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Old Apr 13, 2012, 12:16 AM
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can too high bat. discharge rating damage ESC?

While flying today plane lost all power, evidently my ESC (30A Eflite) bit the dirt while using a 25-50C discharge 1300mAh 3 cell. As this was a powered glider, when power was lost the motor was not even on and plane was in a gentle glide Had been flying for a while with no problem when it came down nose first with no control and upon inspection a dead Rx.

Did some trouble shooting at home, battery still had a charge, hooked Rx up to another ESC and worked fine but the ESC in the plane does not work when hooked to another Rx. The battery was a spare battery. Would the battery have damaged the ESC? The original battery was a 20C, I would think a battery with a larger C rating would not be a problem as long a voltage was correct (in this case 11.1)

I'm a rookie learning as I go, trying to figure out what has failed.
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Old Apr 13, 2012, 12:32 AM
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Sounds like your BEC went bad. It is very doubtful that a higher C rated battery caused the problem. While gliding with the motor off both batteries would have essentially the same voltage because there is not enough current being drawn from either battery to pull the voltage down regardless of the battery's C rating.

Larry
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Old Apr 13, 2012, 12:47 AM
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Sounds like your BEC went bad. It is very doubtful that a higher C rated battery caused the problem. While gliding with the motor off both batteries would have essentially the same voltage because there is not enough current being drawn from either battery to pull the voltage down regardless of the battery's C rating.

Larry
Thanks for reply, didn't think the battery itself was the problem, possible I flew it until voltage dropped too low even for Rx and didn't know it since I wasn't running motor so It wouldn't have shut off as a warning. However when I hooked the battery up to a different plane right afterwards (thinking it had dropped too low) it seemed fine running a different Rx. Oh well.
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Old Apr 13, 2012, 04:04 PM
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Only way a higher C batt could look like it destroyed an ESC would be if you flew with a low-C batt that couldn't supply all the current the motor could handle, then you put in a higher C and now the current exceeds the ESC current rating.
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Old Apr 13, 2012, 04:32 PM
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Originally Posted by Meach_in_GA View Post
Thanks for reply, didn't think the battery itself was the problem, possible I flew it until voltage dropped too low even for Rx and didn't know it since I wasn't running motor so It wouldn't have shut off as a warning. However when I hooked the battery up to a different plane right afterwards (thinking it had dropped too low) it seemed fine running a different Rx. Oh well.
Did you check the voltage of that battery after the flight?

Did you time your flight?
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Old Apr 13, 2012, 07:53 PM
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Only way a higher C batt could look like it destroyed an ESC would be if you flew with a low-C batt that couldn't supply all the current the motor could handle, then you put in a higher C and now the current exceeds the ESC current rating.
The common misconception arises again. Batteries don't force current into the motor/prop. Rather the motor/prop draw the current they need (and only the current they need) from the power source. Having a higher C battery only allows the motor/prop to draw more IF IT NEEDS IT and coudn't get it with a lower discharge rate battery. Using a higher C battery is a good thing, understanding that it adds more weight to the model.

What can cause an issue is using a higher voltage battery without adjusting other parts of the power train. In that case, the motor runs faster and needs (draws) more current. If that current exceeds the ratings for the components then something is likely to fail.
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Old Apr 13, 2012, 08:10 PM
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Rather the motor/prop draw the current they need (and only the current they need) from the power source. Having a higher C battery only allows the motor/prop to draw more IF IT NEEDS IT and coudn't get it with a lower discharge rate battery.
Not even this... Let's try again

The motor will draw whatever amount of current it needs to spin the prop at an RPM that's determined by the input voltage. The only reason a battery with a higher C rating will cause an increase in current draw is because it can sustain higher voltage under load, which translates to more RPMs and higher current draw as a result.

That bit is important, though. When you start sucking current from a pack, its voltage will drop temporarily. A lot of folks don't seem to know this, so it's easy to get confused when trying to understand power system relationships.
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Old Apr 13, 2012, 08:49 PM
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What does all of that have to do with the OP's original post? He stated;

"As this was a powered glider, when power was lost the motor was not even on and plane was in a gentle glide."

The motor was not even drawing current when the problem occured so there could have been no appreciable voltage sag with either the 20C battery or the 25C battery. i.e., his problem was not caused by the C rating of the batteries. Most likely he either had a faulty BEC or his reveiver and servos pulled too much current from the BEC and destroyed it.

Larry
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Old Apr 14, 2012, 06:28 PM
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Yeah, lets go with no rehashing...
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Old Apr 15, 2012, 03:44 AM
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Originally Posted by Lnagel View Post
What does all of that have to do with the OP's original post?
It has everything to do with his question: "can too high bat. discharge rating damage ESC?"
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Old Apr 15, 2012, 03:46 AM
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Originally Posted by fmw View Post
The common misconception arises again. Batteries don't force current into the motor/prop. Rather the motor/prop draw the current they need (and only the current they need) from the power source. Having a higher C battery only allows the motor/prop to draw more IF IT NEEDS IT and coudn't get it with a lower discharge rate battery. Using a higher C battery is a good thing, understanding that it adds more weight to the model.

What can cause an issue is using a higher voltage battery without adjusting other parts of the power train. In that case, the motor runs faster and needs (draws) more current. If that current exceeds the ratings for the components then something is likely to fail.
Exactly.
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Old Apr 15, 2012, 08:56 AM
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If you guys are going to pile on me, OK, lets hash this out.

Perhaps C rating isn't the controlling factor, but you certainly could have a batt that would not supply enough current to melt the ESC, and another that could.

Probably not a real-world example, it'd have to be a really crappy batt and an esc on the edge, but certainly within the realm of battery chemistry/physics.

And I certainly never suggested the battery forces current into the motor in my post- that was an erroneous supposition about what I posted.
Dave
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