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Author Topic: Awesome DC Power Supply Glitch  (Read 1060 times)
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Some time ago, like two or so years ago, I had a Mastec 30v 6A DC power supply. And being the person I am, I frequently used it in a destructive way, melting wire, popping LEDs, ICs, exc. (In a safe and controlled way of course.)
Anyway, after some possible feedback from a small 20kv transformer, it broke, but in an odd way. Since then, the voltage display and output always stayed at around 56 volts DC no matter what the knobs were turned to. I never bothered to test the current, I just attempted to fix it and eventually threw it into a box thinking I could use its parts in the future. Soon after all that, I got a new Mastec HY3010D.

Today I pulled that old broken power supply out and powered it up. To test it, I connected 1200 watts of halogen shop lights to it, it lit them up no problem. The lights were bright enough to leave a noticeable picture of the bulbs burned in your vision for a while if you looked at them for too long.  The current drawn judging by the display stayed at around 6 amps but jumps to over 8 amps when the lights are initially turned on. the voltage stays between 44 and 55 volts when doing this. Realizing my old power supplies new feature, I wanted to test it further. So, using the halogens as a safety load, I successfully managed to fuse and cut metals. It creates a 4mm to 5mm spark that I can only compare in every way to a plasma cutter, of course its not as powerful, but it sounds and looks like a plasma cutter's arc. You know I couldn't resist testing it on some small hobby motors and other small parts. Lol, its really cool.

So, does anyone have an explanation as to why the power supply does this? I'm intrigued.
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Sounds to me like your potentiometers are messed up somehow, probably shorted
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Sounds to me like your potentiometers are messed up somehow, probably shorted

No, I doubt it, even if they were, it wouldn't give me 55 volts at 8 amps. The knobs have absolutely no influence on the output.
There is plenty of digital circuitry in the power supply, most likely fried when it was powering that 20kv DC transformer (which was also fried in the event).  I do recall that when I had certain materials between the contacts of that 20kv transformer and it was producing some ozone with no visible spark, all the segments on all digits of both displays went haywire, they were the red 7 segment LED style displays. Also, the relays within the power supply buzzed in these conditions.

I'll be testing it from the inside later, after I'm done melting through all my screwdrivers. Lol
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Oh, misunderstood, thought the knobs controlled the output voltage/current, and that 8 amps was the max current before the "incident" you never said the max voltage output
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You most likely have shorted out series pass transistors, that is allowing the full rectified and filted raw DC just pass right on through.


Lefty
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You most likely have shorted out series pass transistors, that is allowing the full rectified and filted raw DC just pass right on through.

You know, I think you are right, there are 3 large transistors (2N3055) on the back of the power supply fixed to a large heat sink along with a noticeable warning sticker that says that its hot, do not touch. Surprisingly, after extended periods of time under very high loads, they remain cool. There is another smaller transistor on the main PCB with its own heat sink that puts out a lot of heat, I installed a fan to be safe. I cant read the markings due to its location, anyone know what it is for?
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2N3055 are common and cheap, just buy three and swap them out. That's almost a plug and play repair.

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I cant read the markings due to its location, anyone know what it is for?

Let me look, nope I can't see it either. It's probably the driver transistor that controls the 2N3055s.

Lefty

« Last Edit: February 22, 2011, 08:37:54 pm by retrolefty » Logged

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Quote from: retrolefty
Let me look, nope I can't see it either.

Are you sure? Can you check again? 
lol

I'm not going to bother fixing it, I'll just keep it for its new feature. I got a better one anyway.

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I'm not going to bother fixing it, I'll just keep it for its new feature. I got a better one anyway.

Then why are you bothering us? We are underpaid and unappreciated enough as it is.  smiley-grin

PS: We use to be paid in Karma points but they took those all back.

Lefty
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Quote from: retrolefty
Let me look, nope I can't see it either.

Are you sure? Can you check again? 
lol

I'm not going to bother fixing it, I'll just keep it for its new feature. I got a better one anyway.



Give it to me, I'll fix it, then I'll have one
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