starting a 7.5 hp single phase compressor

[iwire]

Its very common to use an oversized VFD for single phase in, three phase out, with this you only need to change the motor.

This might be interesting:

http://www.baldor.com/pdf/manuals/834-602.pdf

I know Baldor has a soft start...but way too pricey. A vfd isn't going to work since it's single phase,

I think if the soft start is too pricey a VFD will be out of the question.

 

[augie47]

http://www.google.com/products/catalog?hl=en&q=baldor+s23ca&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&biw=853&bih=572&wrapid=tlif133874868186410&um=1&ie=UTF-8&tbm=shop&cid=10166508046141125959&sa=X&ei=Ea_LT8LGOI-k8gS025TvDg&ved=0CG4Q8wIwBQ

$ 436

 

[ActionDave]

What he means is that the voltage goes so low that the clocks (digital) will start blinking 12:00 and will restart from there. He should install a battery in them anyway.

that's exactly what's happening......but only on heavy usage days. (building race cars uses alot of air tools)

If this is happening it makes me wonder- Is the motor coming up to speed correctly?

 

[templdl]

Other than the voltage drop present at the motor have you identified the cause of the voltage drop?
One guy mentioned the POCO transformer, is that the cause?
Where is the service entrance? Is the service drop the issue?
What about the size of cable between the service entrance and the motor. Could that be the issue?

Seems to me that there isn't enough known about what is happening between the POCO transformer and the compressor.

I would be a bit uneasy trying to solve a voltage drop issue with all of what has been suggested when I am sure what is actually the cause of the voltage drop.

 

[boyle78]

I have seen them installed on single-phase air conditioner compressors numerous times so I would think it would be applicable for an air compressor but it's a good engineer or manufacturer question.
With that large of a single phase motor I think you will experience some "blink" regardless of what you do short of installing a soft-start.

This might be interesting:

http://www.baldor.com/pdf/manuals/834-602.pdf

$700 bucks is alot better than what I found before! I did fail to mention that I recently swapped out the older breakers in the house, torqued the main lugs, neutrals, grounds, and the breaker wires....I just spoke to the HO and the bliking alarm clock and flickering lights in the house have drasticaly improved!!! Makes me think I was chasing more problems than just the load of the compressor motor. I still am considering trying to get that soft start in there!

 

[boyle78]

http://www.google.com/products/catalog?hl=en&q=baldor+s23ca&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&biw=853&bih=572&wrapid=tlif133874868186410&um=1&ie=UTF-8&tbm=shop&cid=10166508046141125959&sa=X&ei=Ea_LT8LGOI-k8gS025TvDg&ved=0CG4Q8wIwBQ

$ 436

nice find!!!!

 

[kwired]

I have seen them installed on single-phase air conditioner compressors numerous times so I would think it would be applicable for an air compressor but it's a good engineer or manufacturer question.
With that large of a single phase motor I think you will experience some "blink" regardless of what you do short of installing a soft-start.

This might be interesting:

http://www.baldor.com/pdf/manuals/834-602.pdf

From the first page of the general information section:

Note: Motor loads that require full voltage starting torque to reach full speed may​

not be compatible for use with this control.

Air compressors typically need more starting torque than other loads - it even says on same page they are well suited for fans and pumps which most do not require much starting torque.

If you don't get enough torque to turn the shaft until you start approaching full voltage you are still going to experience similar voltage drop issues. Unlike a three phase motor which you still have rotating field you must create rotating field to get any torque from a single phase motor. Maybe one of our motor experts can tell us how much of full voltage is needed before we will have enough torque to accelerate a load like this. I'm pretty sure it will be a higher percent of full voltage than needed if it were a three phase motor.

 

[hillbilly1]

that's exactly what's happening......but only on heavy usage days. (building race cars uses alot of air tools)

Since it only happens on heavy usage days, it would appear to be a load issue, do they have other large draw equipment running at the same time? Welders, tubing benders and such? The heavy loads may be drawing down the voltage making it harder for the compressor to start.

 

[ActionDave]

Since it only happens on heavy usage days, it would appear to be a load issue, do they have other large draw equipment running at the same time? Welders, tubing benders and such? The heavy loads may be drawing down the voltage making it harder for the compressor to start.

I think so too, also. Inrush when the compressor starts is one thing, but enough to drain all the juice on the whole lot?!!!