The Breakroom > The Water Cooler

A good day at work

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kwackers:

--- Quote from: Bluechip on July 30, 2010, 05:38:52 PM ---But why the 0.57 Volts ???  That seems very strange ..

Can you measure the coil resistance ? Then V should be I x R ?  ie 1.4A x whatever .. or nearly.

Baffled of Belper ..

Dave BC

--- End quote ---
The low voltage is typical of steppers. You need to get maximum magnetic flux as quick as possible to prevent the torque falling off with motor rpm.
So if you have a 0.57v coil and stick that across it, then say it takes 1/10 of second (remember it's an inductor) for the magnetic field (and current) to build up then you can see you wont be able to spin it very fast since you'll want to move to the next step long before the magnetic field has gained any real strength.

To get round this you stick a very large voltage across - usually somewhere between 20 and 200v. As a result the time for the magnetic field and current to build up is significantly less.

Obviously if you keep the voltage at that level the current will very quickly rise past the rated current and fry the motor, so this is where the stepper controllers come in, they monitor the current and switch the voltage on and off (PWM) to keep the current at the rated value - you can often hear this as a whistling or hissing noise emitting from the motor.

Davo J:
Hi Rob,
You wouldn't get that much gear in a retirement package, lol

Great score on all the stuff, :beer: and good to see it going to someone thats going to use it.
You must do a good job at work for those blokes to think of gathering it together for you.

Us hobbyist have to pay high prices to get our bit of gear together for the shed, so it's good to see someone get some gear for nothing. :clap:

Dave

Davo J:
I forgot to add that you need to change the heading to.

Christmas at work, lol

Dave

Bluechip:
Hi Kwackers

Yup, know about the current limiters etc. Made stepper drivers with the L293 which uses it. Must admit I've never met a stepper motor with a coil voltage as low as 0.57V.

If you work it out the output mechanical HP cannot exceed the DC power input, unless you've invented perpetual motion.

Each phase is apparently 0.57V x 1.4A  ie some 0.8W.

Even with all 5 phases on, (not likely), it only gives 4W  ... or ... 0.0054 HP ?? ..that's if its 100% efficient. Also not likely.

It does have a 100:1 reduction g/box on it .. which will jack up the torque at the expense of revs ..

Still baffled ..

Dave BC

kwackers:
What's the steps per turn on the output of the gear box?

Steppers have never been known for tremendous power - the falloff with RPM is too great, but they do have decent torque. Most steppers have some for of mechanical advantage (gearbox, leadscrew etc)

However, (and I'm thinking on the fly here). The DC power isn't going to be correct is it??
For example, if you whack 100v across your motor, then at the point the current increases to 1.4A you're actually dissipating 140w at that instance. So whilst the motor is running I'd think the average power in the motor is much higher.
If I'm correct the DC conditions only really apply whilst it's stationary and in a holding phase.

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