I am trying to run a formerly cordless Dremel with a 12V supply. I know that the dremel runs off of a 4.8V battery, so I would like to see if I can run the motor with 12V PWM without damaging it. However, I haven't been able to find any data for this motor.

The motor is 28.5 mm (1 1/8") in diameter. The front has the word "Johnson" and the symbol of Johnson Electric. There is text on the motor reads:


However, I can't find any motors on their site that match. Any help in either finding a datasheet or safely testing the voltage is appreciated.

enter image description here

  • \$\begingroup\$ You might not find one at all. For the number of Dremels that are produced, they could easily have a custom motor made with no publicly available data. But a 4.8V motor can't usually be run off 12V without damage, not even if you 50% PWM It. \$\endgroup\$
    – DKNguyen
    Apr 15, 2019 at 23:16
  • \$\begingroup\$ I worried about that. Would 40%, which would drop it to 4.8 V average, work? \$\endgroup\$ Apr 15, 2019 at 23:26
  • \$\begingroup\$ No, lower duty cycle is even worse. There usually isn't enough inductance to smooth out the current waveforms enough and adding extra inductance or increasing the PWM frequency so that the existing inductance is able to smooth the current waveform enough is usually impractical and has its own problems. So the motor ends up seeing very peaky stall-like currents and things get worse the lower the duty cycle you go. \$\endgroup\$
    – DKNguyen
    Apr 15, 2019 at 23:33
  • \$\begingroup\$ How about stepping down your input voltage and use 5V PWM instead? \$\endgroup\$
    – Unknown123
    Apr 16, 2019 at 0:48
  • \$\begingroup\$ @Unknown123 That would be my next plan, but the buck converter I got is behaving weird. Possible question on that to follow. I also want to know if perhaps this motor could support 12V, perhaps with temperature monitoring. \$\endgroup\$ Apr 16, 2019 at 3:26

1 Answer 1


You will burn out the motor brush armature interface using 12V on a 4.8V motor with excessing arcing.

This is not a good idea.

Motor RPM increases with voltage and starting current which at full voltage is >10x rated current.

With 4.8V giving 14,000 RPM , 12V would try to go up to 35,000 RPM with a starting current also 250% more than original. Eddy current losses and armature losses with much higher currents result in 2.5x higher arcing voltage on the armature resulting in bridging between armature copper contacts and effectively causing shoot thru on the power supply or arcing short circuits which will burn out the rotating contacts raising the temperature greatly and reducing the MTBF many orders of magnitude to burn out in a minute rather than a month or more of steady operation.

If you want a 35 kRPM Dremmel DIY design, use a better motor and do not exceed rated voltage significantly.

FWIW Dentists use 400k to 800k RPM with a properly designed system.

  • \$\begingroup\$ Aren't dental drills normally pneumatic? Or are they using electric motors now? \$\endgroup\$
    – Hearth
    Apr 16, 2019 at 0:39
  • \$\begingroup\$ Yes they are air turbine motors. E-drills are just for low speed grinding \$\endgroup\$ Apr 16, 2019 at 0:42
  • \$\begingroup\$ e-drills have safety hazards from heat realityesthetics.com/portal/… \$\endgroup\$ Apr 16, 2019 at 0:47
  • \$\begingroup\$ Would using PWM with a lower duty cycle (<40%) work, though? It would keep it from getting as fast. Also, I am currently unsure if the motor is a 4.8V motor, although I will have to assume that if I can't find out more. \$\endgroup\$ Apr 16, 2019 at 1:55
  • \$\begingroup\$ Yes it could work if PWM f << L/DCR of motor. @40%, it could be a 4.5V motor with 0.3V drop. \$\endgroup\$ Apr 16, 2019 at 2:16

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