Help with 3 phase
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  1. #1
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    Default Help with 3 phase

    Hi, I have very little experience with 3 phase. I hooked up my (new to me) delta model 28 bandsaw, when I plugged it in, the transformer was humming even before I turned on rotary phase converter. I turned converter on and the saw ran fine, I turned off converter and did not unplug saw. I left shop for about an hour, when I returned I smelled burning electric and the transformer was real hot and 1 wire on contactor was real hot. Now saw wont start. Any info would be great! Do not want to replace anything if there is underlying problem. thanks

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    Need way more info.
    What if I asked you what was wrong with my vehicle, last time I drove it it ran fine but after it sat for a while it will not start?

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    This is guess is from about 20 feet away but it sounds like when you 'turn off your rotary converter' there is still
    power present at the load machine. Be sure the utility legs are being interrupted by your disconnect.

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    Time to call an electrician..

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    When you turn off the rotary converter, all power to "stuff" should be off on the three phase side.

    Clearly for your setup that is not the case. Get that fixed first. If you cannot see the problem, get a decent electrician who DOES understand 3 phase to look over the problem.

    Once that is done, then the saw, may be set up for the wrong voltage, or the wrong voltage may get applied die to whatever is wrong with the converter wiring.

    About "the transformer". What transformer is that? Is this set up for 480 and you have 230? It sounds as if the transformer is powering the whole saw, wht is that?

    As for the saw, there are a lot of "model 28" under different dash numbers. What do you have?

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    the saw is model 28-633 and yes I think I have power passing to outlet when converter is off I will try to post some pics of component's .

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    img_20190804_184954302.jpg hope this works

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    img_20190804_184831387.jpgpimg_20190804_184831387.jpg hope this works

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    img_20190804_184854909.jpg hope this works

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    OK, got it.

    I assume it runs at 230V, and the transformer is the one mentioned..

    That transformer has to be on because it runs the start circuit, for which there must be power to close the contactor. Not an issue, if set to the right voltage, AND if sized for the contactor load. It looks small for mist any AC contactor, but I do not know that at the present time.

    One issue is whether the transformer is the right size and voltage tap.

    Another is this business of the voltage not shutting off when the RPC is shut down. I would solve that first. That has to happen for safety. Your plug connection will serve as a "disconnect" for any individual machine, but the shutoff thing needs solved.

    After that, the contactor needs to be assessed for it's "VA" draw for both closing, and maintaining closed. The transformer you have there, which appears to be a replacement, looks, as I said, considerably too small. it looks like only a few "VA" in rating, and may be just not sufficient to do the job.

    Bigger ones are available from suppliers such as Digikey and Mouser Electronics. But you need to know what the contactor draws. That number may be available from the paper you have that you posted a pic of. The fuse value for that fuse associated with the transformer will also give a good clue.

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    Quote Originally Posted by metalmanbryan View Post
    the saw is model 28-633 and yes I think I have power passing to outlet when converter is off I will try to post some pics of component's .
    Seconding fuse value need to know.

    While over in the text we can't read off the foto, advise the expected output at X1 X2 off the Xfrmr.

    Confirm that Stancor has eight leads. It very likely IS OEM. Sniff at it - POWER DISCONNECTED !!! - and see if it stinks - or if it is just that burnt lead's insulation that does.

    Standard Transformer Corporation product overheats, that treated paper goes discoloured and brittle. That's part of why they used it. Can't hide the abuse, and it isn't yet showing that.

    Draughtsman got lazy when he wrapped the primary "COM" and "200" taps around the end to save space and make the schematic look "neat".

    The secondary has exactly ONE winding. Primary side, "COM" should be connected, one other only, one presumes "230", neither of those to the "generated" leg off the RPC. Correct for improper tap selection, if any. Fix damaged wire. Check that connections are actually good. it should just Run.

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    As stated by almost all others, first fix the RPC so that all power is removed when off. It sounds like you have a contactor connected to the idler motor but not to the input power to the RPC.

    When you get that corrected be sure that the non generated leg is not connected to the transformer in the saw. It sounds like it is already correctly wired in this regard.

    The transformer is certainly a replacement as it has two primary voltages instead of several taps. It is not known if the output voltage from the transformer is correct as I do not know what is required by your motor contactor and could not read the output voltage of the transformer from the label. See if there is a label on the motor contactor coil to verify the voltages match. Measure the voltage at the output of the transformer and verify it matches the label. If not, it is either damaged or incorrectly wired. Is there a fuse wired in the output of the transformer? The original had a fuse mounted on the transformer. If there is a fuse, it could be blown.
    The best way to determine if the transformer current capability is adequate (barring having data for the contactor coil) is to measure the current drawn when the contactor is activated and comparing it the rating of the transformer. I think you will need to get a new control transformer and these can be found on Ebay or other electrical providers.

    See if you can find someone a little more technically knowledgeable to give you a hand. You really don't have a three phase problem as the control circuit is single phase.

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    There is a gotcha with AC contactors.

    Wgen they are closed, their impedance goes up as the magnetic circuit is closed. When they are open, they draw quite a lot more, which depends on the design. Can be 10x higher current draw just as power is applied, maybe more. So an AC contactor that draws 9VA closed, might draw 90 to 150 VA to pull it in. So the transformer has to be capable of that, or it may not pull in, or may take too long and arc the contacts, etc..

    The poor little guy in there is pretty wimpy lookin, unless I have the scale completely misjudged. Might be as much as 40 or 50 VA, or as little as 20 or 25 VA.

    Need to know what the contactor draws. It won't draw more than its resistance allows..... you can measure the coil resistance, but that is going to probably be a very conservative estimate.... over by 30 to 100% maybe.


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