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Author Topic: computer power supply project  (Read 1133 times)
M0CVA
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Posts: 14




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« Reply #15 on: April 22, 2004, 08:04:53 AM »

It may anger some people even more when I say I've rectified the +12VDC output with bridge rectitification using uberfast diodes (PBYR1645's - my all time favourites!) for an even higher voltage output. Two of these little gems in split rail configuration makes a solid PSU for audio applications.

... and while we all getting hot and bothered under the collar, let's not forget it's only hamradio, itsa HOBBY! There's very little joy that compares when you can ressurect useless junk whilst gaining experience and something usefull you can use. Hakuna Matata ...
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WB2WIK
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Posts: 20635




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« Reply #16 on: April 22, 2004, 12:13:54 PM »

I would never discourage anyone from "projects," homebrewing or modifying gear, especially in association with this hobby.  I agree this can be a great learning experience.

Caveats, though:

-If you have ham gear still under warranty and use a homebrew or otherwise not recommended power supply, and the power supply causes damage to the gear, usually that voids the warranty and any damage won't be covered.

-Adding a rectifier, even a wonderful low-drop Shottky power rectifier, in series with the output of any power supply does *not* simply drop the voltage by the Vf rating of the diode and have no other effect.  That's a ridiculous assumption.  Shottky rectifiers, like bipolar rectifiers, have a Vf/If curve and Vf varies with both forward current and temperature.  A "0.5V drop" Shottky is so rated at a specific test current; at lower currents, it's less, and at higher currents, it's more.  This obviously at the very least has an effect on regulation.  You'll never achieve 50mV regulation, typically the worst-case rating for a regulated 13.8V power supply, if you add a diode in series with its output.

-There's lots to know about how electronic equipment interacts with power supplies.  A lot of our "battery operated" gear, such as the FT-817, isn't very critical and can perform well over a broad range of input voltages; other gear simply can't.  I wrote up a 1-page Technical Correspondence article for QST magazine last year (September '03 issue) which covers more of this.

WB2WIK/6

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W3JJH
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Posts: 1421


WWW

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« Reply #17 on: April 22, 2004, 01:05:27 PM »

And Steve's QST article is well worth reading!
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KB1GTX
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Posts: 462




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« Reply #18 on: April 22, 2004, 05:00:54 PM »

""I've seen enough exploded electrolytic capacitors and charred resistors, magnetic components, and pc boards to want to avoid overstressing components.""

Yes, but it's fun to watch it smoke!

  dave
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K1CJS
Member

Posts: 6055




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« Reply #19 on: April 24, 2004, 10:25:23 PM »

I've reworked a computer supply to power a 25 watt 2 meter mobile, and it works just fine.  If you start trying to power anything more than a 25 watt output rig, you're asking for trouble.  A friend of mine tried it, and found the display going out when he keyed the rig--just not enough amperage supplied, which dragged the voltage down to the point of possibly damaging his rig.  Luckily that didn't happen.  He went out and got a properly rated supply for the rig before he tried to use it again.
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