Would You? 10hp Compressor 3 Phase

[freudianfloyd]

I have the chance to get a very nice Saylor Beall 120 gallon compressor. The problem is that it is a 3 phase unit. I don't know the exact model number off hand, but I know it is a quality made US machine.

Is it worth the cost/effort for a DIYer hobbiest like myself? I know my dad's 120 gallon 10 hp Quincy cost him $1,000 used and another $700 to convert to single phase. Is there a cheaper way? Can a VFD be used?

Or, is it worth buying and then flipping for a tidy profit?

Any thoughts?

 

[rwa2004]

I have been trying to come up with a low cost way to use a scavenged 10hp compressor on single phase and have had no luck. The cost of any sort of conversion to make is single phase would cost more than finding a single phase compressor (or two).

 

[u3b3rg33k]

absolutely a VFD can be used. what voltage? I'd pick it up for $300 in a heartbeat if it's a 208V unit. drive it with a VFD - solve most of your inrush problem with a 2 or 3 second ramp up to whatever HP rating you can afford for the VFD.

Note that at lower than rated RPM, you will not have the cooling airflow you'd normally have. a little maths may need to be done to figure out if that's a real problem.

 

[cvairwerks]

Switching to a 10 hp single phase motor will be less than getting a VFD. For a VFD to run it, you would be pushing $1400 and need a dedicate 50 amp or so circuit. A 10 hp single phase is going to be in the $1000 range. Check the compressor model number and look at the books and see what the required motor hp is. Might be able to drop back to a 7.5 hp motor, which will be about $650.

 

[rlitman]

Switching to a 10 hp single phase motor will be less than getting a VFD. For a VFD to run it, you would be pushing $1400 and need a dedicate 50 amp or so circuit. A 10 hp single phase is going to be in the $1000 range. Check the compressor model number and look at the books and see what the required motor hp is. Might be able to drop back to a 7.5 hp motor, which will be about $650.

Can you even run a 10HP motor on a residential service? Forget about the dedicated circuit ampacity. Just the crazy power draw of a reciprocating piston compressor with that much motor behind it is going to cause power issues for your neighbors.

My 7.5HP single phase compressor does everything I could ask of it. My guess is that this one can be repowered with a smaller motor. Perhaps with a smaller pulley to match.

 

[American Locomotive]

10HP @ 240v with an 80% efficient motor is only ~40A. It's not that crazy. An electric range with all the burners and oven going will use more power.

 

[rlitman]

10HP @ 240v with an 80% efficient motor is only ~40A. It's not that crazy. An electric range with all the burners and oven going will use more power.

The current draw is not crazy, but the current harmonics are. An electric range easily uses more current, but is resistive with a constant current draw that matches the voltage waveform, so it has no harmonics.

When my 7.5HP compressor was running, I used to be able to see the flicker in the STREET lights when they were high pressure sodium. Now that they've switched to LED, that's stopped, but my point is that the current draw is not constant. It drops as the piston retracts, and rises with the pressure in the cylinder, and the noise that such a large compressor motor puts into your electrical system is about as bad as the noise you hear when standing next to it.

I've got a 200A service, but the neighborhood's wiring is pretty old. If you're on a grid where everything is sized for buildings with 400A service and above, I'm sure that no one would notice the electrical noise from a 10HP compressor, but if you're on an old circuit like me, you may get complaints from the power company.

 

[Strouty]

10HP @ 240v with an 80% efficient motor is only ~40A. It's not that crazy. An electric range with all the burners and oven going will use more power.

From experience, the amps to run it are not the issue, it is the inrush. When mine starts it dims my lights a bit, since I share a transformer with the neighbors, I know their lights dim as well. I think it is about 230 Amps when it starts up.

 

[doojus]

If it's a 707 pump, it can either be run by a 10HP or a 7.5HP (at lower RPM). A single phase 7.5 would probably be easier/cheaper to come by.

But yeah, absolutely pick it up at that price. Mine was around $5100 when I bought it.

 

[joe_padavano]

If it's a 707 pump, it can either be run by a 10HP or a 7.5HP (at lower RPM). A single phase 7.5 would probably be easier/cheaper to come by.

