Import Lathe Contactor Questions 12x37

Discussion in 'Tools' started by StephenZ, Oct 5, 2018.

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  1. Oct 11, 2018 #21

    Cogsy

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    Actually, I believe I confused myself and this was a different issue. The one I'm thinking of was a forward/reverse switch going bad and when I pushed and held the button in I would often get the mag switch 'bouncing' in and out but not holding. The motor would start to spool up at this point. Sometimes it would engage, sometimes it wouldn't. As the switch failed over a couple of days it went from being a couple of clicks from the mag switch when trying to start to impossible to get running fairly quickly.
     
  2. Oct 11, 2018 #22

    StephenZ

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    Are you referring to the switches on the front next to the change box? I think I hooked up my meter to them and they were switching on and off..would anything else be wrong that wouldn't show with the multi meter?
    I should have the new power light monday, and the new main relay/contactor is in place now...if it doesn't work, maybe I should just wire up a drum switch or something...lol. For such a small amount of wiring, it sure gives a hell of a pain, doesn't it??
    Thank you for all the help, Cogsy! You're in Aus, huh? Odd question, do people still love Jamie Durie over there?
     
  3. Oct 11, 2018 #23

    minh-thanh

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    I think it looks like this :
    1.jpg
     
  4. Oct 12, 2018 #24

    Cogsy

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    I think my lathe is different to yours, but yes, the switches on the front. Mine simply has an on button and separate off button, and a 2 way direction switch. The on button is a momentary switch that engages a magnetic switch (relay?) with a heavy 'thunk' noise. When the directional switch started to fail (literally began to fall apart internally) it was apparently not giving quite enough contact to maintain the circuit for the magnetic switch and it would throw out. Holding the 'on' button in would generate a succession of 'thunks' as the magnetic switch was trying to stay engaged but kept throwing out.

    Jamie Durie...I have heard the name and I know he used to do something on TV but I'm not really familiar with him. Haven't heard the name for a while so maybe he's not so popular any more.
     
  5. Oct 12, 2018 #25

    StephenZ

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    That’s exactly what mine is doing. Cool...sounds like the contactor is the culprit.
    Ah, yeah...he and I worked together here in the states years ago. Really good guy. Miss that crazy little Aussie! Lol I need to get there to visit.
     
  6. Oct 12, 2018 #26

    Wizard69

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    Comments like these are very common with respect to Chinese lathes and is why I made my previous comment. We had very similar problem with a small lathe at work where the push buttons just didn’t work reliably. In one case I got some life out of the switch by shimming some parts to achieve better engagement until we had time to overhaul with real controls. Long term a controls overhaul may be required!

    The problem here though is we still haven’t nailed down root cause. That can be difficult to do over the net but I wouldn’t be surprised one bit if the issue is in fact a switch someplace.

    The other gotcha that often shows up is loose or bad could connections. I had one example of this at work the other day on a machine that ran for years without issue and then wouldn’t see that be switch input at the PLC. Apparently it has a connection at a terminal made with the terminals set screw pressing against the wires insulation. For whatever reason it ran for years like that and then decided to give upon the middle of the night. Of course things like this aren’t often obvious unless you tear things apart.


     
  7. Oct 12, 2018 #27

    Wizard69

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    It could very well be the contractor, an auxiliary contact or even a contact in the thermal overload. The problem with this Chinese stuff is the difficulty in getting the proper parts.

    This is why you often find the entire contractor assembly replaced on these machines with products that have higher local availability. In that regard I like the Telemacanique (Square D) and Allen Bradley brands as we have good local supply houses. In this day and age of mail order everything, people often ignore local suppliers but I like to think of them as members of the team.

    Some of the Japanese manufactures do really good controls but it is much harder to find local support. We have done work with Automation Direct and the stuff they import but that has mostly been their very good drives, not the controls you would need here.

    I hope this doesn’t sound like a commercial, I just prefer local suppliers as much as possible.
     
