# 3 phase to single phase



## varmit (Apr 19, 2009)

The fan "housing" appears to have been rebuilt recently. The air inlet side may need to be throttled (made smaller) to lessen the air flow. this will reduce motor load.


----------



## joebanana (Dec 21, 2010)

You let the GC give you a motor, said it would work, and you believed him? Oh, my son, you have much to learn. All GC 's know, is how to screw things. People, customers, subs, jobs, etc. Does this house have 220v.? Can't read the nameplates in the photo's, but they should be the same Hp. Motor start surges can be up to 600% of running current, so what's so bad about 60a.?


----------



## circuitman1 (Mar 14, 2013)

i may be wrong but the orignal motor being a squirrel cage motor had more starting torque. is this a capacitor start motor?:smile::smile:


----------



## varmit (Apr 19, 2009)

Also, check to be sure that the fans turn freely. If this has set for a while, the bearings could be tight or seized. The belts could also be misaligned .

Are the sheaves and pulleys the same size as original? Ratios make a huge difference in motor load.

Some of the older motors were a little over built and would put out a little more torque than the cheaper motors of today, even if rated the same HP.


----------



## gpop (May 14, 2018)

you never said if the original motor was wired to high speed or the pulley on the motor is original. If it runs on low and the noise isn't as annoying as high i would wire it there and let it run.


----------



## blueheels2 (Apr 22, 2009)

circuitman1 said:


> i may be wrong but the orignal motor being a squirrel cage motor had more starting torque. is this a capacitor start motor?


Yes it is a capacitor start.


----------



## blueheels2 (Apr 22, 2009)

varmit said:


> Also, check to be sure that the fans turn freely. If this has set for a while, the bearings could be tight or seized. The belts could also be misaligned .
> 
> Are the sheaves and pulleys the same size as original? Ratios make a huge difference in motor load.
> 
> Some of the older motors were a little over built and would put out a little more torque than the cheaper motors of today, even if rated the same HP.


The fans and pulleys are original from 1953 I believe. I wasn’t there for the install. I got a call telling me it was ready. Belts maybe as well as far as I know. I spun the fans and they spin freely but they are heavy.


----------



## blueheels2 (Apr 22, 2009)

joebanana said:


> You let the GC give you a motor, said it would work, and you believed him? Oh, my son, you have much to learn. All GC 's know, is how to screw things. People, customers, subs, jobs, etc. Does this house have 220v.? Can't read the nameplates in the photo's, but they should be the same Hp. Motor start surges can be up to 600% of running current, so what's so bad about 60a.?


So my buddy was the original HVAC contractor on this job but he got squeezed out for reasons he nor I are sure of. In his price he was going to get the correct motor replacement mounted . They pressed me to do it and I knew there were more issues there than I felt like dealing with. So I told the GC get the correct fan mounted and I’ll wire it. So here we are.

Originally the home had a high leg 3 phase service. The only 3 phase loads were this fan and a blower on an HVAC unit in the basement. House now has a single phase service.


----------



## blueheels2 (Apr 22, 2009)

gpop said:


> you never said if the original motor was wired to high speed or the pulley on the motor is original. If it runs on low and the noise isn't as annoying as high i would wire it there and let it run.


The original setup utilized both speeds. They would like to use both speeds again.


----------



## dronai (Apr 11, 2011)

What is the HP rating of the 3 phase motor ?


"When comparing two motors with the same horsepower rating, the single-phase motor will draw significantly more current than the three-phase motor. Because of the larger current draw, larger and therefore more expensive windings are required"

Sounds like you need more HP using single phase power


----------



## blueheels2 (Apr 22, 2009)

varmit said:


> The fan "housing" appears to have been rebuilt recently. The air inlet side may need to be throttled (made smaller) to lessen the air flow. this will reduce motor load.


Everything is original except for the new motor.


----------



## blueheels2 (Apr 22, 2009)

dronai said:


> What is the HP rating of the 3 phase motor ?


3 ph motor was 1 hp on high and 1/3hp on low. New single phase motor has the same ratings.


----------



## blueheels2 (Apr 22, 2009)

dronai said:


> What is the HP rating of the 3 phase motor ?
> 
> 
> "When comparing two motors with the same horsepower rating, the single-phase motor will draw significantly more current than the three-phase motor. Because of the larger current draw, larger and therefore more expensive windings are required"
> ...



This was my initial thought I've just been rooting around for info so they can't blame the way its wired. Works great without the fans attached.


