Electronics > Beginners
24 VDC MOTOR
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jarah:
I am having trouble with the inrush current on a 24vdc motor burning up brushes every couple months. How do I soft start the motor? It has to be automatic and the FLA of the DC motor is 39. What would be the most cost effective way to auto limit the voltage to the motor on start up? I've heard i could just put a resistor in line but I don't know how to choose a resistor. Also, the motor starts up between 40-60 times a minute during the busy period.
Paul Moir:
It depends on a lot; is this a one-of?  Probably just buy a cheap drive with accel control.  Maybe just a inrush limiter would be enough for your app like this: https://www.digikey.ca/product-detail/en/ametherm/MS35-0R550/570-1023-ND/749863
(Sometimes a resistor or inrush limiter is used and then shorted out with a relay for improved efficiency & max torque.)
Rigolon:
Hi,

Here is a link that may help you.
https://www.eevblog.com/forum/beginners/soft-start-a-d-c-motor/

Never tried the circuit suggested by Zero999.
Although I think that this circuit is not able to control speed. But if all you wish is to soft start it's the one I would use.
rstofer:
One start per second just has to be hard on the motor.  Given this start frequency, how soft can the start really be?  It's not like it can take 2 seconds to get up to speed.

I think if I were doing the mechanics of such a thing, I would let the motor run and control the load with a clutch and perhaps a brake.
andy3055:

--- Quote from: jarah on October 28, 2019, 04:38:54 pm ---I am having trouble with the inrush current on a 24vdc motor burning up brushes every couple months. How do I soft start the motor? It has to be automatic and the FLA of the DC motor is 39. What would be the most cost effective way to auto limit the voltage to the motor on start up? I've heard i could just put a resistor in line but I don't know how to choose a resistor. Also, the motor starts up between 40-60 times a minute during the busy period.

--- End quote ---

You may not have installed arc suppression caps from the brush terminals to ground. Most often I have seen small caps like 10/100 pf or so. you can have a range of caps and experiment with them. Some motors have holes in the casing where you can observe the brushes contacting the commutator.
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