Starter contactor intermittant
We have a 3ph Powermatic table saw that has a contactor, and last summer it was acting odd, shutting off in the middle of cuts and at random, sometimes it would just shut off while cutting, when not cutting and just idle, sometimes it would shut off multiple times in a row and then run fine for days.
It ran all fall, and winter just fine, now suddenly again this problems starts up.
The motor always starts up immediately, thing is, the shutting off at random doesn't appear to be related to anything I've been able to associate it with like overload, getting hot from long use etc.
Of course other people's "solution" at work is to blow the contactor box out with compressed air, but it's a SEALED box with a gasket and it's always clean inside and blowing air in it does nothing, least of all fixes this problem.
So today I explored it in detail and opened up the small cover inside to look at the contacts
I pulled out the first half of each and the actual contacting areas were pretty oxidized and burnt, the photo shows the other half of the contacts in place and the bottom 3 can be seen as they were, the upper row of 3 I just touched to some 320 grit sandpaper to clean them to bare metal and put them back in.
After cleaning the bottom 3 and the flat contacts removed (not shown) I put it back together and started it up, works fine so we'll see if this fixes that intermittant problem.
My theory is that these contacts were making a poor connection, and with vibration added in, it would only take a momentary interruption to de-energize the coil and release the contact bar, shutting the saw off.
Just curious if any have run into this and if my theory is in fact correct and the cause of this problem.
The contact surfaces are still silvered and smooth not pitted, so they are not so burned they are down to copper.
Only other thing I can come up with is the contactor coil itself is failing, but I think the contacts being this bad that this is the cause.
Dirty contacts would have been my first guess.
Are you thinking in terms of the heater possibly being bad?
This isn't a Square D, it's some brand I never heard of that I can't remember at the moment, something like Ameri___ with a type 1 nema enclosure.
I can jot it down tomorrow.
I have not had to replace a heater before, it's one component I've only heard of but haven't had to replace or look at for troubleshooting.
We'll see if cleaning the contacts makes any difference in the next couple of days, and if the problem still exists then I'll have to look deeper.
Check the heater numbers and many time you should able find the number stamped on the heater itself but not always the case.
Once you have that heater number and look inside the cover which they generally will have heater slection chart there if not you may have to look up in the internet or check with the contractor manufacter.
I think the heater is set too close to the limit of the moteur.
So the only way you can slove is give us the CV and full load amps plus voltage ( pay attetion if you have 208 volts that can change the number some if you do have 208 volt system let us know ) and we will go from there.
What makes you think there is something wrong with the contactor?
Contactors are held closed by a circuit. Or intiated by a circuit as in a mechanically held contactor. You don't have a mechanically held contactor.
These circuits are OL and sometimes overheat switched.
When either presence is known to the contactor, the contactor coil is dropped. Just like when you turn it off. Same thing.
You're problem most likely is not in that box, but somewhere else. Like your motor and/or the overload you are applying to it.
The contacts don't look to bad from this view?
No need to replace the heaters.
If you do not have to reset the OL when the motor stops, it is not the heaters.
Look for a loose connection in the start stop circuit.
Like JV said, that is and electrically held circuit.
I'm leaning towards what JV is saying. I would be looking at what activates the coil.
A bad connection on one of the 3 phases would typically have the motor slowing down...lack of power.
You should be able to hear the contactor......if the contactor is making noise...coil and related ckts.
A common problem is low control voltage going to the coil. Typically they pull about 1/4a (some more, some less) at 120Vac. If the voltage at the coil gets below 105...your going to start getting drop outs.
Most buckets bring the coil connections to terminal blocks in the front of the bucket or cabinet where you can reach them safely. Also make sure you have a good common connection on the L2 side of the coil.
BTW...see those connections on the side? Those are Aux contacts....typically used to turn on a light or for feedback to a PLC.
This contactor dates back to before my time in this shop and I've been there 16 years.
