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Old 03-01-2012, 11:40 AM   #31
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Originally Posted by Shawn68z View Post
Thats in-correct.


Run time is only effected by the consumption rate, and the capacity of the battery. The C rating of the cell has nothing to do with run time.


Shawn
Shawn - Actually you are incorrect. If the C rating is correct then the reason for the higher value is lower internal resistance. Which will increase the consumption rate. If you calculate the internal resistance then the voltage should be at a slightly higher rate giving more power. More power on identical battery capacities means the higher C rating pack will discharge faster.

We are talking a minor amount of course that I wouldn't worry about. If the C rating IS HIGHER(not fudged numbers) then the higher the C rating the more punch and better the pack should be.

You can find more information here - http://en.wikipedia.org/wiki/Internal_resistance
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Old 03-01-2012, 02:36 PM   #32
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Shawn - Actually you are incorrect. If the C rating is correct then the reason for the higher value is lower internal resistance. Which will increase the consumption rate. If you calculate the internal resistance then the voltage should be at a slightly higher rate giving more power. More power on identical battery capacities means the higher C rating pack will discharge faster.

We are talking a minor amount of course that I wouldn't worry about. If the C rating IS HIGHER(not fudged numbers) then the higher the C rating the more punch and better the pack should be.

You can find more information here - http://en.wikipedia.org/wiki/Internal_resistance
Only true assuming your system can pull that higher c rating. example. if a motor can only pull 25c then the runtime on a 5000mah 40c battery will last as long as a 65c 5000mah battery. If that motor can pull over the 40c rating on the same two packs the runtime would decrease. I doubt the difference would be a whole lot in racing though. How often are our motors pulling their max capacity? Not much or we would be melting wires and speed controls.
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Old 03-01-2012, 02:44 PM   #33
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Only true assuming your system can pull that higher c rating. example. if a motor can only pull 25c then the runtime on a 5000mah 40c battery will last as long as a 65c 5000mah battery. If that motor can pull over the 40c rating on the same two packs the runtime would decrease. I doubt the difference would be a whole lot in racing though. How often are our motors pulling their max capacity? Not much or we would be melting wires and speed controls.
Not true. C rating and Internal resistance are not the same thing. You will get a lower internal resistance with a higher C rating however C rating has nothing to do with the power the battery puts out. It is the value that the battery can handle before it CAN'T put out.

The internal resistance allows the battery to output higher voltage at a regular rate compared to nominal voltage. It would be like having a thicker guage wire. The motor is drawing the same current however the wire loses X amount during that draw. C rating would be like the same example except when the motor draws the current the wire can't handle the current and would melt or fail.

Hopefully that explains it. We are talking about a very small difference here and it is all on the assumption that a 90C battery is rated the identical way to a 50C battery.

Internal resistance was the number one value we looked at for matched batteries racing stock classes. It gave more power however drained your battery more so it wasn't as important in modified where run time was the most important.
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Old 03-01-2012, 08:48 PM   #34
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The lower IR – shorter run time is quite noticeable in many airplanes that are run at a fairly high average load. Normally not nearly as noticeable in variable lower average load car use, but TheZoof and For the win are correct.

Put another way, increased performance is not free.
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Old 03-02-2012, 05:53 AM   #35
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Not true. C rating and Internal resistance are not the same thing. You will get a lower internal resistance with a higher C rating however C rating has nothing to do with the power the battery puts out. It is the value that the battery can handle before it CAN'T put out.

The internal resistance allows the battery to output higher voltage at a regular rate compared to nominal voltage. It would be like having a thicker guage wire. The motor is drawing the same current however the wire loses X amount during that draw. C rating would be like the same example except when the motor draws the current the wire can't handle the current and would melt or fail.

Hopefully that explains it. We are talking about a very small difference here and it is all on the assumption that a 90C battery is rated the identical way to a 50C battery.

