Reply to Thread

Could I ask what the part/model number is on the motor?

Beta

I remember trying to free stuck compressors by running them backwards with capacitors.

Originally Posted by Capz

I called Grainger/Dayton motor tech service the other day. While the original oem cap was no longer available, he suggested a 20uF, 370vac Grainger part to go with the Dayton motor. Claimed the faulty original was a run cap and not a start cap.

I installed it today and it runs perfectly. No need for new motor. BTW, I checked the voltage on the cap leads prior to installing. I saw 200vac continuous. Voltage never dropped out.

I had it running this week without any capacitor but motor would hesitate on start up and with each start it would change direction CW--CCW. With new cap it starts and runs correct direction with each start.

Originally Posted by lytning

20 seems a bit low for a start and a bit high for a run. Probably by the time you get all done it will be cheaper to just replace the motor.

I called Grainger/Dayton motor tech service the other day. While the original oem cap was no longer available, he suggested a 20uF, 370vac Grainger part to go with the Dayton motor. Claimed the faulty original was a run cap and not a start cap.

I installed it today and it runs perfectly. No need for new motor. BTW, I checked the voltage on the cap leads prior to installing. I saw 200vac continuous. Voltage never dropped out.

I had it running this week without any capacitor but motor would hesitate on start up and with each start it would change direction CW--CCW. With new cap it starts and runs correct direction with each start.

Originally Posted by ECtofix

I've only seen a few fan motors that DON'T have an external start cap. I assumed that those had an internal cap. I may be wrong on that, since a phase shift can also be created by other means. However, in refrigeration & HVAC applications, a capacitor is nearly always present.

For any single-phase motors, a phase shift creates an electrically rotating magnetic field. Three-phase motors already have that, so no additional components are necessary to trick it into rotation.

The start components get a single-phase motor rotating... AND rotating in the right direction. A centrifugal switch (or a start relay on heavier loads like a compressor) removes the capacitor and the motor's start winding from the circuit once operating RPM is achieved.

Are certain you're installing a properly rated capacitor for that motor? Otherwise, like others have said, the centrifugal switch in the motor may be faulty.

I removed the original 20uF +/-, 250v, installed a 21uF-25uF, 250v. The exact replacement is not available as already stated. Thanks for you response.

20 seems a bit low for a start and a bit high for a run. Probably by the time you get all done it will be cheaper to just replace the motor.

Originally Posted by Capz

I wasn't sure where to post this but since it is used in a commercial kitchen, figured I hit the refrig gurus. I have a problem I have never seen. I have a small Dayton blower motor used in a Giles vent less hood which will melt the start cap.

Details, small approx 1/4 hp Dayton blower motor, 115/230v wired for 230, data plate 3.7 amps @ 230v, uses a 20uf, 250vac start cap. Last week it melted the original, today I installed a generic Dayton 21-25uf 250vac replacement. (Original oem part made by other than Dayton no longer available at Grainger nor Giles). The generic replacement popped & melted in 5 mins. BUT the motor runs perfectly, no bearing noises, pulls 2.1amps, will start WITHOUT the start cap installed and the unit is working.

The actual line input volts is 249vac. Little high but I can't see this being the issue. I didn't think to check at the actual volts at the cap terminals at the time. But if this motor is running cool & quiet, what can cause this issue? I'm gone to check the volts at the terminals with the motor running, maybe install a 330vac, 20mf start cap.

Is this motor defective? Any ideas?

agree- if you have relay or centrifugal switch its not releasing start winding after start up. also sounds like run cap from rating

I've only seen a few fan motors that DON'T have an external start cap. I assumed that those had an internal cap. I may be wrong on that, since a phase shift can also be created by other means. However, in refrigeration & HVAC applications, a capacitor is nearly always present.

For any single-phase motors, a phase shift creates an electrically rotating magnetic field. Three-phase motors already have that, so no additional components are necessary to trick it into rotation.

The start components get a single-phase motor rotating... AND rotating in the right direction. A centrifugal switch (or a start relay on heavier loads like a compressor) removes the capacitor and the motor's start winding from the circuit once operating RPM is achieved.

