[Boatanchors] 12 volt supply question

Alex [Temple Boatanchors] temple.boatanchors1 at miwww.com
Wed Nov 30 23:03:45 EST 2016

ATX PC power supplies are very inexpensive ($20-$30), highly 
efficient and very lightweight, and basically use the same concept as 
those modern lightweight "wall-wart" wall transformers. But due to 
their switch-mode nature they generate a great deal of RFI in the HF 
regions, specially the lower frequencies bellow 10-15MHz or so, but 
should be fine for use with gear on 6M, VHF, UHF and up. The level of 
RFI perceived in the receiver much depends on how well the radio 
itself and coax to the antenna is shielded and grounded, and the 
distance between the gear and power supply is a factor as well. Also, 
the output is 12V, not the required/desired 13.8V that most mobile DC 
operation gear needs to attain full output power. But with small 
modifications by changing one or more resistors (varies from model to 
model), in most cases one can "fool" the regulator to raise the 
voltage as needed without tripping the protection circuit. Another 
issue is that the power supply usually requires a minimum load on one 
or more of its outputs for stable operation of the regulator circuit, 
as one or more of these outputs are used as a reference voltage. A 
resistor or appropriate incandescent light bulb might do the trick as a load.

I use a 700W ATX power supply that I modified for 14.4V output to 
manually charge a 150Ah lead-acid backup battery bank. It easily will 
charge it at 20-25Amps and generates minimum heat as long as its 
internal fan is running. Basically these power supplies can be used 
as very inexpensive power sources or charger. But while charging it 
basically wipes out my reception on 80 and 40 meters. Then again the 
internal power supply of my nearby Apple TV does pretty much the 
same, only at a lesser degree than the charger.

Just search for "ATX power supply modification", there is quite a bit 
of info out there.

At 07:17 PM 11/30/2016, you wrote:
>OK gang ..   Can someone provide a definitive answer to this 
>question?   I see all kinds of conflicting opinions and would like 
>to know what the thinking is here.  Or, if someone here is using 
>them for that purpose.
>Computer power supplies.   Can they or can they not be used to power 
>ham rigs such as two meter rigs, or even
>low power HF rigs?

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