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Old Sep 26, 2012, 03:42 PM
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Dejavu*Xion's Avatar
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Silly question

Silly question. But i honestly dont know and would like to .....Is it ever not ok to use say a 40c battery in an application be it a plane or a heli wher a 20c battery does fine ? or is it always best to go with the highest c rating one can afford ? In other words would a 40c battery ever be to much for any electronics ? ** Reason i ask is because i saw some battery manufacture claim to have like 150c rated batteries, ( very hard for me to believe) And a response was " why so high it would only damage electronics " **
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Old Sep 26, 2012, 03:56 PM
RC Helicopter Pilot
TheWoodCrafter's Avatar
United States, CA, Westminster
Joined Mar 2010
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Quote:
Originally Posted by Stixx44 View Post
Silly question. But i honestly dont know and would like to .....Is it ever not ok to use say a 40c battery in an application be it a plane or a heli wher a 20c battery does fine ? or is it always best to go with the highest c rating one can afford ? In other words would a 40c battery ever be to much for any electronics ? ** Reason i ask is because i saw some battery manufacture claim to have like 150c rated batteries, ( very hard for me to believe) And a response was " why so high it would only damage electronics " **
That "C" rating is the discharge rate and will not have an affect on your electronics at all.

And that 150C you saw, is completely B.S.
That is MaxAmps and they always are lieing.
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Old Sep 26, 2012, 04:13 PM
Dude, I do fly all day long!
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San Jose, California
Joined Dec 2007
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Originally Posted by Stixx44 View Post
** Reason i ask is because i saw some battery manufacture claim to have like 150c rated batteries, ( very hard for me to believe) And a response was " why so high it would only damage electronics " **
As Bart simpson would say "haha"
I believe I saw on a thread here on RCG where maxamps was asked to provide proof and he sorta shied away. Until they can come up with conclusive proof, it's rubbish.
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Old Sep 26, 2012, 06:19 PM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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Just to be slightly pedantic, you are correct regarding the electronics but not the motor. A genuinely high rate battery will have a lower internal resistance and will deliver higher voltage at any particular current. For 99.9% of cases it is no problem but in a few marginal applications (the EDF guys working at the limit of motor capacity for example) you can possibly toast a system by putting in a higher C rating battery and drawing more power. For almost all of us it is not an issue.

Your second statement is however correct.

Quote:
Originally Posted by TheWoodCrafter View Post
That "C" rating is the discharge rate and will not have an affect on your electronics at all.

And that 150C you saw, is completely B.S.
That is MaxAmps and they always are lieing.
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Old Sep 26, 2012, 06:51 PM
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Originally Posted by jj604 View Post
<snip> A genuinely high rate battery will have a lower internal resistance and will deliver higher voltage at any particular current. <snip>
I have seen this in other threads but I have not seen the results of someone testing it. I would love to see a reference to such a test if you have one.

I was an electronics technician, USN, many moons ago and probably have forgotten a bunch but still I am a skeptic. I agree that a lower internal resistance would present a higher voltage but I honestly don't think the difference could be measured with typical hobby grade equipment. I believe it would be insignificant.

Glen
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Old Sep 26, 2012, 07:33 PM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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Glen, we tend to discuss and post some results about this on this thread

http://www.rcgroups.com/forums/showthread.php?t=1577989

Consolidated results here

http://www.rcgroups.com/forums/showt...1#post20484169

Sorry can't get access to any specific graphs at the moment as am out but here's some real numbers to think about. I recall Bob Smith tested an Overlander 2200 "25C' and a 2200 ""60C" and got cell IR's of 11.9mOhm and 4.5mOhm respectively.

A 4S these would be pack IR's of roughly 48 and 18 mOhm.

Then at 25C which is 55Amps, the voltage drop due to the battery IR is 2.64V vs. 0.99V.

The difference in voltage discharge curves is quite noticeable in testing at currents equivalent to real loads.

It is particularly obvious in the little single cell small packs I tested where battery IR makes a huge difference to performance. Changing from a crappy Flightmax 160mAh to a Thunderpower or Hyperion makes the difference between successful flight and brown out on some 1S systems even at modest currents.

John
Quote:
Originally Posted by ggcrandall1 View Post
I have seen this in other threads but I have not seen the results of someone testing it. I would love to see a reference to such a test if you have one.

I was an electronics technician, USN, many moons ago and probably have forgotten a bunch but still I am a skeptic. I agree that a lower internal resistance would present a higher voltage but I honestly don't think the difference could be measured with typical hobby grade equipment. I believe it would be insignificant.

