Shopsmith Forums

I have an old mark vii with an AO Smith motor that had a bad start relay. I replaced it with a new supec. It starts ok now but I'm not entirely satisfied with it.
I'm investigating replacing it with an oem or one that I can cross reference but I can't find my part # anywhere online. There are alot of potential/start relays on ebay. but I don't know exactly what is comperable spec-wise to my RBM ?.
I've attached a pic of my old relay and a pic of a White-Rodgers relay part #'s w/ specs.
thanks, lenny

I mispelled it. I replaced it with a Supco apr5.

What is it that you are not satisfied with?

The spec sheet indicates to me that it should be capable of being set to operate correctly.

And thank you for 'discovering' it.

It starts cold fine. If I wait 4-5 minutes to restart, it start fine.
But if I try to start right away after a quick adjustment (say 30 seconds to 3 minutes) it buzzes for almost a second before it starts.

lahola1 wrote:It starts cold fine. If I wait 4-5 minutes to restart, it start fine.
But if I try to start right away after a quick adjustment (say 30 seconds to 3 minutes) it buzzes for almost a second before it starts.

Where is the knob set? Have you tried to determine where the threshold(s) be.

It is set at about 220v. I tried it at a couple different places but didn't seem to make any difference so I left it there. Do you know what it should be set at?

I only have a working knowledge of electricity. My dad was a maintenence electrition for 3M for over 30 years, I wish I had listened to him more.

I have 0 experience with that relay, but I would seek a proper setting as follows:

Set it up so that you have access to terminals for the relay coil(Terminals 2 and 5).

I am assuming you have an AC voltmeter(Dad's tools?).

Get the motor running and measure the AC voltage across the relay coil terminals(2,5).

Set the start relay knob to one mark below that reading.

This may not eliminate the 'problem', but it will at least set the relay to match the motor.

It may be that the relay's internal circuitry has a slow decay after the motor is turned off. Not a problem with refrigeration duty cycle. Tis a nuisance with a SS.

No, they're my tools.
I can't access the terminals without dismanteling the headstock or at least dropping the motor pan.
I tried turning the POT on the Supco and the dopey thing just pushed in so I may have to dismantle anyway this weekend.
What is that voltage I'm trying to read across 2 and 5; the changeover from start to run capacitor?

As far as my original question goes, with your understanding of electricity and motors, is there any relay on the White- Rodgers chart I posted similar to what ths motor would need; such as the 90-63. If not, do you know what these specs should be for this motor?

The reason for measuring the voltage developed when it is running full speed is to determine a reliable setting for when the relay picks and opens the start circuit. You want it to disconnect the start circuit when it APPROACHES the run voltage(slightly below the run voltage). I am assuming one mark is reliable.

There is no way to adjust the drop out voltage(as it coasts down to a stop). I believe the circuitry is sluggish in that regard and interferes with starting when restarted too soon. I am somewhat surprised that it works at a 220 setting. I would not have expected the voltage to be that high.

With a run voltage measurement, we stand a better chance of selecting a white-rogers relay that will work.

I dropped the motor to acess the start relay. On closer insp I found it was set at about 240v (just FYI).
The running voltage at 2 and 5 is 267v.

Also FYI the 1st time I turned the motor off it took a coule minutes to decay back to 0 v.
Every time after when I turned it off, volts when to 0 v fairly fast all tho it when to OL (600v)1st and then decayed to 0v.

if that means anything or not, I don't know.
I reset the POT to approx 200v and tried a quick restart; still had a slight delay even with no load on the motor.

Let me know what you think.
Thanks, Lenny A.