Is it possible to "soft start" this single phase motor?

I work at a bean-to-bar chocolate factory, and frequently use a vibratory sieve (the cylindrical silver thing on the table):



There is a junction that attaches the vibrator mechanism to the single phase motor:



and is supposed to use three of these [pretty expensive] special rubberized bolts; but those break more often than we prefer (every few months) likely from the torque/ stress of the abrupt start up of the single phase motor.

So instead of using the rubber bolts, we have simply been using zip ties like so:



Which works just fine, but these also break/ need to be replaced about once a month. It is an easy fix, but I got to thinking.. It would be nice to figure out a way to soft start the motor (or use some form of VFD); so that this vibratory mechanism undergoes less stress upon start up. This way we could use the original rubber bolts instead of zip ties, too.

Here are the motor's specs:



115 V | 60 Hz | 4.0 Amps | 3430 RPM | 1/3 HP

And here are some other doo-hickies that look important:



I admittedly know very little about motors/ electronics; but I'd like to try to find a possible solution to this issue so that I can propose it to my employer.

Thank you!

The oldfashion way is to give the motor more mass
So bolt a steel disk to the lower flange

Peter

The motor shown is a Capacitor Start Motor. It is not designed to "soft start".

You have a coupling issue.

Solve your problem with a better coupling.

John

What John said. You can get a Lovejoy coupling from virtually any supply house either with the correct shaft bores or one you can bore to size.

I waited to see what others said before posting. I agree that it appears to be a capacitor start with a potential relay instead of a centrifugal switch. I think it might be possible but I am sure the designers didn't intend it and I wouldn't render an opinion without testing it myself. If you used a Variac and brought up clean AC voltage, it probably would work but with any sort of pulsing system, who knows?

Bill

I'm seeing bad application of the rubber mounts.

look for a higher quality, and maybe a different configuration.

The reason you generally can't "soft start" that type of motor is that the capacitors needed to make it start are not rated / intended to be in the circuit for any length of time, they are take out either by a centrifugal switch, or as in your case, a special device called a "potential relay" (the black box next to the capacitor can). When you slowly increase the voltage (which is what a "soft starter" does), you end up stressing the capacitors because they are not rated to be in the circuit that long. In addition, the charging current of the capacitor when you first energize it will appear, to the devices inside of the soft starter, to be a short circuit and can cause them to malfunction and/or short themselves out. You could TRY it, but understand your risks; it might damage the motor, it might damage the soft starter, or both.

Another option, and maybe one to try IF that motor burns out, is to replace it with a 3 phase motor and use a VFD to power it, one that takes single phase input and provides a 3 phase output. You can use that to make the acceleration as smooth and gentle as you want it to be.

With larger permanent split motors, an option is to only put the speed controller/soft starter on the main winding, and not on the auxiliary/start. That way the capacitor doesn't see the nasty waveform.

I imagine you could do something similar with a cap start, as long as it doesn't take too long for the start switch to open.

I really appreciate this thorough "layman's terms" response, @Jraef!

Just curious: based on the photograph of the motor's specs in the OP, what would a 3 phase equivalent of the motor? How would I go about locating one of those?

d'Arsonval said:

The motor shown is a Capacitor Start Motor. It is not designed to "soft start".

You have a coupling issue.

Solve your problem with a better coupling.

John

Click to expand...

Yup. Redneck way is to bolt one flange through the sidewall of a truck or tractor tire, the other flange through the opposite sidewall.

I DEFY you to wear that rig out with but a one-third HP motor, even if size restricts you to a taildragger aircraft landing-gear tire!

Mought last a long time even with a good grade of reefer-dolly tire?

DO let us know if you FIND sech of a critter as a decent reefer-dolly tire. Seem to have gone extinct, if not also stinkey, those have.

thermite said:

Yup. Redneck way is to bolt one flange through the sidewall of a truck or tractor tire, the other flange through the opposite sidewall.

I DEFY you to wear that rig out with but a one-third HP motor, even if size restricts you to a taildragger aircraft landing-gear tire!

Mought last a long time even with a good grade of reefer-dolly tire?

DO let us know if you FIND sech of a critter as a decent reefer-dolly tire. Seem to have gone extinct, if not also stinkey, those have.

Click to expand...

You are on to something there!

Somewhere in these cobwebs of my old memory I have seen something like your talking about that used a belted rubber as the misalignment/absorbent for a shaft connection. I may have seen something in my earlier years that used multi layered pieces of heavy canvas rather than rubber belting.

Since those zip ties seem to last a while, I don't believe it is so much starting up, but the vibrating bowl that is the real problem.

Something along this line is what I am thinking however, there may be something even better off the shelf.

tmt said:

You are on to something there!

Somewhere in these cobwebs of my old memory I have seen something like your talking about that used a belted rubber as the misalignment/absorbent for a shaft connection. I may have seen something in my earlier years that used multi layered pieces of heavy canvas rather than rubber belting.

Since those zip ties seem to last a while, I don't believe it is so much starting up, but the vibrating bowl that is the real problem.

Something along this line is what I am thinking however, there may be something even better off the shelf.

View attachment 279786

Click to expand...

Small as this device is, you could probably just use a single flat sheet of cord-in conveyer belting, one set of holes spaced in between the other.

Or loop it. But the small tire does all that FOR you...

what hapens if you use a smaller start capacitor?