The brand is: Telemechanique, Cat #A203C magnetic starter class A-20
The motor is a Baldor 3ph, 230/460v 5hp saw duty TE, 13/6.5 amps
The issue is this machine randomly shuts itself off with NO LOAD at all on it, or during a cut, it might run 2-3 hours just fine one day and another day it's shutting off 5 minutes after you turn it on and repeatedly shuts off every time you turn it back on.
Sometimes it will keep shutting off repeatedly and then suddenly it will run fine for days or weeks.
It was doing this last summer and then suddenly it ran just fine all fall and winter, now were into June and all of a sudden it's started doing this random shutting off again.
This table saw is very heavy duty, cast iron top, not one of those portable tablesaws you see in people's garages or the back of pickuptrucks. The other day it shut off repeatedly at random while I stood there and watched it run with no load at all on it.
It also shut off when a worker was cutting some strips of 1/8" thick phenolic, if cutting that thin material with a phenolic cutting blade using a 5 HP 3ph motor is overloading it in any way, well I'm done with Powermatic and Baldor motors LOL!
It's not like this saw gets used to rip 16 foot long 12/4 oak planks, we have two Altendorf sliders for this, the Powermatic is usually used to cut small things, 1/2" plywood, MDF, trimming poplar boards, or angle cuts where we need the opposite angle the Altendorf blade tilt gives.
The saw is similar to this new model:
When the saw suddenly shuts off, pressing the start button turns it immediately back on without fail, every single time.
I am disinclined to think it's a problem with the motor itself, at least at this point, it's a quality Baldor motor, does not get hot, it runs well. I believe this motor is not the original, I doubt the contactor is either, they both seem newer than the saw and not the brands Powermatic used on these saws.
Here's the other thing- vibration, I have known the blades have a small amount of runout due to the arbor which I know is not running true, it's good and tight but seems it is bent just enough to cause a slight runout on the blades and that in turn produces a little vibration. Also, the 3 belts were slightly slack and they were generating some vibration as well.
I tightened up the belts this morning and the vibration is reduced.
You are correct, those contacts are not terrible, not pitted or half gone, but they were not in the best shape, so they were cleaned up last night, reinstalled and test run for 10 minutes.
The saw ran fine, I ran it this morning for 10-15 minutes again, and it did not shut down.
Over the next couple of weeks with use- will confirm or deny the dirty contacts and maybe also the vibration were the cause(s)
We also have a large German made bandsaw that has a contactor as well, but this contactor is a Furnas and it's a magnetic type.
I opened it up this morning and it's contacts were not great looking either, I cleaned those.
This one has a remote starter switch the saw does not, what happens with this one is you turn it on and the contactor doesn't always "catch" and it shuts off, sometimes you have to hit the starter button several times before it finally stays on, once running it stays running reliably.
In this one I opened the remote starter switch, and it's a Siemens unit, I noticed one of the 3 wires had darkened the contact area, and one of the 3 hold down screws was not as snug as it should have been.
The Furnas contacts were much more involved to get at that the Telemechanique, here's the Furnas with one of the contacts loosened;
Not bad, but still not likely to make a real good contact.
I think on this one the issue might be in the Siemen's switch, I was not able to do much with it being the housing of the switches is so narrow, I cleaned out some of the carbon and crud where the wire had been arcing a little, put it back together and it was non functional, opened it up again, loosened and retightened the screw hold downs, and it works.
So I think on the bandsaw it's the remote switch is the problem. Like the saw it has done this at random, for periods of time follwoed by long periods where it functions perfectly, followed by cycles where it malfunctions again.
Quick question....on your start switch....
You push the yellow button and it starts? Then to stop it you smack the big red button? (also called an Emergency Stop)
Then to restart you have to pull the E-Stop and hit the yellow button?
If so...you have a relay in there wired for self latching.
Basically, when you push the yellow button it energizes the relay. The relay will have at least 2 sets of contacts. One set goes to the motor contactor. The other set is wired in parallel with the starter with the E-Stop button in series. When you energize the relay, it holds it's self in. When you hit the E-Stop, it breaks the ckt causing the relay to de-energize and kill the contactor.
