DSG 13x30 Lathe Electrical Problem

DSG 13x30 lathe. Built 1974. Worked fine for years. Now runs for a few minutes then the contactor falls out of latch and machine shuts down. Pressing the motor start button does nothing. Pushing in the contactor the motor runs but contactor won’t latch. Wait a while, then it’s working again, maybe. Sometimes have to wait a day, sometimes only a minute. Any suggestions? Anyone have a schematic? Here’s a pic of the electrical cabinet.

Neither C1 or C2 will pull in or latch. C3, coolant pump, works fine.

Here's a electrical diagram, but no guarantees its the same as my panel is obviously different than yours (Mines a 1966 13 x 42, electrical diagram was mined from web or contributed by some good soul here, cant remember) I Was going to attach it but there's a small size limit on pdfs

Electrical drawing.pdf - Google Drive

When I had problems I put in new contactors, figured if one 50 year old contactor is gone, put all new in. It was small dollars done with surplus/used stuff

You didn't mention what type of device starts the lathe..a push-button or a lever. I see reversing mags so it's obviously able to run FWD as well as REV. When it won't run FWD have you attempted to start it in REV.

Electrics don't self heal so what you're looking for is a loose or fouled connection in the circuit somewhere.

A wiggy or multi-meter would make short work of finding the gremlin.

Does the lathe have a cover over the belts, etc, that has a micro-switch the kills the control circuit if you open the door? Those are the things to look at first.

Is that little piece laying in the bottom of the enclosure something important?

Stuart

Look at door interlock switch for dirt, grime, or adjustment, or maybe loose heaters...Phil

Agree with others on looking at NC contacts for doors, chuck guards, etc, after that its possible that the run/stop 3-wire setup has an issue. The NC contact on Stop not seating properly will definitely cause issues. The other NC is the contact for the overload heater section, which I think is below C1, C2 in your setup. Could be a mechanical issue with the "latch" or it could actually be an overheat on one of the 3 lines, but that wouldn't usually be intermittent without a manual reset.

Its also possible the contactor interlock (its a NO though) for Rev rotation is stuck closed and the lathe does not want to engage Fwd. But that is unlikely to be intermittent.

Thanks for the suggestions. All good ideas. I think I’ve isolated the problem to the overload relay which seems to be overloading but might also be mechanically damaged. Before I go replacing things I want to understand this device better.

Here is the identical part for sale on ebay

NIB MTE Overload Relay 3 Phase 25-60HZ UOL1/3 Red Box | eBay

Is anyone familiar with this device? I’m familiar with the Allen Bradley style heaters that reset by pushing them. A rack spins a small pinion gear that resets the heater. But this is different. The 3 heaters screw in across the center similar to AB style. But there’s a single red push button at the end that doesn’t seem to do much. If you look closely you can see a small red arrow next to this that can be moved to “hard” or “auto” position. What is that for? At the other end is a pointer that can be moved to different amp settings. What is that for? The heaters are like these

Set of 3 Heater Elements 01-153-10 MTE 01.000153.010 | eBay

I have the 7•5 installed. Seems like that might be 7.5 amp but with spindle turning, no load, I’m already drawing 6.6 amps. Also note the box in the ebay item this looks to be one of the higher amperage heaters.



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I am not at all familiar with that style, but the common two positions, when available, would be 'Hand' or 'Auto'..not 'hard'. This denotes if the overload resets automatically when cooled or needs to be reset by hand!

Typically, a solid state O/L would be current adjustable within its range, but I've never seen a traditional O/L that's adjustable, usually the heaters themselves have to be changed. I don't know what you've got, in that regard.

Stuart

Yes, Hand or Auto. Wish someone would chime in with some experience with this type of overload relay. The heaters do look like small heating elements but unlike the American style they don’t go open when overloaded. Instead they somehow trigger the relay and cause it to open circuit the contactor coil which of course shuts the machine down. For now I replaced the heaters with a copper strap. No more problems. But I still don’t know if the heaters are bad or the relay has a problem.


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Typically, a O/L heater does just that..it heats. Current flowing through the heaters create heat, and when that heat meets the design of the heater wires they trip a bimetal strip located near them which in turn drops out the control circuit of the mag. Heater are only 'bad' when the burn/fail 'open' which isn't often. The relay mechanism will gunk up and fail more often and this means replacing the O/L relay. This style couldn't be more "American"!

There is little rocket science here! Again..even a Harbor Freight multi-meter would narrow your search something fierce.

Stuart

Edit. Have to ID'd the current rating on the O/L's you have? They must be at least equal to the FLA of the lathe...and they must be all the same and installed properly in the relay. Bypassing the intended safety feature of the relay with solid copper straps is inviting disaster.

The heaters I’ve seen prior to this look like this:

PLC Hardware - Allen Bradley W30, Used in PLCH Packaging

These are super common. The heating element along with the bimetal strip and trip mechanism are combined in this piece which can be purchased with different current ratings.

This English made product is different. The heater only heats, and although they are replaceable it appears they must be matched to the rest of the device which contains the bimetal strip and trip mechanism. The heaters I have are 7•5 but that doesn’t look to be a current rating but may correlate to one.

Of course I have a multimeter, that’s how I isolated the problem to this device and also how I measured the 6 amps flowing through the heaters.

I jumpered the heaters only to debug the problem. The question remains, why does 6 amps which is a reasonable current for the lathe to draw trip this device? The heaters could be defective and overheating, seems unlikely, or the bimetal strip or trip mechanism could could have developed a hair trigger, also unlikely. Since it appears I have to buy the heaters separate from the device I’d like to narrow the problem.

Thanks for the help.



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Well..if your lathe ran perfectly for years, you've changed nothing and now the mag trips out and won't reset until it cools I would say your thermal device has grown tired, which isn't uncommon, OR, there is some mechanical issue that is taxing the motor more than before.

If your heater designation of 7.5 isn't some type of code but is the actual trip current, then your no-load reading on the lathe is very close to that..too close.

So..as your O/L relay is free standing, so to speak, installing a newer one wouldn't be a big chore. The very best next thing to do, IMHO, would be to get an Amprobe and measure each leg of the motor for a bit. This will tell you exactly what's going on in that department.

The problem is, the O/L is kaput, or the O/L is fine, doing its job and telling you 'Mr. Lathe' is working me too hard.

Not to flog a dead horse, but a loose connection on anything near the heater or overload will create a high resistance hot spot and may influence a thermal trip.

Stuart