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#1 Paul Bruening

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Posted 19 September 2008 - 02:34 PM

Hal, John or any takers,

I've ordered a dirt cheap 24Vin&out PWM with potentiometer control off of sleazebay. I've got a 24V (27.5V actual) power supply. I've also got a variable voltage power supply. Do you think this PWM will handle the 27.5V or will I have to use the variable at 24V? I'm trying to control the speed on this gigantor 24V DC motor for my Mitchell NC scan head at 23.976 fps.

Are there any tips or warnings you could throw me since this is the first time I have wandered out of the old fashioned rheostat zone and into the PWM zone?
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#2 Hal Smith

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Posted 19 September 2008 - 10:44 PM

Hal, John or any takers,
I've ordered a dirt cheap 24Vin&out PWM with potentiometer control off of sleazebay. I've got a 24V (27.5V actual) power supply. Are there any tips or warnings you could throw me since this is the first time I have wandered out of the old fashioned rheostat zone and into the PWM zone?

You rang?

Should be just fine at 27.5 VDC, in the world of DC supplies 24 and 28 VDC are pretty interchangeable. My biggest concern would be back EMF glitches propagating back from the motor to the PWM's electronics causing problems but if the PWM controller is reasonably well designed for motor loads that shouldn't be a problem. You may find you get an audible "sing" from the PWM's operating frequency that you'll need to address unless you only need MOS.

My latest insanity is using an ABB single-phase to three-phase variable speed controller to drive an Arri blimp three phase sync motor. I've got everything together now to run some tests. What I want to do eventually is built an external phase lock loop circuit to crystal lock the motor. I'll probably use my Tobin TMC-55Aa Milliframe controller as the sync speed reference source. The ribs on top of the motor rotor that are used for inching the motor in a blimp have great possibility as use as interrupters for a LED/photocell tach source to sense motor speed. The reference could be done from the nominally 60Hz driving the motor but Clive Tobin recommends higher tach frequencies to stay in a PLL's "sweet spot".
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#3 Paul Bruening

Paul Bruening

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Posted 20 September 2008 - 12:45 AM

My latest insanity is using an ABB single-phase to three-phase variable speed controller to drive an Arri blimp three phase sync motor. I've got everything together now to run some tests. What I want to do eventually is built an external phase lock loop circuit to crystal lock the motor. I'll probably use my Tobin TMC-55Aa Milliframe controller as the sync speed reference source. The ribs on top of the motor rotor that are used for inching the motor in a blimp have great possibility as use as interrupters for a LED/photocell tach source to sense motor speed. The reference could be done from the nominally 60Hz driving the motor but Clive Tobin recommends higher tach frequencies to stay in a PLL's "sweet spot".


Interesting. Can you find a tach sensor that will patch directly into Clive's controller? I like the micro control selector wheels and buttons on his controller. I've wondered if I could find a similar digital potentiometer for cheap to replace this dial type. I'm using a $10.00, hand-held tach to read speeds. I can't integrate it into the system. As you are aware, finding a tach that can resolve an eventual output shaft speed of 23.976 is a challenge. I'm thinking of multiplying the motor speed of 1798.2 by 5, through a gear set or pulley/belt to get past the resolution issue on this tach. Do you have a source for tachs that can resolve .00 or .000?
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