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| How to limit inrush current into DC motor simple way? |
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| 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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