"C" rating criteria of Lipo packs  
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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> "C" rating criteria of Lipo packs
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"C" rating criteria of Lipo packs - 2/21/2008 10:24:27 PM   
OhD


 

Posts: 427
Joined: 10/23/2002
From: west hills, CA, USA
Status: online 		Has there been any discussion anywhere on the criteria used to determine the C rating of large packs? It would seem that the voltage drop at the continuos xxC current would be one and perhaps the thermal time constant would be another factor. I'm sure there is no RC Industry standard but there must be something in the battery industry.

Jim O
       Post #: 1

RE: "C" rating criteria of Lipo packs - 2/23/2008 4:32:52 AM   
jetdryvr



Posts: 79
Joined: 1/19/2004
From: Vacaville, CA, USA
Status: offline 		Jim O,
I think you got yor answer by all of the replies
Good luck trying to do 30c for very long. You are right....either voltage or temps get unacceptable pretty quickly.

This website is great for plotting battery discharge graphs at up to 20c for some larger cells also. Typically it looks like 20c discharges on "30C" batteries last for about 170 seconds and then they are "spent". Let alone the temps. I can't imagine 30c graphs with "30c" rated batts. I do understand burst/sustained/continuous etc.

http://www.elektromodellflug.de/datenbank.htm
Erik

(in reply to OhD)
       Post #: 2

RE: "C" rating criteria of Lipo packs - 2/23/2008 8:15:01 AM   
jetdryvr



Posts: 79
Joined: 1/19/2004
From: Vacaville, CA, USA
Status: offline 		This is somewhat related:
Discussion - C-Rating Trickery

--------------------------------------------------------------------------------

Am I the only one who noticed the following?

Lets say we are all producing 20C Lipo's that are 2000mah, and weigh 200 grams that can do 40 amps. Then, ACME (Not a real lipo company or representing any real company) wants to be able to say we have a 30C capability.
Well, you take your 2000mah battery and call it a 1400mah. 1400mah X3 (for 30c) gives you 42 amps. Hey, look at that, we have a 30c lipo.

One cool thing is that people who are not pushing the "C" rating will get long run times just like it is a 2000mah battery (cuz it is).

So what's wrong? The weight!!! and Measurements.
I am sure no company would ever do this and I would never accuse one of doing this, but it seems interesting when you actually look at battery DIMENSIONS and WEIGHTS and then compare.

Things that make you go, "What the...hey?"

(in reply to jetdryvr)
       Post #: 3

RE: "C" rating criteria of Lipo packs - 2/23/2008 1:04:05 PM   
Red Scholefield



Posts: 4973
Joined: 12/8/2001
From: Newberry, FL, USA
Status: online 		The battery industry has never used this rating. It is unique to the hobby market and for all practical (except for marketing) purposes somewhat meaningless.

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Red S.
AMA 951 Leader Member

(in reply to OhD)
       Post #: 4

RE: "C" rating criteria of Lipo packs - 2/23/2008 6:38:26 PM   
jetdryvr



Posts: 79
Joined: 1/19/2004
From: Vacaville, CA, USA
Status: offline 		I was using "Battery Company" synonimously with packager/marketer of Lipo's. You summarized it very well though Red.

(in reply to Red Scholefield)
       Post #: 5

RE: "C" rating criteria of Lipo packs - 2/23/2008 7:04:21 PM   
Red Scholefield



Posts: 4973
Joined: 12/8/2001
From: Newberry, FL, USA
Status: online
quote:

ORIGINAL: jetdryvr

I was using "Battery Company" synonimously with packager/marketer of Lipo's. You summarized it very well though Red.


Right, This is something that far too many modelers don't understand, most packager/marketers of LiPos know the technology little better than the poor guys they are selling to. Some even less. I expect this will shake out over time so that reality will set in when it comes to rating. When that happens we will see ratings that are realistic. A rate that can you continuously discharge a pack without exceeding a temperature limit that would significantly compromise the cycle life of the pack. Or am I just dreaming?


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Red S.
AMA 951 Leader Member

(in reply to jetdryvr)
       Post #: 6

RE: "C" rating criteria of Lipo packs - 2/23/2008 9:19:17 PM   
SilverFoxCPF


 

Posts: 58
Joined: 1/5/2008
From: Bellingham, WA, USA
Status: offline 		Hello Red,

Dare I say... Dream on...

Tom

(in reply to Red Scholefield)
       Post #: 7

RE: "C" rating criteria of Lipo packs - 2/23/2008 10:31:25 PM   
SilverFoxCPF


 

Posts: 58
Joined: 1/5/2008
From: Bellingham, WA, USA
Status: offline 		As long as we are dreaming...

I would like to see the criteria for the maximum current that can be drawn going along these lines...

This cell, when discharged at this maximum current, will see a cell temperature rise of a maximum of 10 degrees C (18 F), will have a mid point voltage of 3.5 volts, and will be capable of delivering 90% of its labeled capacity.

Warning, continual discharge at this maximum rate will result in a 50% reduction in cycle life.

Here are the discharge graphs illustrating this...

The graph would show 3 lines. One for the 5 hour discharge capacity, one for a 1C discharge capacity, and the third one would show the maximum discharge capacity and voltage under load.

Is this so much to ask for...?

Tom

(in reply to SilverFoxCPF)
       Post #: 8

RE: "C" rating criteria of Lipo packs - 2/24/2008 12:57:04 AM   
SUPERSPORT


 

Posts: 49
Joined: 8/3/2003
From: Hilliard, OH, USA
Status: offline 		What is this c rating? I'm shopping for batteries for my T-28 Trojan and keep seeing this. What is better? A higher or lower number?


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Great Planes SE5a.
ParkZone T-28 Trojan.

(in reply to SilverFoxCPF)
       Post #: 9

RE: "C" rating criteria of Lipo packs - 2/24/2008 10:20:58 PM   
SilverFoxCPF


 

Posts: 58
Joined: 1/5/2008
From: Bellingham, WA, USA
Status: offline 		Hello Supersport,

If your battery pack was labeled as 1000 mAh, and rated for a maximum of 2C, the maximum current you should draw from it would be 2000 mA.

Tom

(in reply to SUPERSPORT)
       Post #: 10

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