The Shop > Electronics & IC Programing
single phase motors.
DavidA:
Dave,
I burnt a bit of midnight oil an and managed to work out how the switch should be wired. So now it works correctly.
The secret seems to be that the run winding needn't be switched. It stays the same in both forward and reverse.
So, switching the start winding becomes a simple change-over switching operation.
As it's wired at the moment I don't have a centre off position on the switch. Two forwards and a reverse. I know why this is but as I will be turning the motor on and off with the zero-voltage stop-start switch it doesn't matter. Most of the time I will be in forward for normal turning. I do know how to fix it, but have had enough of switches for the time being.
Dave
Bluechip:
Dave
That's right, one winding is always 'On'. ie. Not switched.
Just 'end for end' the other one. Doesn't matter which, but usually the start winding.
But if the motor is running and you just change over the start winding the 'run' usually wins and the motor now has the run winding going one way and the start trying to go the other.
As that winding is in series with a capacitor it's current is restricted by the reactance of the cap, so it doesn't have the guts to do much. ( If it's 10uF the Xc is some 318 ohms @ 50 Hz).
Did a cap. run motor 3-4 years ago 330W for a mate ( drove an extractor fan ) someone wired it up just with a DPDT switch and it didn't reverse. Just went slower and growled a bit .. so I cobbled up a box with 2 switches and told him to switch it off, change direction, switch it back on. A bit clumsy but it did the job.
He was then able to have a blow or suck as circumstances required.
So, if you have a 'NVR O/L Stop Start' wotsit you're in business ... :thumbup:
Dave BC
DavidA:
Dave BC,
Way back in this post you remarked...Why not ask Machine Mart ???..
Today, I was messing about with the switch again and just out of curiosity I emailed Machine Mart.
They replied with two diagrams within three hours.
Credit where it is due.
Dave. :thumbup:
DavidA:
Yesterday I had reason to go to Bradford and decided to call in Machine Mart and see if they had one of the electric motors that I am using in stock. My aim being to ask to look in the contact box and see how the thing was wired up.
I still had the receipt for the original purchase back in July 2008.
They didn't have one there, but had a similar motor which they allowed be to look at.
But more interestingly, when the assistant typed in the code for the motor he said that they were marked down for discontinued line. And that they would be replaced by a different one.
Now, the good bit.
The motor was still available for £23 +vat. (£27.60). Would I like one ?
Now , the original cost me £76.36 inc vat. The new version is going to cost £95 +vat.
Sure I would like one. It seems they are held at Some place in the midlands, and it will arrive at Bradford next Monday. I will have to collect it as from there. No sweat.
So, If you want or will be needing a single phrase 1 HP motor then ring MM and tell them you would like to know if motor code number 010210080 description motor 1 - 4 - 1 BOF is still available.
For £27.60 you can't go wrong. Just don't order the new expensive one by mistake.
You will have to collect from you nearest MM.
Dave.
hermetic:
Just to clarify a few points here chaps, to reverse any single phase motor, you reverse the polarity of the start winding, this is often marked as Z1 and Z2, but with motors coming in from all over the globe, your experience will probably vary! It doesnt matter if the start winding is just a winding, a winding and a capacitor, or a winding a capacitor and a centrifugal switch, if you treat the whole circuit as "the start winding" swap the wires over where it connects to the live and neutral, and the motor will reverse. As correctly stated above, a single phase motor on the run winding will operate in either direction, if started without the starting circuit and spun by hand, it is the start winding that gives a directional kick to the motor, reverse the kick, and you reverse the motor. As the OP has already discovered, the clever bit is linking the reversing switch so that it does this, and they are all different. You should always allow the motor to stop before reversing it, or you risk damaging the start winding.
Phil
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