Garbage In, Garbage Out...

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Well, as Joe pointed out in his comment on last night's post, the blue plume didn't appear from the controller, but almost from the motor itself. To get the controller to lower the revs down to anything like resulted in partial stalling and uneven drive, with the concomitant odour of stressed motor as a result. A hasty shutdown and some research followed.

It appears that the simple Triac controller descends into instability at its lower limits: all it's actually doing after all is chopping the sine wave of the AC current in order to effect the frequency-change necessary to alter the induction motor's speed: resulting, ironically enough, given Joe's remembrance of my squaring up some dodgy timecode back in the day, in guess what? Transients of a very square nature: I thenk yow! This might be OK if they were regularly spaced, time wise, but in this case, they're most definitely not, a recipe for a fried Crompton Half Horsepower. Given that the cost of a proper, industrial-strength speed controller is probably more than the entire lathe is worth makes me think that fifteen or twenty quid for a new motor pulley might be quite good value.

By the way, the cardboard box featured is not to return the controller, which after all is intrinsically not at fault - it's just the wrong tool for the job, after all (make a good light dimmer) - but for the no-contact tacho, which I've had precisely two days and which has died after being used only a couple of times. Garbage in, garbage out: I think I'm going to try and get hold of an old-fashioned 'digital' (i.e click-wheel) revolution counter off Ebay and do it properly with a stop-watch... Keep you posted! 
 

Comments

  1. Joe Stoner7 July 2021 at 20:43

    IF I remember correctly hard sine waves can be smoothed with a resistor (probably only need it at the lower speeds) so you've got to reverse engineer it mate!!! We need our multi-meter back eh? BTW Our "esteemed" PM (I'm working on a variant of BoJo, which is TOO friendly, on the lines of JoBooboo ish!) GOOD to see the Speaker point out that it was PRIME MINISTER's Questions NOT Leader of the Opposition Questions. I thought that Kier needed to push at that OPEN DOOR he's a fucking lawyer for Christ's sake!! ATB Joe

    ReplyDelete
    Replies
    1. sideways7 July 2021 at 21:00

      It's not just the edges/transients - it's the lumpy timing, as it's dependent on capacitors charging/discharging to fire the triac into action via a diac: a bit of a crude method with no hard timing...

      I didn't see PMQ's, but we were wondering here how long it would take the new Speaker to grab onto that one - now there's form, Starmer might feel more inclined to exploit that one...

      Delete
    2. Joe Stoner7 July 2021 at 21:33

      Entirely different point mate I just thought that there is no doubt that our "system" has caused Klimate Khos and have done since the 1970s, one James Lovelock said in a lecture, that I attended, that we wern't on the cliff edge we were falling THEN!! Just how MUCH money have they extracted from the planet & the poor? I'm publishing this here as a form of copyright cos I'm going to ask an old mate of mine Geo Magnussen (Prof of Economics at Oxford) to quantify it but he'll either nick the idea or ignore it. He is at the end of his not entirely academic carrer, he had MANY years at a Swiss Bank!! Any thunks fellas??

      Delete
    3. sideways7 July 2021 at 23:04

      Aren't you a bit off piste here?

      Delete

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