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Old Jan 27, 2015, 11:33 AM
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Affect of C rating on EDF peformance?

I would like to know if anyone has some experience to what affect the Lipo C rating has on the EDF thrust output?

Let's say a 25, 55, and 70C lipo of all the same capacity, and the rated EDF current (~20C) is all under the continuous ratings of said lipos. What % are we talking? Very small?
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Old Jan 27, 2015, 11:44 AM
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HUGE impact on performance. High amp draw will draw lower C rated battery voltage down fast and it will give much fewer usable cycles.
Go with the best C rating you can afford. For me 45c with a top brand name battery like GensAce gives decent performance for the money. 45c cheap Chinese batteries, will not do the same.
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Old Jan 27, 2015, 11:56 AM
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Thanks. It just feels like all that extra "C" is a waste of money, not to mention any weight savings I can get...but if performance reduction is significant than that IS a concern.
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Old Jan 27, 2015, 12:01 PM
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I'd say it depends on how high and how long the actual load is as well. In other words, for something like a 6S Foamy where you tend to be operating at high throttle for more of the flight if your load is approaching 20C then yes, you want at least a 40C pack and you will notice the performance difference a lot. For a 10 or 12S big plane where the load is more like 15C because you are carrying bigger packs sometimes 30C is fine. 20C & 25C packs universally seem to be garbage in my experience. I've had good luck with 30, 40 and higher C packs.
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Old Jan 27, 2015, 12:09 PM
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Thanks. If it helps any, I'm looking at a 6 or 7S app with an 80mm fan running a 5000mah latest TP Lipo. But I may already have the answer, as I now notice TP has a new pricing structure and the 55C is actually cheaper than the 25C by a significant amount.
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Old Jan 27, 2015, 12:33 PM
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55c cheaper than 25c?
Can you post a link to your vendor?
Thanks!
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Old Jan 27, 2015, 12:45 PM
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Sure:

http://www.thunderpowerrc.com/Products/AIR-BATTERIES
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Old Jan 27, 2015, 01:09 PM
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Thanks!
Looks like TP are getting more competitive in price.
That's good!
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Old Jan 27, 2015, 01:14 PM
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Indeed. I have no info, but it has all the feelings of the 55C being from a different supplier than the other two. But either way, it's got TP's blessing...so for what it's worth...which could be good or bad depending on your prior TP experience.
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Old Jan 27, 2015, 01:18 PM
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Quote:
Originally Posted by FNFAL View Post
Thanks. If it helps any, I'm looking at a 6 or 7S app with an 80mm fan running a 5000mah latest TP Lipo. But I may already have the answer, as I now notice TP has a new pricing structure and the 55C is actually cheaper than the 25C by a significant amount.
I'm no way a master with electrics but have been recently getting involved in them due to my growing interest in EDF aircraft. Over the past several months I've been putting a Habu 32 together and of course doing the very wise thing of asking lots of questions from very experienced EDF pilots, vendors, etc. in regards to power configurations and batteries.

From what they've all indicated, yes, if you increase the c rating, you will increase the output numbers. It is important to know that there is a formula that they use to determine this. The formula includes the kv rating of the motor you're using and how many cells, mah and discharge rating of the batteries you're using.

Most everyone I have discussed this with pretty much say the same thing about the mah size. The mah basically is the "size of the tank" or how long it will run. The c rating is how much the battery is capable of dumping. Of course all the numbers do play a role in how much power output is. I don't know what that formula is however.

The quality of the battery is another factor in how long the battery will perform and can be used. Cheaper batteries most times have a shorter service life than compared to the more top end expensive batteries. I've used both e-flite and Thunder Power. Thunder Power are the batteries I use in my Habu 32. E-flites are what I use in stuff like my foamy Habu and Stryker.

