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Thread: power supply

  1. #1
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    May 2002
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    Question power supply

    Building a power supply for my B/Port CNC
    Planning to run the 3 motors now on the machine and one more for the 4th axis
    ? How big a bridge rectifer do I need?
    eddie
    please visit my webpage:
    http://motorworks88.webs.com/

  2. #2
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    Dec 2002
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    Howdy

    My Larken 8 amp drives took a 2kva 48 volt (dual 24 tap in series) transformer with the bridgeport caps it makes 68vdc.

    Using a 35 amp 1000 volt bridge I have lost several. Inrush, hitting the e-stop cuts power to the drives, empties the caps, when you hit the bypass button it rushes back in and blowes (once in 1000 times) a bridge.

    I am making as per Thrud's suggestion a 100 amp stud diode bridge using heat sinks. I can post pictures. I just drilled it into the UHMW insulator. (I used my cnc and cheated)

    My problem, I like to leave all the fixtures on my table, that makes me work on the other end of the table. Runs right off the end of the table. (my fault)

    What you building? You going ahead and using Larken drives? or Geckos? Servo (stinker)??
    I want servos and rutex drives... I have the nema 42 steppers.

    My machine has made more parts in the last year then the last ten before I bought it.
    I went through the geckos like hard candy for a while thou.

    I'll help anyway I can. I'd go ahead and use the parallel port, download turbocnc files, read the connection part. I am using a hex-inverter on the logic pins. Put a extra par-port in and go ahead and wire up the spindle, coolant, and home switches-end limits.
    I am converting the program to use a ac28 pamux parallel board, with input modules for the limits. I bought the code. It is smoother then the qstep I was using in windows. Fast as hell too. I figure about 140 ipm on the table. I put a old 400mhz pentium 3 with floppy only on it. Have the P4 back in the house. The faster computer was not needed there. I am now researching modeling programs. Looks like I will have to write my own. I am studying DirectX in visual basic.

    http://www.dakeng.com/turbo.html
    pascal code, free compiler costs 20$

    Where you at?

    David



    [This message has been edited by ibewgypsie (edited 02-01-2004).]

  3. #3
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    Dave
    Got the machine at the end of last summer.
    B/P Boss.Came with all the "old" stuff.Boards etc were burnt out.
    Between work and kids, I only got the thing cleaned up and now going to make a start at getting it to run.
    Plan on using Geckos and the motors that are now on the machine. Not sure if they are good,but I guess I will find out.
    Using the large transformer on the unit as part of the power supply along with all the capactors I took off it.
    I sent John S a pic of the unit and if he could post it that would be great!!
    Thanks for the offer of help.
    May take you up on it from time to time
    I did build A CNC lathe last summer/fall
    It works great.Made 12 door parts for the local health board on Friday
    Let you know how things go
    take care
    eddie
    please visit my webpage:
    http://motorworks88.webs.com/

  4. #4
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    If you do decide to use Geckos, take them apart and make sure you have a consistient pressure on the Mosfets. I put some silicone glue under them (between mosfet and board, not on the heat sink grease side) let it partially harden then put it on the heat sink, tighten up after it dries and the rubber in the silicone holds pressure on the mosfet holding it up against the sink.

    Use external sinks, fans, and grease. Mine ran just fine till I went production. THEN when I needed it, was on unemployment it died one new drive after another. ANother thing to do is get the braking current dump circuit from Mariss of Gecko drive. When the heavy table slows from a fast move it generates current. With no where to dissipate it the voltage climbs to the point where it eats out itself.

    After all the negociations with gecko, Mariss offered to purchase back all my gecko drives.

    I'd go ahead and purchase the canadian Larken drives if you can.

    I am a old time electrician, I wired the E-stop panic button into the main supply w'solid state relay shutting off power to the axis drives. I am leaving that as is, but wiring the limits through the parallel port. (downstream) Turbocnc looks at the limits and the Escape key as a software-estop. I purchased three (4) point opto-22 I/o cards. They isolate the cube type solid state relays from the logic. You can use them in input or output by wiring them to the appropriate pins.

    I have 3, if you need one you can have it for ebay cost ($8+postage). That'll leave me one spare.
    Also, the hex inverter gates for the port, they have to have a simple radio shack ic board soldered up, can you do that?

    I understand what it is to save and build under family obligations. I have several projects that are breaking my heart. A pretty decent harley is sitting here needing paint and some minor mechanical work. I'll get to it soon.

    I also have (3) 60volt/60amp transformers, but shipping would be crazy as they weigh about 80 pounds each.

    David...

    Post pictures, I'll take some of mine too if you like.

    [This message has been edited by ibewgypsie (edited 02-02-2004).]

  5. #5
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    David,

    Using a solid state relay as an E-Stop isn't safe. You should use something that physically interrupts the connection, like a mechanical relay. I've seen many a solid state relay fail shorted. In your application you won't even know it has failed until you need it.
    Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

  6. #6
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    Evan, Having a contactor with making and breaking it spikes the electronics in the stepper drives. One of the geckos that fried did so while putting in a fuse, it arced.

    I have had relays weld shut, breakers weld shut. These new opto relays if you get the right one they are zero crossing on On and off.

    I am not worried, soon the estops will be wired in with the software. I have to make some changes in the program to see the pamux rack. (DMA)

    I am Pretty happy with my machine. I did install a breaker panel on the side for the transformer and quit buying fuses. The panel mount breakers were more expensive then the whole panel and breakers.

    David

  7. #7
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    Still not a good plan David. On all the Xerox equipment I worked on they had mechanical main power relays for the main on/off wired via a low voltage control circut through all the door interlocks. Some of those machines ran on 50 amp 230volt. They also used zero crossing solid state relays to control the fusing system heaters, I've seen them fail regularly, that's why they have overheat fuse links mounted right next to the fuser roll. Spikes pose no problem if you use a couple of L/C filter circuits after the relay. One of the big machines had five computer systems in it and more motors and steppers than ten BP's with no problem from spikes. While it's true relays could stick contacts shut it's pretty rare when run within ratings.
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