Tiny DC motor control
Tiny DC motor control
(OP)
Gents
We normally deal with nice 3 phase 400V motors but have a little project on the books where we need to provide simple speed (pot on the panel door) to a couple of tiny DC motors. They are PM 50V 1.7A 60W. Control can be fairly crude and motors aren't heavily loaded.
Looking around the choices seem to be
A card which takes 110V, rectifies it and then uses electronics to PWM the DC out to the motor. (http://www.kbelectronics.com/data_sheets/kbic.pdf or similar)
Or
Something similar the first option but the DC is supplied by a standard 48V PSU. (http://ww w.quasarel ectronics. com/3067-d c-motor-sp eed-contro ller-4-100 v-7.5a.htm or similar)
There isn't a lot of difference in cost, the second type is cheaper but balances out once you add the cost of the 48V psu.
For simplicity's sake I'm leaning towards the first option but have slight concerns because the motors are pulsed with rectified 110V AC (about 155V DC?) the brushes and insulation are going to be seeing voltages about 3 times nominal. Is this going to shorten life appreciably? Cause extra noise? Any other downside?
The motors come with a little 2.2uF + 2 x 22nF + 470R + 2 x 1.8mH filter, is this going to be enough or do I need to add a choke too.
All comments & suggestions welcome
We normally deal with nice 3 phase 400V motors but have a little project on the books where we need to provide simple speed (pot on the panel door) to a couple of tiny DC motors. They are PM 50V 1.7A 60W. Control can be fairly crude and motors aren't heavily loaded.
Looking around the choices seem to be
A card which takes 110V, rectifies it and then uses electronics to PWM the DC out to the motor. (http://www.kbelectronics.com/data_sheets/kbic.pdf or similar)
Or
Something similar the first option but the DC is supplied by a standard 48V PSU. (http://ww
There isn't a lot of difference in cost, the second type is cheaper but balances out once you add the cost of the 48V psu.
For simplicity's sake I'm leaning towards the first option but have slight concerns because the motors are pulsed with rectified 110V AC (about 155V DC?) the brushes and insulation are going to be seeing voltages about 3 times nominal. Is this going to shorten life appreciably? Cause extra noise? Any other downside?
The motors come with a little 2.2uF + 2 x 22nF + 470R + 2 x 1.8mH filter, is this going to be enough or do I need to add a choke too.
All comments & suggestions welcome





RE: Tiny DC motor control
RE: Tiny DC motor control
An SCR, or thyristor, controller lets parts of the mains cycles through and the shorter the voltage 'cut outs' the lower the average voltage across the motor. So, if you read voltage vith an instrument, you will probably see voltages that correspond to what the data sheet says.
But, if you look at the voltage with an oscilloscope, you will see parts of the sine wave with peaks around 150+ That may be more than your 50 V motor can take - or the motor doesn't matter. It depends. If the motor has a high armature reactance, it will probably be just fine. If not, there will be a high ripple current that can make the brushes arc or the torque less smooth or heat the motor too much. Insulation is usually not a problem - but if the motor data sheet says that insulation is less than some 1000 V, you may need to be careful.
I would go for the low voltage pure DC option. Or at least run a thorough and prolonged test if I chose the SCR option.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Tiny DC motor control
The filter has little chokes & caps in it which I guess would get rid of some of the peaks & ripple, I was thinking of adding a 10 or 20 mH choke in there too
RE: Tiny DC motor control
RE: Tiny DC motor control