In regards to brand new battery prices, higher c rated batteries will always cost more than lower c rated batteries, unless you're dealing with cheap stuff you're buying on line from outside the U.S. (primarily from China). Because you really don't know what they are doing with batteries over there. They may have a cheaper 55c rated battery compared to the 25c rated battery. but cheaper perhaps because it's made of materials and components that may have a half the service life of the 25c rated batteries they are producing and selling.
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Old Jan 27, 2015, 01:35 PM
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All good points and ways to consider...thanks...
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Old Jan 27, 2015, 02:48 PM
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United States, MN, Hermantown
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You might find this of interest:

Battery Load Test Comparisons
http://www.rcgroups.com/forums/showthread.php?t=1767093

This cuts it t the quick --

Lipo's for Jets?
http://www.rcgroups.com/forums/showt...2259983&page=4

Full thread here: http://www.rcgroups.com/forums/showthread.php?t=2259983
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Old Jan 27, 2015, 03:32 PM
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Another thing to take into consideration is if you're running an XXXXXkv motor but the battery is only rated at xx c's discharge rating, the battery can become damaged plus the battery could be a reason that the motor doesn't reach it's full potential because of a lower c rating.

It was a completely odd way of thinking for me when some of the experienced EDF guys were saying that it's the motor that pulls the power out of the battery....not the battery pushing the power to the motor. I had always thought that it was the other way around where the battery is pushing the power out to the motor.

So from what I am understanding, the C rating is the power rate that the battery is capable of unloading. If the motor pulls more than what the C rating is, the battery gets damaged and the motor doesn't get the power that it needs to run at it's full potential.

So basically from what I understand about it is, the c rating of the battery should be chosen in a way that accommodates the specs of the motor that it is providing power for. So for example, if the motor is set up for a 45c rated battery and you put in a 70c battery, this won't have much of an impact on the motor's power output. However, with the same motor running on 45c battery, if you were to use, for example a 25c rated battery instead, the motor would be pulling more out of the battery than the battery is designed to discharge and this will damage the battery. The damage is seen as overheating, puffing, etc. So bottom line is when choosing the c rating on a battery, you want to choose the one that accommodates the specs of the motor that it will be providing the power source to. Increasing the c rating of the battery being used won't increase the power specs of the motor.

On the other hand, if you increase the number of cells of the batteries being used, this will greatly increase what the motor does more than increasing the mah and c rating. However, this could also result in the motor burning out. I know guys who have factory strykers and instead of running a 3s , they put a 4s in it and it runs like a rocket. However, it works for only a little while but results in motors burning out.

I'm new at electrics so if I have it wrong or if there is something missing from this, please let me know.
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Old Jan 27, 2015, 04:23 PM
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Thanks guys. I will continue to explore the links, etc. Yoko, yah, you got it right. It does take a new way to look at it sometime.

based on a 5000mah, I calculate I have a motor/fan combo that will draw about 20C.

I know that the lower internal resistance in a higher C rated battery (eg. 25C vs 70C) will allow for a little more current (~Watts) within the system as the system resistance also is lowered. But it can't be more than a few percent (%) I'm thinking - like single digits.

All assuming the Lipo holds voltage (flat 3.7v discharge). If you operate under its continuous rating that should hold true.

So is there a benefit to not "over-doing" the C rating and more closely matching the components? Perhaps saving weight and allowing for a larger capacity lipo for flight time for example? Or go up a cell count?

Or, I think what some are saying, running too close to even the suggested ratings will over stress the lipo, causing shortened life.
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Old Jan 27, 2015, 04:29 PM
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The only damage I've heard of in regards to c ratings is when using a battery with a lower c rating than the motor is capable of pulling. The damage is ruined batteries (puffing, overheating, etc.). I've not heard of motor damage because of a higher c discharge rating of the battery being used. Good question though, increased number of cells yes, increased c discharge rating yes, no, possibly? I don't know the answer.

Another question is, does c ratings impact physical battery weight? Does a 25c 4s 4000mah weigh more or less than a 65c 4s 4000mah battery or visa versa?
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