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Thread: DM4400-what size 3 phase motor for rotary converter

  1. #73
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    Default Re: DM4400-what size 3 phase motor for rotary converter

    Yes, the big isolation transformer, the secondary is the lower voltage side in this case. Yes, the grounds are any part of the machine or electrical cabinet, and the grounds connected to the transformer shelf are machine grounds.



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    Default Re: DM4400-what size 3 phase motor for rotary converter

    Jim, I think you may be onto something. I checked all the secondary terminals against ground and got about 27 ohms consistently. I was pretty surprised at first so I checked several ground areas, always got the same thing, so no question about it. I also checked the meter carefully that I wasn't getting M or K, just plain ohms.



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    Default Re: DM4400-what size 3 phase motor for rotary converter

    YES! WE HAVE LIFTOFF!

    Once I found the problem with the secondary (many thanks Jim), then I had to ponder for a while how to trace that problem. Finally it dawned on me, just disconnect all the secondary connections and go from there. Once I got that done, the resistance was infinite, okay, so far so good. Then it was just a matter of re-connecting one by one until I found a pair that were suspect. I reconnected everything else except those two, and there it was: no ground fault on the amp, the spindle initialized and I was able to run it through all the speeds. I'm stoked! Well, the spindle bearings are clearly shot (really loud) but at least that's a lot more my element than the electrical.

    About that pair of wires, I'll have to trace that down and see what it feeds, the schematic should help. I checked the resistance between each wire and ground, one of them was the 27 ohms, and the other was about 20K. Does that mean anything, like which side of the connection is the more problematic?

    At this time I had re-installed the second amp, which has not been converted to the single phase, so Jim you were right, it does run on single phase without the rectifier, but it sounds like the rectifier is the preferred way to go because of the power available. Is my understanding correct on that?

    Well, many many thanks to both Jim and Marty for your help with this. And hopefully this will be invaluable help to someone else bumbling around with their cnc electronics.



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    Default Re: DM4400-what size 3 phase motor for rotary converter

    AWESOME Too bad about the spindle bearings.

    Sorry, I have no idea about the wire pair, you are just going to have to trace them down.

    I really don't think it will make any difference which rectifier you use, the 3 phase or the new single phase. They both do the same thing, the 3 phase rectifier just has an additional diode pair for the third leg.

    I'm happy to be of some help.



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    Default Re: DM4400-what size 3 phase motor for rotary converter

    I believe I've traced the pair on the schematic to a motor thermal switch. Don't know if you can make it out on the pdf--page 90 (page 1 of the schematic). The two single phase inputs are connected to the lower two coils on the transformer, and the suspect pair are the 115V connections. Those lead to page 3 (of the schematic) which leads back to page 2, where the thermal switch is in zone J14. I can't find any mention of the switch in any other place. It should be in the troubleshooting section, but I couldn't find it. Anyway, it does make sense to look for that, possibly the switch is stuck closed or has a bare wire.



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    Default Re: DM4400-what size 3 phase motor for rotary converter

    The thermal switch shows normally closed, and the 27 ohms now makes some sense. That would be about the resistance of the relay coil. I would just leave it disconnected and run without the thermal switch if the machine runs OK, you are not going to be loading this machine too much anyway. If you want to connect it, then installing a small control transformer (240/120, 100VA or so) to run the fan, the +/- 15 V PS, and the thermal SW circuit might be the way to go. This would keep the drive power section isolated from everything else.



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    Default Re: DM4400-what size 3 phase motor for rotary converter

    Short lived victory. The wiring diagram bears a pretty strong resemblance to this machine, but so far some of the particulars are wrong. That circuit controlled some of the ATC moves; there are three motors connected with the ATC, and 2 of them got disabled. Unfortunately one of the two controls the drawbar, so I can't even use a tool manually. So I can either have the spindle turning or I can have a tool in the spindle, but not both. Well, it will have to wait until another day.



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    Default Re: DM4400-what size 3 phase motor for rotary converter

    Maybe it's time to take a break, one thing after another. But that's half the fun of doing stuff like this.

    Now I guess it's just a matter of getting the enable signal to the motors. We'll be here to help.



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    Default Re: DM4400-what size 3 phase motor for rotary converter

    Problem solved (with fingers crossed); turned out to be pretty easy, even for a novice like me. After studying the schematics some more, I realized that the same 115V connection to the thermal switch also connected with the ATC relay board (pdf page 104, schematic page 11, CN2 on lower right of board). Not coincidentally this board controlled the two motors for the ATC that had been disabled. I traced the cable from CN2 to the terminal block that tied it with the thermal switch and removed it, then threaded it directly to the transformer secondary connection that I had removed. This bypassed the thermal switch (for the time being) and brought it back to being isolated from the machine ground. Once I completed that, everything initialized finally.

    Case closed on this issue. Time to move on to the next part of the project.

    Dan



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    Default Re: DM4400-what size 3 phase motor for rotary converter

    Happy the hear it worked out.

    You're going to be a CNC tech before it's over



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DM4400-what size 3 phase motor for rotary converter
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