^^^THIS. I recently assembled a frankenpressor using a Rolair K30 pump, a new Leeson 7.5 HP single phase motor, and an 80 gal tank. Runs just fine on my home electrical system, and I haven't really noticed any dimming of lights issues.

I will say that 24 SCFM is PHENOMENAL. This unit doesn't even breathe hard when media blasting, running a die grinder or cutoff tool, or anything else. I LOVE this compressor - especially after waiting for my alleged "5HP" compressor (that only needed 15A - do the math) to keep catching up with my blaster or air tools.

 

[u3b3rg33k]

Can you even run a 10HP motor on a residential service? Forget about the dedicated circuit ampacity. Just the crazy power draw of a reciprocating piston compressor with that much motor behind it is going to cause power issues for your neighbors.

My 7.5HP single phase compressor does everything I could ask of it. My guess is that this one can be repowered with a smaller motor. Perhaps with a smaller pulley to match.

with a VFD you don't necessarily need to put on a smaller motor / pulley. just run it at a lower RPM, and it'll have less HP. actual HP isn't determined by the size of the motor, it's determined by the load. the motor needs to be sized to provide enough torque to run your load at whatever shaft speed you need.

Assuming it's a 4 pole motor, you could put a smaller pulley on the motor, and then pick an operating speed that provides adequate cooling while only drawing the amount of current you want it to. you could even get fancy and use a pressure transducer to adjust the motor speed based on tank pressure.

The current draw is not crazy, but the current harmonics are. An electric range easily uses more current, but is resistive with a constant current draw that matches the voltage waveform, so it has no harmonics.

When my 7.5HP compressor was running, I used to be able to see the flicker in the STREET lights when they were high pressure sodium. Now that they've switched to LED, that's stopped, but my point is that the current draw is not constant. It drops as the piston retracts, and rises with the pressure in the cylinder, and the noise that such a large compressor motor puts into your electrical system is about as bad as the noise you hear when standing next to it.

I've got a 200A service, but the neighborhood's wiring is pretty old. If you're on a grid where everything is sized for buildings with 400A service and above, I'm sure that no one would notice the electrical noise from a 10HP compressor, but if you're on an old circuit like me, you may get complaints from the power company.

this is less of an issue with a 3 phase motor on a VFD -
1. a 3 phase motor has smoother power draw than a single phase motor
2. a VFD will by it's design have a smoother power draw than a motor because of the DC capacitor bank between the supply and the load (the VFD).

From experience, the amps to run it are not the issue, it is the inrush. When mine starts it dims my lights a bit, since I share a transformer with the neighbors, I know their lights dim as well. I think it is about 230 Amps when it starts up.

Inrush is in large part solved with a VFD - you can soft start it by bringing it up to speed over a longer period of time vs starting it direct on-line. i think this is the major limiting factor for single phase motors in residential applications. even motors used in commercial applications are put on VFDs so they can keep their demand pricing down (they get charged a multiplier for peak draw).

 

[rlitman]

...I will say that 24 SCFM is PHENOMENAL. This unit doesn't even breathe hard when media blasting, running a die grinder or cutoff tool, or anything else. I LOVE this compressor - especially after waiting for my alleged "5HP" compressor (that only needed 15A - do the math) to keep catching up with my blaster or air tools.

Yeah, I know exactly what you mean. When I bought my compressor, I wanted something that could run my DA non-stop. Blasting in my cabinet uses more than that. My biggest air sink is my rivet buster. That thing claims to use 40 CFM, and maybe it does, but for as much trigger time as I can muster, my compressor still has no trouble staying ahead of it.

 

[u3b3rg33k]

a quick google for a new, full price 10hp single phase drive:
https://www.wolfautomation.com/products/ac-drives/ac-drive-10hp-230vac-1-3-phase-ip20-35a

 

[rlitman]

with a VFD you don't necessarily need to put on a smaller motor / pulley. just run it at a lower RPM, and it'll have less HP. actual HP isn't determined by the size of the motor, it's determined by the load. the motor needs to be sized to provide enough torque to run your load at whatever shaft speed you need.
...
this is less of an issue with a 3 phase motor on a VFD -
1. a 3 phase motor has smoother power draw than a single phase motor
2. a VFD will by it's design have a smoother power draw than a motor because of the DC capacitor bank between the supply and the load (the VFD).

