Power supplies

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Bob Quale
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Power supplies

Post by Bob Quale » Sun Dec 08, 2002 6:51 am

I have been watching this site for a while and have found it very informative. Now I have a question. I need a power supply for making little circuits. Digital, timer, op amp ect. I'm just learning about electronics. Can I buy a surplus swiching supply and make it variable or do I need a supply with isolation. Some of the swiching supplies have minimum current ratings. Some of the surplus houses sell a supply with meters and such. Is that a swiching supply dressed up? Does it matter? I'm not sure the difference between switching and not. HELP!!<p>Thanks for the help BOB

russlk
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Re: Power supplies

Post by russlk » Sun Dec 08, 2002 7:21 am

A useful power supply will have plus and minus 12 volts and plus 5 volts. If the supply only has +- 12VDC, you can obtain +5 VDC easily using a 7805 or simular regulator IC. You probably don't need a variable supply, a variable voltage can be obtained using a potentiometer and emitter follower. Most switching power supplies on the public market are isolated, don't use one that is not. For your purposes, it doesn't matter if the power supply is switching or linear, the linear supply will be heavier.

greg123
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Re: Power supplies

Post by greg123 » Sun Dec 08, 2002 7:52 am

Isolation is very important. If your looking to build one your self, i have lots of schmatics that you can have.

Bob Quale
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Re: Power supplies

Post by Bob Quale » Sun Dec 08, 2002 8:00 am

American sience and surplus has a supply for about $85.00. Is it worth it to build one at this cost? I would think by the time I get the transformer and other parts I would be better off buying one and get to building stuff. What is the difference between linear and swiching for practicle purposes?<p>Bob

Bob Quale
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Re: Power supplies

Post by Bob Quale » Sun Dec 08, 2002 1:46 pm

So is it feasable to think i can buy a surplus power supply from a computor, like all electonics sells and use it? Or should I spend the extra and by a Elenco or similar. Some of the surplus ones have a minimum current rating. If i under power it what will happen? Thanks again for all the imput. <p>Bob

russlk
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Re: Power supplies

Post by russlk » Sun Dec 08, 2002 4:10 pm

A computer power supply requires some control signals, someone here can tell you how to make it work. Usually the 5 volt output requires a load, you can just put a power resistor load on it. It will not regulate with no load.

teknuts
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Re: Power supplies

Post by teknuts » Sun Dec 08, 2002 9:43 pm

Check out http://www.dalbani.com in florida. Good power supplies at great prices....

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frhrwa
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Re: Power supplies

Post by frhrwa » Thu Jan 09, 2003 11:35 am

check your e-mail, I sent you some info that you may be interested in..
JESUS”…… don’t leave EARTH without HIM!

hlreed
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Re: Power supplies

Post by hlreed » Thu Jan 09, 2003 11:54 am

I use an old PC, XT power supply on my bench.
Jameco has a full page of switching power supplies from $40 up.<p>web page
Harold L. Reed
Microbes got brains

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haklesup
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Re: Power supplies

Post by haklesup » Thu Jan 09, 2003 7:54 pm

If you do use a PC power supply, read the output specs (sticker on side) carefully. Note that very often the 5V and/or 12V supplies do not guarantee regulation until a minimum current load is applied. In other words, it may not be 5V under no load or small load conditions.<p>AT supplies are easier to use, ATX supplies need to have a sense line connected to ground or the supply will seem dead.<p>Teknuts is right, Dalbani does have some good deals, I've used them before.

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