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    Default Fuses fast or slow blow?

    Ok my CNC milling machine, has 2 fuses between the main transformer and the rectifier I don't know if it has the right fuses or not, 250v 15 amp fast blow. Could I use slow blow fuses or is that a bad idea?

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    Keep the fast blow, might save the solid state stuff ...Phil

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    How fond are you of the sensitive electronic components?

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    Quote Originally Posted by Phil in Montana View Post
    Keep the fast blow, might save the solid state stuff ...Phil
    Quote Originally Posted by rons View Post
    How fond are you of the sensitive electronic components?
    Ok thanks guys, fast blow it is.

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    The bad truth is even fast blow are not fast enough, you should spend big bucks and buy electronic fuses, they are made to blow in half of a cycle, but cost is quite high $100.00+...Phil

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    Quote Originally Posted by catch22 View Post
    Ok thanks guys, fast blow it is.
    Stay with the original fuse delay time and amperage. Probably won't make a difference if you deviate some. But better to be safe.

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    The typical application of a fuse is to protect the wiring supplying power to a device from overheating. They do not protect the equipment at the end of the wires.

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    Quote Originally Posted by catch22 View Post
    Ok thanks guys, fast blow it is.
    Manual generally TELLS yah which. Download one if you have not.

    "Semiconductor" protection fuses are plentiful. Just not often locally stocked, nor cheap, regardless of source.

    Faster the better when in doubt.

    - Worst case, you've blown expensive fuses. But they were MADE to blow and there are more where they came from.

    Go with too SLOW when in doubt?

    You blow the equipment, not the fuse.

    It was NOT made to be expendable. There might not BE ANY replacement.

    And now yer plucked.
    Last edited by thermite; 04-13-2020 at 07:00 AM.

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    I'm kind of interested in what machine has "two fuses between the main transformer and the rectifier."

    I've had plenty of machines with isolation transformers and a bunch with DC drives, but I can't think of any with rectifiers connected to the line ... or external rectifiers of any kind, actually.

    The main fuses in all the control cabinets I've had have been the electronic insta-blow type, btw, but still ....

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    Quote Originally Posted by EmanuelGoldstein View Post
    I'm kind of interested in what machine has "two fuses between the main transformer and the rectifier."

    I've had plenty of machines with isolation transformers and a bunch with DC drives, but I can't think of any with rectifiers connected to the line ... or external rectifiers of any kind, actually.
    WTF did you think the lines off the drive isolation step-up/down transformer were encountering inside that packaged DC Drive, VFD, or a(ny) PSU?

    Marshmallows, mayhap?

    RTFM. Right on the schematics.

    WHEN used at all, any "fast acting", "semiconductor", or otherwise sensitive fuses go on the Drive, PSU, or load side of a transformer. "Instrument" fuses protect what it sounds like. The leads as they enter.


    Standard or Slo-Blo take up the lumped inductance hit, upstream, act only if you should have a dead-short in the wiring, transformer, unprotected rectifiers destroyed shorted, capacitor bank gone Bolshevik, etc.

    Those "upstream" don't give a damn that a Rectifier itself can be a rather precise "fast blow" fuse of sorts, and diodes are not uncommonly used as exactly that.

    "QO" class CB is usually better than fuses for the upstream. Common-trip thing.

    Faster ones, yet, can be had as well. A Heinemann speciality for nearly a hundred years, already, to name one.

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    Quote Originally Posted by catch22 View Post
    Ok my CNC milling machine, has 2 fuses between the main transformer and the rectifier I don't know if it has the right fuses or not, 250v 15 amp fast blow. Could I use slow blow fuses or is that a bad idea?
    Suggest that you only take advise from electrical engineers.

    Ohms law rules... LOL

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    Quote Originally Posted by thermite View Post
    WTF did you think the lines off the drive isolation step-up/down transformer were encountering inside that packaged DC Drive, VFD, or a(ny) PSU?
    The wired connections with fuses go to a DRIVE, moron. They don't go to a rectifier. I have never seen a rectifier connected to the isolation transformer. In fact, these days an isolation transformer is unusual.

    Therefore, have some amount of curiosity as to what machine this is.

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    Quote Originally Posted by rons View Post
    Suggest that you only take advise from electrical engineers.
    Or those of use who teach the minority of them worth the BOTHER.
    Last edited by thermite; 04-13-2020 at 06:22 AM.

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    Quote Originally Posted by EmanuelGoldstein View Post
    The wired connections with fuses go to a DRIVE, moron. They don't go to a rectifier. I have never seen a rectifier connected to the isolation transformer. In fact, these days an isolation transformer is unusual.

    Therefore, have some amount of curiosity as to what machine this is.
    I did say "RTFM"?

    OP GOT the guidance he NEEDED, and from experienced experts. More than one.

    He isn't meant to be a victim of your silly head games.

    You thought those "DRIVES" were solid Wakefield Deltacast? No active components inside?

    Rectifiers, buppy. Rectumfryers.

    RTFM, Not the only thing you are bat-blind about.

    DC Drive, common Thyristor class, the rectifiers are controlled, line freqency, no incoming capacitor bank.

    Where TF ELSE would the incoming line GO if NOT the rectifiers?

    VFD the first thing the line hits are the rectifiers for the capacitor bank.

    Where TF ELSE would the incoming line GO if NOT the rectifiers?

    Switching PSU or linear, either one, similar. Those don't work worth a shit without power, either. H-Bridges? Servo Amps? Damned "rectifiers" in one form or another. Again.