Inrush is in large part solved with a VFD - you can soft start it by bringing it up to speed over a longer period of time vs starting it direct on-line. i think this is the major limiting factor for single phase motors in residential applications. even motors used in commercial applications are put on VFDs so they can keep their demand pricing down (they get charged a multiplier for peak draw).

VFDs aren't magic. Slowing the frequency not only lowers the current draw (and horsepower), but also lowers the motor efficiency. Just look at the motor plate to see the 50hz derating.

Capacitor banks do not smooth power draw. They just shift the voltage waveform with respect to current, potentially improving power factor. But the combination of the capacitor bank with the stepping of the inverter creates multiple ring wave surges every second. While that will be above the frequency that your eyes can distinguish (so you won't see lights flickering), it is still damaging to motor windings over time. That's why VFD's are known to shorten motor lifetimes. Even ones rated for inverter drive.

Yes, the VFD can fix the inrush issue. Actually, it can do that REALLY well.

 

[Strouty]

Inrush is in large part solved with a VFD - you can soft start it by bringing it up to speed over a longer period of time vs starting it direct on-line. i think this is the major limiting factor for single phase motors in residential applications. even motors used in commercial applications are put on VFDs so they can keep their demand pricing down (they get charged a multiplier for peak draw).

Yes, the VFD can fix the inrush issue. Actually, it can do that REALLY well.

The only trouble with the VFD is that you technically need a 20HP due to the 50% rating. Also a VFD can be used for to ramp up a single phase motor as well.

I looked into all this before deciding to just find a single phase 10 HP motor. I still need the appropriate starter, mine is only rated for a 7.5 HP single phase motor.

 

[freudianfloyd]

Thank you for the responses everybody. The compressor is our old backup at work, so it was always maintained and in pretty good shape. The facility manager is the one who asked if I wanted it, and then when I said yes, he said how much will I pay for it? He said how about $300? I just emailed him back $200 and I will get it out of his way today. I will keep you updated.

 

[u3b3rg33k]

The only trouble with the VFD is that you technically need a 20HP due to the 50% rating. Also a VFD can be used for to ramp up a single phase motor as well.

I looked into all this before deciding to just find a single phase 10 HP motor. I still need the appropriate starter, mine is only rated for a 7.5 HP single phase motor.

The derating only applies to using a 3 phase VFD on single phase. if you're using a VFD meant for single phase input, no derating is required. The "CFW700 Single Phase" VFD I linked to above is intended to run a 10hp 3 phase motor on a 60/1/230 supply.

fwiw i thought it was a derating to 66% as you're using 2/3 of the input circuit for 100% of the power.

 

[Strouty]

The derating only applies to using a 3 phase VFD on single phase. if you're using a VFD meant for single phase input, no derating is required. The "CFW700 Single Phase" VFD I linked to above is intended 10 run a 10hp 3 phase motor on a 60/1/230 supply.

Except that VFD is just a 20HP one with a single phase 10HP sticker.

I get what you are saying, but either way you are paying for a 20 HP unit.

 

[u3b3rg33k]

Thank you for the responses everybody. The compressor is our old backup at work, so it was always maintained and in pretty good shape. The facility manager is the one who asked if I wanted it, and then when I said yes, he said how much will I pay for it? He said how about $300? I just emailed him back $200 and I will get it out of his way today. I will keep you updated.

the only thing i haven't heard is what's the input voltage? it needs to be equal to or below your supply voltage - if it's a 460V motor you may have a hard time running it with a VFD. if it's 230/208, no problem.

 

[Strouty]

Make sure to check the tag, a lot of motors will work on both high and low voltage with a simple swap of the wires.

 

[freudianfloyd]

the only thing i haven't heard is what's the input voltage? it needs to be equal to or below your supply voltage - if it's a 460V motor you may have a hard time running it with a VFD. if it's 230/208, no problem.

I believe it can be run on 208V.

 

[freudianfloyd]

Yes, it does have wiring for high and low voltage.

 

[u3b3rg33k]

Except that VFD is just a 20HP one with a single phase 10HP sticker.

