AC or DC Power Supply?

Rob_In_MO · Sep 24, 2017

Hello all. New to the forum, not new to radios.

For years i've been running an external DC supply (Astron, homebrew, etc.) to power my scanners and Ham rigs. I'm not a fan of switching supplies, as they're over-prone to rf hash.

What's the consensus on here - use a small wall-wart (like comes with most newer models) or power from a clean DC supply like an Astron, etc?

Just wondering if i'm being too over-protective or paranoid about powering base/mobile units at home.

jaspence · Sep 24, 2017

AC or DC

If you plug it into the wall, all home power supplies run off AC current. The output for most devices in radio/electronics will be DC. The two terms have nothing to do with the way the power is converted. The quality of the internal components is what is most important. https://benchmarkmedia.com/blogs/ap...audio-myth-switching-power-supplies-are-noisy This link may help you understand. I have both for my equipment, and I cannot tell the difference. Most of my noise comes from other electronics, not the power source.

prcguy · Sep 24, 2017

If your going to use a wall wart I would go for one supplied with the unit as its going to have the proper voltage and should be low RFI. I have some wall warts labeled 12V that actually put out 17V with no or little load. That could damage some equipment that draws little current keeping the voltage too high.
prcguy

AK9R · Sep 24, 2017

RF noise from switch mode power supplies is, I think, an old myth. Modern switch mode power supplies designed for communications use by people who know what they are doing, such as those from Astron, Iota, Samlex, etc., are very clean and probably cleaner than they were in the early days. Old-fashioned linear power supplies are heavy, big, and not efficient users of electrical power.

That said, there are a lot of consumer electronics devices being sold today with cheap, poorly designed switch mode power supplies. Every one of those wall-warts is a potential noise source because many of them contain switch mode power supplies. If you are diligent about electrical noise in the shack, you will probably want to eliminate every wall-wart and power everything from a single quality-built switch mode power supply that will provide enough power for the devices in the shack.

The downside is working out the various voltages that your devices might require. If everything in the shack will run from a nominal 12 volts DC, then you're all set. If you have devices that require 5 volts, 6 volts, 9 volts, etc., then you have a problem. Simple linear voltage regulators, like the venerable LM 78xx or LM 317, are not very efficient. OTOH, buck converters are more efficient, but potential noise sources themselves.

If it were me, I'd get rid of all the wall-warts. But, your approach will have to be one that suits you.

Rob_In_MO · Sep 24, 2017

Thanks for the replies. Looking at an oscilloscope will show you how much AC ripple is in the DC output of any power supply - switching or linear. My homebrew is cleaner than most wall-warts i've tested, and every bit as clean an my Astron RS-20.

My little homebrew has a 12v 4-amp transformer and i'm using an LM338 (5-amp version of the common LM317) with a heavy heatsink. A 1-k resistor and it's a perfect 12.7 volts and quite stable. Larger 25v filter capacitors than are needed, but that's not a bad thing either. Having tested it with a variable resistor, the absolute maximum output voltage is 14.5v (if something should happen) thanks to a hefty bleeder resistor. Runs 24/7 and as cool as a cucumber with a continuouis 1.5 amp load.

W9BU - I'm in complete agreement. I'll keep doing what i'm doing. I'm sure, as others have pointed out, that switching supplies have come forward leaps and bounds since early models were introduced.

AC or DC Power Supply?

Rob_In_MO

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jaspence

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prcguy

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AK9R

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Rob_In_MO

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