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Does voltage really matter for Aluminum Anodizing or is it all about the AMPs?

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  • Does voltage really matter for Aluminum Anodizing or is it all about the AMPs?

    In the sticky thread on CC, Acidrain makes the statement "At any rate, you'll need to accurately measure and hold the current (amps) that are going to the part (just let the volts do whatever they need to in order to maintain the amps)."

    I am new to Anodizing, have yet to successfully do my first part yet all the articles I've seen seem to mix and match voltage and amps as if they are interchangable, which they are not.

    I'm building diving flashlights where the LED itself requires CC amperage of up to 9Amps in a handheld application, yet the voltage is under 4 volts.

    I have yet to purchase a rectifier based on the Amperage requirements I don't need to as I can just use the same CC drivers I use for the LED.

    I have no idea how "energetic" the acid/current reaction should be but I did a test at 3Amp and it looks like a glass of bubbly champagne so clearly there's a reaction... but is it the "right" reaction or am I looking for more of warm soda hitting ice?

    Thanks,
    Codiak

  • #2
    Re: Does voltage really matter for Aluminum Anodizing or is it all about the AMPs?

    The easiest way for most to get their brains wrapped around voltage and current is to compare it to water. The amperage does the work as water does in hydro applications. It takes a certain amount of amperage to anodize a certain amount of surface area. As the coating grows, it adds to the circuits resistance. To be able to maintain this set amperage the voltage will have to rise. Compare this to a garden hose. If you have a hose that you need to get 5 gallons a minute to fill a container and you restrict the hose, you will cut down the volume of water out the hose. With this restriction, the only way to get 5 gallons a minute, would be to increase the pressure. The amperage does the work at a set volume and the voltage is the pressure that pushes it through the circuit. If the circuits resistance increases then the voltage must increase to maintain a set amperage.

    In your dive lights the circuit resistance is low and consistent. In anodizing the resistance grows steadily as the coating grows.
    The acid/current reaction you refer to will vary with current density and material grade but is usually closer to the bubbly champagne or a little stronger.
    Read up on DC current and Ohm's law. It might give a better understanding on the correlation between voltage/amperage.
    Hope this helps without too much redundancy.
    SS
    Last edited by sswee; 03-15-2011, 11:53 PM.

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    • #3
      Re: Does voltage really matter for Aluminum Anodizing or is it all about the AMPs?

      The bubbling can be deceiving... many people look for bubbles as a requirement or an indication that anodizing is taking place. That's not quite true. Although a small amount of bubbling does occur, it's not what you are looking for.
      The term rectifier is kind of an old school term. What you really want is a CC/CV power source. The load is calculated in amps. Using the 720 rule (there is a calculator in the sticky), you first determine what current density (CD) you want to use. Caswell coaches the LCD (low current density) method. It is perfect for hobby anodizer for a lot of reasons. LCD is generally between 4.5 and 6 amps per sq. ft..
      Lets say you are anodizing at 6 amps per sq. ft... using the calculator, you'll see in order to build 1 mil., you will anodize for 2 hours. This is true regardless of size of the part. The bigger the part, the higher the amps, but you will still anodize for 2 hours to build 1 mil.
      BTW, you will never build more than 1 mil. It's just not possible without going to type III anodizing, which is way more involved.
      So, to set the power source, carefully measure the total surface area of your part in sq. ft., multiply by your CD to find the amps needed. Turn the volts all the way up, and the amps all the way down. Turn on the PS, and slowly turn up the amps until you get to your calculated needs for that run.

      You say you haven't successfully anodized yet. Have you tried anodizing? If you are having problems, just tell us what you've done and what the results were. Once you get it, it's pretty easy, but there is a learning curve with many failures along the way. Best thing is to experiment on known alloy types. 6061 is a good learning alloy.
      I do things.

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      • #4
        Re: Does voltage really matter for Aluminum Anodizing or is it all about the AMPs?

        Ha, Sswee beat me to it, but we both add to the discussion...
        One more thing, many people are expecting a certain voltage. As Sswee said, the volts will go up and down depending on needs. For the same reason, not everybody's set up is the same, and therefore resistance will be different between systems. There is no set rule for what the volts will do.
        Set the amps and let the volts do whatever.
        BUT, the volts are an indicator, so do pay careful attention to what the volts are doing. If they go up, there is resistance. If they go up a lot, you may have lost connection on one of your parts, and are now "over anodizing" the remaining parts. If the volts drop to zero, you've lost all connection.
        It's always good to take careful notes during each run. When everything goes just right, and especially if you are anodizing many runs of the same part, you will begin to see a pattern. Once you start noticing what alloys do what, etc., you'll quickly recognize when there is a problem, and be able to correct it without wasting a bunch of time.
        I do things.

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        • #5
          Re: Does voltage really matter for Aluminum Anodizing or is it all about the AMPs?

          Thanks guys,
          I am very familiar with Ohms law. My issue is I keep seeing references to required volts in one sentence and amps in another and couldn't tell which was in fact the critical measure, now I know, thanks!

          The driver I use shunts excess voltage to a FET to maintain constant current that high output LEDs require, thermal resistance is in fact a major issue for the LEDs.


          I'm working with 6061 extruded in a 1:3 water:acid, wiring to the bath flashlight circuit rather then the LED would give me 8 hours of runtime on a charge at 3amps. Nice. Will have to run some tests.. Cooling the FET will be the biggest hurtle.

          Thanks again

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          • #6
            Re: Does voltage really matter for Aluminum Anodizing or is it all about the AMPs?

            is that 1:3 acid to water or water to acid. If you are running 3 parts acid to one part water you will have some negative results. I know it might be a typo but just wanted to get that clarrified. When I started the person that helped me out had me running 1:1 with not so consistant results.

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            • #7
              Re: Does voltage really matter for Aluminum Anodizing or is it all about the AMPs?

              You're right, 1:3 acid/water (more water than acid). It's also important to note that the ratio is with bettery acid (not lab grade sulfuric).
              Most people that are starting out and learning from the internet are reading 1:2, but there is no need to go that strong.
              The LCD method works very well and creates a very durable coating up to 1mil. It's actually scary how well it works. It's also laughable when you talk to commercial anodizer who say it can't be done safely at home.
              I do things.

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              • #8
                Re: Does voltage really matter for Aluminum Anodizing or is it all about the AMPs?

                Finishes I get are more consistent and far more durable than what I was getting commercially.

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                • #9
                  Re: Does voltage really matter for Aluminum Anodizing or is it all about the AMPs?

                  I think the commercial anodizers don't want you to know how easy it is to do it in the home, because they will lose business. I am actually amazed at how inexpensive it is to start a really good setup.

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