The Breakroom > The Water Cooler
A good day at work
Bluechip:
Don't really know ..
All I've done is nail some stepper drivers together and they've worked. :scratch:
I would think all that happens is the magnetic field in the stepper coil would increase more rapidly than at the nominal voltage.
As soon as the current reached whatever is determined by the sense resistor and the comparator setting it would switch off. Momentarily, until the clock reset the drive, and we start all over again. So, we have some period where there is no drive to the coil. Usual PWM stuff.
Where this leaves the average current I don't know ??
Gonna give up. Just keep thinking in circles ...
Dave BC
kwackers:
--- Quote from: Bluechip on July 31, 2010, 10:09:36 AM ---Don't really know ..
All I've done is nail some stepper drivers together and they've worked. :scratch:
I would think all that happens is the magnetic field in the stepper coil would increase more rapidly than at the nominal voltage.
As soon as the current reached whatever is determined by the sense resistor and the comparator setting it would switch off. Momentarily, until the clock reset the drive, and we start all over again. So, we have some period where there is no drive to the coil. Usual PWM stuff.
Where this leaves the average current I don't know ??
Gonna give up. Just keep thinking in circles ...
Dave BC
--- End quote ---
Giving this more thought, if you look at the current curve through the inductor for the values we're considering then we're operating on a tiny part of it at the start so we can consider it to be linear.
If we then assume the motor is spinning fast enough so the controller doesn't do any work (thus removing it from the equation) such that each step occurs just as the max current (1.4A) is reached and the voltage we stick across each phase is 100v.
Then it as we switch phases, the current is zero and over the period until the next step builds up to 1.4A at which point we step and do it again. Allowing for the (essentially) linear part of the curve we're operating on and a power supply of 100v then the average current is 0.7A so therefore the power is 70w.
I'm sure there are other factors, but I think we recognise that there's no way a stepper is only generating a couple of watts - plus this describes a mechanism that explains why power increases with increasing drive voltage...
(That blew some cobwebs away. :smart: )
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