compressor question

[Truro Offroad]

So the compressor at work here I plan on taking home soon. I found the motor I need for it, but its still a pretty price motor.

My question is could I replace the 5hp motor with a 3hp motor and change the pulleys on it to achieve the same thing the 5hp motor was doing?

Reason for thinking this way, is the 5hp motor also needs a mag starter, where as I believe I can get a 3hp that does not require a mag starter

[dan]

if you replace the 5hp with a 3hp, you may not be able to turn the pump, unless you do change the pulley size, then you will be decreasing the pumping capacity, as you will be slowing it down.

[itsakeeper]

what he said
3ph motor ?

[Truro Offroad]

motor on it now is 3ph, the motor i need even tho it is a single phase still needs a single phase mag starter.

talked to the company who makes the compressor today.... i could go to a 3hp motor if i wanted, i would just have to make sure the ratio's and rpms of the pump were the same..

i think i will just bite the bullet and get the 5hp motor and the mag starter.

pump only runs at 750rpm...very quiet running. had it running today at the shop

[Creepy]

you won't regret going with the bigger setup in the long run.

[itsakeeper]

if there is nothing wrong with the 5hp motor except that it is 3ph I may have a solution for you - when I get to work later this morning I'll have a look and post up

[Truro Offroad]

you must have a rotary or static converter? that was my other thinking

[itsakeeper]

I was thinking of a frequency drive, I have a 5hp one here in the shop but its 575v - a new one would be $450, 230 1ph in and 230 3ph out - all kinds of parameters for programming which you wouldn't need

[Truro Offroad]

Well using that drive at $450 is still economical, a new motor my cost is $410+ freight and taxes, and then another $100 for the mag starter.

With the drive, I could just use the Mag starter the comp is on now.

[itsakeeper]

www.emersonct.com/products/ac_drives/commander_sk_-_general_purpose/overview.aspx

work computer won't let me copy and paste link so if this doesn't work let me know
you may need a enclosure so that the wiring isn't exposed - its called a nema 1 kit at about $60

[Hawkes]

Apr 16, 2010 11:43:55 GMT -4 itsakeeper said:

I was thinking of a frequency drive, I have a 5hp one here in the shop but its 575v - a new one would be $450, 230 1ph in and 230 3ph out - all kinds of parameters for programming which you wouldn't need

I read this today and said WTF is Bill talking about? So I stroll into my favorite engineers office and say, WTF is Bill talking about?

He grabs a pen and makes some swirls and explains what I saw on an internet search, he says frequency drives are a great way to convert single phase to 3 phase.

So I have a few questions. Does the frequency drive allow for motor start up current? and how much current? Motors can draw 5 times running current on start up. They come with controls? As Bill said the motor doesn't need any fancy controls but other things like a lathe may benefit from them, which is my next point, I wonder if you can run two things off it, since 3 phase tools are often cheap, but one at a time might be good too. Might want to investigate how to fuse the 3 phase side, not sure if it needs protection on both sides of the drive or just the single phase side.

And for the important question, what is the parasitic draw of the drive when it's not being used but powered up?

Sounds like a good idea if other large tools are in your future.

[theonlybull]

very interesting. i've been around frequency drives, but i didn't know they could run off single ph, all that i've seen, are 3ph......

[itsakeeper]

Does the frequency drive allow for motor start up current?
Yep, depending on the drive 150-200% for a second or so maybe more, depends on the drive and its service factor

They come with controls? yes, there are more parameters than most people will ever use and all from the keypad or remote

I wonder if you can run two things off it ? yep, and you can run several together with one being the master and the others the slaves

Might want to investigate how to fuse the 3 phase side, not sure if it needs protection on both sides of the drive or just the single phase side.
the drive will shut off if overloaded and that can be programmed as well

And for the important question, what is the parasitic draw of the drive when it's not being used but powered up?
there is a loss when converting from single phase 110v or 230v to 230v 3ph, and that will also depend on which drive is selected and the service factor

from the $450 I mentioned you can spend thousands on the same size drive with options, enclosures, etc.. There are some available for 3000psi washdown at 6" if you want to pay the cash

[itsakeeper]

Apr 17, 2010 22:16:00 GMT -4 theonlybull said:

very interesting. i've been around frequency drives, but i didn't know they could run off single ph, all that i've seen, are 3ph......

some will run off 110v or 230v single phase but always kick out 3ph power - also DC available usually in 90v

[theonlybull]

good to know. may come in handy someday