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  #1  
Old 01-09-2004, 07:20 AM
David Peterson David Peterson is offline
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electro etch stencil

I built the electro etch unit and when I try to etch my logo in steel, the DC current melts the stencil. I'm able to use AC just fine with three second bursts, but within 1 second, DC melts the stencil. Any ideas why this would be happening? Thanks guys.

-Dave
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  #2  
Old 01-09-2004, 08:55 AM
Agletric Agletric is offline
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Dave,

What voltage is the DC set at?

I know with mine, The DC and AC are only a switch and rectifier's difference, but the DC still etches hotter than the AC (numerically, the DC is still the lower of the two). If your transformer has a center tap, and you're going from end to end, try switching one for the center.

Lower voltages take longer, but build up less heat.

Dan <><
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  #3  
Old 01-09-2004, 10:17 AM
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Bob Warner Bob Warner is offline
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In addition to the above, What stencil material are you using? What voltage is the transformer?


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Old 01-09-2004, 11:43 AM
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sjaqua sjaqua is offline
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Another thing to look at it what material is behind the felt on your pad. The salt solution will transmit every bit of heat generated. Nothing transmits heat so well as water. I use stainless steel as the contact behind the pad. Other metals may generate resistance and thus heat.

As to the voltage question. Voltage doesn't generate heat so much as watts do. Put a meter between the pad and the clip and check the amps and the voltage on both DC and AC. See if you have a major jump in either when you switch over.


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  #5  
Old 01-10-2004, 07:44 PM
David Peterson David Peterson is offline
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I have a piece of stainless steel backing the felt. When I put the voltmeter on it, the AC is 30V and DC is 24V. I tried testing Amps, but the meter I have only does milliamps. It went off the scale. I built the etcher that's at this website.
http://www.chriscrawford.com/knives/...al/Default.asp

Thanks.

-Dave
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  #6  
Old 01-14-2004, 09:15 AM
PaulD PaulD is offline
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Just a thought, Chris' tutorial has the center wire of the transformer output (secondary) hooked to ground.

This is not a ground wire and depending on other wiring/componet issues may cause a high current path. try disconnecting it and tape it over.

Also make sure the negetive wire from the rectifier is NOT grounded to the case or the ground wire from the line cord.


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Last edited by PaulD; 01-14-2004 at 09:21 AM.
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  #7  
Old 01-15-2004, 12:51 PM
David Peterson David Peterson is offline
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Paul,
I tried disconnecting the middle transformer wire and taping it off, but no luck. The negative wire from the rectifier doesn't seem to go to ground, so that's good. I tried the DC current without the middle tranformer wire, and it still melted the stencil. I may have to wait for more stencil material before I can do any more testing on DC. The AC works like a champ though.

I really appreciate everyone taking the time to help me out. You all never let me down.

-Dave
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  #8  
Old 01-15-2004, 01:54 PM
Agletric Agletric is offline
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Dave,

If you've tried zapping it with the rectifier connected across the center tap and one of the outer taps(I assume that's what you ment), you should have been running 12vdc.

Did you check this voltage? (You'd be checking if the center tap is really a center tap.)

12vdc should be fairly low (I run 22vdc for 3-5s with no problem). . . I'd think it might be your electrolyte conducting a bit too much. Than means more amps, and the internal resistance of the blade(wow -- that's wierd for an electrical engineer to say) is melting the stencil.

two options:

One, buy a good electrolyte with the stencil (I bought both, matched, from IMG -- not nessisary, but might help)

two, Buy a power resistor and put it in line with the DC path. That will limit the current. A 10 ohm resitor will limit a 12v short circuit to 1.2A. Radio shack sells such a resistor which should stand short bursts of 1.2A.

Dan <><
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