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  8. Oct 13, 2018 #28

    StephenZ

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    Ok...bear with me here. I'm losing my patience...lol. I took the original contactor apart and it had some parts falling out. I got it back together and it seemed to work ok. Suddenly, I had reverse spindle direction. no forward...still pretty exciting. I swapped the fwd/rev switch wires to see if the switches were bad. No. it still only wanted reverse. So I swapped the wires to the direction contactors to see if they'd allow forward. It popped the thermal overload breaker and now I don't have reverse anymore either.... Ok... I used the new CU-11 contactor and put it in place of the forward contactor. Still nothing...and no reverse still. Mind you, all this is still without the green 'power indicator' bulb even in the socket?! WTH?

    I also measured voltage from my transformer. With power switched on, it's in the 27v range. under load, it's 18-20v.. Does that seem like a low voltage that wouldn't hold the contactor closed?

    Well, I have a new transformer, but the wire block is a little different. I hooked 220v up to what says 220/0 and it was giving me 28v output. Problem is there's no ground on the low voltage side, so I left it off. Again, no spindle movement... I'm so over this. Any thoughts on the correct wiring to this trans?
    Old on right: wired 220v lines to 20&21
    30 low v to the 2a fuse (5.5-6v?)
    31 to thermal and on to everything (24v)
    E ground
    IMG_0394.jpg
     
  9. Oct 13, 2018 #29

    ignator

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    In this thread and the related one, there have been schematics that show a transformer with a 6volt output winding. Your transformer does not have this (old or new). You must find or make a schematic diagram specific to your lathe. The marked up diagram I posted (#20 of this thread), I believe to be close to your lathe. But this only has one indicator lamp.
    The "E" terminal is for EARTH ground, and is for safety only, in the event a winding faults to the steel laminated core. This earth ground wire should be connected to one of the screws mounting the transformer.
    For some reason you think the "green 'power indicator'" has something to do with making this work. I think I recall you indicating there are 2 lamps, one comes on when power is applied, the other when the safety control circuit is enabled. Don't fall into a hole believing the lamp is the problem, as was indicated in the other post.
    Can you please post a valid schematic that you believe your lathe has!
    There is a VA (volt amps rating) required to pull a contactor solenoid mechanism closed. If you exceed the transformers capability you can get this operation (not pull in the contactor solenoid). This can be from a damaged transformer, as well a damaged contactor coil. For your lathe to operate, the power required from the transformer has to pull in 2 contractors.
     
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  10. Oct 13, 2018 #30

    StephenZ

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    Yes! sorry, I've calmed down after a night's sleep...:) Your schematic from #20 looks to be the one. I only have one indicator lamp, too. I agree with not thinking the light bulb is the problem, I'm just keeping it in the back of my head as I tinker.
    I saw from your #20 post, the KA is energized while no direction is selected, correct? Then, did you mean that when a direction is selected, KA de-energizes (mag releases) and the KA1 or 2 energizes? Was that the safety system you referenced? (I'm just trying to understand all of it properly). If that is the case, that's what happens. When power is turned on, the KA energizes...when a direction is chosen, KA de-energizes, but nothing happens. I felt like when I chose a direction, and KA de-energized, I could push in KA to get movement, not KA1 or 2. At any time with only power on and no direction selected, I can press KA1 or 2 to initiate the motor.
    The pathways and wiring all make sense as I look them over, I think I get lost with all the wiring that goes back and forth between the contactors. I assume it's done to prevent accidental spindle starts, switching directions accidentally, etc...for safety. I kind of wish I could just get new guts and wire it myself, so I know it all...:)
    Thanks for dealing with me on this. I'm not used to needing help on anything...feels weird.
    -Stephen
     
  11. Oct 13, 2018 #31

    BaronJ

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    Hi Stephen,

    I'm a bit late to this thread but have you actually disconnected the motor and checked that it runs properly when wired directly ? The motor capacitor could have gone bad or a loose wire.
     
  12. Oct 13, 2018 #32

    StephenZ

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    Welcome to the party..lol. I can manually engage the contactors and the motor jumps to life. Would it make a difference wiring directly? I can do that easily, but the motor seems ok.
     
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  13. Oct 13, 2018 #33

    BaronJ

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    Hi Stephen, Sorry I thought that I'd read that the motor had stopped running when manually closing the contactors.
     
