Smoke In The Shop

[Chris Rosenberger]

We got home last night from a short vacation. So today I was resting up from the vacation & piddling in the shop. This afternoon I decided to mow the yard. I came in the shop for a break & could smell smoke from an electrical source. I could also see it in sun rays. I traced it to the air compressor motor. The overload button on the motor was tripped. The breaker was not tripped. I could not find any problems, so I pushed the reset buttom & turned the power back on. The motor ran fine. Some dust came out of the motor when it started. I got a flashlight & looked inside the motor. The bottom 1/3 of the windings are black from overheating.
What would cause this? This is an 80 gallon 2 stage CH compressor that is less than 1 year old.

What is involved in converting it to 3 phase? I have a 3 phase motor.
I do not know how the pressure switch connects with a starter.

[Steve Stube]

What HP? Do you have 3 phase power available?

[David Klear]

There should be a "head pressure" relief valve somewhere. If this thing isn't working the compressor will try to start with pressure in the pump that it can't overcome and trip the breaker or the overload switch. i would make sure that you don't have to big of breaker on the line also.

[Chris Rosenberger]

The motor does not have a HP number on it. It is rated at 17 amps. That is around 3 hp.
Yes I have 3 phase power.

[Steve Stube]

Having the 3 phase power available makes it a fairly easy swap. If your magnetic starter is already 3 pole you will be all set to hook it up assuming the pressure switch provides the power to the starter coil already.

Other factors are speed of the two motors (if the speeds, rpm's, are different you will need to make the appropriate pulley size change and at the same time insure enough pulley wrap to transfer the motor HP without slippage), size of the motor shaft, motor frame size.

[Dev Emch]

Its hard to say what happened here without seeing it. But it is a single phase motor and I think its safe to assume that you have no unloaders on this compressor. I have seen this myself. My old compressor was a 1/2 hp portable dayton from the 1960s. Often, it could not start by itself but just humm. I had to kick the flywheel with my sneaker to get it running. This worked as long as I was there. One night, i went in to eat dinner and during dinner, I heard the breaker in the laundry room trip. I ran out to the shop and found the compressor motor blowing black smoke. That was the end of this motor.

If a motor cannot revolve during start up, the windings begin to overheat and eventually cook the varnish insulation. This produces an odor you will not soon forget! Because most inexpensive compressors do not have unloaders, this puts the motor under an undue strain. Staring motors under full load is not a good idea. In most applications, this never happens.

Another thing to check out is whether the compressor motor actually tried to start up and was never able to release the start up windings. In a single phase motor, there is a centrifual cutout switch in the aft bell. When these get goobered up with sawdust and other debris, it prevents the start up coils from disconnecting after start up. This too will smoke a motor in no time flat. One reason I dont like single phase motors.

If you use your compressor only when its needed, you should consider changing it over to three phase. But if you have a phase converter and only use it when you need to run three phase, this may not be a good idea. Some folks keep the compressor wired and on all the time. As long as your air system does not leak, the compressor will not turn on. It will only run when an air demand is made. In such a case, three phase is not a good idea.

To convert to three phase, you need a motor that runs about the same speed. It does not have to be exact just close. If the motor runs twice as fast, then you cannt use it. You will need a three phase motor contactor. The pressure switch can be used to activate the contactor pull in coil. There may already be one but you need to verify this.

Let us know what you plan on doing...

Best of Luck...

[Steve Schoene]

I'm confused about three-phase power--not having it available at my location. Why does he need another motor if he has three-phase power available from the grid?

[David LaRue]

Chris,


Why not let the warranty handle a replcement motor?

D

[Dev Emch]

Steve...
The motor he has is a single phase motor. Three phase motors are different than single phase motors.

[Chris Rosenberger]

Thanks for the replys. The compressor does not have a starter on it. It is wired direct from the disconnect to the pressure switch. I will be adding a starter when I convert it to 3ph. I have a 5hp 3ph motor the same rpm as the 1ph motor. I get 3ph power from the grid & use the compressor when needed. It is always powered on.

Dev, could you explain what an unloader is? Can it be added to a compressor.
I am attaching a picture of my compressor.

[Dev Emch]

An unloader is a form of compression release. You see these on large chain saws and heavy duty single cylinder, pull start diesel engines. Its built into the head of the machine.

Check out my shop tour #1: Here is the URL

http://www.sawmillcreek.org/showthread.php?t=24608

In it, you will find my compressor pictures. Note the head of the pump. You see those "mushrooms" sitting up there? See how copper line goes down to the crank case? These are the unloaders. When a compressor starts up, they are open and only close when the crank case pressure builds to a certain level. Once the motor is running, the unloaders are closed and the pump is pumping air.

No. I have never seen a pump with no unloaders get retrofit to have them. You need to get the pump with unloaders for this to work.

[Chris Rosenberger]

Thanks Dev.
I was looking for a compressor like you have, before I got this one. I could not find one so you see what I ended up with. Maybe some day I will find one.

[Steve Stube]

Chris, you probably have an unloader valve in conjunction with your Hi-Lo pressure switch. Look for a small tubing air line besides the pipe conection between the pressure switch and your tank check valve. The actual valve is the same as a tire tube valve and vents to the atmosphere once you get to cut-out pressure. It stays open until just after cut-in pressure is reached on the next pump up cycle. When you switch to 3 phase operation the pressure switch will not be used to close the circuit and provide power to your motor as it does now, instead it will be wired to complete the circuit to the coil of your new magnetic starter (to be added) which will in turn provide power (3 phase feed) to the motor.


I believe that Dev's is a centrifigal unloader on the Quency and depends on pump rpm to operate.

[Chris Rosenberger]

Steve,
Thanks for the information.
It does have the unloader on the pressure switch.

[David Duke]

I was having the same problem with the unloader not opening up and the unit would try to start under a load causing the breaker to trip, my unit didn't have any adjustment mechanism on the unloader but I was able to bend the release arm and make it work, haven't had any problems since.

[Steve Stube]

Chris, there should be a little lever there also so you can trip and unload the compressor manually. This feature can be very handy if the compressor starts pumping and then looses power before reaching the cut-out pressure (where it normally unloads the compressor head), reinstating the power will cause the compressor to start again under load - not good for the motor. This is a good reason for manual reset overloads. You can trip the compressor unloader before reseting the power and start with a free-wheeling compressor. Centrifigal unloaders take care of this automatically as the rpm's drop to zero, they unload the head/s.