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Author Topic: ATX supply to power mobile rig?  (Read 3247 times)
N1TWC
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« on: May 29, 2008, 01:46:00 AM »

Hi folks,

I suspect that I'll get laughed out of the forum for asking this, but humor me.  

I've been using strictly HTs ever since being licensed, but in the interest of emergency preparedness, I bought a used Kenwood TM-731A dual-band mobile for use as, primarily, a base station.  My problem is buying a power supply that won't cost more than the radio.  Does anyone have experience hooking up their radio to the +12V lead of a PC's ATX power supply (which, at least the few I have lying around, claim to supply ~19A)?  Is this a MAJOR faux pas?  I can deal with a little noise leaking into the rig, but I certainly don't want to damage the radio.

Any thoughts?  Thanks!
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K8GU
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« Reply #1 on: May 29, 2008, 06:43:51 AM »

The big problem with this is that the computer power supply was designed to supply power to a computer, not a radio.  This has a number of consequences.  You'll have to wire-up some switching logic to control the ON/OFF.  I'm also not sure what kind of regulation you'll have, particularly with nature of the current draw of a radio (intermittant spikes on TX) vs a computer (relatively constant while turned ON).

Although I'm all for scrounging, I think this might not be a good opportunity.  You ought to be able to get something reasonable for less than $50, and possibly quite a bit less.  There are a lot of old two-way systems that had small Astron supplies.  If you asked around the right places, you might be able to get one for a song...
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WA7NCL
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« Reply #2 on: May 29, 2008, 08:11:56 AM »

Computer supplies have poor regulation on the 12V outputs because the primary regulation loop is on the logic supply voltages.  The 12V output is also set for 12.00V and most ham radio transceivers (especially HF rigs) will not put out full power at 12V.  Lastly, cheap computer power supplies, especially the older ones (think junk box here) are likely to be big time RFI sources.

There are a lot of mfgrs of ham radio power supplies out there.  You would be better off buying a reliable one, rather than blowing your radio up or screwing around with something from the junk box.
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KD8CGF
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« Reply #3 on: May 29, 2008, 11:33:13 AM »

    Your question has been answered many times in the past.  Google "St Louis Switcher".   May 2002 QST has a good article, if you're an ARRL member, download it at http://www2.arrl.org/members-only/tis/info/pdf/0205035.pdf
    Also see http://www.antentop.org/007/files/ct2ilq007.pdf for other links.
    I bought a new ATX P.S. at CompUSA 18 months ago for $20, chopped all the power lines off & terminated them except for one to power my IC-2200H (2M), added a load resistor (forget if it was on the +5VDC or +12VDC line) to stabilize the voltage.   Only cost over & above the ATX was for the the load resistor & the connector to match my transceiver.  I did not try to increase the voltage above +12 VDC, but understand that this can be done by either changing settings on the ATX or by substituting components at key points on the circuit board, but you would most likely need a schematic and/or repair manual for the computer p.s. you buy or recycle.
    I've had no trouble using this modified power supply at all power levels but the highest for my IC-2200H.   The p.s. I created will not provide the highest (75W) power level for my rig, but this is not important to me.
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NA0AA
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« Reply #4 on: May 30, 2008, 02:38:49 PM »

Good quality, well regulated supplies designed for Amateur use are so inexpensive there's little reason to use anything else expect for experimental purposes.

Regulation and RF noise are your biggest challenges to these supplies.  One challege is that they are not designed for heavy on-off loads demanded by communications gear.

If you are serious about emergency preparedness, an Astron with the BB [Battery Backup] can help you.
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N4KZ
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« Reply #5 on: June 04, 2008, 05:46:20 AM »

Good quality switching power supplies large enough to power a 100-watt HF rig are available on the market for $80-100. That makes it hard to justify trying to convert a computer power supply that might not do what you want and/or could damage your radio.

73, N4KZ
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KD8CGF
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« Reply #6 on: June 04, 2008, 04:44:23 PM »

   For my pocketbook there's a big difference between $20  and $80-100.  
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N2IK
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« Reply #7 on: June 04, 2008, 05:40:52 PM »

These computer power supplies lack overvoltage protection (Crowbar) and if they decide to fail with excessive voltage output will take your radio with it. If you are on a tight budget with an old radio not worth much, go ahead. But I like a safe supply so I do not lose my expensive dual bander or my HF rig.

Incidently you can get a switching supply from Jameco with overvoltage protection that will run a 50 watt HF rig for about $60.00 new. They work OK. I have had mine for about 5 or 6 years now. A used Astron or Samlex supply is about the same cost. IMHO the best investment in ham radio is a good power supply able to handle your present and anticipated future needs. Don't ask me how I know that.

Good luck,

Walt N2IK
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K1CJS
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« Reply #8 on: June 09, 2008, 03:53:33 AM »

I did convert one once--not an ATX supply, but an older one with the power switch hardwired instead of transistor switched.  It worked fairly well, and I still have it--for an emergency backup for everything BUT my radios.  I never used the radio connected to it on full power, and because of that, I never had a problem.

If money (cost) is you're primary concern, you're best bet is to go to Wally World and get a lawn tractor battery, ($15 to $20) and a 1 amp charger (another $20).  When you can afford a proper supply, you'll already have a backup supply ready made if you lose power.  If you can't afford the charger, get a cigarette lighter plug and recharge it (the tractor battery) off a car while its running.
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N8EKT
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« Reply #9 on: June 20, 2008, 11:15:54 AM »

Not a bad question at all!
I have used computer power supplies for years!
They work VERY well!
I run my repeater off a 300 watt atx supply and I have a kenwood 731 as a link radio also running on a atx supply!
No problems what so ever!
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K9FV
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Posts: 480




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« Reply #10 on: July 02, 2008, 06:33:01 AM »

Simply amazing the number of "hams" who are scared to experiment, scrouge parts... and seem to be "made of money" - in my book there is a LOT of difference in $80 and $5 - which is more what I would expect to pay for a USED computer power supply.  There are many articles out there on how to do convert computer power supplies to a usuable power supply.  So what if it only provides 12 VDC, that will power a VHF rig to get into the local repeater.

The hertiage of hams is to build radios, but now, gasp, horrors to even think of building something as simple as a power supply.  Honest folks, you can learn a LOT by building - and it's a LOT of fun.

rant mode off:

73 de Ken H>
K9FV
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KE4DRN
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« Reply #11 on: July 02, 2008, 05:46:45 PM »

hi,

just a reminder to anyone who wants to work on
these switchers, use extreme caution, there is
over 400V inside these power supplies and it will hurt.

always discharge the capacitors before working on them.

73 james
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KC0SKE
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« Reply #12 on: August 20, 2008, 04:25:40 PM »

I'll go against the grain here.... I converted an ATX power supply it wasn't the best but for my budget, I had a mobile radio to talk to the tower. I highly doubt you'll do any damage to the radio...Theres a far better chance the radio will just shut off.
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