How to determine DC servo motor voltage

Ignoramus30076 wrote:


Hmmm, that's 280 Watts. Hard to say how much is being turned into heat in the motor and how much in the worm and table, but that is a fair amount of power. I suspect you can't run it long at that speed before the motor starts really heating up.
Jon
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Jon, what is guaranteed is that all power, 100% of it, is converted to heat. The table spins and does no useful work. The question is how much is dissipated in the table and how much is dissipated in the motor.
The numbers to keep in mind is amps. At lower speeds (say 20-30 volts) the motor uses 3 amps, at higher speeds (70 volts) the motor uses about 4 amps. So the amps stays about same, and what it means is that the torque and resistance losses do not change much.
I ran the motor at lower speed for 15 minutes, it warmed up, but not that much. I would say, it increased in temperature by 10 degrees or so.
I would, therefore, think that at higher speeds it would not be much different for the motor, but obviously a lot more heat goes into the table.
At any rate, this is a rotary table and is highly unlikely to see high duty cycle. This is not what rotary tables do, if I am thinking right.
i
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On Wed, 04 Aug 2010 00:00:58 -0500, Ignoramus30076

You are indeed quite correct. Its low cycle time.
Gunner
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Gunner Asch wrote:

He already indicated that Troyke had no information on this RT.
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wrote:

Sorry..must have missed that post.
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On Mon, 02 Aug 2010 10:54:59 -0500, Ignoramus18921

2000 RPM is a good conservative number. Small, high performance servo motors are usually rated around 6000 RPM. Perhaps a bit more for brushless motors, less for brushed.

Continuous current is generally limited by winding insulation and heat dissipation; peak current by the magnet material. The peak current for motors with inexpensive magnets is typically 2 or 3x continuous. The ratio for fancy motors with magnets that are more resistant to demagnetization may be 7:1 or greater. The motor's proportions and construction may be the best clues.
--
Ned Simmons

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OK, good to know that 2,000 RPM is generally safe. This is a very plain looking brushed servo motor.

OK. Interesting. I ran this motor for 15-20 minutes yesterday, turning the rotary table at 30 or so volts (I do not remember if it was 30 or 20).
The current was 3.something amps. I tend to explain this by the fact that the worm is preloaded and thus hard to turn. I will take the table apart to find out more to see if there is anything blocking movement.
Anyway, three times that is 10 amps.
My guess is that this is a 10 A, 80v motor. I will measure it better tonight when I take off the encoder cover.
i
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Ignoramus18921 wrote:

I assume that you mean max continuous amps. That is a matter of the insulation class of the motor. The most conservative common class has a rating of 100 degree C over ambient, IIRC. You can Google it.
So to determine the max current, you lock the rotor and apply increasing amounts of current until a steady state 100 degree C increase is found. The temperature is determined by measuring the resistance and using the R(T) function. You can Google that too.
Bob
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