AC Relay for Router Starting

[Plugger]

I would like to automate my design a bit more...

I have a 3.25 hp Porter Cable router - 120V, 15Amp

I believe, when the router starts it draws up to 5 x the current. So, does this mean I need a relay capable of handling 75Amps??? (15Amp x 5 = 75 Amp)

I looked at solid state relays in this amperage range and the cost started getting up there. Could I use a coil relay in this range with a diode across it to allow the inductance-caused back emf out??? Or, do I need a contactor?? What's the difference -- relay, contactor , motor starter???? It seems to be a gray area that depends on the motor size.

Thanks!

[Al_The_Man]

A contactor is a bit more rugged than a relay and usually set up for three phase switching complete with auxiliary contacts for interlocking or retaining etc, they also have the allowance for an overload to be attached.
You can pick up contactors fairly cheaply on ebay, new they are typically $300.00.
For a relay, you should be able to use the P&B PRD series, they have AC or DC coils and go up to 30amps.
They are reasonably priced around $30.00.
If you get the double pole, you can parallel up the contacts.
Al.

[WayneHill]

Plugger,

My CNC router uses two relays to start the variable speed router motor. The first contactor was too low amperage for motor. So I wired in a second higher amperage relay that triggered from the first relay.

Steve Stallings of PMDX told me one time, 'Do not to use solid state relays with variable speed motors'.

my $.02

[Boltz]

I've been reading up on inverter drives for my vacuum pump, and those transients from a vfd can be pretty wicked.

I think the best bang for the buck would be an air conditioner relay.

I have an older window air conditioner with electromechanical control, and I wanted it to rig it up with a real thermostat, such that it would turn completely off when it got down to the setpoint.

A little searching on ebay turned up a single pole 30 amp relay for AC use for about $15, and a nice steel box to put it in for about $12. Both parts SquareD, brand new. Maybe 40 bucks total with shipping. Robertshaw line voltage thermostat for about $15.

Anytime I'm switching more than 5 amps and doing it several times an hour or more, I like to have a steel box around it. I've seen some pretty scorched contactors.

-Jim Hart