Baldor motor capacitor start vs potential relay question

spdjnky_42 · Mar 27, 2015

Hey guys been a while. Always seem to get good advice here. Have another question for you. I am looking to buy a buffing wheel with some decent power. New Baldor units are about $400. They are only around 3/4hp. I found a guy with a handful of 115/230v units. They are old Baldor 1250 models. They are 2hp and run on either 110v or 220v. He is asking $350 which is fair since they are $1500 new. He has one he says just uses a capacitor to start. Then he has three that use a potential relay to start. However, the potential relays need help to work. I know how to bypass the relay for a split second to test for bad relay. What is your opinion on the older model vs the units with the potential relay? Unsure which to buy. TIA

sch · Mar 28, 2015

Just curious, are these 3 phase motors with variations on the static converter idea to run on 1 phase power?

L Vanice · Mar 28, 2015

sch said:
Just curious, are these 3 phase motors with variations on the static converter idea to run on 1 phase power?

Both types mentioned are capacitor start single phase motors. I think the potential relay is an alternative design which replaces the commonly used centrifugal switch.

Larry

neilho · Mar 28, 2015

As Larry wrote...

The potential relay is just a more modern way to start the motor. Cheaper than a centrifugal switch, and easier to replace, too.

jim rozen · Mar 29, 2015

"However, the potential relays need help to work."

What kind of 'help?'

Do the motors start well on 240 volts but not on 120?

I have seen cases (in particular Leroy Somer motors - french company - who set
their motors up as dual voltage but do not change the start circuit when they switch
voltage. The potential relay start circuit as configured for 240 works poorly when
the motor's properly configured otherwise to run on 120) where the engineering
on potential relay circuits is not correctly and the potential relay chatters when
starting the motor on the lower voltage.

If the potential relay is indeed chattering when it tries to start the motor
on the lower voltage setting, then there's an easy fix for the problem. If that
is not the problem something else is wrong and that bears investigation.

GeoD · Mar 29, 2015

At least some potential relays only work if mounted in the correct orientation. Gravity on the plunger is part of the design.

Newman109 · Mar 29, 2015

GeoD said:
At least some potential relays only work if mounted in the correct orientation. Gravity on the plunger is part of the design.

That's correct and, of course, the potential relay must be matched to the voltage that it is to run on. The ones that I have are 240 volt Steveco/White Rodgers 90-66. They are designed to pull in between 208 and 239 volts and they drop out at 130 volts. They are not dual voltage.

jim rozen · Mar 29, 2015

"They are not dual voltage. "

Please tell THAT to leroy somer. And pfeiffer vacuum as well....

Newman109 · Mar 30, 2015

jim rozen said:
"They are not dual voltage. "

Please tell THAT to leroy somer. And pfeiffer vacuum as well....

You also said:

Do the motors start well on 240 volts but not on 120?

I have seen cases (in particular Leroy Somer motors - french company - who set
their motors up as dual voltage but do not change the start circuit when they switch
voltage. The potential relay start circuit as configured for 240 works poorly when
the motor's properly configured otherwise to run on 120) where the engineering
on potential relay circuits is not correctly and the potential relay chatters when
starting the motor on the lower voltage.

If the potential relay is indeed chattering when it tries to start the motor
on the lower voltage setting, then there's an easy fix for the problem. If that
is not the problem something else is wrong and that bears investigation.

Not sure what you mean here. You comment is sort of cryptic since I don't know Leroy Somer or Pfeiffer Vacuum. I was merely referring to the Steveco (White Rodgers) 90-66. The box and instructions clearly state that it is for 240 Volt operation.

Lakeside53 · Mar 30, 2015

L Vanice said:
Both types mentioned are capacitor start single phase motors. I think the potential relay is an alternative design which replaces the commonly used centrifugal switch.

Larry

There is one type of Baldor that uses a three phase motor and simply has a capacitor between two legs to induce a phase shift sufficient for starting the lightly loaded motor. I have a 3/4 hp Baldor set up (factory) this way. No centrifugal switch and simple for their manufacturing. I haven't seen this on their 1.5 hp models though.

L Vanice · Mar 30, 2015

Lakeside53 said:
There is one type of Baldor that uses a three phase motor and simply has a capacitor between two legs to induce a phase shift sufficient for starting the lightly loaded motor. I have a 3/4 hp Baldor set up (factory) this way. No centrifugal switch and simple for their manufacturing. I haven't seen this on their 1.5 hp models though.

