12V Motor Power Supply

[mc123]

Hi,

I have a Leeson 12 VDC, 1/3 HP, 1750 RPM, Model# 108046.00 motor. The motor's full load current is 27A. I have a 12V, 33.3A power supply that I would like to run the motor with. The problem is, however, the motor won't start with the power supply. I can get the motor to run with a car battery, but when I hook it up to the power supply, all it does is hiccup a little.

I am guessing that the starting current draw for the motor is well over the full load current of 27A. Is there any way to bypass this needed starting current - possibly using a capacitor? Basically, I would like to be able to run this motor without spending $300 - $400 on a new Leeson motor controller.

Thanks,
Mark

 

[LarryFine]

Mark, you could always use the battery as a super capacitor to provide starting current, and then recharge after the motor is running.

 

[Besoeker]

Hi,

I have a Leeson 12 VDC, 1/3 HP, 1750 RPM, Model# 108046.00 motor. The motor's full load current is 27A. I have a 12V, 33.3A power supply that I would like to run the motor with. The problem is, however, the motor won't start with the power supply. I can get the motor to run with a car battery, but when I hook it up to the power supply, all it does is hiccup a little.

I am guessing that the starting current draw for the motor is well over the full load current of 27A. Is there any way to bypass this needed starting current - possibly using a capacitor? Basically, I would like to be able to run this motor without spending $300 - $400 on a new Leeson motor controller.

Thanks,
Mark

Yes, the starting current for a DC motor is many times rated current.
A capacitor won't help.
A series resistor or a number of them that you progressively short out as the motor runs up is a conventional way of doing this.

 

[Besoeker]

Mark, you could always use the battery as a super capacitor to provide starting current, and then recharge after the motor is running.

I did think about that too. It would work provided the voltage drop wasn't too much. It sounds like the PSU Mark is trying to use has a current fold back characteristic rather than a linear current limit.

 

[gar]

100629-1545 EST

mc123:

I have to assume you have permanent magnet brush type motor. On this assumption I would expect that maybe 10% of rated current would be sufficient to overcome friction of an unloaded motor, and it may rotate with possibly much less than 10% of rated voltage.

If there is any mechanical load on the motor, such as a gear box, then more input power is required.

I seriously doubt your DC power supply is really a 12 V 33 A unit. How big and how heavy is the power supply? At 12 V and 33 A you have a 400 W supply and I might expect a transformer type to weigh maybe 15 to 30 #.

A servo motor I have will just overcome static friction at 0.3 A. This is about a 1/2 to 1 HP continuous duty unit. I believe it is about a 180 V device. Scaling this to 12 V puts us in the ballpark of 4 to 5 A to overcome friction for your motor. 1.5 volts on my motor armature is adequate to cause rotation. So the motor internal resistance is less than 1.5/.3 or 4.5 ohms.

Put a voltmeter across your motor when connected to your power supply. What is the voltage? If less than a 0.1 V, then the power supply is current limiting. If you have access to a 0.01 ohm resistor, then put it in series with the motor and measure the voltage drop across this resistor to determine your current flow. #12 copper wire is 1.6 ohms per 1000 ft. You can make an adequate resistor with 0.01*1000/1.6 = 6.25 ft of #12 copper wire.

If you really had anything like 30 A thru this copper wire it would warm substantially and you would get a measurement error. But this error would be of no consequence relative to your need.

.

 

[dicklaxt]

Did you try to start it direct across the battery the second time after the PS wouldn't push it,,,,,,,,,,you may have smoked it on the first try without a current limiter of some kind........hope not, good luck

dick