Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

DC Power Supply Has AC Signal?
DC Power Supply Has AC Signal?
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 4th January 2004, 02:04 AM   #1
newbie1 is offline newbie1  United States
diyAudio Member
Join Date: Jan 2004
Location: California
Default DC Power Supply Has AC Signal?

Hi I am new to the forum and have a question about DC current in general.

I just picked up a DC power supply from Radio Shack (13.8V 3A). It seems to register the correct DC voltage when measured. However, I noticed that there is an AC voltage of 29V as well. I tried testing a 9V battery for AC voltage and it registered 19.4V. This made me suspect there is something wrong with my meter?

Just thought I would ask the experts first, and if I am wrong and this is a normal phenomenon would 29V of AC from the Radio Shack PS harm a DC circuit?

  Reply With Quote
Old 4th January 2004, 03:25 AM   #2
AudioFreak is offline AudioFreak  Australia
Warp Engineer
On Holiday
AudioFreak's Avatar
Join Date: Oct 2001
Location: Queensland, Australia
DC Power Supply Has AC Signal?
Your radioshack power supply is almost certainly a SMPS (switch mode power supply) and will have some high frequency ripple (AC), given the high frequency, it's a little unpredictable how your meter will measure it(it would almost certainly give you a bogus figure). The 9 volt battert basically shouldn't register any AC so I'd suspect that your meter is no good. Try putting a fresh battery in the meter, you'd be amazed at how somethings behave with a flat battery.
- Dan
  Reply With Quote
Old 4th January 2004, 06:11 PM   #3
Nasty Ned is offline Nasty Ned  United States
diyAudio Member
Join Date: Jan 2004
Location: Chico
As the webmaster mentioned the ripple is standard. The most accurate way I know of measuring it would be with an oscilloscope, but not many people have one of those just lying around. The meter should read the AC wave "riding" on the DC signal..... but 29V seems way too high for a 14 V powersupply.
  Reply With Quote
Old 4th January 2004, 08:07 PM   #4
Richard C is offline Richard C  United Kingdom
diyAudio Member
Join Date: Jul 2003
Location: Nottingham, England
This is clearly a result of the way your meter works (or doesn't) on the AC range and has nothing to do with ripple, the AC battery reading proves this.

You do not have 19.4V AC at the terminals of your battery, end of story.
  Reply With Quote


DC Power Supply Has AC Signal?Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Power tube bias increasing with signal. tubesrock Tubes / Valves 2 23rd July 2008 03:23 AM
Grounding of opamps. Signal or Power? Arx Chip Amps 1 23rd July 2007 08:47 AM
Hypex UcD 180AD + signal wires, Power Supply ST, Hypex Transformer TR100A c10h12n2 Swap Meet 7 7th July 2007 03:55 PM
Class-D modules no-signal power Pierre Class D 1 28th June 2006 11:38 AM
HP 35660A Signal Analyzer power supply needed alaskanaudio Parts 2 8th February 2003 12:34 PM

New To Site? Need Help?

All times are GMT. The time now is 09:43 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio