Problem driving motor with SMPS?

Question

I'm running a 24V DC pump from an off-the-shelf switch mode power supply (XP Power ECS100US24). The pump motor is rated 75W, the PSU 100W. I'm using a couple of mosfets to switch on the motor and I'm soft-starting it by running it for 0.5 seconds with a series resistor. I'm also using some power diodes to drop the voltage to the motor to about 20V, so it's not running at anything like 75W (confirmed by measuring the current).
However, when I switch on the pump it runs for 1 or 2 seconds then the power supply shuts down completely. It remains completely dead for up to 1 hour (thermal fuse?).

Are there known issues with using SMPS with DC motors? What could be causing this and can anyone suggest things to try?
I already have a 220nF cap and a reverse-voltage protection diode across the motor, and the series diodes should prevent the motor trying to push current into the PSU's output. I also tried putting a 2200uF cap on the PSU output.

James · Accepted Answer

Typical starting current for a motor is 7 times the running current. or about 30 amps in this case.
Since the trip occurs at about 1 to 2 seconds, the motor never starts successfully.  I looked up the specs of the power supply, it has a output overload protection of 150% (6.26 amps) .   It doesn't have a short time transient  specification (motor starting). The power supply is basically built for a constant output.

First step :You could increase the soft start time to 2 ( or more) seconds, use a resistance of 6 ohms.
    Second  step: put a battery on the output  of the power supply to supply start up current or use an ultra capacitor to supply starting current(EXPENSIVE)

other ideas   staged soft start,  current limiting circuit,

mardell · Answer

a number of those previous automobiles had a unfastened floating tension shaft that could come out of the pinion equipment interior the decrease and the pinion might flow somewhat ingredient procedures so which you had a no longer common time putting it lower back interior the decrease unit. Spin the strain shaft and notice if the prop shaft spins. additionally. It takes a great style of practice to get a tension lower back interior the crank shaft. those 4 the tooth splines have been the worst. you need to save the strain spinning as you attempt to push it into the crank. The opposite had sq. seize dogs so it might spin in the two guidelines, the forward had a ramp seize face so it might basically spin backward by using the prop. (you do no longer want that), so put in opposite and spin the prop forward. this ought to rotate the strain clockwise and not screw up your water pump. (If it is not a pull and bypass) placed a smear of grease on each and every thing,--the impeller, the splines of the strain and the shift shaft end . which will help. no longer particularly finding at it, i will basically advise you replace the water pump besides. looks may well be deceiving. additionally verify and alter your decrease unit oil --only in case you need to reseal it.

Problem driving motor with SMPS?

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