[bigalow]

I have a Bodine 1/8hp motor and an SCR drive. I have only a speed reference pot 10K for an input. I dont have a FRW or REV otption. I need to reverse the motor every 2 sec.
I was going to use a 2 HD relay's with Silver contacts to switch the output polarity of the drive.
I need rec of type of relay that could withstand this extreme duty switching.
I figure the contacts will arc and limit the life of this simple solutiion?

[Al_The_Man]

You could use DC switching relay with magnetic arc blow-out such as the P&B PRD-11DH0- style.
For that kind of duty cycle my preference would either be a 4 quadrant SCR drive which gives you ±10vdc input capability for FWD/REV with one pot.
Or one of the PWM servo drives off ebay such as Advanced Motion 25A8 or B15A8.
Also SCR drives when fitted with a reverse switch have a stop that prevents moving from full forward to reverse and vice-versa.
It is best to allow the motor to accelerate through the drive, not bang it directly in the opposing direction at full voltage.
Al.