Need help with "low power" 5 hp Saylor Beall 704 compressor

shepherm · Jan 24, 2021

I have search and search, but haven't found a solution to my problem. So I'm going to see what you guys think, and thank you for any feedback you can provide. I bought this compressor yesterday from a guy who said it had low power. The motor data plate is missing, so I'm not sure if its a wiring issue or something else.

Here is a video of the motor running loaded and unloaded, and the wiring.
Youtube Video

How it is wired:
Hot 1 => wire 1, 2, 8
Hot 2 => wire 3, 4, 5

Wire 1, 2, 3, and 4 are gray
Wire 8 and 5 are red

Wire 8 goes to four capacitors that are in series, and goes into the motor. I checked the capacitors and all measured within their printed microfarad.

I check the resistance between the wires:
1 to 3=> 1 ohm
2 to 4=> 1 ohm
8 to 5=> 1.4 ohm

dalmatiangirl61 · Jan 24, 2021

Spitballing, either its a 3 phase motor that someone added caps to so it would run on single phase, or it is a single phase "farm duty" motor, I cannot tell without a data tag. Won't help me, maybe one of the smarter guys can tell if you will map out wiring and how the caps are connected.

shepherm · Jan 24, 2021

dalmatiangirl61 said:
Spitballing, either its a 3 phase motor that someone added caps to so it would run on single phase, or it is a single phase "farm duty" motor, I cannot tell without a data tag. Won't help me, maybe one of the smarter guys can tell if you will map out wiring and how the caps are connected.

Thanks for your reply. I thought it might be a 3 phase too but this is way out of my league... Here is a rough sketch of how it seems to be wired.

dalmatiangirl61 · Jan 24, 2021

I'm leaning towards saying its 3 phase, just not sure. If so, 3-4-5 would be the star connection, caps would be shifting phase one the one winding. Are you using numbers on the metal tags? No 6-7?

I've changed out caps and bearings in a few of the farm duty motors, always wondered if they were just a 3 phase motor with caps, or if they were truly different. Been too long since I was in one, don't remember them having a centrifugal switch.

Phil in Montana · Jan 24, 2021

Looks like single phase motor, you are missing the centrif. switch, or it could use a starting relay, but something has to drop out the start winding. Also it should have a run cap...its awol to...Phil

shepherm · Jan 24, 2021

dalmatiangirl61 said:
I'm leaning towards saying its 3 phase, just not sure. If so, 3-4-5 would be the star connection, caps would be shifting phase one the one winding. Are you using numbers on the metal tags? No 6-7?

I've changed out caps and bearings in a few of the farm duty motors, always wondered if they were just a 3 phase motor with caps, or if they were truly different. Been too long since I was in one, don't remember them having a centrifugal switch.

Yes, the numbers are from the metal tags on the wires. No 6 or 7.

Phil in Montana said:
Looks like single phase motor, you are missing the centrif. switch, or it could use a starting relay, but something has to drop out the start winding. Also it should have a run cap...its awol to...Phil

Thank you Phil. I'm assuming I would need to pull the motor apart to find the centrifugal switch. Hmm I'm not sure where the run capacitor would go in the box..

Phil in Montana · Jan 24, 2021

Switch would be inside, might be bad, have you tested the caps?...Phil

shepherm · Jan 24, 2021

Phil in Montana said:
Switch would be inside, might be bad, have you tested the caps?...Phil

Okay, I guess I'll plan to pull it apart this coming weekend. Yes, I did check the microfarads with my fluke. They all showed within the range listed on their labels. With that said, only the newer looking cap sparked when I discharged the terminals before removing the wires. I'm not sure if that means anything or not.

Phil in Montana · Jan 24, 2021

No means nothing, before you pull it apart, try putting a switch in the cap line so you can disconnect them by hand when the motor gets to speed.. se if it runs better...Phil

Strostkovy · Jan 24, 2021

Before tearing into the motor, pull of the belts, plug the compressor outlet, and spin the wheel by hand. If it spins freely you could just have shot valves or rings in the compressor head.

The way I would test is run it with a noncontact tachometer and an amp clamp. If amps are low, and speed is normal, the motor is fine but the compressor head is done.

If it's doing anything other than running properly, something will get hot. These sorts of motors don't draw low power unless they are near their synchronous speed.

shepherm · Jan 24, 2021

Phil in Montana said:
No means nothing, before you pull it apart, try putting a switch in the cap line so you can disconnect them by hand when the motor gets to speed.. se if it runs better...Phil

That's a great idea! Thank you!

Strostkovy said:
Before tearing into the motor, pull of the belts, plug the compressor outlet, and spin the wheel by hand. If it spins freely you could just have shot valves or rings in the compressor head.

The way I would test is run it with a noncontact tachometer and an amp clamp. If amps are low, and speed is normal, the motor is fine but the compressor head is done.

If it's doing anything other than running properly, something will get hot. These sorts of motors don't draw low power unless they are near their synchronous speed.

Click here is see video of motor running

The compressor turns pretty easy by hand and the motor spins without a load (see video above). I will buy a amp clamp, I've been needing one just haven't bought one yet.

Do you guys think the winding should be in series, not parallel like they are wired now? I guess my question is should wire 2 and 3 be disconnected from the hot wires and wired together? Right now I believe its wired like the top, but the bottom looks correct.

Thanks again for everyone's thoughts.

