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Anodizing rectifiers

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  • Anodizing rectifiers

    I have been anodizing parts off and on for a few years now using a battery charger for a rectifier. I have a job that requires me to anodize some larger parts and larger quantities of parts. I don’t want to overload my battery charger and damage it so I would like to get a rectifier for this purpose. I also would like to be able to control the current better than I can with the battery charger. I know where I can purchase a new rectifier but was wondering if anyone knows of a source for plans or kits to build one capable of 20 amps.
    Thanks, Mark
    Mark Hockett

  • #2
    Here ya go. 120/12vac at 25 amps transformer, 1602 in stock, $19.95. Buy two and put them in parallel and you get 50 amps, cheep.

    http://www.surpluscenter.com/item.asp?UID=2005041316474217&item=15-1103&catname=electr ic

    Get some diodes out of a car alternator and build a full wave bridge on a heat sink. You can either use an autotransformer on the input or use 12dc headlight bulbs on the output to help regulate it. You can also make your own tappable wire wound resistor using some steel wire wound on a clay pot or similar.

    [This message has been edited by Evan (edited 04-13-2005).]
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    • #3
      I haven't been into this lately, but not long ago there were shottky diodes available that were high current and relatively cheap. They also have a low forward voltage drop, which means two things- one, they will waste less voltage from the transformer, and two, they will heat less than a normal rectifier when high currents are being drawn. They are typically for use in high frequency switching power supplies, but nothing says they can't be used at 60 hz.
      As Evan says, you can use diodes from an alternator, you just have to remove them, and remount them on two separate heatsinks, wiring them up into a bridge configuration. Two diodes of one polarity mount on one sink, and two of the opposite polarity mount on the other. One sink is the positive output, the other is the negative. Of course, you have to isolate at least one of the heatsinks from the metal case of the box you use.
      You can also look into the alternator rebuild kits, which will have a set of diodes, plus as a bonus you get at least one ball bearing, possibly two, and maybe one is a needle roller bearing. If they are useful to you or not- whatever. If you consider purchasing new diodes, (rectifiers, whatever you want to call them, same thing basically) the cost might well be more than the rebuild kit.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        Hi. I have 6 diode rectifiers, mounted on a bridge. Came out of 3PH welder. These should easily handle your need. You should be able to control the AC input with a variac. I got these from Dave Cofer a couple years back.

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        • #5
          if you bild up a bridge rectifier with diods to the + side and scrs to the - side you can control how often the bridge is runing and ther for the voltage or current.

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          • #6
            SCR's are diodes so you can probably cut your parts count some by eliminating the diodes. You'll need a bit more complexity if you want more than half-wave rectification, tho.

            Lamps, as it happens, are interesting constant current devices (current is rather constant over a wide applied voltage range - not perfectly so, but damned close) and so make for very interesting current controllers. A set of 4 lamps with ratings of 1, 2, 4, and 8 amps can be used to step current limiting from 0 to 15 amps, depending on which ones are in the circuit (in parallel). Add one more for 16 amps and you double that, and so on. They are excellent for protecting against short circuits if the applied voltage is with the lamp's rating.

            dp

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            • #7
              Lamps are also an excellent indicator of a good circuit through the parts, always a potential (heh) problem when anodizing.
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