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Convert PC Power Supply for C.B use?

T23

Active Member
Apr 17, 2010
645
12
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I m looking at converting a PC power supply to use for a C.B, does anyone have any information?



T23
 

They're 12v, not 13.8v.

Also, switching power supplies are known to produce RFI.

Good luck!


Generally you can raise the 12 volts up to at least 13 volts but the noise is still a factor to deal with. I was contemplating using a gang of switching PC supplies to make a 40-50 volt supply to power some MFR-151G 300 watt power modules I have but the thoughts of trying to cure all that RFI scared me back to my senses. :unsure:
 
Yeah, I figured it out PM me for details these things are rock soild when conversion is done, you can get one of those alternator hum cancelers to cut the noise out.


T23
 
I have had relatively good luck doing this also. Seems most computer power supplies are not too noisy. Sometimes you will find one that puts a noise level in your receiver. I can tell you from experience an alternator whine filter will not get rid of noise from a switching power supply. Unlike in the case of the alternator where we want to filter out relatively low frequency AC ripple, the switching supply creates RF hash. This RF is actually radiated from the power supply circuits and is not easily filtered out. It's usually picked up by the antenna and removing it will confirm it's radiated RF and not ripple on the DC line.
 
I have had relatively good luck doing this also. Seems most computer power supplies are not too noisy. Sometimes you will find one that puts a noise level in your receiver. I can tell you from experience an alternator whine filter will not get rid of noise from a switching power supply. Unlike in the case of the alternator where we want to filter out relatively low frequency AC ripple, the switching supply creates RF hash. This RF is actually radiated from the power supply circuits and is not easily filtered out. It's usually picked up by the antenna and removing it will confirm it's radiated RF and not ripple on the DC line.

Agreed. The noise from a switching power supply is not simply a high pitched whine superimposed on the DC voltage but rather a true wideband RF signal that is radiated out into the air.
 
Good points... Maby extra power supply case shielding? there not very good stock.

They got so many holes in them I aint surprised they have RF noise.


T23
 
Good points... Maby extra power supply case shielding? there not very good stock.

They got so many holes in them I aint surprised they have RF noise.


T23

The holes are not too big of a deal as they are quite small as compared to the size of the wavelength involved and aren't that much different than the vent holes in other RF related gear. The big problem is that none of the wires are RF bypassed and the signal basically uses them as transmitting antennas and radiates all over the place. Extra shielding would help but the wires need to be bypassed as well.
 
I would think the computer PS would work well, as a computer needs good clean DC to function. The computer PS is a switcher type and the switcher's frequency S/B above the human audio range. The only drawback is the 12V vs 13.7V. You should be able to adjust the voltage by changing the resistive divider, or adding a silicone diode in series with the sensing voltage pick off in the +5V side of the PS. The +5V is the only voltage that they regulate, the 12V and the rest follow the +5V. Be carefull the PS has high voltage (as high as 340VDC via a voltage doubler with capacitor storage), can be lethal!
 
Thanx for that Xbox Power Supply idea man... I forgot I had an old one of those, it should be perect for my HTX-100...


T23
 
I would think the computer PS would work well, as a computer needs good clean DC to function. The computer PS is a switcher type and the switcher's frequency S/B above the human audio range. The only drawback is the 12V vs 13.7V. You should be able to adjust the voltage by changing the resistive divider, or adding a silicone diode in series with the sensing voltage pick off in the +5V side of the PS. The +5V is the only voltage that they regulate, the 12V and the rest follow the +5V. Be carefull the PS has high voltage (as high as 340VDC via a voltage doubler with capacitor storage), can be lethal!

Typical switch frequencies are around 15-30 KHz depending on the power supply and load. Not all PC PSU's are bad and even the ones that are bad do not have dirty power on thier lines. As stated before, most of the noise is generated as RF and the computer still sees clean power on the supply rails. I can take a handheld scanner or HT and program it to receive AM mode and hear all kinds of noise when I wave it near my computer but the computer works fine.
 
Is there a way to tell the amperage that I am putting out on a converted supply without standard equipment?


T23
 

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