Soft start for single AC phase motor?

umnik

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I have an AC induction motor, single phase, 3 HP, 220V. Once it gets running, it consumes noticeably less than 20A. I have 220V, 20A outlet. And when this motor starts it frequently trips circuit breaker on motor startup, but never, once it got running. Obvious resolution is to install 30A outlet and call it a day. Well, may be I will do it one day. But for now I would like to check other options. Is there such thing as soft start device for such device which will prevent high amperage draw on startup?
 

tazzat

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Cant you convert it to 3 phase (remove cap) and use a VFD?
 

umnik

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Tazzat, I know about VFDs, but the motor I have is single phase motor. I never heard about conversion of such motors to three phase.
 

tazzat

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Depends on the motor they used.. often they use a 3 phase motor and just add a cap to run it on 1 phase..
The pump to my steam shower runs on 1 phase but the motor i 3 phase whit a cap.
 

umnik

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That is the motor
 

umnik

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JimDawson,
Yes, it looks like what I am looking for. Though there is one caveat that I found in tech spec. It says 15 starts per hour, hmm, that the limitation. Interesting, why is that? Will research more on that. And thank you for the link.
 

Janderso

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It has to have something to do with heat generation I would think??. 15 starts per hour, interesting.
I love this forum.
 

Flyinfool

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What do you have this motor on? Is there anything you can do to the equipment to reduce the starting load?
The nameplate says 22 amp, you probably should have it on a 30A circuit anyhow. The running amps will be highly dependent on the motor load. As you add load the amps will climb.
 

JimDawson

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JimDawson,
Yes, it looks like what I am looking for. Though there is one caveat that I found in tech spec. It says 15 starts per hour, hmm, that the limitation. Interesting, why is that? Will research more on that. And thank you for the link.
There is some heat generated when starting, so needs time to cool between starts. With better thermal management they could make it work with more starts. Doesn't look like there is much heat sinking on that unit. For it's designed use (HAVC) it probably doesn't need more than that. There may be others that have a higher cycle rating.
 

umnik

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What do you have this motor on? Is there anything you can do to the equipment to reduce the starting load?
The nameplate says 22 amp, you probably should have it on a 30A circuit anyhow. The running amps will be highly dependent on the motor load. As you add load the amps will climb.
It's Grizzly 3hp cyclone dust collector. Yes, 30A circuit will work, but I explained the reason why I want soft start. I have Grizzly sliding table saw, which is 5HP and never tripped circuit breaker on 20A circuit. Not a cyclone. They put 22A, that is what it draws on startup only.
 

JimDawson

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Unloaded a 5HP single phase will draw about 15 amps, and the start up load will momentarily be up in the range of 30 or so amps. The start load on a table saw is pretty low, it only has to spin up the blade. On the cyclone, the accelerated mass (impeller) is much higher than a saw blade, thus requires a much longer time at high current draw to spin up. It takes the breaker a little while to read that overload.

All breakers are not created equal, there is some minor differences in the trip time when comparing ''identical'' breakers. Older breakers will normally trip earlier than a new breaker. You can also buy breakers with different thermal curves, ''A'' being the fastest, ''D'' being the slowest. A ''D'' curve breaker is normally used for high starting loads. I don't know if you can buy breakers with different curves for a standard breaker panel.
 

mksj

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The 22A is not what it draws on start-up, it is actually much higher than that, 22A is for full Hp output. Motors have various different rating depending on the actual Hp vs. peak and the service factor. You can install different breakers with different thermal curves that will not trip on start-up (typically D-curve) and code allows you to oversize the breaker by 125% to allow for start-up. So technically this would be a 25A breaker, but this assume that the running amps (under all loads) does not exceed the wire ampacity which is not the case here. In addition, although the breaker is 20A the wire capacity is not designed to run at a full 20A continuously.

They do sell single phase soft starts, but they are not inexpensive and if I recall they are limited to certain types of motors.
 

umnik

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The 22A is not what it draws on start-up, it is actually much higher than that, 22A is for full Hp output
But if it 22A constant draw, which means about 4.5HP power, not 3hp as it rated. But I will argue about that, I am not that well educated in motor intricacies. I just gathered some info what people observed. Folks who tried to run that dust collection report that cyclone trips standard breakers frequently, but once it started it works without tripping until you turn it off. That is why I got the idea to use soft starter.
 

mksj

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You are not accounting for the efficiency and performance factor of a single phase motor which is often around 60% or less. The motor nameplate is the full load running amps. You can always put a clamp amp meter on the line and see what it is drawing, but I wouldn't want to be pulling 17+ amps from a 20A circuit for an extended period of time. A fan/pump also has a logarithmic type load so it is running at load when on at rated speed/output (assuming there is some load variation based on suction), vs. a table saw which would be running at a lot less amps when turned on and the laod would be based on the material being cut over what time frame. The basic idea is not to burn down the house. Not an electrician, but I would look at the actual motor load and then see if I could get a 20A panel breaker with a D curve which allows for a longer start-up period without tripping, otherwise a soft start is an alternative but these are limited to the number of start/stops in a given time period.
 

umnik

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Yep. It is beter to be healthy and wealthy rather then poor and sick ;-)
 
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