Electronic hum from power supply

[DylanMadigan]

I'm sorry I'm sure theres answers out there but I'm having a hard time finding them. My speaker buzzes a little and when I transmit others hear it on the radios on my power supply. The power supply is rated for what it is doing, I think the capacitors (i think) just aren't so great.

I messed with electronics a little in school. Could I just take a good sized capacitor and connect it over positive and negative where DC power comes out of the back to get rid of that buzz? If so how would I know what capacitor I can use without causing an explosion of sorts?

I threw together some low voltage stuff in school to build a bridge rectifier and turn an AC signal into a smooth DC signal and power a light (with an oscilloscope) but that was like a kit thing so I already knew that the components where rated for that.

 

[RFI-EMI-GUY]

I'm sorry I'm sure theres answers out there but I'm having a hard time finding them. My speaker buzzes a little and when I transmit others hear it on the radios on my power supply. The power supply is rated for what it is doing, I think the capacitors (i think) just aren't so great.

I messed with electronics a little in school. Could I just take a good sized capacitor and connect it over positive and negative where DC power comes out of the back to get rid of that buzz? If so how would I know what capacitor I can use without causing an explosion of sorts?

I threw together some low voltage stuff in school to build a bridge rectifier and turn an AC signal into a smooth DC signal and power a light (with an oscilloscope) but that was like a kit thing so I already knew that the components where rated for that.

You could filter it at the terminals, but it might not be effective. The power supply might have a shorted pass transistor or bridge diode and you would get a buzz. What kind of power supply is this? Can you find a schematic? What is the voltage at the terminals, with no load?, with radio in receive mode? In transmit mode?

In absence of a schematic, I would measure the voltages as above, then with the unit off, measure the diodes and transistors for normal conduction versus shorted.

If satisfied the regulator is working as designed, replace all the electrolytic capacitors inside with new.

Sent from my SM-T350 using Tapatalk

 

[slicerwizard]

The proper thing to do would be to open up the power supply and replace the large electrolytic capacitors. Their sizes (in uF) and voltage ratings are printed right on them.

If you don't want to do the proper thing, then toss some big electrolytics on the output + and - lines. As long as their voltage ratings exceed the power supply output voltage, you're fine. So 16V caps for a 12 to 14 volt supply. And make sure you get the polarity right when you wire them up - otherwise, it will be a spectacular show...

 

[cmdrwill]

" My speaker buzzes a little and when I transmit others hear it on the radios on my power supply. "

May be RF getting into your radio. Did you test the setup with a dummy load instead of the antenna?

 

[lmrtek]

Yes a capacitor can be placed across the terminals and yes it would be effective IF that is the problem
But as pointed out you should see if it does it on a dummy load to isolate if it is actually rfi causing the sound or actually the supply.
And power supply ratings are deceptive to say the least
If your radio is rated to draw 10 amps Max then you need a power supply that supplies at least 12 amps CONTINUOUS.
Most manufacturers have deceptive model numbers.
The Astronomy RS12A for example is only a 9 amp supply and the RS20A is a 16amp supply
As far as sizing the capacitor, it will need to be at least 35vdc working voltage and you allow 2000mfd per amp for the total capacitance needed for filtering.
So if you have a conventional linear type power supply that
produces 12 amps continuous, it should have about a 24,000mfd filter capacitor
The Astron RS20a for example is a 16 amp continuous power supply
and it uses a 32,000mfd capacitor.
So if you are just beginning to notice some ripple, adding a capacitor that is say half the original value should clear up the ripple if it is capacitor caused