Are certain you're installing a properly rated capacitor for that motor? Otherwise, like others have said, the centrifugal switch in the motor may be faulty.

I' m thinking along the same lines too. May not be necessary. Guess i could run a cord and manually test the motor wired at 115 to see if it'd start or not without a cap.

Even though a fryer hood, no fryer grease in/on the motor. It's very clean and sealed off from the grease.

I think you may be on to something Hurtin. The cap may only be necessary for 115v application.

Is this a totally enclosed motor or open? I'm thinking grease + open with centrifugal switch = stuck switch and blowing caps.

Originally Posted by hydra

Correct me if I'm wrong, but isn't a 20uF a run cap not a start cap?

It's unclear. The specs for the replacement cap he listed was a range, 21-25uF. This would indicate a start cap as run caps typically have a fixed value.

Does it have a bleed resistor across the terminals? Not sure if the smaller start caps have one. The larger ones, for a capacitor start, capacitor run compressor all have bleed resistors and will be in the 80 - 108+ uF range...

The curious thing is such a small, light duty motor with a cap at all. I'm wondering if it needs a cap at all when wired for 230? Maybe the cap is intended for use with 115 only and it just happened to work for a few/four years until it finally melted the cap?

Thinking this as he stated it runs nice and cool without cap?

Correct me if I'm wrong, but isn't a 20uF a run cap not a start cap?

Originally Posted by Capz

Grainger using the blower assy parts listed it as a start cap. But I am not 100% sure it is a start cap other than what the Dayton parts break down states. I did plan on trying to use a run cap too in order see how it reacts. The cost is under $10. BUT, how is this motor running WITHOUT the cap if it is a run cap? remember my first post, the motor currently will run without the blown cap wired up.

What exactly is EMF? How high can EMF voltage get in a 240vac set up?

Back EMF...voltage generated by the motor and, by design in some set ups; used to take the start cap out of the circuit.

Back electro motive force, if I recall the specific term correctly.

i can only think of the start switch is staying on for too long to pop the start capacitor

Originally Posted by MicahWes

Are you sure this isn't a run cap? It is unusual for motors in low-torque starting applications like a small direct-drive motor to apply a start cap. Also, remember that the voltage rating on the cap is for back EMF purposes and has nothing to do with line voltage.

Grainger using the blower assy parts listed it as a start cap. But I am not 100% sure it is a start cap other than what the Dayton parts break down states. I did plan on trying to use a run cap too in order see how it reacts. The cost is under $10. BUT, how is this motor running WITHOUT the cap if it is a run cap? remember my first post, the motor currently will run without the blown cap wired up.

What exactly is EMF? How high can EMF voltage get in a 240vac set up?

Yeah...depends on the motor set up. Is it in fact a capacitor start induction run motor with the start cap hangin' in too long due to a centrifugal switch not taking it out?

Since you gave a range of uF ratings I have to assume it is indeed a start cap...and with a very low VAC rating of 250V I would also guess a centrifugal switch. A start relay like a potential relay or a current relay would need much higher BEMF needs to take the start cap out.

I'm in the wrong neighborhood...but curious to learn the outcome.

Are you sure this isn't a run cap? It is unusual for motors in low-torque starting applications like a small direct-drive motor to apply a start cap. Also, remember that the voltage rating on the cap is for back EMF purposes and has nothing to do with line voltage.

If the start switch sticks closed only sometimes, it will blow the cap. in a short time.

So is there a centrifugal switch in the motor? When the motor gets up to full speed the centrigugal switch takes the capacitor out of the circuit?

If it blows the cap in 5 minutes, I would put a new cap in and do an amp draw, see if it is pulling amperage for an extended period of time. Maybe motor is slowing down, or centrifugal switch is cutting in and out.

Thanks caheiman, yes I confirmed the wiring is correct. 2x. The motor is original from new in 2009. This is a small hood above a fryer with a direct drive motor blower in the hood..

I use 3/4hp motors on the roofs for oven hoods & make up air. No start caps either.