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View Full Version : Difference between 10C, 15C, 20C, etc?


jbflier
07-06-2007, 10:35 AM
I have some 4S-1P 4000 lipo's that are rated at 10C and someone told they aren't very good for sport flying a Funtana 40 conversion with an AXI 4120 motor. What does the "C" rating actually mean to the performance of the battery? Thanks in advance for any thoughts/comments........:)

Gnascher
07-06-2007, 12:36 PM
C rating is a measure of peak output capacity a battery is supposed to be able to sustain without damage. For example, a 20C 1000mAh battery is capable of a continuous output of 20A.

The formula is:
(C x mAh) / 1000 = MaxAmps

Sometimes you'll see a battery rated something like 15C / 20C burst. This means the battery could sustain a 15C output rate for the entirety of its discharge cycle with an occasional short burst to 20C.

This calculation is also useful (actually critical) when charging lipos too. You should never charge a battery at greater than 1C. At 1C, it should take 1 hour to recharge a fully depleted battery.

So, for the example battery above, the max CHARGING amps at 1C would be:
(1C x 1000mAh) / 1000 = 1A

The example battery should be charged at 1Amp.

jbflier
07-06-2007, 01:49 PM
Thanks for the prompt reply.....If I understand this correctly, these batteries should be ok for general sport flying. I don't 3-D or anything outrageous; I simply tumble around a little with simple acrobatics and hopefully land without incident. I do understand the charging concept of 1C or 10% of capacity. These are simply new packs purchased about a year ago and seem to work fine. I quess 15C or 20C would be better. Someone just put a question mark in my mind about the 10C performance thing, but these came from True R/C and weren't that expensive. Thanks again.......

darylm44
07-06-2007, 03:08 PM
I am a newbie also, so my comments may not be accurate.

A lot depends on the prop that you use with your motor. For example, with the same motor one prop may cause the motor to pull 9 amps while another prop would cause it to pull 12 amps. Once you determine how many amps your motor will pull you can then determine the battery size you need.

Say you need to be able to pull 12 amp. You could do this with a 12C 1000mAh (12*1000/1000= 12amp) battery or you could use a 10C 1200mAh (10*1200/1000) battery, or any other combination as long as the formula = more than 12 amps.

It's not that the plane won't fly if the battery pack is only 8 amps, but it will probably puff on you at some point and ruin the battery.

If this is not correct please post the correct calculations

Ohiopete
07-06-2007, 03:54 PM
Darylm44 is correct.

What you need to do is beg, borrow or purchase a Wattmeter. This way you can determine what amps you are actually drawing with your specific motor and prop combination. It will be cheaper than ruining a lipo pack or two.

slipstick
07-06-2007, 04:54 PM
I do understand the charging concept of 1C or 10% of capacity.
Not wishing to be over picky and it may just be a typo, but 1C is 100% of capacity NOT 10%....if you charge at 10% you'll be waiting a very long time ;).

Steve

jbflier
07-06-2007, 10:25 PM
Slipstick; Thanks.....I am a patient person, but...........:tc:

Red Scholefield
07-07-2007, 01:14 PM
If you discharge at the rating these vendors put on the packs you will have a significantly reduced service life. :sad:
Of course if you are a LiPo vendor this isn't all that bad. ;-)


I have some 4S-1P 4000 lipo's that are rated at 10C and someone told they aren't very good for sport flying a Funtana 40 conversion with an AXI 4120 motor. What does the "C" rating actually mean to the performance of the battery? Thanks in advance for any thoughts/comments........:)

jbflier
07-07-2007, 01:33 PM
Thanks to all that replied to my original thread. From each comment I quess I can assume that these packs are "OK" for sport flying, but wouldn't be recommended for high performance, or all out flying. As I mentioned these are being used in a 6lb Funtana 40 with an AXI 4120/14 motor, Jeti 75 amp Opto ESC, and an APC 15x6 e-prop.........:tc:

slipstick
07-07-2007, 02:57 PM
That's a pretty big prop for a 4120/14, even on 4S. Motocalc shows it at over 55A.

Since your battery is only rated for an absolute maximum of 40A you might have real problems. If you really want to use that battery you NEED to measure the current first and then maybe try a smaller prop, something like 13x6.

Steve

Tram
07-09-2007, 03:28 AM
10C packs would be fine for... "Sport" flying..

If you plan on doing all out 3D, you might want a lil' higher C rating...

I look at the C rating as an "abuse" number, if you will.. How hard CAN you push them?

Jeff
www.CommonSenseRC.com

Red Scholefield
07-09-2007, 04:27 PM
10C packs would be fine for... "Sport" flying..

