motor conversion
- Thread starter Joe Venus
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Three possibilities:Joe Venus said:
1) Replace motors.
2) Rotary converters.
3) VFD units.
Easiest? Probably #2.
ptonsparky
Tom
- Occupation
- EC - retired
If you are converting from three phase to single phase you will have to increase the size of your conductors to accomodate the larger current but otherwise 5 hp equals 5 hp be it single phase or three.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
What he said.
But, 5HP single phase motors are not all that common and there are good reasons for that.
But, 5HP single phase motors are not all that common and there are good reasons for that.
brian john
Senior Member
- Location
- Leesburg, VA
petersonra said:
But if they are available, the cost of replacement will most likely be less than the cost of rotary with the added loss in efficency.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Joe Venus said:
Possible, but not in the least bit practical. Why don't you instead tell us why this is important to you. Chances are about 99.999% that even if you find a rewind shop willing to take on that project, it will cost you multiples of the cost of a new single phase motor just in labor. Lary Fine's choice number 2 is definitely the easiest for the average person to implement if you have one motor per site. If you have multiple motors at one site, a Rotary phase Converter (RPC) may be the better choice. But even then, pumps are often great candidates for using VFDs as a way to save energy if they don't need to run at full output all the time. VFDs often pay for themselves in energy savings in as little as 18 months.
wirenut1980
Senior Member
- Location
- Plainfield, IN
Starting Inrush?
Starting Inrush?
If a phase converter is used to provide 3 phase from single phase to a motor load, I know that the full current requirements will be roughly 1.732 times the 3 phase full load current requirements. But what about inrush? Does that also multiply by 1.732? Thanks!
Starting Inrush?
If a phase converter is used to provide 3 phase from single phase to a motor load, I know that the full current requirements will be roughly 1.732 times the 3 phase full load current requirements. But what about inrush? Does that also multiply by 1.732? Thanks!
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
I'm not sure I understand the question. Are you suggesting removing the motor, sending it to a shop, and having it come back as a 5hp single phase motor? I doubt that can even be done. The stator slots will have been designed to accomodate a three-phase wiring scheme, and I don't think they would serve the purpose of accomodating a single-phase wiring scheme. You would have to ask the repair shop.Joe Venus said:
But are you instead suggesting tossing out the old motors, and replacing them with single phase motors of the same hp? That can be done, but I can't imagine why you would want to. Can you tell us what is the problem that you are trying to solve?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Jraef said:
I hear these kind of numbers thrown out and I cringe when I hear them, because often they are just plain not true.
VFDs can only reduce your energy cost when they reduce your energy usage. The only way this happens is if you can reduce the amount of work being done by your motor. A fairly common application is a fan. reducing the motor speed reduces the energy loss because the fan now moves less air. This is OK if you don't need as much air, or you were using a damper to create back pressure to control your air flow, which does create energy loss.
There are about 750 watts in a HP.
Forgetting the losses from just turning the motor, let us say you can reduce your energy usage by 25% (not generally realistic, but, it could happen). 25% less energy used on a 10HP motor would amount to about 13000 kw-hr of energy saved per year, if the thing ran 24/7. Most motors never run that much. Do the numbers.
Most often, when the numbers are run honestly, the payback period is way out there, except in a very few cases. That does not make a VFD a bad idea, because there are good reasons to use them for other reasons as well, just be careful of what the energy scam artists tell you.
Also, keep in mind that some customers have electrical rates that are based on peak demand and the per kw-hr charge is pretty low (like 2 cents) but the demand charge is way up there. You won't see much change in your bill if all you do is reduce your peak demand by an infinitesimally small amount.
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