----------



## dronai (Apr 11, 2011)

Look here, sizing a motor for a fan

https://heatingcooling.fergusonhvac.com/2016/06/15/use-the-fan-blade-to-size-the-motor/


----------



## varmit (Apr 19, 2009)

A three phase motor will generally have better starting characteristics than a single phase motor. Also, if the single phase motor does not accelerate quickly,
it will not open the centrifugal switch to engage the run windings, so the motor will run hot and have little torque.

Options:
1. Install a VFD with single phase input and three phase motor. ( This would 
also let you ramp the fan up slower and more quietly.)

2. Up size the motor to at least a 2 or 3 HP single phase motor. ( The fan 
assembly does not appear to have room to do this.)

3. Change the mechanical gearing on the fans.( Larger sheaves on the fans and 
smaller on the motor.)


----------



## joebanana (Dec 21, 2010)

varmit said:


> Also, check to be sure that the fans turn freely. If this has set for a while, the bearings could be tight or seized. The belts could also be misaligned .
> 
> Are the sheaves and pulleys the same size as original? Ratios make a huge difference in motor load.
> 
> Some of the older motors were a little over built and would put out a little more torque than the cheaper motors of today, even if rated the same HP.


Good point about ratio's, can make all the difference.


----------



## oliquir (Jan 13, 2011)

9 amp with no load is too high, there is a problem with motor or connections


----------



## Wirenuting (Sep 12, 2010)

Are the belts new and the right size? (A,B,C & length?)
Are the bearings clean and greased?
Are she shives groves?

If the belts are new and the shives are grooves badly, The belt will grab and hold tightly as it spins causing the motor to over work. Loosing the belt does not help that.


----------



## gpop (May 14, 2018)

Does the pulley on the motor have threads showing and a set screw. If so its a adjustable pulley. 

I know the mechanics i use to work with would install adjustable pulleys on the fan motors and forget to adjust them. What looks like a tiny difference in the pulley ended up being the difference between a fan running or tripping.


----------



## micromind (Aug 11, 2007)

oliquir said:


> 9 amp with no load is too high, there is a problem with motor or connections


I agree......I can't read the nameplate but I'd expect a 1 HP single phase motor to draw about 10 amps full-load at 115 volts and maybe 3 or so no-load. 

If both speeds were engaged at the same time, it'd be a lot more than 9 amps, same thing if the start winding was not cut out. About the only thing I can think of is shorted windings on adjacent coil turns. That would cause higher no-load current and much higher full-load current. 

P.S. Whatever dunce decided to get rid of the 3Ø and go with single phase should be given a fair trial then shot.


----------



## 460 Delta (May 9, 2018)

micromind said:


> I agree......I can't read the nameplate but I'd expect a 1 HP single phase motor to draw about 10 amps full-load at 115 volts and maybe 3 or so no-load.
> 
> If both speeds were engaged at the same time, it'd be a lot more than 9 amps, same thing if the start winding was not cut out. About the only thing I can think of is shorted windings on adjacent coil turns. That would cause higher no-load current and much higher full-load current.
> 
> P.S. Whatever dunce decided to get rid of the 3Ø and go with single phase should be given a fair trial then shot.


Most likely the utility was pitching a fit about the second transformer and the metering of it probably without a demand meter for a residence. But I thought the same thing, WHY would you tear out three phase and install single, what a step backwards.


----------



## blueheels2 (Apr 22, 2009)

460 Delta said:


> micromind said:
> 
> 
> > I agree......I can't read the nameplate but I'd expect a 1 HP single phase motor to draw about 10 amps full-load at 115 volts and maybe 3 or so no-load.
> ...



Yeah the new service was free if single phase and was going to be be a significant cost of 3 phase. The discussion never got far enough to hear how much more expensive.


As far as belts, pulleys, etc I am not very experienced with that stuff. That’s why I told the GC get your HVAC guy to install it and I’ll wire it. But the HVAC guy they hired told them to suck it so they threw it on me. I threw it back on them. And here we are.


----------



## JRaef (Mar 23, 2009)

Both motors are the same HP 3phase or 1phase is not part of the HP equation. 

New motor FLA is 12.4A at high speed, you mentioned it draws 20A after the starting current settles down and that is not right. The motor is overloading. You have either wired it wrong or there is something drastically wrong with the motor itself. 