  14. Oct 13, 2018 #34

    BaronJ

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    Hi Stephen,

    Looking at post 20, I assume the correct circuit for your machine. Manually operating KAf or KAr should run the motor in either direction. Without power via KA neither of the other contactors will pull in or hold in.
    The power to operate KAf and KAr comes from the transformer low voltage supply. Probably via the start and stop buttons. One of which will be normally open and the other normally closed.
    DO NOT OPERATE KAf or KAr TOGETHER ! They have a looped back contact that prevents them both from being energised at the same time.
     
  15. Oct 13, 2018 #35

    ignator

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    KA is used as a safety interlock, this ensures that your direction selector on the lathe apron is in the neutral position, the intent, that the spindle will not spin until you are "at the wheel" wanting it to go. Its intent is in the event of a power outage, the lathe will not come back on until you move that lever back to the off position.
    So NO, KA must remain energized when you select a direction of spindle. If it does not, then there is some issue, either its coil has overheated and requires excess current from the 24 volt transformer to remain engaged, or the transformer overheated and can't provide the power to keep it engage, (or a loose connection), when you select either the forward or reverse contractor to engage (Km1, KM2). Loose connections can look the same. And as it was working before you brought it home, this is very possible. Or you are not powering it from the same voltage. I think you indicate this is a 220VAC system. If so, then ensure the motor is wired for 220. The nameplate shows Low and High voltage wiring chart, so ensure you have this correct.
    I've seen where they only change the wiring to the run windings, as the start windings are in the circuit for such a short time, that the motor design does not change them between high and low input voltage. If you haven't already looked up how the motor direction is changed, one of the windings, typically the start winding, has it's leads reversed, that is what the 2 contactors are doing (flipping the start winding connections). The start winding has a start capacitor in series, as well a centrifical switch that opens the connection to it after the motor has spun up to speed. You can typically hear this, as well when the motor is coasting to a stop, hear it click back closed.
    If you look up "3 wire stop start circuit" with google, you will see what the KA relay circuit is doing. The coil can only get 24v power if the direction switch is not selecting FWD or REV. That is the 2 switches marked SA1 and SA2 on the diagram. That is what initially powers the KA solenoid coil to close the contacts. Note once this occurs one of the KA switches, then applies the power to the coil to keep it energized
    Quick note on start stop push button control:
    (in a 3 wire start stop button circuit, the start switch, a normally open switch, powers the relay coil , and an auxiliary switch of that relay, then keeps the power going to it through the stop switch which is normally closed, when you press stop, the power is removed from the coil). This KA circuit is very similar.

    Then in series with the direction contactors is one of the 3 KA switch contacts. There is one in the circuit for REV coil circuit, and one for the FWD coil circuit.

    Note that the SA1 and SA2 are what is called single pole double throw switches, as when you move the lever for forward or reverse, the connection that would normally power the KA coil, is opened, and the 24 volt from the transformer is redirected to the FWD, REV contactor coil, but since a switch contact of the KA relay latches the 24 volt to the coil, it stays engaged. And there as others have said, is an interlock to ensure you don't energize the FWD/REV contactors simultaneously. KM1 and KM2 are the coils for motor direction contactors, that you have figured out how to manually close, and have proven there is no issue with your motor.
    If the KA relay ever opens, as you indicate, when selecting motor direction, the issue is either a loose connection or a bad KA coil, or 24 volt transformer.
    Please check that the motor is wired for 220VAC. Hopefully you have all the wires still connected properly, then verify that KA can close, and does not open again when you select motor direction. If it does check the KA switch that closes to keep the power to the KA coil. Check what the 24 volt transformer voltage does when KA is energized, and you then energize KM1 or KM2 for motor power. If it does not droop excessively then either a loose connection or a bad coil needs to be determined. Check what the 24 volt is at these coils. You need to track down the fault.

    Again KA must stay in the circuit as it has switch contacts in series with the motor contactor. You need to figure out why it is dropping out when you engage motor direction.
     
