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From: Robert Baer
X-Mailer: Mozilla 4.75 [en] (Win98; U)
Subject: Re: transformer design 24Vac0 to 16Vac 5 ~ 30 VA etc
Date: Sun, 15 Dec 2002 11:29:31 GMT
NNTP-Posting-Date: Sun, 15 Dec 2002 03:29:31 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
Joseph Goldburg wrote:
> Hi all,
> I am looking for pointers on the WEB were to find info
> on designing and making these transformers.
> I am a hardware engineer but my transformer theory is
> about 10~15 years old (lost in the grey matter)..
> How would you select suitable cores and formers, coil dial, wire lengths
> and turns etc.
> Any WEB pointers or recommended books would be appreciated.
> Example of Spec's
> Input 24V ac
> Output multi-tapped sencondary 12Vac 500mW 9Vac 6Watt
> Output multi-tapped secondary 16Vac 500mW, 5Vac 4Watt, 3Vac 2Watt
> Small cores but low cost
> Thanks in advance
Best way is to get power transformers from a surplus store and re-wind
Design Number = square root of power.
Turns per Volt = 24 / Design Number.
Total cross sectional Area = 0.29 * Design Number.
Choose wire size so that cross sectional area in circular mils is
equal (or close to) to the current rating in milliamperes.
These numbers are based on the old silicon steel transformers
available in the 1940s, and yield a generous "safety" factor with modern
There is always plenty of room for all windings, and one does not have
to compensate for I*R wire loss.
I have hand wound hundreds of transformers using these formulas, from
a Popular Mechanics booklet printed in 1941.
It says they are good for 50-133 cycles per second; i only worked with
60Hz line frequency.
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