    Go figure.

    Or mayhap they do work off nothing more than "the Communist Party Line"?
    In the magical realm of China. For pretentious, posturing, schmekels?

    Good luck with THAT!

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    Quote Originally Posted by thermite View Post
    RTFM, Not the only thing you are bat-blind about.
    Look, stupid fuck, incoming line voltage goes to fuses then a disconnect, then (in old days) to an isolation transformer, then thru more fuses and contactors to the various components, control circuitry and drives. There ain't no fucking rectifier directly connected to the transformer in any machine I've ever owned or touched.

    And no the current does not go directly to any internal rectifiers straight away because if the control circuitry does not come up before the power circuitry, there is no way to ensure that you won't get two phases turned on at the same time = direct short. KABOOM !

    DC is a slightly different situation but again, I have never seen a machine where the control does not have to come up first, then you hit a button to bring in a contactor to connect power to the drives. No direct connection "from transformer to rectifier" ever.

    We could put what you know about cnc controls into a teacup and have enough room left over for a quart of Pennzoil.

    I'm still kind of intrigued by the op's statement. Either he has it entirely wrong or this is an unusual setup.

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    Quote Originally Posted by Phil in Montana View Post
    The bad truth is even fast blow are not fast enough, you should spend big bucks and buy electronic fuses, they are made to blow in half of a cycle, but cost is quite high $100.00+...Phil
    If yah KNOW yer basic Diodes, have plenty of variety in the drawers of the Hell box, yah can (sometimes) "soixante-neuf" a pair and cheaply test the right ones for a damned decent substitute.

    Sometimes. Low-power end, that can be cheap as dirt, once sorted.

    Early-on, I fergot to put shrink-tubing or tape over some glass-encapsulated ones.

    Didn't do THAT twice!


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    Quote Originally Posted by EmanuelGoldstein View Post
    Look, stupid fuck, incoming line voltage goes to fuses then a disconnect,
    Sheesh.. Got that shot bass-ackwards too, haven't you?

    When not in the same NEMA box - as fused disconnects are - the same pattern is meant to be followed, one disconnect or several in sequence. A disconnect function at the supply side of the fuses.

    That's what lets you safely place and REPLACE those fuses, dummy!

    "RTFM"

    Seems as if you have never had "personal" hands-on at anything electronic more complicated than a "puter keyboard? Never done board-level repairs? Never reverse-engineered a complex system? Never WROTE the manuals?

    Can read a functional BLOCK diagram, but NOT the schematics that detail what is actively at work INSIDE those several functional blocks?

    Ever wonder why drives have an "ENABLE" switch as well as a "RUN"? Or circuitry to control the functional counterpart is assured to take place, sequencing-wise, on power-up? Even a first-generation IBM "PC1" PSU & MB has that function - and already OLD, too. The need even predates the transistor.

    Or why the modest power for controls is often not even FROM the same source as the greater power to be controlled?

    No. You wouldn't, would you?

    Reading a manual and understanding it is too much like honest work.

    No fear. China has technoids that DO understand this stuff.

    Fair bet they've been keeping your arrogant ass in noodles and tofu the whole damned time you've been their guest?

    They see to the work. You handle the politics and Bu Ci.

    They're good with that. Gweilo are meant to be "expendable" in China. With "sell by" dates, even. No longer useful? Too much annoying baggage?

    Screw out the old, screw in the new, emphasis on the "screwing". Same as burnt-out light bulbs.

    They have family reputations to protect. Hired-in Barbarians, not so much.

    Ever wonder what your date is?

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    Last couple of Hypertherm inverter plasma cutters I had the cover off of, had in this order...
    1. Line cord
    2. main switch
    3. rectifier

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    Quote Originally Posted by digger doug View Post
    Last couple of Hypertherm inverter plasma cutters I had ...
    Douglas, jesus ... here, let me help you :

    CNC milling machine != plasma cutter. If op had said "my cnc plasma cutter ..." then I'd never have said a word because I don't know shit about those. Or induction hardening or press brakes or undersea diving apparatus or gas turbines or nuclear reactors.

    But I know for a fact that the vast majority of CNC milling machines do not have a standalone rectifier connected to L1 L2 L3 with two fuses -- which is what op described.

    I am still a little curious about what mill this is and what control.

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    Quote Originally Posted by digger doug View Post
    Last couple of Hypertherm inverter plasma cutters I had the cover off of, had in this order...
    1. Line cord
    2. main switch
    3. rectifier
    Not sure when those became a "CNC milling machine" as the OP has, but even so... we can deal with a random surprise...

    Did I forget to say "RTFM"?

    https://www.google.com/url?sa=t&rct=...SJIFtszcxnaiYb

    Page 86

    F1 and F2 are tapped FROM the supply to the rectifiers, feed the supply side of the CONTROL transformer.

    Fuses are on page 60. "Fast" for this model.

    https://www.google.com/url?sa=t&rct=...8VYja-S7cguUEA

    Same again, page 101
    Fuses are on page 61. Slo-Blo for this model.

    Are we all on the same page, and NOT wandering about somewhere in CHINA, now?

    R T F M !!!

    More manuals are "out there", most anything, lo, these many years. Already.

    - Cheaper than printing and mailing them. Faster. They stay clean longer

    - Saves the maker's a lot of money on dealing with telephone calls from .. WTF name is he using THIS year? Seamoss? Or Goldbrick?



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