RF-45 clone motor issues.

[Thoro]

I have a ZAY-7045F/G which is as I believe to be an RF-45 clone.

It has a 2HP single phase twin capacitor motor that is wired for 220V.

Here's the issue. Intermittently it will get stuck in "start". Upon starting the motor from stopped, it will make a screeching howling like sound. If I turn it off, and back on, usually this will solve the issue and it will start as normal. Now, one time, this happened, and it would not go away. So I took the motor off the machine and disassembled it to find that the contacts on the centrifugal start switch inside the motor had "welded" together. They spung apart easily, and I filed them clean and that solved the issue of it being permanently stuck, but it still intermittently sticks on startup.

So my question is, how can I remedy this? It seems fixable, i'm just missing the trick. I'm attributing it to a cheaper chicom motor and even cheaper parts being used inside. But maybe I'm wrong. I was wondering about something like dielectric grease on the contact maybe? But really, what would help here I think is to understand what is causing the issue of "welding" the contacts and then moving forward from there. This really makes using the mill a bit of a hassle at times, and I don't want it to stick permanently like it did before while I'm in the middle of a project again.

So here I am reaching out to those more knowledgeable with electric components for advice.

Thanks in advance.

 

[Ray C]

I have a ZAY-7045F/G which is as I believe to be an RF-45 clone.

It has a 2HP single phase twin capacitor motor that is wired for 220V.

Here's the issue. Intermittently it will get stuck in "start". Upon starting the motor from stopped, it will make a screeching howling like sound. If I turn it off, and back on, usually this will solve the issue and it will start as normal. Now, one time, this happened, and it would not go away. So I took the motor off the machine and disassembled it to find that the contacts on the centrifugal start switch inside the motor had "welded" together. They spung apart easily, and I filed them clean and that solved the issue of it being permanently stuck, but it still intermittently sticks on startup.

So my question is, how can I remedy this? It seems fixable, i'm just missing the trick. I'm attributing it to a cheaper chicom motor and even cheaper parts being used inside. But maybe I'm wrong. I was wondering about something like dielectric grease on the contact maybe? But really, what would help here I think is to understand what is causing the issue of "welding" the contacts and then moving forward from there. This really makes using the mill a bit of a hassle at times, and I don't want it to stick permanently like it did before while I'm in the middle of a project again.

So here I am reaching out to those more knowledgeable with electric components for advice.

Thanks in advance.

I'd say you're on the right track... I've never had one of those motors apart but, is there any way you could use a very fine piece of #200 or #400 emery cloth instead of a file to clean the contacts? The contacts should have almost a polished look and any burrs will cause arcing and eventual sticking.


Ray

 

[Thoro]

Hmm, OK. That makes more sense. I remember the contacts being a bit pitted, seemingly eroded from arcing. I'm wondering how far is too far on material removal of the contacts

 

[John Hasler]

I have a ZAY-7045F/G which is as I believe to be an RF-45 clone.

It has a 2HP single phase twin capacitor motor that is wired for 220V.

Here's the issue. Intermittently it will get stuck in "start". Upon starting the motor from stopped, it will make a screeching howling like sound. If I turn it off, and back on, usually this will solve the issue and it will start as normal. Now, one time, this happened, and it would not go away. So I took the motor off the machine and disassembled it to find that the contacts on the centrifugal start switch inside the motor had "welded" together. They spung apart easily, and I filed them clean and that solved the issue of it being permanently stuck, but it still intermittently sticks on startup.

So my question is, how can I remedy this? It seems fixable, i'm just missing the trick. I'm attributing it to a cheaper chicom motor and even cheaper parts being used inside. But maybe I'm wrong. I was wondering about something like dielectric grease on the contact maybe? But really, what would help here I think is to understand what is causing the issue of "welding" the contacts and then moving forward from there. This really makes using the mill a bit of a hassle at times, and I don't want it to stick permanently like it did before while I'm in the middle of a project again.

So here I am reaching out to those more knowledgeable with electric components for advice.

Thanks in advance.

Once the contacts have welded it usually takes more than just restarting to break them loose. I suspect that there is a mechanical problem in the switch such that it binds occasionally. The welding may have been a side-effect of the switch staying closed too long due to the binding and so getting much hotter than normal. Did you clean all the grease out of the switch?

 

[Thoro]

Didn't clean the grease out..... So you think it could be the centrifugal switch mechanism hanging up?

 

[John Hasler]

Hmm, OK. That makes more sense. I remember the contacts being a bit pitted, seemingly eroded from arcing. I'm wondering how far is too far on material removal of the contacts

AC contacts like that are usually a little disc made of two kinds of material (though the boundary between the layers may not be visible). Once the top layer is gone the contact is done for. Don't try to sand off all the pits. Just get a flat surface.

