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Problem driving motor with SMPS?
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.
Thanks James. The motor certainly is getting up to speed within the 1 or 2 seconds.
Previously I was doing a ramped startup using a PWM power controller and getting the same problem. I blamed the controller which is why I went over to the series resistor.
I like the idea of a current limiter. I can make a simple 2-transistor current limiter and put it in series with the motor. It will drop a couple of volts but I can take out 2 of the diodes to compensate.
2 Antworten
- JamesLv 6vor 10 JahrenBeste Antwort
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,
Quelle(n): retired electrical engineer. - mardellLv 4vor 4 Jahren
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