I get what you are saying, but either way you are paying for a 20 HP unit.

The only thing that has to change is the input side - you don't need a drive capable of 20hp, you only need the input side (rectifiers and capacitors) from a "20 hp" unit. so you don't NEED a 20hp drive, even if that's what you're delivered.

 

[Strouty]

The only thing that has to change is the input side - you don't need a drive capable of 20hp, you only need the input side (rectifiers and capacitors) from a "20 hp" unit. so you don't NEED a 20hp drive, even if that's what you're delivered.

Again, you can't use a 10HP VFD on single phase power if you want to run a 10HP 3 phase motor. The "single phase" rated VFD you showed is either modified or a 20 HP rated unit. Really it is about the amp rating more than the HP, but most people rate them by HP.

 

[u3b3rg33k]

VFDs aren't magic. Slowing the frequency not only lowers the current draw (and horsepower), but also lowers the motor efficiency. Just look at the motor plate to see the 50hz derating.

Capacitor banks do not smooth power draw. They just shift the voltage waveform with respect to current, potentially improving power factor. But the combination of the capacitor bank with the stepping of the inverter creates multiple ring wave surges every second. While that will be above the frequency that your eyes can distinguish (so you won't see lights flickering), it is still damaging to motor windings over time. That's why VFD's are known to shorten motor lifetimes. Even ones rated for inverter drive.

Yes, the VFD can fix the inrush issue. Actually, it can do that REALLY well.

They sure feel like magic! we love them at work - they save tons of money. all the motors they drive are premium efficiency with shaft grounding rings. most of the big drives have output filters for longer runs.

for home use, i'd try to keep the output run as short as possible and not worry about it too much. the hour meter will turn a lot slower than it did at work.

efficiency (and cooling) is why i mentioned changing the pulley size. target the 90% desired operating condition for ideal operating conditions, and use the VFD to speed it up if you want full power (unless full power is the goal because you want that much cfm all the time). remember freudianfloyd, if you use a VFD, you'll have to re-wire the controls so you're not switching line power with the pressure switch. the drive won't like that. it's best to set up some controls - check the VFD conversion thread: https://www.garagejournal.com/forum/showthread.php?t=320064

Again, you can't use a 10HP VFD on single phase power if you want to run a 10HP 3 phase motor. The "single phase" rated VFD you showed is either modified or a 20 HP rated unit. Really it is about the amp rating more than the HP, but most people rate them by HP.

Agreed it's about current - it's symantics at that point. if you're comparing a purpose built single phase 10HP motor rated single phase input VFD to a 15/20hp rated 3 phase input that lacks/has defeatable phase loss shutdown, all you really care is about is "which one is more cost effective to buy?". if you can pick up a used 3 phase 20hp 230v unit for cheap, that's the path i'd take.

 

[u3b3rg33k]

Well it's mine. $200 and since I'm already at work, shipping is not an issue!

I may even have it sold before I get home.

or never mind all the VFD talk and just make $!

 

[Strouty]

I may even have it sold before I get home.

What? .

 

[freudianfloyd]

What? .

My plan is to install it at my house, unless the cost to do so is too high. I am just a hobbiest after all. I was talking to my dad about it, and he knows somebody who would like to buy it off of me if I decide not to keep it. I haven't decided for sure what to do, but if I could make a big enough profit on it, it may be worth it to use the profit to buy a smaller single phase compressor. My garage set up is currently an attached garage and an old pole barn. If I was to hook this up, it will be quite some time before I will have the setup to do it.

I by no means meant to waste anybody's time on answering my questions, I originally meant to buy it for myself unless it was more money to convert it than it was worth, but if I could get it cheap enough, maybe I could make a profit on it if I don't keep it for myself. Does that make sense?

 

[Strouty]

I was wasting my own time, you just happened to get in the way.

Just don't ask us for any help if you want to use PVC for your airlines.

 

[American Locomotive]

VFDs aren't magic. Slowing the frequency not only lowers the current draw (and horsepower), but also lowers the motor efficiency. Just look at the motor plate to see the 50hz derating.

