Arcing relay on single phase cap start AC motor

[laker]

I have a problem with a 1.125 HP 3450 RPM 120V single phase capacitor start w/relay AC motor used on woodworking equipment. The stock RBM SPST NC double make contact relay opened and not being able to find an exact replacement I replaced it with an Omron SPDT 25Amp with single make contacts. I also replaced the start capacitor 161-193 UF. The problem I have is a slow/no start under load which seems to be caused by severe arcing of the relay contacts. They arc on starting and after the motor gets to speed when the relay is deenergized. Soon the contacts become pitted and the start becomes even worse. When I start the motor with just the capacitor in the circuit it starts fine--but of course the start winding remains in the circuit using lots of current (40A). Any suggestions?

 

[SteveKW]

#1. Don't start it under load.
#2. Get larger contacts or go to an electronic start switch.
#3. It would probably work better if the relay was NC and then energized to open the contacts.

 

[jbartos]

Suggestion: Considering that the existing relay has NC contacts, then another solution could be to apply a 1.5 HP motor under an assumption that the existing motor has a relatively large mandatory load at the start.

 

[buzzp]

You need to find a relay with a pilot duty rating equivalent to 1.125HP @ 120VAC. If this is what you have and still have problems then do as suggested, dont start under load or buy a larger pilot duty rated relay for this application.