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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Dennis Toth on January 31, 2015, 10:15:25 AM

Title: How far can you go with voltage for a motor nomally running a 4S pack?
Post by: Dennis Toth on January 31, 2015, 10:15:25 AM

PLEASE DISREGARD THIS WAS ALL DISCUSSED LATE LAST YEAR, I JUST DON'T KNOW HOW TO REMOVE IT.

Guys,
I am working on a new ship and will need to save some weight in the battery. Looking at my choices it seems that using a higher voltage pack like a 6S could cut 1/2oz vs the 4S to get the 5 min flight. My question is if the motor is generally run with a 4S pack, could I use the 6S and just reduce the throttle a bit to hold the same lap time?

It seems that going up in voltage should not put the motor into an overheat situation as long as the rpm is reduced to basically the same point as it would with the 4S. What am I missing?

Best,       DennisT

Title: Re: How far can you go with voltage for a motor nomally running a 4S pack?
Post by: Tim Wescott on January 31, 2015, 02:50:13 PM

This is the full-on electrical engineer explanation, just because.  So forgive me if it's too abstruse.

These circuits work by chopping the voltage from the battery, and depending on the motor to average the voltage out to make a somewhat steady current.  So when you're running at 50% throttle, the motor doesn't see 12V -- it sees 24V alternating very rapidly with 0V.  The motor has a property called inductance, which means that it more or less acts as if it's just seeing a steady 12V.

However, it doesn't quite smooth out the 24V entirely -- there's a phenomenon called "ripple current" caused by the motor inductance not smoothing things completely.  There's also a phenomenon called "eddy current", that happens no matter what.  Both of these will tend to use cause the motor itself to heat up.

But, unless the problem is extreme, you're probably OK.