Reversing an electric motor

[Tuba Dave]

I want to put a 3/4 hp motor on my bandsaw (woodworking type). I have a Marathon electric that I have been using for 25 years as a bench buffer. I would like to reverse the polarity to run it the other way to drive the saw without modifying the table, etc.

I have used it for years as purchased new. This is a dual voltage motor, and it has been running on 230v. I opened it up, reversed the two leads as directed on the label, plugged it in and it tripped the breaker. I have 120v in my shop, and have used this motor on 230, but I wired it up for low voltage, reverse polarity, and it still trips the breaker.

I switched the polarity back to low voltage, original direction, and it works fine. Back to hi voltage, original direction and it works

So I have a motor that works fine wired to run CCW on either hi or lo voltage in a 120v shop. According to the label, I can reverse the polarity to make it run CW. However, neither hi nor lo voltage with reversed polarity will work.

I did install a new power cord on this. Does it matter which is Line1 and which is Line2 (black or white from the wall)? If so, why does it work one way and not the other? I thought AC switched direction all the time.

Any idea what is going on?

BTW in the picture of the wiring, starting from the bottom left and going CCW, the studs are #1, #4 (across the bottom along the red wire), #3 (with black, orange and white attached), and #2 is hiding behind the ground. The screw in the middle is not involved

 

[markba633csi]

You must be either mis-connecting it, or possibly creating a short when you put the cover on.
It has to be one of those two. I suspect the former since it runs in one direction. Third possibility is a factory error on the diagram.
Are sure you are identifying the terminals correctly? I really can't tell from the photo which is which
Let's try this: Put it back to the way it works and snap a picture, close up. Preferably 120 volt (low)
-Mark
ps no it doesn't matter which is line 1 and line 2

 

[Tuba Dave]

I am not replacing the cover

I have switched the wires several times and it works only on one polarity. I have followed the diagram, and it works one way so I know I am identifying the terminals correctly. There are numbers printed on the cardboard lining.

I have a feeling this was never intended to run CW. Or there is a problem with the label. There is no difference internally in the structure between CW and CCW, and it works one way, so I am assuming all the connections etc internally are OK. The only thing that changes is the way the electricity flows. Unless there is something here I don't understand (100% possible -- my skill with electricity ends at the wall socket)

Physically, there is a difference between the high and low voltage wiring, but again, both structures only work with one polarity.

(Fully demonstrating ignorance, he asks ... ) Does the capacitor care at which polarity the thing is set? Maybe a fault there would stop the "starting" spin before the velocity switch kicks in. I forgot to mention the shaft spins easily by hand in both directions.

My SIL (a professional electrician -- he is also stumped) is tracking down the manufacturer to see if he can get a schematic of this motor. He has never seen a diagram like this, he thinks there should be 6 terminals, not 4.

 

[Flyinfool]

+1 on are you sure you are numbering the terminals correctly?
Are the 3 wires with the yellow crimp on terminals the line wires coming in? Are you sure? Mixing up the black and white line wires with the black and white motor wires could likely cause the issues you are having.

Can you include pics of the wiring in a working condition and a pic of the cardboard lining with the pin numbers?

 

[Tuba Dave]

OK problem solved. I noticed red was grounding out. It has been pointed out to me that red and black, the power leads, will be hot in one polarity and neutral in the other. There is a pretty nice dent on the capacitor cover. I removed it and noticed it was the red lead going to the cap. Wired to run CW in low voltage without the cap cover BINGO!!

When Red was neutral, no problem. When reversed, and red became hot, it was grounding out.

Thanks for all your help!

I can take the dent out of the cap cover (I remove dents from musical instruments all day!) and I'll be up and running this afternoon!

 

[brino]

Great trouble-shooting!
Thanks for letting us know.

-brino

 

[markba633csi]

There you go! I was correct, sort of, it was a short and possibly a shock hazard prevented
-Mark