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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Larry Renger on February 18, 2011, 10:08:04 AM

Title: ESC voltage drop
Post by: Larry Renger on February 18, 2011, 10:08:04 AM: I assume that like most transistor circuits, the output maximum voltage from an ESC is less than the input. Anybody know what the typical drop is? Or how to measure it? The motor responds to the output volts, not input, and I think that may be worth considering in our calculations.

I did a search, and didn't find anything that (to me) answered the question. ???
Title: Re: ESC voltage drop
Post by: Dennis Toth on February 18, 2011, 11:35:07 AM: Larry,
What has been kicking around here has been about 1 volt drop. I haven't seen anyone post any specific Motor/ESC combination data. Does the ICE data logger record this number?

Best, DennisT
Title: Re: ESC voltage drop
Post by: Igor Burger on February 18, 2011, 01:16:18 PM: Larry, you have to calculate effective voltage as:

battery no load voltage - current * ( resitance of battery + resistance of wires + resistence of ESC + resistance of winding )

I think your question is what is the voltage drop on ESC only ... so if the current is up to 40A, and resistance could be ~2mohm, then the voltage drop will be 40mV when fetts are open. If we run in PWM partial throttle, everything is different and depends on % of throttle because we have 1/ switching loses (the resistance is higher) and 2/ the average current in fetts is higher than average current in battery leads.

and an example, this page shows ESC resistance for Jeti ESC:
http://www.jetimodel.cz/index.php?page=product&id=42
Title: Re: ESC voltage drop
Post by: Tim Wescott on February 18, 2011, 03:04:08 PM: Quote from: stuntguy13 on February 18, 2011, 11:35:07 AM
What has been kicking around here has been about 1 volt drop. I haven't seen anyone post any specific Motor/ESC combination data. Does the ICE data logger record this number?
That sounds like way too much. Modern FETs have channel resistances measured in milliohms, and while the switching losses and other effects that Igor mentioned do tend to multiply that, I can't believe a factor of 50 or 100.
Title: Re: ESC voltage drop
Post by: Andrew Borgogna on February 18, 2011, 05:56:44 PM: If memory serves me correct, the voltage drop across a normal silicon junction is .8V BUT the output transistors in a ESC are MOSFETs (Metal oxide semiconductor field effect transistor) and these guys have very very low voltage drop. It's in the microvolts (I think) anyway its why they are used in power control systems. I am guessing there is more voltage drop across the wires and the connectors than the MOSFETs.
Andy
Title: Re: ESC voltage drop
Post by: Larry Renger on February 18, 2011, 09:58:34 PM: Gee, I am so happy to know that the Rozmeri is 52x25x12. And especially that the Pocet clanku NiXX can vary from 6 to 18! Now life is complete. S?P
Title: Re: ESC voltage drop
Post by: John Cralley on February 19, 2011, 06:34:02 AM: Quote from: Larry Renger on February 18, 2011, 09:58:34 PM
Gee, I am so happy to know that the Rozmeri is 52x25x12. And especially that the Pocet clanku NiXX can vary from 6 to 18! Now life is complete. S?P

Hey Larry,

Click the center flag (British?) in the upper left and get it in English that even I can read!!! H^^

John
Title: Re: ESC voltage drop
Post by: Larry Renger on February 19, 2011, 08:17:43 PM: Aw shucks, you ruined my fun! VD~ But why do they say resistance = 2x 1.0? why not just 2 ?
Title: Re: ESC voltage drop
Post by: Igor Burger on February 20, 2011, 12:37:58 AM: Because one winding is always connected to battery by two sets of fetts, from + and also from - pole of the battery. If they say 2x1mohm it is clear and noone asks "only one or both?" ;D

It is the same like some producers of motors give the internal resistane of one winding only ... for example AXI ... but combined resistance in delta is in reality different (smaller).