I am surprised that a three phase motor would need a phase shift to start.

Larry

jim rozen · Mar 30, 2015

"Not sure what you mean here. You comment is sort of cryptic since I don't know Leroy Somer or Pfeiffer Vacuum.
I was merely referring to the Steveco (White Rodgers) 90-66. The box and instructions clearly state that it is for 240 Volt operation. "

A minor rant. The french motor manufacturer Leroy Somer uses that relay in their motors, but configure the start windings for
120 volt operation using that relay. It doesn't work well. They botched the engineering. I had to unwind that to get the pump
to start reliably.

When pressed closely as to why their pumps did not work on 120 volts, the tech said "most folks get those running somehow and
just never shut them off.....

Hence the minor rant above.

Bill D · Mar 30, 2015

I have an old Stanly grinder that has a capacitor but no switch. I think it is called capacitor run. It is slow to get to speed. I had another with a bent shaft and a bad cap that ran fine if you spun it by hand to get it going in the correct direction. that model was made from 1931 to 1937. No idea if the internals changed
Bill D.

spdjnky_42 · Apr 3, 2015

Thanks guys I bought the older unit without the potential relay, as it worked with no issues. Does hooking this up 240v vs 120v require rewiring inside the motor? I know everything I wire nowadays does not but I am not sure on this. Also does the overheat limit switch require changed on 120v vs 240v, does anyone know? The manual mentions it, but doesnt go into detail. And the manual is about two decades newer. Baldors rep is about 2 dacades younger than that LOL

Lakeside53 · Apr 3, 2015

The wiring changes are in the bottom mount. If it really is 2hp, that exceeds the typical 120v 15 or 20 amp supply. You "might" get away with it on a 20 amp circuit 'cos 2hp developed is heavy grinding; all depend on the startup loading. Yes, you will need to change the thermal overload as the current is 2X on 120.

If you can still read the motor plate, from the model, spec and serial number Baldor can supply you with the exact schematic and component details. They did this for an old 1960's grinder I rebuilt, and even told me the exact manufacturing date and factory location,

Cyclotronguy · Apr 3, 2015

Not three phase with a cap that I've seen from Baldor as single phase units.. but the little 6" and 7" grinders models 612 and 712 were perminant split's. Thats like a normal cap start single phase motor, with the exception that the cap is a small value run cap, which limits current.

Cyclotronguy

Lakeside53 · Apr 3, 2015

L Vanice said:
I am surprised that a three phase motor would need a phase shift to start.

Larry

It does when you run them on single phase, which is why they add a capacitor to the smaller three phase motor on the 3/4 hp buffer units.

spdjnky_42 · Apr 4, 2015

Lakeside53 said:
The wiring changes are in the bottom mount. If it really is 2hp, that exceeds the typical 120v 15 or 20 amp supply. You "might" get away with it on a 20 amp circuit 'cos 2hp developed is heavy grinding; all depend on the startup loading. Yes, you will need to change the thermal overload as the current is 2X on 120.

If you can still read the motor plate, from the model, spec and serial number Baldor can supply you with the exact schematic and component details. They did this for an old 1960's grinder I rebuilt, and even told me the exact manufacturing date and factory location,

Thank you I will check into it. I have either (240v vs 120v) at the location. It seems to run fine on a 15A circuit. However, it is 20A 120v and a 2hp unit. Its a beast and you cannot put a load on it since its only 1700 rpm, if you tried. I can put in a 20A circuit, unless it would be better to run it on 240v?

sticks · Apr 4, 2015

1 PH? Dedicated circuit (NEMA 6-15, 6-20, etc). Use higher voltage config wherever/whenever possible. 1750rpm for 10" pad vs 3450 for 6" (sfm) or may be considered a weapon.

IMO, with a 2hp motor on a 120v 15A circuit the arbor nuts are pretty much a full load.

Baldor motor capacitor start vs potential relay question

Plastic

Hot Rolled

Diamond

Titanium

Diamond

Aluminum

Diamond

Diamond

Diamond

Stainless

Diamond

Diamond

Diamond

Plastic

Stainless

Stainless

Stainless

Plastic

Cast Iron

Similar threads