28 VDC AC/DC Adaptor

This is the place for any magazine-related discussions that don't fit in any of the column discussion boards below.
Post Reply
telcotech
Posts: 8
Joined: Thu Dec 02, 2004 1:01 am
Contact:

28 VDC AC/DC Adaptor

Post by telcotech » Fri Dec 03, 2004 3:59 am

Hi,<p>I have a telephone system that requires a 28VDC 600mA wallwart. VoiceLogic Voice Pro System.<p>An original adaptor that came with these units had these markings on it:<p>Class 2 Transformer
Model No: DDU280060
Input: 120 VAC 24W
Output: 28VDC 600mA<p>I can't seem to find a replacement, I would like to know if anyone has a suggestion as to where I could find one, or, how about suggestions for building one.<p>At this point, you may be thinking, why dosen't he just open the old one and look inside, I wish I could, my system came without one, I took the numbers off a working unit at another location.<p>To build one, my question would be to just use a 28 volt transformer and build a rectifier, or to use a regulator. Due to the sensitivity of the equipment, I would assume the original was regulated, but, I can't seem to locate a 28 volt DC regulator and don't really know how to use an adjustable regulator and keep it stable enough.

User avatar
jwax
Posts: 2200
Joined: Mon Feb 09, 2004 1:01 am
Location: NY
Contact:

Re: 28 VDC AC/DC Adaptor

Post by jwax » Fri Dec 03, 2004 5:28 am

28 VDC wall wart seems like an oddball. I'd go with a 28 VAC transformer, bridge, and filter cap. If you need regulation, a LM317 will work.
www.allelectronics.com for your transformer ($3.50), $.50 for a LM317. :D

Engineer1138
Posts: 458
Joined: Thu Feb 05, 2004 1:01 am
Location: Minneapolis, MN
Contact:

Re: 28 VDC AC/DC Adaptor

Post by Engineer1138 » Fri Dec 03, 2004 7:39 am

Unless it's 28VDC *regulated*, you can probably get by with a 24VDC unregulated supply rated at a higher current. The 24V supply will output 28V, but at a lower current than its 24V rating.<p>Try www.digikey.com

dyarker
Posts: 1749
Joined: Fri Aug 22, 2003 1:01 am
Location: Izmir, Turkiye; from Rochester, NY
Contact:

Re: 28 VDC AC/DC Adaptor

Post by dyarker » Fri Dec 03, 2004 8:23 pm

For 28VDC unregulated use a 20VAC to 22VAC transformer, full-wave bridge rectifier and capacitor. (a 28VAC transformer would rectify to almost 40V peak)<p>Chances are that the telephone system internally regulates the 28V to 24V.<p>If the system labeling says something like 26V - 30V for power in, that probably means it can run on two 12V SLA batteries in series. (So the phones work during power outages.)<p>Another alternative, a 24VAC transformer (easy to find), rectify, and filter. Regulate to 28V with a 7824 with a 3.9V zener diode in series with the common pin to common. Do not connect common the power supply to ground; telephone systems often use grounded positive.<p>C U L -
Dale Y

telcotech
Posts: 8
Joined: Thu Dec 02, 2004 1:01 am
Contact:

Re: 28 VDC AC/DC Adaptor

Post by telcotech » Fri Dec 03, 2004 9:32 pm

Thanks for the input, I checked a working power supply, it output 35 VDC with no load. I would assume it is not regulated, so, would you suggest using a
28 VOLT 1.5 AMP POWER TRANSFORMER CAT# TX-2815 from All Electronicswith a bridge and filter cap?<p>Also, what size filter cap should I use?<p>Thanks

Enzo
Posts: 276
Joined: Tue Sep 14, 2004 1:01 am
Location: Lansing, Michigan, USA
Contact:

Re: 28 VDC AC/DC Adaptor

Post by Enzo » Sat Dec 04, 2004 1:17 am

The surplus houses usually have a selection. Marlin P Jones used to have pages of them. Jameco has a number of 24v units in warts adn non warts. Unless you want a project, you might consider getting a complete power supply if you want to get away from wall warts. For about the price of parts, an open frame supply can be had ready to roll. Adjustable even.

User avatar
Chris Smith
Posts: 4325
Joined: Tue Dec 04, 2001 1:01 am
Location: Bieber Ca.

Re: 28 VDC AC/DC Adaptor

Post by Chris Smith » Sat Dec 04, 2004 10:41 am

ALL ELECTRONICS<p>28 VOLT 1.5 AMP
POWER TRANSFORMER
CAT# TX-2815

rshayes
Posts: 1286
Joined: Tue Mar 04, 2003 1:01 am
Contact:

Re: 28 VDC AC/DC Adaptor

Post by rshayes » Sat Dec 04, 2004 11:38 am

Try looking at Mouser Electronics (www.mouser.com). They list over 500 items under the heading Power/Power Supplies/Plug-in AC Adapters. These are all wall warts of various sizes and ratings. You might even find a match for the connector.

telcotech
Posts: 8
Joined: Thu Dec 02, 2004 1:01 am
Contact:

Re: 28 VDC AC/DC Adaptor

Post by telcotech » Sat Dec 04, 2004 1:42 pm

Thanks for the replies, Inoticed that Jameco offers supplies from Reliapro, which have the same part number format to the supply I need, I emailed them and hope they may be able to get the exact replacement, if not, I think I will try a 24 or 30 vdc supply.<p>Thanks

Post Reply

Who is online

Users browsing this forum: No registered users and 35 guests