Phase convertor question?

[mad57]

Im looking into getting a 20 hp rotary compressor, 3 phase , whats the cheapest i can get into a phase convertor for this application? thks

 

[930dreamer]

The cheapest way would be make your own.

 

[larry_g]

100 amp load and cheap do not belong in the same conversation. I would guide you to http://www.practicalmachinist.com/vb/transformers-phase-converters-vfd/ where they are dedicated to this problem. Good luck.

lg
no neat sig line

 

[Steevo]

Remember that a phase converter that will run a 20HP motor will likely put you at the capacity of a 100A panel. That's a lotta load!

 

[Kevin C]

Sounds like a lot of CFM.... Possibly a tiny bit more than you need?

 

[A_Pmech]

A cheap 25 HP converter is a couple thousand. A top of the line rotary converter is about double that. Add at least another thousand or so for wire and fusible disconnects or a scrounged motor starter.

 

[JohnK007]

I always thought using an RPC in a compressor application was not a good idea. The reason being that because the compressor kicks on with a pressure switch and is hard to predict when it will call for the motor to turn on, you have to leave the RPC run all the time. Since an idling RPC is still consuming juice (a 20 HP idler is consuming quite a bit of juice!), it is not very economical in the grand scheme of things.

 

[Full Throttle]

I would not entertain the idea. a 20hp motor gets expensive to replace from bad power, the cost of compressor,converter and repairs lots of money

I work for Trane doing industrial HVAC and Automation, we deal withh ABB technologies who supplies our frequency drives for fans and pumps, I am certified for startup on the drives and I am wanting to say that on type of drive they make will allow single phase line and make 3 phase load, 20hp range would be around $2K. something for you to look at and think on.

and with this the motor would be controled by the frequency drive, you would have your pressure switch send the signal to the drive to ram the motor up.

 

[Mmfh]

I have a 25 hp RPC, 10 hp compressor, I'm having a hard time with starting that compressor.

If this is a rotary screw compressor, it may run all the time and just kick a pressure valve in and out to keep the pressure at max. Phase converter would only have to start it once a day, or whenever you turn on the compressor.

Its a big unit for home power, might want to really think about it.

Mm

 

[A_Pmech]

(a 20 HP idler is consuming quite a bit of juice!), it is not very economical in the grand scheme of things.

Not really...

An idling phase converter has a very poor power factor. That is to say the majority of the input current is out of phase with voltage. Thus, a much lower power draw than would otherwise be the case based on a current measurement alone.

The only power being used is that consumed by the bearings and magnetizing power due to core loss, electrical resistance, etc. For a properly balanced 40HP rotary converter that's around a kilowatt more or less. So, idling a converter capable of starting a 20HP motor for 8 hours will cost about $0.88

It is also possible to build a circuit which will start and stop the converter with the compressor, but that's too complicated to get into here. The VFD is also a good solution, especially if the OP has no plans for other 3-phase equipment.

All of this is predicated on the OP having a sufficient incoming service (and transformer) to supply the required power. Residential services, as a rule, employ heavily undersized transformers.

 

[mad57]

Thanks for the insight.... i figured it would not be cheap per say, my best bet would be to just buy the biggest 220 compressor i can find and spend the 4gs or so just on that, i did like to quiet operation of the screw but cant have it all, not to mention im pretty giving in my shop space and have many friends come buy when im not there and cant count on them figuring out a multi start compressor. thks for the info.

 

[JohnK007]

Didn't realize that AP, thanks for the info. I stand corrected.

 

[brewchief]

Thanks for the insight.... i figured it would not be cheap per say, my best bet would be to just buy the biggest 220 compressor i can find and spend the 4gs or so just on that, i did like to quiet operation of the screw but cant have it all, not to mention im pretty giving in my shop space and have many friends come buy when im not there and cant count on them figuring out a multi start compressor. thks for the info.

You can buy single phase rotary screw compressors, northern tool shows a few options.