Thread: Single phase 240 volt motor running backwards?

Reversing the Active and Neutral on a single phase motor will not make it go in reverse.
You have to reverse either the start winding or the run winding but not both.

OK Thanks . Do you have any idea why a motor that ran right is now running left at its new home ? Nothing was touched with wiring or anything .

Just a guess but if the start cap has failed, it could run happily in either direction with a push start.

If there was stray magnetism or it is slightly unbalanced etc, it could be getting that kick start accidentally.

If it’s safe can you try spinning it the right direction then switch on?
I think that will show if it is the start cap, or the start circuit at least.

Is the start cap the start capacitor? It had a rough trip home as I knew I would be renewing and probably replacing the motor . So the plastic broken cover became worse and it got a little wet as well.

Start cap = start capacitor. The reason Russ has given is the only thing I can think of that will reverse a single phase motor. Seeing the photos in the other thread, I think he might be right.
Check the terminals on the capacitors. Make sure they are not wet/covered in crud. Be careful though. They hold a wicked charge and will give you a painful kick if you touch them. I always short them out with a big screwdriver before I poke around in there.

Very odd. Are you absolutely certain it was running in the correct direction at the seller's house? Any chance he just bunged that motor on it to sell it without confirming it ran the right way?

Originally Posted by russ57

Just a guess but if the start cap has failed, it could run happily in either direction with a push start.

If there was stray magnetism or it is slightly unbalanced etc, it could be getting that kick start accidentally.

If it’s safe can you try spinning it the right direction then switch on?
I think that will show if it is the start cap, or the start circuit at least.

Thanks Russ .
I can spin it safely before giving it some power but at the moment power is just by an extension lead being plugged in so I think it should be possible . A lead with a switch at its end would make it easier. Or a switch on the machine side.

Originally Posted by NCArcher

Start cap = start capacitor. The reason Russ has given is the only thing I can think of that will reverse a single phase motor. Seeing the photos in the other thread, I think he might be right.
Check the terminals on the capacitors. Make sure they are not wet/covered in crud. Be careful though. They hold a wicked charge and will give you a painful kick if you touch them. I always short them out with a big screwdriver before I poke around in there.

Thanks for the warning NC . I am aware of that danger thankfully .That info came to me by reading threads on capacitors in microwave machines. so I look at them and that is all . The motor is all dry now but in a sorry state.

Ive never been game to try and short one out though. I don't trust just the plastic handle on a screw driver. As putting plastic or PVC between me and a charge Like on playing around with cars and motorbike engines spark plugs and just holding the insulated lead has given me a small shock a number of times. Why that happens I have no idea?? Is there a way of being double sure that a charge wouldn't get around a plastic handle to me ? Like standing on a thick block of wood as well ? A rubber mat I suppose is better?

Here's the top of the motor. It was all taped up but rolling it around in the back of the ute positioning it had it all come loose.

It seems to have two capacitors and something joining them that is pointing away in the picture. Two capacitors, that's another thing Ive never seen before on motors. Has that to do with the hard start compressors go through pushing the piston and air ?

IMG_4276a.jpg

Rob .

Originally Posted by jack620

Very odd. Are you absolutely certain it was running in the correct direction at the seller's house? Any chance he just bunged that motor on it to sell it without confirming it ran the right way?

Yes Jack I'm certain. He had it cutting wood in front of me and it had to be running to the right to do that. And I rang him and double checked once I saw what was happening here. I thought there may be a chance there was a small reversing switch I hadn't come across in all that mess on top as I wasn't doing any poking around in there as I had been running it . I'm about to load cutter pictures in the thread I put up on the machine here if you want to see machine pictures un related to electrical problems.

F Berry and Sons Sowerby Bridge Yorkshire Lathe

Rob

Originally Posted by auscab

He had it cutting wood in front of me and it had to be running to the right to do that.

OK, well I'm stumped. I'll be watching this thread with interest!

I couldn’t get the motor to go the right way by spinning first and adding power as it was still spinning. Tried many times and it just spun left.
Problem has been solved by going out to my motor stash and coming in with a 2 HP 3 phase motor that had the same pulley size and two of the mounting holes lined up exactly! And the belt tension was exactly the same as the previous motor! How often does that happen? The motor used to belong to my Wadkin Bursgreen table saw which I upgraded to 3 HP years ago. Now I can do some test cuts. You ever had a mate with a few beers in him telling you off for all the so called “rubbish “ that you were shifting when you moved house. How many hundred did that just save me . Good on the hoarders I say .

IMG_4292.jpg

Rob .

there are motors with 'start capacitor' and 'run capacitor'.
a picture of the nameplate on the motor may help.

i was wondering if a failed run cap would result in backwards running but i've forgotten the little i knew of the intricacies of those exotic things.

but i think your solution is probably better overall given the state of it and the symptoms.

russ