Tim --
See below -----
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-- Specializing in small, cost effective
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Robert L. (Bob) Smith
Smith Machine Works, Inc.
9900 Lumlay Road
Richmond, VA 23236 804/745-2608
[EMAIL PROTECTED]
----- Original Message -----
To: "Multiple recipients of list CHIPDIR-L" <[EMAIL PROTECTED]>
Sent: Monday, November 22, 2004 11:20 AM
> Hello Group,
> Maybe a little off topic but hopfully somebody can help or steer me to
> someone who can.
> I have a relatively large power transformer I believe was from a computer
> related application. It has core dimensions of 1 1/4 x 5 1/4 x 4 3/8 and I
> am trying to get an idea of it's power rating. I has three primary taps
for
> 105, 115 and 120 volt operation and 2 secondaries.
> One secondary has a centertap with large lugs for a high current 5 volt
> supply. By stepping up the load over a few hours, I was able to get the
> OTHER ONE, WITHOUT a centertap and smaller lugs, to provide 12.38 amps at
> 26.44 volts,
Well, 12.38 x 26.44 = 326.83 VA . . . .
> drawing 3 amps input at 120 volts.
And you are drawing 360 VA at the input. So if you are any where near unity
power factor, your transformer loss is about 33 watts . . . .
> By feel it seems to get a little to warm to touch after an about hour. I'm
> guessing it's at least 100 degrees f.
which just about matches the above observation.
> The numbers on it are as below but I was unable to find out anything
with
> them.
> ECT-100-115-20
> 72149-2405A2
> How can I determine the capable amperage without overloading it?
A transformer in continous duty and not driven into core saturation is
typically a thermally limited device. So its "capabable amperage" is
whatever you can draw without exceeding the operating temperature limits of
the materials from which it is constructed.
Given most modern materials (cores, windings, insulation paper), I would say
that if you can touch it without burning your fingers you are operating
pretty conservatively. The ultimate limiting temperature rise is determined
by the materials from which it is made.
> Also most
> of the supplies I have seen use a centertapped winding with a full bridge.
Not likely. Center tapped windings normally operate into a half-bridge (two
diodes). Full bridges (four diodes) normally operate without a center tap
except to create dual (negative and positive) outputs.
> Could I still get the same results by using it without a centertap and
> create my own ground reference or is this the wrong animal to use to build
a
> high power supply?
"High" power is a relative term. If you were only observing 100 F at 360
VA, you can probably push this transformer to 500 VA. Is that high power
for you???
> If so, can anyone use it?
Anyone skilled in the arts of power supply design should be able to.
Best wishes, Bob Smith
>
> Thanks and sorry for the long post
>
> Jim
>
>
> --
> Author: Tim Johnson
> INET: [EMAIL PROTECTED]
>
> Fat City Hosting, San Diego, California -- http://www.fatcity.com
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--
Author: Bob Smith
INET: [EMAIL PROTECTED]
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