If you plan on doing all out 3D, you might want a lil' higher C rating...

I look at the C rating as an "abuse" number, if you will.. How hard CAN you push them?

Jeff
www.CommonSenseRC.com

Can you tie service life to these "abuse" numbers? In other words, what can one expect when discharging at 20C vs 10C for a pack "rated" at 20C?

Mike Freas
07-09-2007, 10:16 PM
You have two options.

1. Buy another 4000 mah pack and wire them to make a 8000 mah pack good for 80 amps.

2. Buy another 4000 mah 20 C pack.

I fly a 10 lb Telemaster on 58 amps WOT but with more voltage(5S). I'm going to say you may be able to prop that motor to pull just under 40 amps but it fly sport only and not 3D. With your current setup pulling 40 amps you have just under 100 watts per pound....98.6 to be exact.

I agree that prop is to big. My 4120/18 turns a 14X10.

Tram
07-09-2007, 10:40 PM
Can you tie service life to these "abuse" numbers? In other words, what can one expect when discharging at 20C vs 10C for a pack "rated" at 20C?

No, I have no data as to how long a 20C pack should last, in terms of lifespan, when discharged at 10C..

It would be a neat test to do though.. Take a 20C and discharge it at 20C over and over and see what you get for lifespan.. Then take a 20C and discharge it at 10C.. I would be tempted to think the 10C discharged pack would have several more cycles available to it.. I would think the lifespan should be longer, but there are lots of things I think that are wrong.. ;)

Maybe abuse is the wrong word, but for some people it seems to correlate the idea better..

A 10C battery can be pushed or pulled or abused (or X, Y and Z or pick your own uphamisim for "C") harder than say a 5C pack..

Likewise, a 50C pack and be "pushed" harder than a 25C pack..

That is the only reason I use the word abused.. People who need to suck alot of juice out of their packs in a rapid fashion, would be better off with an high C rated pack..

Now, what is the benefit of a 50C pack and only using it at 8C? I see zero benefits.. You've paid an exhorbent price for a pack that is being extremely underutilized. Sorta like tryin' to go squirrel huntin' with a 30.06.. Just doesn't make sense.. :D

Jeff
www.CommonSenseRC.com

Mike Freas
07-09-2007, 11:40 PM
Yeah,

I also think that pack life at max rated discharge depends of the quality of the cells. I beat the piss out of an old Tanic pack that I won at a fun fly pulling 19 amps from it's 700 mah capicity and it keeps coming back for more. On the other end of the scale I pulled 19 amps from a 2100 pack I got and it puffed in less then a year.

TRASHBUG
07-15-2007, 12:10 PM
No, I have no data as to how long a 20C pack should last, in terms of lifespan, when discharged at 10C..

It would be a neat test to do though.. Take a 20C and discharge it at 20C over and over and see what you get for lifespan.. Then take a 20C and discharge it at 10C.. I would be tempted to think the 10C discharged pack would have several more cycles available to it.. I would think the lifespan should be longer, but there are lots of things I think that are wrong.. ;)

Maybe abuse is the wrong word, but for some people it seems to correlate the idea better..

A 10C battery can be pushed or pulled or abused (or X, Y and Z or pick your own uphamisim for "C") harder than say a 5C pack..

Likewise, a 50C pack and be "pushed" harder than a 25C pack..

That is the only reason I use the word abused.. People who need to suck alot of juice out of their packs in a rapid fashion, would be better off with an high C rated pack..

Now, what is the benefit of a 50C pack and only using it at 8C? I see zero benefits.. You've paid an exhorbent price for a pack that is being extremely underutilized. Sorta like tryin' to go squirrel huntin' with a 30.06.. Just doesn't make sense.. :D

Jeff
www.CommonSenseRC.com (http://www.CommonSenseRC.com)

What is considered the life span of a battery? Has anyone set a standard?

Perhaps discharging at the max sustained C rating and calling it a goner when it will hold less than 75% of its rated capacity?

I agree that using it at less than it's rated capacity will lengthen it's life span but lets put them to the test that (in theory) they were designed for and see what happens. If I put a lipo on the shelf and never use it, it will have a great life span;-)

The numbers will be all over the board and useless unless there are a set of criteria that everyone works with.

Just a thought??

Tram
07-17-2007, 04:12 PM
You know, that is really a good idea.. Let me see if I can talk to one of our product abusers and see what kind of tests we could run.. Maybe we could put that on our packs as well.. an "estimated" life span..

Jeff
www.CommonSense.com