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Thread: EDM (DIY) - PWM power supply question.

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    Default EDM (DIY) - PWM power supply question.

    Hi Guys

    New to the forum – so I’m going to kick off with a subject I have been toying with for sometime now, in my mind: EDM - more specifically: PWM power supplies - the one part of EDM machine construction that has to date held me back from attempting to put one together.

    I've read through the comments on an earlier thread in this section of the forum about DIY EDM, and while the basic principal is well conveyed, the big limitation in examples and theory presented lies in the limited info on PWM power supplies.

    Having “Googled” lots of different EDM related topics (and patents), it’s clear that not much is said on the net either about the subject.

    Of course manufacturers have lots of money tied up in IP secrets (intellectual property), but its not so much subject detail like voltages, currrents and pulse durations, as it is software development to run the machines where the secrecy really lies.

    Can someone give me some idea of typical voltages/currents used in the milling/machining of different metals - say, aluminium on the one hand and steel on the other. What are the typical DC voltages and currents used in wire and/or die sink EDM milling?

    Another point I am keen to get some insight into is pulse duration.
    Typicaly, where do we find pulse durations falling in EDM machines, in terms of timeframe – are they in the micro-sec or milli-sec range of timeframes?

    A big part of the cost in EDM milling (read as: “damned if I can afford to buy a SODICK, or similar, EDM power supply!!”) is of course the PWM power supply/generation – and its quite pointless investing in professionaly made PWM electronics for a DIY xy axis EDM machine, but, other than for possible changes having to be made to pulse duration and waveform shape (sine or triangular -to- square), is there any reason why a high current/high voltage R/C model PWM motor controller could not be used (or adjusted to be used), such as one of the following(?):

    www.electricwingman.com/jeti/spin-200.aspx

    and/or

    www.alltraxinc.com/Products_AXE.html) .

    Or, what about some of the PWM power supplies been used in Hydrogen production kits, such as these(?):

    www.hhoconnection.com/pwm_controllers_1.html

    Some of these even have that all important ability to adjust frequency (pulse duration) ?

    The 3 characteristics of EDM power that enable clean milling to be undertaken are:

    - Voltage
    - Current
    - Pulse Duration


    ... and the relationship between these 3, plus frequency (as in rest time between pulses, or "duty cycle/duty ratio") ….. just ideas – any input/comments would be appreciated.

    Thanks guys

    Benben

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    Registered mdynac's Avatar
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    first off, why would you use a "Pulse Width Modulated" power supply in the first place???

    i am not sure of its function as a programmable pulse generator/pulse amplifier.....which is what an edm power supply is......

    and not a PWM amplifier.......


    a benchtop pulse generator is a very good start.
    if its programmable, even better.
    5Khz to 55KHz 1us to 3us pulses

    80 volt 20 amp pulse amplifier, is a good starting point.

    in other words drive your homebrew pulse amplifier with your benchtop
    pulse generator, and you have an edm power supply.
    albiet basic, it will work just fine.

    and you just keep building up from there.

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    MDYNAC

    I don't dispute the benchtop pulse gennie + amp approach . My thinking was along the lines of an alternative apporach - and a potentialy cheaper one at that.

    I could put together a 40Amp PWM psu plus extra bits, for a couple hundred dollars. I'm not sure I could put a benchtop pulse gennie + amp together for that.

    The potential problem with PWM power supplies: most do not come off the shelf with ideal pulse durations for EDM work. Reworking pulse on/off times on most modern PWM psu's should involve little more than getting holding of a schematic for the product, identifying the resistor/capacitor timing circuit (which is what is used on most IC/microcontroller controlled PWM psu's), and changing the values accordingly.

    A discussion regards ideal pulse on/off values for EDM work is a difficult one.
    A quick read through info on the net shows that pulse on/off times vary hugely - different EDM machine manufacturers suggest different pulse times depending on the tool material, the material been cut, cutting speed, cutting voltage, amperage required - which in turn are in no small part a function dielectric distance, dielectric constant of the fluid and even the temp.... and on and on it can go

    So what is the ideal pulse on/off time?
    It's very much dependent on the above, but from what I can see on the net, if you can cover 5microsec - 1millisec, one would pretty much cover most of what a DIY'er would be doing at home.

    Your idea regards a pulse gennie + amp is great - and yes, there are a number of points and potential restrictions in seeking to resolve the matter with a PWM psu, but they are not insurmountable. This is no more an alternative and substainly cheaper approach, with the potential to offer just as good a quality milling/finish, if one understood the requirements and selected equipment that accomodated those requirements.

    ..... which goes back to the original question: not withstanding that a benchtop pulse gennie is an alternative - is there any reason anyone can see why a PWM psu could not serve as the basis to a power source for EDM milling/maching?

    By the way - any idea what a pulse gennie + 40A amp would cost?



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    Registered mdynac's Avatar
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    pulse gen, 2 555 timers and a 7406 = one pulse gen 1 dollar total cost
    you will neet 2 caps and 2 pots also so maybe 5 bucks total or so.

    pulse amplifier, some irfp 240's about 6 in parallel should do.....

    i'm not going to draw you a schemo, but it should be self explanatory....

    i take it you are not an experienced electronic technician....
    maybe that explains the whole "PWM" thing

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    No, no - don't trouble yourself - I'll figure out some schematic alternatives for those components and run it through SPICE or something similar - lets see how well these parts work in reality.

    Thanx



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    well these parts work fine in reality

    any manual sinker out of taiwan
    uses these circuits, thats where i got them from.......

    i repair edms for a living, i do know almost all edm brands circuitry, as i am a component level repair tech.

    so go ahead and spice it up.....

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    FWIW, I have a complete commercial pulse generator and control. Its out of an old blue Charmilles Andrew. Mdynac has seen it. Scrap to me, $100 makes it yours.

    Karl



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    No power section - just square wave pulse section?

    Some info on min/max pulse on and off times would be helpful, and what about display and control - could you send me a few pic's so I could see exactly whats included.



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    Quote Originally Posted by BenBenly View Post
    No power section - just square wave pulse section?

    Some info on min/max pulse on and off times would be helpful, and what about display and control - could you send me a few pic's so I could see exactly whats included.
    I have that too. As I can use it on my existing machine, it has value to me. But we can deal.

    Not much to see. Mdynac is an expert on these units. He's forgot more than I will ever know. I have the entire control cabinet from a blue charmilles Andrew.

    Karl



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    see above

    Andrew Pulse Generator

    first off the andy generator is a beauty.....
    great starting point.

    specs

    -200 vdc pulse output (note negative pulse)

    pulse width = variable from 750 ns to 2.25 us

    pulse rate variable from 5khz to 52khz

    peak current variable from 48 amps to 268 amps peak. (note this is peak current)


    there is no display on the andrew, just three knobs

    1. pulse rate

    2 pulse width

    3 peak current

    hopefully karl will post some photos.....

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    Unless you're coming to get it yourself, I'm just offerring the dozen or so cards and the card cage. This wouldn't take long to remove and easy to ship. I'm not interested in spending a day+ tearing down and packing for shipping.

    karl



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    Some pics of exactly whats on offer here would help.



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