Wanting to change 3 phase motor to single phase motor on a Coltri MCH-16 Compact

[Peter_C]

I have a Max-Air CE90 which is effectively the same as the MCH-16. I took it from 3 phase to single phase using a Leeson motor, and have had zero issues with the motor. I can not remember the frame sized that I used, but have never found it hot. It was very easy to wire up just dropping one leg, and the motor came with the starting capacitor built onto it. For the pulley I just machined it out a little larger to the size of the new shaft. I don't put a lot of hours on my compressor, but that just means it will last longer. The compressor system was paid for fairly quickly calculating at $10 a fill for nitrox, even with consumable expenses. Plus it was the only way I was going to get nitrox in Sonoma County.

If anyone wants a nice 3 phase 7.5hp motor let me know.

 

[dchango]

Well the issue is I need to turn the compressor at 1550 RPM, the compressor pulley is 16 7/16”, my drive motor is 3520 RPM, so I would need an 8” drive pulley. After researching the internet and not finding much of anything on where one would measure a pulley. I think I have figured out how you measure a pulley, well it depends on the size of belt you are using. Being my compressor uses an A belt, I needed a drive pulley that uses an A belt and is around 8”. Which led me to the BK90 the OD is 8.75, the PD (pulley diameter?) using an A belt is 8.00, the PD using a B belt is 8.40, it all relates to where the belt rides on the pulley. Also, I found a cool site that also calculates pulley ratios and can even figure what size belt you are going to need. http://www.blocklayer.com/pulley-belteng.aspx .

Thanks
Damon

 

[roastbeef]

Go to your local convey/drive belt supplier they will tell you how to properly measure pullies for the correct RPM your seaking.

 

[oldschoolto]

This is wrong. The amperage will be higher but the kilowatt hours will not be higher. You pay for kilowatt-hours.

If amps x volts = watts how does a higher amp motor use the same kilowatt-hr ? I was told/understood that a 110 volt 20 amp motor would use/cost more to run then a 220 volt 10 amp motor... And a 3 phase would be cheaper than the 220v motor....

What am I missing ????? does it not cost more to use a 100 watt light bulb than a 60 watt....

Jim...

 

[frogman62]

You are being too picky 16.4 in pulley X 1550 rpm divided by 3520 RPM motor equals 7.22 diameter pulley. Buy an "A" groove pulley that is as close to 7.22 inch outside diameter as possible. Quit worrying about where the belt sits; pulleys have been standardized forever. If the pulley measures 7.0 or 7.5 it won't make any difference to the compressor. 7 inch pulley will turn compressor at 1502 RPM. 7.5 in pulley will turn the compressor at 1609 RPM. If you are only pumping to 3500PSI 1600 rpm will be OK -- If you are pumping to 5000PSi use the 7 in pulley - slower is better at higher pressures.
Jim Shelden

---------- Post added October 23rd, 2013 at 09:19 AM ----------

With regard to electricity cost - in a residence without 3 phase electricity the only issue is the amp draw difference between 115 and 230 volts. For example a 5 HP single phase motor draws 56 AMPS on 115 volts and requires a # 4 wire and at least a 60 amp breaker (roughly equivalent to an electric welder circuit). The same motor draws 28 amps on 230 volts and requires a #8 wire and a 30 amp breaker. Easier to do in a home circuit panel -- they both will require a dedicated breaker and circuit - smaller size wire and breaker is less expensive than larger. Electrician will be the same labor or DIY.
Electricity cost to run the compressor will be exactly the same.
Jim Shelden

 

[BRT]

If amps x volts = watts how does a higher amp motor use the same kilowatt-hr ? I was told/understood that a 110 volt 20 amp motor would use/cost more to run then a 220 volt 10 amp motor... And a 3 phase would be cheaper than the 220v motor....

What am I missing ????? does it not cost more to use a 100 watt light bulb than a 60 watt....

Jim...

Amps times volts = watts. You pay for watts. The 240 volt motor at 10 amps is 2400 watts and the 120 volt motor at 20 amps is 2400 watts. The 3 phase 240 volt motor at 5.78 amps times 240 volts times 1.73 for the other conductor is also 2400 watts. Remember that in motors and other inductive or capacitive loads it is not actually amps times volts but amps times volts times the power factor, but amps times volts is close enough to understand the concept

 

[oldschoolto]

Amps times volts = watts. You pay for watts. The 240 volt motor at 10 amps is 2400 watts and the 120 volt motor at 20 amps is 2400 watts. The 3 phase 240 volt motor at 5.78 amps times 240 volts times 1.73 for the other conductor is also 2400 watts. Remember that in motors and other inductive or capacitive loads it is not actually amps times volts but amps times volts times the power factor, but amps times volts is close enough to understand the concept

Thank you..... You never stop learning...

Jim....

 

[BRT]

Thank you..... You never stop learning...

Jim....

Which is why I keep reading this forum.

 

[frogman62]

BRT,
The cost of the motor is different (not electricity) -- same HP rated motor uses very close to the same electric cost. I just grabbed a price on single phase motors vs.three phase motors of the same HP from a supplier to show the difference
5 HP 1 phase $429, -- 5 HP 3 phase $499, -- 5 HP 3 phase explosion proof $659
Jim Shelden

 

[BRT]

BRT,
The cost of the motor is different (not electricity) -- same HP rated motor uses very close to the same electric cost. I just grabbed a price on single phase motors vs.three phase motors of the same HP from a supplier to show the difference
5 HP 1 phase $429, -- 5 HP 3 phase $499, -- 5 HP 3 phase explosion proof $659
Jim Shelden

I can always buy 3 phase motors of the same quality cheaper. Single phase motors have capacitors and a start switch. 3 phase motors don't have these extra parts. Plus the starter can be smaller and cheaper.