AC Motor Ramping Startup

[leonar40]

I am using an AC motor in my project. I would like the motor to ramp from stop to full speed (1700rpm) over several seconds when you turn it on. Currently it goes from stop to full speed as soon as you turn the power on. Is there a simple circuit or other way to ramp the speed of an AC motor? If this was a DC system then I could use a simple RC first order circuit to ramp the input voltage. Is there a way to make this work with an AC system?
Thanks for your time,

Jason Leonard

 

[GordS]

Sounds like a job for a soft starter. Basically, these units gradually increase the voltage applied to the motor. This gradually increases the torque generated by the motor so it gradually accelerates. These are off-the-shelf units made by many companies. Check the internet.

 

[jraef]

1 phase or 3 phase motor? It is difficult to soft start most 1 phase motors.

"Venditori de oleum-vipera non vigere excordis populi"

 

[leonar40]

Actually it is called a split-phase motor. The motor that I am using is the Bodine-Electric 42R-0253 AC motor. The website is:

http://www.bodine-electric.com/Asp/ProductSeries.asp?Context=5&Name=42R Series AC Induction Motor

The more that I learn about starting these things, the more I think that I should just get an AC controller. Bodine has what looks like a pretty nice one for $200. Then not only would I be able to ramp up the starting speed, but I could set the speed to whatever I wanted.

 

[jraef]

They don't make it clear enough in my opinion, but you CANNOT use their VFD on that particular motor. That is a 1 phase motor that requires external capacitors, and the VFDs, although able to use 115V 1 phase input, will give a 230V 3 phase output and can only be used on 3 phase motors.

You could however consider using the 0273 version of that motor, which is 230V 3 phase, and then use the inverter which will create 3 phase from your 115V 1 phase source. That motor appears to use the same housing and frame, it is 1/4HP instead of 1/6HP. But with a VFD, the extra power should not be a mechanical risk becasue you are soft starting and those VFDs have current limit.

My one comment on using these small motors from Bodine (from my personal experience) is that they have a tendancy to overheat when running at low speeds from a VFD because their fan cooling is apparently inefficient below 1/2 speed. But if you don't plan to run slower than that, no problem, they are a good quality motor.

"Venditori de oleum-vipera non vigere excordis populi"

 

[busbar]

 
On jraef’s 3ø-motor suggestion, if your could accommodate a 230V 1ø input, Bodine lists a ‘closeout-priced’ VF drive for $89.

http://www.bodine-electric.com/Asp/CloseoutDetails.asp?Context=21