28 VDC AC/DC Adaptor

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telcotech
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28 VDC AC/DC Adaptor

Post by telcotech »

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.
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jwax
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Re: 28 VDC AC/DC Adaptor

Post by jwax »

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
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Engineer1138
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Re: 28 VDC AC/DC Adaptor

Post by Engineer1138 »

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
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Re: 28 VDC AC/DC Adaptor

Post by dyarker »

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 -
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telcotech
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Re: 28 VDC AC/DC Adaptor

Post by telcotech »

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
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Re: 28 VDC AC/DC Adaptor

Post by Enzo »

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.
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Chris Smith
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Re: 28 VDC AC/DC Adaptor

Post by Chris Smith »

ALL ELECTRONICS<p>28 VOLT 1.5 AMP
POWER TRANSFORMER
CAT# TX-2815
rshayes
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Re: 28 VDC AC/DC Adaptor

Post by rshayes »

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
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Re: 28 VDC AC/DC Adaptor

Post by telcotech »

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
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