Internal resistance was the number one value we looked at for matched batteries racing stock classes. It gave more power however drained your battery more so it wasn't as important in modified where run time was the most important.
The original discussion did not account for internal resistance. Just because a pack has a higher c rating does not mean it has a lower internal resistance. I was making the point about the c ratings (being the maximum that can be put out) if your system is not capable of pulling 40c then a 65c is going to give you the same run time. Now if you want to throw IR into the mix then sure. The same c rating packs with differing IR will produce different run times and power output. My only point was that c rating, by itself, has little to no impact on run time.

I wish more guys talked like you guys do. In my opinion the internal resistance is something that is more important than c rating. Thanks for the good discussion.
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Old 03-02-2012, 01:53 PM   #36
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While C and IR aren't exactly the same thing, they are strongly related. Simply can't achieve a high discharge rate with high internal resistance. A higher IR than expected for a given C suggests either degradation or perhaps less than accurate rating.

Fully agree that IR is a more practical measurement for us, just as it has been for well over 20 years.
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Old 03-02-2012, 02:14 PM   #37
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I think the OP's question should have read like this.
How much current can a 13.5 draw in blinky mode?

Or... If I buy a 65c battery is it a waste of money?
Should I stick with the inexpensive 40c for blinky mode?

That's what I want to know anyway.
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Old 03-02-2012, 03:09 PM   #38
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Originally Posted by 6376vette View Post
The original discussion did not account for internal resistance. Just because a pack has a higher c rating does not mean it has a lower internal resistance. I was making the point about the c ratings (being the maximum that can be put out) if your system is not capable of pulling 40c then a 65c is going to give you the same run time. Now if you want to throw IR into the mix then sure. The same c rating packs with differing IR will produce different run times and power output. My only point was that c rating, by itself, has little to no impact on run time.
I wish more guys talked like you guys do. In my opinion the internal resistance is something that is more important than c rating. Thanks for the good discussion.
There is no industry standard for C rating on batteries.
You can use the C rating as a guide with the same manufacture brand name.

This is the most important thing to look at voltage drops on the battery under a load.
Dynamic timing (boost)on your ESC uses more and more amps (load on battery) to increase motor timing by blasting the coils with voltage.

Voltage is speed.
Power (Watts) = voltage X Amps
As above formula - the higher the Amp draw the lower the votage may drop.

Test your batteries under a load and you will be surpised at the real C rating or internal resistance.

Last edited by Mr RCTech; 03-02-2012 at 05:47 PM.
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Old 03-02-2012, 03:20 PM   #39
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Originally Posted by jgroenhof View Post
I think the OP's question should have read like this.
How much current can a 13.5 draw in blinky mode?

Or... If I buy a 65c battery is it a waste of money?
Should I stick with the inexpensive 40c for blinky mode?

That's what I want to know anyway.
As much current as you can in a race without a drop no more then
3 tenths per lap time at the end of a race.

Using a chassis dyno this is what I found:

17.5= 27 amps peak
13.5= 37 amps peak
10.5= 47 amps peak

You don't really need to buy a chassis dyno.
Just use a meter in your vehicle and run on the track to measure drops to adjust your mechnical timing.

Just install between the battery and speedo:
http://www.hobbyking.com/hobbyking/s...eter_100A.html

Last edited by Mr RCTech; 03-02-2012 at 05:55 PM.
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Old 01-20-2013, 12:02 AM   #40
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Old news. The latest SMC packs are excellent. The puffing problem may have been packs bought from China/Hong Kong that were cheap copies using the SMC label.

On second thoughts, please go ahead and believe this wrong statement, go and buy someone else's pack, and then I will be able to beat you with my SMC pack!!

Seriously, SMC is a very good cell, good price, no puffing problems and excellent performance. HTH
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Old 01-20-2013, 12:12 AM   #41
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Reedy, thunder power, speed zone are my three choices. I've been running the 6500/65c reedys for the past month or so and they've been run at least 2 cycles per pack each day with no drop off in performance. My new 7000/65c reedy packs will be here Monday to try out for snowbirds. The thunder power and speed zone packs were just as good. I've run Orion in the past and they didn't seem to do as well, however I'm really liking their weight transfer pack in my buggy!
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