Electronics > Projects, Designs, and Technical Stuff
How to limit inrush current into DC motor simple way?
Chriss:
Hi!
I have to build a prototype of some DC motor controller which will be made with PWM...
But at the very first moment I would like to make some mechanical testing where the desired DC motor will be driving a shaft
but the PSU which should power the DC motor is a switching mode PSU one.
So, I think this kind of PSU's didn't like much the inrush current, especially not from a 12VDC motor which should consume around 6A continuously.
I'm thinking somehow to protect the PSU from the inrush current until I finish the testing and for this I'm searching for some
simple solution to do this for the mentioned motor.
Maybe to put a cap in parallel the motor terminal so when the motor is starting the cap would fast delivery the energy to the motor.
But here I have a bit problem to take the correct value of cap.
Can somebody help me to figure out what cap could I use for this ?
Or is there a more simple solution to make this testing on the safe way?
Thanks for any idea and help.
My best regards.
Gyro:
Hi,
A capacitor would do exactly the opposite, It would present a low impedance to the fast PWM edges, increasing the peak driver current! You can use capacitors for electrical prush brush noise suppression, but that would be in the <100nF range.
If you want to limit the peak current, then a low value series resistor would help, maybe around 0.1 -0.5R
Chriss:
Thanks for the faste response.
Sorry, I didn't mentioned, for now in the testing time, I will not use the pwm...
Gyro:
Ah, ok. As mentioned, a small capacitor would help reduce high frequency brush noise getting back to the PSU. A resistor is still the simplest current limiter though, even though it will get very hot if you stall the motor!
Chriss:
The motor should never stall but I assume the resistor will go very hot even during the normal running time of the motor, cos the ~6A...
What about to put an inductive coil in between the motor and the psu?
That would also suppress the current I think.
When I finish the test and make the controller then I will use the software soft start with pwm and I assume that will work, but for now to run the motor and the mechanic part for 1-2h it should serve but not kill the psu...
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