Overvolting /overamping motors - Page 1
Forum section: electronics / beginners

author: electromateria
author_rank: Regular Contributor
timestamp: October 12, 2021, 04:11:28 am
content: Are there any good resources when it comes to overvolting motors??I'm curious if I have a 24v rated hub motor can it handle intermittent short (2-3 second) bursts of 36v every 1-2 mins? Is it ok to use overvoltage as a kind of electric motor "turbocharger" or will it quickly destroy the motor? Say I'm overtaking someone on an ebike, I could have a button to dump extra voltage from a separate battery pack to go faster for a very short time.How do I know how many amps to put into a 24v motor? Do I need to research the motors specs or can some kind of testing need to be done? What happens if the voltage is correct but I put too many amps? Is it generally forgiving or will it burn up quick?

author: james_s
author_rank: Super Contributor
timestamp: October 12, 2021, 05:15:37 am
content: You can't "put too many amps" into something if the voltage is correct. The motor will draw amps based on the voltage pushed into it and the mechanical load placed on it, you cannot vary these things independently. The higher the voltage the more current it will draw. The greater the mechanical load, the more current it will draw.

author: gcewing
author_rank: Regular Contributor
timestamp: October 12, 2021, 07:28:23 am
content: Most motors can withstand a moderate amount of overvoltage without harm. How much and for how long will depend on the motor, how much load is on it, how well cooled it is, etc. Your suggested boosting for short periods is quite likely okay, but watch the temperature of the motor. If it gets too hot to touch you're probably overdoing it.

author: geggi1
author_rank: Frequent Contributor
timestamp: October 13, 2021, 07:29:55 pm
content: Just remember that many of the motors used on E-bikes are not DC motors but 3 phase AC motors with a variable frequency drive.The reason for this is; the motor is smaller/lighter and its simpler to adjust the speed. You will also get more torque on the motor and longer battery life.If you increase the voltage you will only damage the frequency drive.This is the same way as its done on most electric RC stuff like cars and planes.

author: james_s
author_rank: Super Contributor
timestamp: October 13, 2021, 10:31:14 pm
content: Increasing the voltage on brushless motors absolutely increases the power. I have numerous brushless powered RC airplanes and using a battery with a higher cell count makes a huge difference in performance. Obviously there are limits, if you go too high you will damage something. Usually it's the motor that overheats if you try to push it too hard, either with too much voltage or by swinging a prop that's too large or too aggressive in pitch.

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 13, 2021, 11:07:04 pm
content: If you put the volts up but add resistance at the same time, dc motors ramp up to their top speed for some reason I cant fathom yet.

author: gcewing
author_rank: Regular Contributor
timestamp: October 13, 2021, 11:30:07 pm
content: Quote from: Capernicus on October 13, 2021, 11:07:04 pmA brushed permanent magnet DC motor will reach a speed where the back emf equals the applied voltage minus the voltage dropped by any series resistance. If the motor is under no load or a very light load, the current required is minimal, so the voltage drop across the resistance is small and the speed will be determined mainly by the supply voltage.Adding series resistance reduces the maximum torque the motor can produce, and makes the speed fall off more quickly with increasing load. Adding load to the motor makes it draw more current, which means more voltage lost across the resistance, and less back emf needed to balance the remaining voltage, so lower speed. And at the other extreme, when the motor is stalled or starting, the resistance limits the current and therefore the torque.

author: amyk
author_rank: Super Contributor
timestamp: October 13, 2021, 11:46:38 pm
content: On the really-short timescale, insulation breakdown is the limiting factor; on longer timescales, it's thermal dissipation.Look at photonicinduction channel on YouTube for some actual examples...

author: Circlotron
author_rank: Super Contributor
timestamp: October 14, 2021, 12:45:02 am
content: A car starter motor is a good example of an electric motor that is overloaded but only run for a brief period. If you had a big enough battery and cranked the engine for long enough it would cook the starter motor, but cranking for just a few seconds, especially if starting from cold, is quite okay. It saves using a much larger, heavier and more expensive electric motor for no benefit.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 14, 2021, 06:07:06 pm
content: Industrial servo motors (not the hobby RC servo type things), but the motors used in "real" motion controller, robot CNC machines etc. are (almost?) always specified for both a "steady load" and short time "bursts" of power, (for example during acceleration).These bursts regularly have 2x to 3x the torque of the "continuous" mode, and it's limited by overheating, and thus the amount of "extra" torque, motor mass etc.Have a look at this motor catalog for some examples:https://www.damencnc.com/userdata/file/DELTA_ASDA-B2_Catalogue_English_2019.pdf

author: james_s
author_rank: Super Contributor
timestamp: October 14, 2021, 07:23:09 pm
content: Quote from: Capernicus on October 13, 2021, 11:07:04 pmThis is very simple. The torque of a DC motor is directly related to the current it can draw. If you add resistance to the supply you will limit the current (because Ohms law) which will limit the torque. If you limit the torque, obviously it will take longer to accelerate the mass of the rotor.