contactor for DC control

[roger wiegand]

I've finally gotten fed up with the on again-off again (or more often, neither on nor off without standing on one foot while reciting Jabberwocky and pressing the button "just so") performance of the radio control switch I have on my dust collector. I want to replace it with hard-wired switches located in 3-4 positions in the shop, wired with 4-way switches so that the collector can be turned on or off from any switch. This has led me to the world of "contactors" for remote control of motors.

My DC has a 3hp 240v motor and runs happily on a dedicated 20 A circuit.

I think that what I need to control it is a 2-pole contactor rated for a 3hp single phase 240 V motor with 120 V control circuit.

My question is that as I look at devices that seem to be described in exactly the same way the prices vary from $12.99 to over $600, and I don't have a clue what distinguishes them. Models that are called "motor starting contactors" seem to run about 5x the price of "definite purpose contactors", but I haven't found a description of how these differ from each other. The cheaper ones give motor horsepower ratings, giving the appearance that controlling a motor might be a possible "definite purpose".

Anyway, I'd appreciate if someone can enlighten me as to which I should use. Thanks!

[Rod Sheridan]

Hi Roger, definite purpose contactors are typically lighter duty than a motor starting contactor.

One of the main differences will be in the ability to handle high locked rotor currents when starting motors.

Your dust collector probably doesn't have very high locked rotor currents.

I would recommend the 30 ampere contactor as it can handle 180 amperes of locked rotor current which should be larger than your application.

Here's a chart for a typical definite purpose contactor.

Contactor.PNG

Regards, Rod.

P.S. I use them in my shop for machinery starting as well.

[roger wiegand]

Thanks. Sounds like if I get a definite purpose contactor I should be fine-- I think you just saved me a bunch of money. I'll probably skip the really cheap Chinese ones on ebay on general principles.

[Jim Becker]

I bought mine at a local electrical supply shop...probably was about $30 or so at the time. I forget the exact price, however.

[Curt Harms]

This will give you a place to start.

https://www.mcmaster.com/#definite-p...ctors/=16a5bft

I bought a definite purpose contactor from Grainger years ago. I control it with one centrally mounted switch. Wireless controls are really cool -- if they work and if you don't lose the controller. It's also possible to control a contactor with a wireless controller, that way the wireless circuitry is controlling a small load, likely in the milliamp range.

[Chris Padilla]

I think I bought a Cutler-Hammer definite purpose contactor off eBay for around $20-30 to build my remote controller. It has a 120V coil to control a 240V/30A circuit. FWIW, I found a Stanley brand remote lamp control module and it has been going strong for me for 5+ years and likely longer. Before that one, I went through 2 of a particular brand (don't recall) before finding the Stanley. I can turn m DC off/on from 30' away with no problem. Honestly, I'm surprised how long and how solid this control module has been for me.

If you're going hard-wired, you'll need two 3-ways on either end of your circuit and then put as many 4-ways in the middle as you want.

[roger wiegand]

Thanks, I actually ordered one from McMaster a couple hours ago!

This will give you a place to start.

https://www.mcmaster.com/#definite-p...ctors/=16a5bft

I bought a definite purpose contactor from Grainger years ago. I control it with one centrally mounted switch. Wireless controls are really cool -- if they work and if you don't lose the controller. It's also possible to control a contactor with a wireless controller, that way the wireless circuitry is controlling a small load, likely in the milliamp range.

[Bill Dufour]

I would buy a good american brand name motor starter from ebay. Cost under $50 delivered. This will have overloads to protect the motor. Get one that is adjustable amp rating so you do not have to buy heaters(extra money) sized for your motor.
Also you need to decide on control voltage. common is 240, 120, 24 get one with the correct coil voltage you will be using. 120 is called low voltage controls. anything below that requires a transformer and a place to mount the transformer.
Bill

Sqaure D. or Allen Bradley are just two good brands.

something like this buy more amps
http://www.ebay.com/itm/Allen-Bradle...AAAOSwcLxYIin4

[roger wiegand]

The model from McMaster cited above is installed and working perfectly with a 120V control circuit. I think it was a Siemans. I wish I'd done this years ago rather than fighting with the radio control.