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  16. Oct 13, 2018 #36

    StephenZ

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    Ignator, thank you for that! It all made sense and I'm going to start tracking down everything again, with a good plan this time. I'll report back with voltage readings and findings. Meanwhile, I managed to draw a wiring diagram for my lathe. I hope I did a decent enough job on it. Oh, and the model of it is Harbor Freight#43681 12" x 37" gap bed lathe. IMG_0396.jpg
     
  17. Oct 13, 2018 #37

    StephenZ

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    So, with power on, no direction selected, the transformer has 22v coming out of #2 and 4v coming out of #1 and KA is energized.
    When reverse is selected #2 is 24.7v and #1 is 1.4v KA is de-energized
    When forward is selected #2 is 25.5v and #1 is .75v KA de-energized also
    (I still have no light bulb in the power indicator...coming monday in the mail.)

    EDIT: Good Lord. I put the old LED bulb back in and the light works...wth!? I've pulled the contactors out to check connections, but I'm going to do it again. stupid electrical gremlins.
     
    Last edited: Oct 13, 2018
  18. Oct 14, 2018 #38

    StephenZ

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    Ok. some tentative good news. I think it's figured out. (knock on wood) So the KA contactor was bad. I switched stuff around as I traced and tested all the wiring and put a new one in place and got reverse spindle to work. The light bulb is also working. Forward isn't working right now. I swapped the switches, and they're both good. I also switched the auxillary contactors on the direction contactors and still no forward. So far, I traced currents while the spindle is running and it seems like the forward contactor isn't getting the 'go ahead' from the reverse contactor via the 17 wire. I think. If that's the case, I think the reverse direction contactor has an issue. It runs fine for reverse, but isn't signaling the forward to go.
    Does any of that sound correct? It seems like the signals and currents from KA were correct...anything I'm missing?
     
  19. Oct 14, 2018 #39

    ignator

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    StephenZ; OK, a reply to post #37;
    The KA relay, probably is not the problem, but the wiring to the hold switch, or that switch is preventing it from staying energized.
    Also the schematic I've been using came from post #3 RM-MN, as he posted Harbor Freight schematic link to SKU: 43681.
    You need to check the KA holding contact, and it's wiring, I don't think that relay is bad, as the coil pulls in.
    upload_2018-10-14_14-12-43.png
    So look at this diagram again, note the (top in this diagram) KA contact that is circled, this is either is oxidized, or the wires are loose. If you can take the relay apart, and check for the contacts being clean, if they are, you should be able to get low ohms measured when you manually close the KA relay solenoid. IF you do, check the wiring to ensure the 24 volts from the transformer is making there, and out to hold the KA coil energized.
     
  20. Oct 14, 2018 #40

    ignator

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    Reply to post #38;
    Using the wire numbers from the diagram for the 43681 lathe, did you "mess" with any of the wiring going to the FWD/REV micro switches that the direction lever actuates?
    As these are single pole double throw, there is a common connection, and a NO, NC (normally open, normally closed) terminal. If you swapped the wires on one of these, that can explain why you can't get forward.
    Note the 24 volts from the transformer is connected to the common terminal of SA1, the normally closed terminal of this is connected to the common terminal of SA2, and from there the NC terminal is connected to the KA coil. This is the safety circuit that ensures you have the selector in a neutral (non FWD REV) position.
    Note the NO terminals of SA1 and SA2 are connected to a KA relay contact, through an interlock contact to prevent FWD and REV from simultaneously being energized. These are what power the KM1 and KM2 motor contactors.
    You need to follow the wiring diagram, and using the ohm meter of your VOM (or multi meter if you call it that), trace the signal path.

    In your post #37 "22v coming out of #2 and 4v coming out of #1" you must be using ground of the machine to measure, and not the terminal #1 from the transformer, this will not give the correct reference, but it's close enough. For the low volts, you should use one of the transformer leads for a reference for voltage measurement to the coils. That would be marked as a 0 (I think that's what it is, but might be a 4, as the scan quality is poor). Note this low volts is isolated from the AC mains power. Your old transformer had a chassis ground that was for isolation protection, the diagram shows this as a line between the primary and secondary windings. And shows AWG20 GREEN for the wire of this.
     

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