Phil in Montana · Jan 24, 2021

What is your supply voltage 120 or 240... the windings should be parallel
for 120 volt and in series for 240. Your print is 120 volt hook up. for 240 you will also need to move the start winding to the center tap, also if you were supplying 240 to the print you have shown the amps would be off the chart...Phil

Strostkovy · Jan 24, 2021

Definite loss of starting torque. What's the capacitance and voltage ratings of the capacitors? I'm 90 percent sure those should be in parallel. If there is a stuck open centrifugal switch it will start (or fail to start) like this. If it is stuck closed, everything would work normally but the motor would "growl" once up to speed and the capacitors will overheat. If it is meant to start and run off of the same capacitors, there will be no switch but it will require a lot of run rated capacitors in parallel, which is what I think you should have here.

Start capacitors in series make no sense. The heating in them is due to resistance, so it's not really any easier on the capacitors than a lower capacitance capacitor doing it by itself. Parallel makes lots of sense, as that distributes the heating load.

Strostkovy · Jan 24, 2021

Also, those windings should probably remain in parallel, as this motor is probably not intended to run on 120V, being 5hp. Those windings are separate largely so you can reverse the polarity of one relative to the other to reverse the rotation of the motor.

Running one winding in series with the other regular winding and the capacitor shifted winding in parallel would not distribute power across the windings evenly at all.

And, as mentioned, you can really only get away with that configuration if you have a motor with a centrifugal switch, and I don't think you do. But even if it does have one, low voltage configuration for a 5 horsepower motor is guaranteed to be 200V or more.

Ziggy2 · Jan 24, 2021

That is a 3 phase motor that has been converted for single phase use. Farm Duty is often one name type reference. The caps are basically a static phase converter. The motor will produce about half the normal expected power.

Strostkovy · Jan 24, 2021

Alright, I watched your full video and that looks more like a 2hp motor to me, which would make the 110V low voltage winding a possibility. If that's the case, then the capacitors can be in parallel, but shouldn't be in parallel at 240V.

The blue terminals are definitely not factory, and I think someone tried messing around in there to fix terminals and mixed something up and gave up. But it sure sounds nice on whatever voltage the video showed it idling at, so I'm not convinced of that either.

In any case that one oddball capacitor isn't the right one to have in there if the capacitance doesn't match.

This is a website that has a leeson farm duty motor wiring diagram: Electric Motor Whole sale

I now have no clue what you actually have without seeing inside the motor.

Ziggy2 · Jan 24, 2021

Strostkovy said:
Definite loss of starting torque. What's the capacitance and voltage ratings of the capacitors? I'm 90 percent sure those should be in parallel. If there is a stuck open centrifugal switch it will start (or fail to start) like this. If it is stuck closed, everything would work normally but the motor would "growl" once up to speed and the capacitors will overheat. If it is meant to start and run off of the same capacitors, there will be no switch but it will require a lot of run rated capacitors in parallel, which is what I think you should have here.

Start capacitors in series make no sense. The heating in them is due to resistance, so it's not really any easier on the capacitors than a lower capacitance capacitor doing it by itself. Parallel makes lots of sense, as that distributes the heating load.

You parallel capacitors to increase the capacitance, it has nothing to do with heat load. Capacitors in series allow you to increase the working voltage of the capacitor bank.

SomeoneSomewhere · Jan 24, 2021

Strostkovy said:
Also, those windings should probably remain in parallel, as this motor is probably not intended to run on 120V, being 5hp. Those windings are separate largely so you can reverse the polarity of one relative to the other to reverse the rotation of the motor.

Running one winding in series with the other regular winding and the capacitor shifted winding in parallel would not distribute power across the windings evenly at all.

And, as mentioned, you can really only get away with that configuration if you have a motor with a centrifugal switch, and I don't think you do. But even if it does have one, low voltage configuration for a 5 horsepower motor is guaranteed to be 200V or more.

To reverse the rotation, you would need to reverse the start winding vs the main winding(s). Having one main winding in one direction and the other in the other direction would not work - your motor would likely sit there and buzz loudly.

This is a reasonably common design where each main winding gets 120V and the start also gets 120V - the start winding doesn't need to draw a huge amount of current if you don't need a massive starting torque, so it's only a little bit unbalanced and only during starting. It's "good enough" and means you don't need a second series-or-parallel pair of start windings and start caps. I agree that it's odd for a motor this large to be dual-voltage, though.

Just because I haven't seen it said here yet, assuming the resistance measurements are accurate, this isn't a three phase motor. The resistance readings would be symmetrical.

Strostkovy · Jan 24, 2021

Ziggy2 said:
You parallel capacitors to increase the capacitance, it has nothing to do with heat load. Capacitors in series allow you to increase the working voltage of the capacitor bank.

Paralleling capacitors is often done to keep capacitors running cooler. You can run capacitors in series to increase the working voltage, but that math almost always works out that the capacitors run cooler rated at the higher voltage, lower capacitance, and in parallel.

SomeoneSomewhere · Jan 24, 2021

Ziggy2 said:
You parallel capacitors to increase the capacitance, it has nothing to do with heat load. Capacitors in series allow you to increase the working voltage of the capacitor bank.

True, but capacitors rated for motor starting voltages are readily available; it would be unusual to put them in series except to allow motor voltage changes.

A shortage of capacitance could possibly cause these symptoms.

Need help with "low power" 5 hp Saylor Beall 704 compressor

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