Using a 3-Way Contactor Switch as a DPDT

[Namako]

I'm scratching my head trying to figure out if I can somehow wire up a 3-position selector switch (e.g., some combination of NO or NC) as a DPDT to control a reversible 120VAC 1/3hp motor on my mill.

I use these switches to control other elements in my system, and I'd like to maintain the look...

Does anyone with more electrical experience than I have any thoughts?

 

[alien]

You can add extra NO and NC contacts on the bottom. As many as you need. I would suggest 4x NO total.

 

[Namako]

Yeah, my thought was there was maybe some combination of NO/NC contacts that might allow me to emulate a DPDT, but I'm still scratching my head on what that combination is, and then there's the wiring...

 

[tophmck]

Re: the combination of contact blocks you need, what are you confused about?

You say a 3 position switch, so you want center off -- is that right? If so, alien hit the nail on the head. You want 2 NO on each side, so 4 NO contact blocks total.

If you don't want center off, then you'd use a 2 position switch instead, in which case you'd use 2 NO contact blocks on one side and 2 NC contact blocks on the other.

 

[Namako]

Re: the combination of contact blocks you need, what are you confused about?

You say a 3 position switch, so you want center off -- is that right? If so, alien hit the nail on the head. You want 2 NO on each side, so 4 NO contact blocks total.

If you don't want center off, then you'd use a 2 position switch instead, in which case you'd use 2 NO contact blocks on one side and 2 NC contact blocks on the other.

No, I'm trying to wire a reversible AC motor to run forward and reverse, with center off. I guess I'm more visual... A normal DPDT toggle switch has 2 banks of 3 terminals, or maybe more correctly, 3 banks of paired terminals. NO/NC contacts only have a pair of terminals. So, do I stack three of them? And of so, how to stack them? It doesn't seem possible.... But then again, I'm electrically-challenged at times.

 

[tophmck]

Again, you need a total of four NO contact blocks.

Regarding how to wire it, let's start with a SPDT switch with center off. For this you would need 2 NO contact blocks, one on each side of the switch. On one end of the contact blocks, you run a wire from the one to the other. Voila, you now have a SPDT switch with 3 terminals!

To make it a DPDT switch, you just add another pair of NO contact blocks, one on each side of the switch, and do exactly the same thing -- run a wire from one to the other.

Make sense?

EDIT: Out of curiosity, what's the motor you're using?

 

[Namako]

I'm trying to hook up an old 1/3hp Delta Milwaukee Band Saw Motor (NF-60A040) I pulled off of eBay, running it through a Baldor 10:1 speed reducer to a Monster Mill, hence the need to be able to reverse it.

The motor clearly states that it is reversible, but doesn't offer a wiring diagram on the label. There are two wires (black, white) that come forward from somewhere deeper within the motor, out to two terminals mounted on a PCB that can be easily seen when the cover plate is removed.

The current switch (SPST) is mounted through a hole in the motor's case, and is wired in-line with the load wire (simple on-off), so the motor is not currently wired to be reversible.

I'll play around with 4 NO contacts, and see if I can't electrocute myself over the next couple of days

 

[Namako]

What would we do without weekends??

OK, sometimes I need someone to slap me upside the head and repeat over and over... "listen to what I said!!!"

I thought about the 4 NO contacts, and finally decided to try and flip my thought process 90 degrees... gee, NOW I GET IT!!!

I drew up a schematic so I wouldn't slip back into my box... see if this accurately reflects what you were telling me...

Thanks for sticking with me, tophmck!!

 

[tophmck]

Yep, I think you've got it. If the engine can be reversed by flipping the polarity, that should do it. The only thing I'd add is that you don't really need separate terminal blocks, since you can just use the terminals on the N.O. contact blocks to make your connections. I hesitate to draw diagrams, since I'm no engineer and don't know exactly how things are supposed to be drawn -- but something like the attached.

Good luck!

EDIT: Also, have you confirmed that you can reverse the motor simply by swapping the polarity? I'd check this before you order the parts for the switch, as this isn't the case for many motors.

 

[Namako]

As it happens, my motor states that all I have to do is switch em, and it'll reverse directions. I haven't actually tried it yet, but I'll run with the label for now. As for the terminal blocks, yeah, I get a little carried away at times... I hate wire nuts!!! . Thanks for the (had to be repeated because I'm dense) input! Now off to put it into practice.