The Shop > Tools
micro mill electricals problems, help please!!
lordedmond:
Paul
Be careful with your expert he no doubt come back and say the controller is outputting AC , but it's pulse width DC
No doubt john can explain more eloquently than I but it's output is on for a time and then off for another time period , eg on for 50% off for 50% gives you approx half speed , that's what the pot does it varies the on off ratio hence the speed .
Note the volts remain the same but it's only switched on for a short time for low speed and on for longer to give higher speed .
To test you need a load and an oscilloscope
Stuart
steampunkpete:
I suggest that before the motor is written off a burnt out / fried, it is tested to check that is indeed the case.
Putting AC into a DC motor will only damage it if the stall-current - time integral is sufficient to raise the temperature inside the motor to the point where there is some critical damage (such as loss of insulation or commutator distortion).
What the PM DC motor does if it is fed AC depends on the nature of the input, the electrical characteristics of the armature, the mechanical time constant of the armature, the thermal properties of the system and, to a lesser extent, frictional forces. A typical response is that the armature will vibrate at 50Hz - it will hum happily to itself (until it burns out, if it is going to).
If the AC has only been applied BRIEFLY then there is a good chance that the motor is OK (remember that if he has tested it a 110V AC then he has put less power into it than its 240V DC rating). You could test it by carefully connecting it to a 12V car battery and a fuse which should be enough to get it turning. (NOT via the cigarette lighter in your car, just in case!). If it turns its probably still good. If it doesn't turn its definitely :(
John Rudd:
Yup I agree with Pete,if the applied ac source was on for a brief period then theres a fair chance it might have survived the ordeal... :zap:
A little more than 12v dc will be needed tho' to get it to spin up.....24v more like...
This where a variac comes in handy...( with a bridge rectifier of course...) for testing....
Growler testing will reveal any probs with the windings...
lordedmond:
Good grief there John not heard the term growler for a long time .
We did not call them by that name in the winding dept but the name is very not PC now
Coil and a hacksaw blade it what we used a long with the normal drop test and IR of course
But we only did DC motors to about 100hp but the converters 6 phase in DC out were about 500hp with open knife switch starters
I hope I have not confused Paul with my ramblings
Stuart
pmdevlin:
ha ha, I was confused the minute the fuse popped! Stuarts comments regarding pulse width are going to make things very difficult for me regarding any recompense for the motor, if indeed its burnt out, I reckon he will still insist its ac output so I am snookered really.; I do think he is a genuine guy and is probably making a huge mistake without knowing, anyway, I'm off to get the controller now, if he says he still hasn't touched it its coming home anyway, for a destination close to the East coast.! :mmr:
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version