Glen
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Old Sep 26, 2012, 08:44 PM
The 6 P principle works for me
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Ventura CA
Joined Aug 2007
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Quote:
Originally Posted by Stixx44 View Post
Silly question. But i honestly dont know and would like to .....Is it ever not ok to use say a 40c battery in an application be it a plane or a heli wher a 20c battery does fine ? or is it always best to go with the highest c rating one can afford ? In other words would a 40c battery ever be to much for any electronics ? ** Reason i ask is because i saw some battery
manufacture claim to have like
150c rated batteries, ( very hard
for me to believe) And a response
was " why so high it would only
damage electronics " **
Hi S44! Answering last ? first, the highest lipo rating that I have been able to verify is about 35C. If you only need a 20C lipo then buy a 20C lipo! You will save money! Please keep in mind that until you can check your lipo, it will be dificult to verify that it is a true 20C lipo. Michael
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Old Sep 26, 2012, 09:01 PM
Need More PURPLE !!
Dejavu*Xion's Avatar
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Joined Aug 2012
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Thanks for the answers fellas..Glad to see that you all agree...Also funny how you all knew i was talking about "MAXAMPS" ..HA....I Predominately fly helis. While a 20c is fine for easy circuits. I prefer the larger c ratings for all the known reasons..I was just curious if ther is such a thing as to much ( Im starting to see other Legit companys offer up to 65c now ) ..again thanks for the heads up, After 3 years I'm still learning my way around watt's -amps ect..
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Old Sep 26, 2012, 09:22 PM
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United States, CA, Westminster
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Quote:
Originally Posted by jj604 View Post
Just to be slightly pedantic, you are correct regarding the electronics but not the motor. A genuinely high rate battery will have a lower internal resistance and will deliver higher voltage at any particular current. For 99.9% of cases it is no problem but in a few marginal applications (the EDF guys working at the limit of motor capacity for example) you can possibly toast a system by putting in a higher C rating battery and drawing more power. For almost all of us it is not an issue.

Your second statement is however correct.
John,

Most of the motors we use can handle a wide range of voltage.
After all they are rated in RPM / volt and not an actual voltage.
One of my helicopters, I run 10S packs but some guys run 12S packs with different gearing, with the same motor.
The point being I find it hard to believe that a higher discharge rate pack could possibly provide enough of an increase in voltage to cause damage.
Guys are constantly jumping to the hottest, newest, highest C rated battery they can buy with no reported problems that I have ever heard about.
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Old Sep 27, 2012, 03:17 AM
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Rugby, UK
Joined Feb 2007
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[QUOTE

Sorry can't get access to any specific graphs at the moment as am out but here's some real numbers to think about. I recall Bob Smith tested an Overlander 2200 "25C' and a 2200 ""60C" and got cell IR's of 11.9mOhm and 4.5mOhm respectively.

A 4S these would be pack IR's of roughly 48 and 18 mOhm.

Then at 25C which is 55Amps, the voltage drop due to the battery IR is 2.64V vs. 0.99V.

The difference in voltage discharge curves is quite noticeable in testing at currents equivalent to real loads.

John[/QUOTE]


Taking this to the next step as John seems to have nipped down to the pub instead of finishing the argument (!) I ran a test some time ago plotting actual motor power against supply voltage with a real setup fed from a high power stabilized psu. The relationship is approx. a square law; ie if you drop the voltage to 0.9 ie 10%, then the power drops to 0.81 ie 19%.

Going through the calculation for the above figures suggest a power difference of 22%.
When the packs are hot, the difference would be somewhat less, but the real difference is likely to be 15 - 20% which is very noticeable.

I flew last weekend with a Nanotech 2200 3S real C of 17 and a GensAce 2200 3S real C of 26, and the difference in performance in the same model was very obvious at WOT.

Wayne
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Old Sep 27, 2012, 05:05 AM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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Absolutely correct, I agree with you - but I carefully didn't say the voltage was the issue. It is the power. If the voltage rises then for the same motor/prop combo so does the current. It is the product of the two that is the problem. A motor will fail by heat overload not voltage overload in practice and heat is a result of the current squared. It doesn't take a whole lot of increase in current to cause a significant increase in power = heat.

Just to be clear, I'm not trying to make a big deal out of this. For almost all caes we are in agreement. Like you, I have never seen or am likley to see this problem with the stuff I fly. But I do know that some of the EDF guys smoke stuff regularly (motors and ESCs I mean ) and are on the very limit of what a motor can tolerate.

John

.
Quote:
Originally Posted by TheWoodCrafter View Post
John,

Most of the motors we use can handle a wide range of voltage.
After all they are rated in RPM / volt and not an actual voltage.
One of my helicopters, I run 10S packs but some guys run 12S packs with different gearing, with the same motor.
The point being I find it hard to believe that a higher discharge rate pack could possibly provide enough of an increase in voltage to cause damage.
Guys are constantly jumping to the hottest, newest, highest C rated battery they can buy with no reported problems that I have ever heard about.
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Old Sep 27, 2012, 07:06 AM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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John does not argue ,like me he often choose to post a fairly short answer which many fail to understand. It is difficult to answer a complex question in less than 500 words and some of us get tired of answering the same questions over and over and it seems to me that extremly few know how to use the Search function or even find the correct Forum to Seach in.

IMO a very large percentage of the post oin B & C Forum really belong in the Power Systems Forum , Beginners Forum, Rafdio Forum,Glow to Electric, Electric Helis, Off Road Cars,Boats, etc. etc...

Charles
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Old Sep 28, 2012, 10:25 AM
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San Diego, California
Joined Dec 2004
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"Glad to see that you all agree..."

Couldn't that be considered a "FIRST"? :-)))))))))))))))))))))

p.s. The only "slily" question, is the one you already know the answer to.

Les
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