brushless e.s.c voltage

[bentech]

is there a way to check the volatge that the brushless e.s.c give to the motor?? i try tu put a mutimeter on 2 of the 3 connector that plug in to the
motor and give it throttle to 0-100% the reading was 0.00 to 8.3 volt.
i have to put the multimeter to ac mode and the thing that i dont understand is i use a 3s lipo battery that read 12.6 volt with the multimeter. so why i dont have 12.6 v at the motor connector at full throttle ?? the e.s.c is
programed the right way so why a 4+ volt difference between the input of the e.s.c and the output?? maby i dont test it the right way ??

[Ron W3FJW]

Pulsed voltage is hard to measure without a scope. My brain is rusty but everything being equal, you're reading an RMS voltage (average) rather than the peak voltage as most voltmeters do. Multiply it by 1.414 to get the peak voltage. It will vary depending upon the frequency of the signal as most meters are calibrated at 60 cycles..

[jeffs555]

Like Ron said, you really can't measure it correctly without a scope. The voltage on the windings is not a sine wave and the 1.414 ratio between RMS and peak only applys to a sine wave. Also, unless you have a true RMS meter it will only read RMS correctly for a low frequency sine wave. Most meters just measure the average AC voltage and scale it to display RMS assuming that the signal is a sine wave(ie multiply average by 1.11).

[bentech]

ok thanks!! thats why i was getting a 8.3 volt reading.
i wanned to test it because i want to know what is the top speed of my rc8 and
the motor spin almost at the same r.p.m on 4s vs 8s ???
so i wanted to test my e.s.c cause i dont understand why the rpm is not
twice higher on a 8s battery.

[bentech]

can i use the same calculs on a 4s-5s-6s ect...
i multiply the reading each time by 1.414 ??

[Ron W3FJW]

Use the 1.11 figure Jeff gave you. I didn't take into consideration the fact that it wasn't a sine wave.
One thing I'm curious about (now that it's been brought up) is not the full voltage applied to the motor at all times and the pulse width varied by the ESC for speed control whether it be at a 3khz low or 12khz high rate even though it's a 3 phase AC motor??