My guess is that you connected it for 120V and are feeding it 240V, that will make the motor over saturate and pull high current that is just making heat, not torque, but it will appear to run “normally” because doubling the voltage does not affect the speed on this type of motor.

PS: noticed that the motor can ONLY be wired for 115V, so if you ran 240, there’s the problem. But also, the way a starter/controller changes speeds on a 2 speed 3 phase motor is totally different than on a 2 speed 1 phase motor, so it you didn’t totally change out the speed selection method, it may be what is causing the problem.


----------



## just the cowboy (Sep 4, 2013)

micromind said:


> P.S. Whatever dunce decided to get rid of the 3Ø and go with single phase should be given a fair trial then shot.


Judge is out skiing, can we shoot him first then give him a fair trial.


----------



## micromind (Aug 11, 2007)

just the cowboy said:


> Judge is out skiing, can we shoot him first then give him a fair trial.


Yes we can....and since he refuses to answer any questions, we'll take him out back and shoot him again.


----------



## JRaef (Mar 23, 2009)

micromind said:


> ...P.S. Whatever dunce decided to get rid of the 3Ø and go with single phase should be given a fair trial then shot.


JRaef for the defense, in absentia.


It could be that a previous owner had 3 phase equipment for a home machine shop business, then sold the house. The new owners don't need the 3 phase for anything else and don't want to pay the surcharges that some utilities put onto 3 phase residential service drops and/or the demand meter charges just to run a couple of attic fans. My father had his own home based industrial business and had a 3 phase service drop when he built his house so that he could test machines. After he passed away and we went to sell the house, none of the potential buyers wanted the 3 phase drop once they found out that PG&E was going to charge them a demand charge. So I had to rip and replace his panels.


If you must shoot him anyway, shoot him in the leg but try to miss his femoral artery...


----------



## micromind (Aug 11, 2007)

JRaef said:


> JRaef for the defense, in absentia.
> 
> 
> It could be that a previous owner had 3 phase equipment for a home machine shop business, then sold the house. The new owners don't need the 3 phase for anything else and don't want to pay the surcharges that some utilities put onto 3 phase residential service drops and/or the demand meter charges just to run a couple of attic fans. My father had his own home based industrial business and had a 3 phase service drop when he built his house so that he could test machines. After he passed away and we went to sell the house, none of the potential buyers wanted the 3 phase drop once they found out that PG&E was going to charge them a demand charge. So I had to rip and replace his panels.
> ...


The PUCO around here doesn't have a demand charge for my 120/208 3Ø 4 wire resi service. My bill has KWHR only. 

Also, back in the 70s there were several subdivisions that had 240 ∆ 3 Ø services. They were a basic single phase split-bus panel with a ∆ breaker that fed the A/C unit. Always FPE.........

And again, the bills had only KWHR on them.

I guess different PUCOs have different charges for different services.


----------



## MOA (Mar 12, 2008)

To get those fans up and running won't be cheap. The original HVAC guy knew it and quoted accordingly. That's why he was bumped. Those fans are vintage and are probably constructed of steel and cast-iron. If you can get your wiring sorted. You could run each fan with its own 115v motor. Possibly wire one motor on HIGH speed and the other on LOW. That may add some adjustability to the two motor scheme. There appears to be motor mounting slots prepunched in the centre of each fans support braces. OR you could run a larger HP 230v motor for both. Good luck


----------



## blueheels2 (Apr 22, 2009)

just the cowboy said:


> micromind said:
> 
> 
> > P.S. Whatever dunce decided to get rid of the 3Ã˜ and go with single phase should be given a fair trial then shot.
> ...



Thought I Said it earlier but the service was moved about 500’ on the property. It was free to move it single phase and it was going to be very expensive to keep the 3 phase. When told this the homeowner decided to go with single phase.


----------



## blueheels2 (Apr 22, 2009)

MOA said:


> View attachment 139654
> 
> 
> View attachment 139656
> To get those fans up and running won't be cheap. The original HVAC guy knew it and quoted accordingly. That's why he was bumped. Those fans are vintage and are probably constructed of steel and cast-iron. If you can get your wiring sorted. You could run each fan with its own 115v motor. Possibly wire one motor on HIGH speed and the other on LOW. That may add some adjustability to the two motor scheme. There appears to be motor mounting slots prepunched in the centre of each fans support braces. OR you could run a larger HP 230v motor for both. Good luck


Yeah I felt from the beginning the motor is too small but the “motor guy at Grainger says it should work” is what I have heard.


----------