I'm betting you have a bad connection somewhere between the switches and the relay. In fact, I wouldn't be surprised if the relay was not loose in it's socket.
I thing we agree there based on the symptoms and all, I've felt that the magnetic coil pulling in the contact bar is letting go (for whatever reason)
at random, either because it's own power is just barely enough or getting interrupted, or possibly the vibration I mention in my last post might have been just enough to do it.
The contacts are clean and the vibration is reduced by tightening the 3 belts on the motor, we'll see this week or next if what I've done has solved this!
The original 1988 paperwork for this says they used a Furnass starter contactor, it doesn't specify the brand motor used but all of the contactors listed on the sheet were furnass, the contactor can be be seen in the photo, it's obviously replaced the original one, and before my time.
Its a magnetic starter/contactor and is not a mechanical contactor according to your description and part number.
If you have a coil that pulls in the contactor, it is magnetic.
If you must physically engage the starter/contactor it is a mechanical contactor.
If it drops out for no apparent reason, I still say its not the contactor. Could be anything including a loose wire.
Have you measured current across the motor?
Are you 100% positive you have the correct heaters installed?
High current equals low voltage. The coil requires about 80% of the voltage listed on it. Should the voltage fall below this threshold, the coil could not keep the starter pulled in.
You are using line voltage for the control? Right?
So to my way of looking at these, I would still consider this a "mechanical" starter but automatically actuated by pressing a button instead of moving the contacts in manually by hand.
I did not dissassemble to unit enough to get down into the guts of it, just in far enough to expose the contacts and remove them which was very simple on this.
Do the heaters have a tendency to become defective over time?
A loose wire is a definite on the band saw which uses a remote start/stop switch, on this table saw I have not found any loose wires or any connections which look burned or oxydized.
The only thing I found was the contacts were dirty, and the belts on the motor were loose and causing some vibration which was also being transmitted to that contactor box.
The box is not rigidly attached, it sort of hangs under the table top near the motor, so it would make sense it gets some measure of vibration.
The vibration, while not a lot, might very well explain why this happened last summer, was fine all fall and winter and then suddenly starts happening now- June is the month as well as December I normally spend a couple of days and go over all 50+ machines and clean, oil, lube, check belts, replace parts as needed etc etc. so it would make sense the problem went away last summer and didn't appear again untill NOW just a week before I normally check all the machines.
I am pretty sure the belts were loose a year ago, and again now, and possibly the vibration may be the cause.
I had cleaned the contacts AND tightened the belts the other day, so far the saw has only been used briefly a couple of times since (with no problems) but it could take a week or two before it sees enough use to determine if this problem has been fixed.
For now I'll go conservative on this and see how it runs over the next week or two, so far it seems from two brief test runs, that the problem has been solved, if not I'll have to dive further into your suggestions and so on.
Electro Mechanical would be an accurate description.
Heaters don't come and go...in fact, I'm willing to bet that all your problems are related to the coil and related start/stop.
Follow the wires that go to the starter coil....I bet you have a relay in there...and I bet that is your problem...either loose in the socket or a loose wire on it.
Its still not a mechanical contactor. A mechanical contactor has physical push buttons on the contactor for start/stop. No coil.
You have a magnetic contactor. Or as Dawg put it, electromechanical.
You can check that you have the correct heaters by looking at the list inside the starter, starter cover or finding the cut sheet for those contactors.
If the heaters are over sized, high current can exist without the heaters responding. This very well could drop out the coil on low voltage.
If you plan to continue doing this type of work, I highly suggest you get a a current clamp meter. Amp clamp.
This along with a multimeter is absolutely required for troubleshooting issues like this.
If you buy a good multimeter, it will accept an amp clamp input.
This way you kill two birds with one stone.
Find a current clamp and take some readings. This is your next step.
|All times are GMT -5. The time now is 10:24 AM.|