- - - Updated - - -

Didn't clean the grease out..... So you think it could be the centrifugal switch mechanism hanging up?

Well, it's something I've run across before. They stick open more often than closed, though. I'd get the switch out on the bench and go through it and try to eliminate all possible causes of binding. Clean up the contacts as well, of course. Possibly you need to weaken the spring a bit.

 

[silence dogood]

While you are about it on repairing the motor, check the capacitor. Short it first to eliminate any residue charge and check with an ohm meter. It should measure infinity. Also, if you see any bulges or cracks, replace.
Mark (Silence Dogood)

 

[Wireaddict]

I'd like to add a few things: first, as already mentioned, the contacts have a thin layer on them. This is silver which is a better conductor & apparently resists welding so you don't want to sand them much. If they're bad you might try taking the switch contact assembly to a motor shop to see if they have anything that'll fit, if not you need a new motor. Also, if you check the starting cap, use an ohmmeter & if it's good it'll read infinite as mentioned but beware when you first connect a discharged cap to the ohmmeter that it'll read a short then the resistance will slowly climb toward infinity as it charges. This is because the ohmmeter uses scale multiplying resistors which limit the current & may cause the charging time to take several minutes. Motor shops & places like WW Grainger sell motor run & starting capacitors.

 

[Craig_J]

I have a similar machine which came with the same type of motor. After less than 20 hours of use the starting capacitor blew up spectacularly. I attributed this to the centrifugal start switch sticking, although I had no notice other than an unusual humming. The distributor of my machine readily agreed to replace the motor, but I asked them for the same size 3-phase motor (which they offer on other versions of the machine). They were reluctant ("The wiring is not correct for a 3-phase motor!") but I assured them that I would take responsibility and they sent me a new Chinese 2HP, 3phase motor, I gutted the wiring and added a TECO VFD, and now I have a variable speed drive with NO capacitors or contactor relays.

I originally thought to get a Leeson metric 2HP motor locally (as I had done a similar conversion on my Grizzly 10x22 lathe), and was asking the dealer if they would cover it under warranty, but gave up when I found out the the shaft of the motor on my mill was smaller, the same size as a 1.5HP motor. It was much easier to get the factory to supply the replacement 3-phase motor, as drop-in fit, than buy the Leeson, turn and key its shaft, etc.

While I was waiting for the new motor to arrive from China, I cleaned up the explosion and tested the remaining run capacitor, which was good, and tried a new starting cap (just for a few seconds!) to determine that the centrifugal switch was indeed welded. After removing the temporary start cap (150uF), I also found out that the motor would start okay without it, although it was slow to spin up on the highest speed gearing and I am not at all sure it would have been safe to run it this way for an extended period.

A note about the conversion to VFD: you have to completely rewire the controls to do this. The VFD generates 220V 3 phase power from the 220V single-phase line. Its start, reversing and E-stop functions are all controlled by low voltage signals. So If you can handle the electrical changes, you get a superior machine: no start or run capacitors to fail, no centrifugal start switch, programmable start, stop, and E-stop speed ramps. Most machinists will also tell you that a 3-phase motor is simply more powerful than a single phase of the same nominal rating. I set the output frequency range to go from 30-90 Hz, which is equivalent to 1/2X to 2X the nameplate rpm in each gear range; I still use the gears to optimize the power for various operations. I am very happy with the conversion.

I have attached a photo of my mill. Note the new box to the left of the controls with the VFD. I welded this up to fit but of course the VFD could be mounted externally in a stand-alone enclosure. If you have access to the Yahoo Mill/Drill group there are more pictures under "Craig's RF-45 clone." If you are interested in going the VFD conversion route I can also supply a wiring diagram of the way I did it.

Craig

 

[Craig_J]

After posting the message about my exploding cap and subsequent 3Ph +VFD conversion, another thought occurred to me: Both my original 1single phase 1HP, 120V lathe motor and the 2HP, 240V mill motor used the same capacitors --150uF starting cap and 30uF run cap. This suggests two things: one, that if the start winding impedance is as low as I think it is, the start current would be 2X as much on 240V as on 120V. Since the 1HP lathe motor could be hooked up for either 120V or 240V, I would think the centrifugal switch would be much more abused at the higher voltage and current. In any case, the starting circuit is a weak link. Secondly, the phase shifted run current would be inversely proportional to the cap value, or 1/5 the starting cap current. The 3ph motor is superior because all three windings are equivalent and all contribute to establishing the direction of rotation. And, like I said, no switches, no capacitors....
Craig