You're confusing "efficiency" with "power". If you slow a motor down with a simple V/Hz VFD, you will lose power. The motor is spinning slower, running at a lower voltage, but the current will remain the same. That means less power. We have plenty of dual rated 400v50Hz/460v60Hz motors at work, and the nameplate efficiency is the same for both power configurations.

Capacitor banks do not smooth power draw. They just shift the voltage waveform with respect to current

A VFD's internal DC bus capacitors, coupled with the drive's input filtering greatly smooth the current pulses going into the drive. A VFD will have ~120 input current pulses a second. Much faster than the 5-10Hz pulses of current a traditional piston compressor would have

 

[rwa2004]

Please do follow up with how you figure out to run this, as I am in the same boat.

I did not want to go the route of a $1,500 VFD - because if I was to do that I could just run x2 5hp compressors during the few times my demand was that high. VFD's really don't pay for themselves on compressors, IMO.

For all the reasons listed above. I had considered setting up my 10hp compressor pump with x2 5hp motors - one on each side. The pump has x3 belt grooves and I would use x2 for the motor that starts first and x1 for the motor that is delayed by a few seconds. This would lessen the Amp in-rush. The unloader (and empty after cooler) would make it so 5hp is sufficient to start it.

What do you guys think?

 

[thecj3man]

I bought a used Saylor Beall 707 a couple years ago. I repowered mine with a 7.5 hp single phase motor. I love it. It is a great compressor.

 

[u3b3rg33k]

You're confusing "efficiency" with "power". If you slow a motor down with a simple V/Hz VFD, you will lose power. The motor is spinning slower, running at a lower voltage, but the current will remain the same. That means less power. We have plenty of dual rated 400v50Hz/460v60Hz motors at work, and the nameplate efficiency is the same for both power configurations.

A VFD's internal DC bus capacitors, coupled with the drive's input filtering greatly smooth the current pulses going into the drive. A VFD will have ~120 input current pulses a second. Much faster than the 5-10Hz pulses of current a traditional piston compressor would have

on that note:

93.6% at 50 or 60Hz. 25hp @ 60Hz, 20hp (80%) at 50Hz. What you'd expect from a 20% freq reduction.

 

[doojus]

Can you post some pics of it? If it's in anywhere near good condition, there's no way it would cost more to repower it than it's worth. As I mentioned these compressors are north of $5k new.

 

[tarbellb]

I was trying to run a 10hp 3 phase motor on big wood planer for a long time, its just really hard to find and justify the project.

VFDs are only cheap up to about 5hp, then they jump in price (there are some misleading retailers/specs out there)
Finding a 7.5hp single phase motor is also hard and typically expensive.

Unfortunately anything above 5hp gets much more complex and expensive in typical homeowner / small shop setups.

Flip it for some cash and buy something you can plug and play is my opinion.

 

[freudianfloyd]

Can you post some pics of it? If it's in anywhere near good condition, there's no way it would cost more to repower it than it's worth. As I mentioned these compressors are north of $5k new.

It is model 755-120.
View media item 84876

 

[doojus]

It is model 755-120.
View media item 84876

Man, that thing looks pristine!

This should give you a better idea of what you have:

https://www.paxontool.com/saylor-be...vibrationpadsautomatictankdraininstalled.aspx

 

[freudianfloyd]

Man, that thing looks pristine!

This should give you a better idea of what you have:

https://www.paxontool.com/saylor-be...vibrationpadsautomatictankdraininstalled.aspx

I just spoke with the facility manager that was getting rid of it. Apparently this was just the backup compressor and when they replaced the main compressor with a new screw type, the main became the backup and this one was just removed from service. He said there isn't anything wrong with it, and it has low hours on it.

 

[Boilerhouse]

Note that at lower than rated RPM, you will not have the cooling airflow you'd normally have. a little maths may need to be done to figure out if that's a real problem.

If considering a VFD, you may wish to check with the manufacturer and make sure a reduced speed does not affect lubrication as well.

 

[Strouty]

From what I can see it is a 707 pump. It is capable of using a 5HP or 7.5HP motor too, all you would have to do is change the pulley diameter so the motor had the power to turn it at the proper RPM. I would call the manufacturer and ask questions. While you could sell it, not being able to run it will kill the price. I would just replace the motor and run it.

Saylor Beall