
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Old Dec 10, 2012, 07:40 AM
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I wish somebody would make one commercially! Now that you've posted the circuit, it's too late to sell it to a potential manufacturer!

Quote:
Originally Posted by cseb73 View Post
Hi,

I have made my own LiPo internal resistance tester. It has some inacurancies, but I think it is quite useable. The big advantage is that it is free, the disadvantage is that you have to make your own, I just give every plan I have for it.

http://cseb.hu/lipo_rin

Critical components (except the microcontroller) can be ordered as a free sample from the manufacturer. the microcontroller can be disassembled from a faulty ESC. :-)

Regards,
Csaba
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Old Dec 10, 2012, 07:54 AM
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Originally Posted by sailr View Post
I wish somebody would make one commercially! Now that you've posted the circuit, it's too late to sell it to a potential manufacturer!
Hi,

No point in making it commercial. You can buy it at HobbyKing for USD40. :-) It is a very simple circuit. No manufacturer would pay for it.

Regards,
Csaba
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Old Dec 10, 2012, 08:09 AM
Stop scaring my donkey!
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Link to HK product?
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Old Dec 10, 2012, 09:05 AM
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Originally Posted by JohnathanSwift View Post
Link to HK product?
http://www.hobbyking.com/hobbyking/s...ga_Meter_.html
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