READER FEEDBACK
EVERYTHING FOR ELECTRONICS
THUMBS UP FOR
ANEMOMETER
Just wanted to say I really enjoyed
the article by Michael Simpson on
making the anemometer. I don't know
of any hobbyist who hasn't attempted
or at least thought of making a home
weather system.
Dan Bacon
MISSING FEATURES
ON POWER SUPPLY
Robert Reed’s interesting article
on a Test Bench Power Supply (March
2007) includes many desirable features
and a number of clever ideas. I am
troubled by what I consider to be two
fundamental problems:
1. The inability to adjust the
maximum current means you cannot
use the device to conveniently test
diodes (especially LEDs), or to recharge
Nicad or similar batteries.
2. The unit is not designed for a
typical use at five volts at near full
current. The unit will overheat at this
load, and the output voltage will
cycle as the regulator goes into and
out of thermal overload (as noted by
the author). When working on a
circuit on the bench, one does not
want to be worrying about the power
supply overheating!
I built a dual bench supply in 1966
(from a 73 Magazine article), which
has both adjustable voltage and
current, and still use it daily. The
adjustable current is a feature I simply
could not do without. I’d like to see a
follow-up article by this obviously
talented author, which adds current
adjustment (perhaps another LM317)
and better heat control.
Paddy Johnson
myriad of special batteries this would
demand quite a variety of safety
measures built in. Nor was it intended
to be a component tester either. However, the reader has two choices on
these options: 1) Go to National Semi's
website and download the LM317 data
sheet. There you will find additional
info on the LM317 as a current source
that you may want to incorporate into
this design. 2) An outboard constant
current source is a very simple circuit
to build requiring one transistor and a
couple of resistors. These options were
deleted from design for several reasons
as mentioned in the article: simplicity,
compactness of size, and personal lack
of desire for these options.
As to item two, I don't know if I
understand the question correctly, but
the 5 VDC supply is rated for one
ampere of current and the article states
the heat dissipation is well within the
devices range, as verified by actual case
temperature measurements, and this
was with all supplies loaded. In fact, I
have actually run any of the outputs at
1.5 amps for short periods of time
( 15-20 mins.) and experienced no
problems. Does the reader understand
that all devices are heatsinked to
the chassis? I hope this answers the
readers questions satisfactorily.
Robert Reed
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ENCLOSURE
ENQUIRY
The Test Bench Power Supply
article was wonderful, informative, and
the photos were of exceptionally high
quality. Many details are included,
but extremely little is said about the
methods to be used in working the
aluminum to form the enclosure. In
particular, how do you cleanly cut out
the rectangular holes for the meters in
the front panel?
WEB CONTENT/NV STORE
Michael Kaudze
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Debbie Stauffacher
Copyright © 2007 by T & L Publications, Inc.
All Rights Reserved
Response: Well, let me see. Where do
I start? As to item one, current limiting
and constant current were deleted from
design for reasons stated in the article.
The supply was not meant to be a
battery charging device, as with today's
6 May 2007
Judy May
Union, KY
Response: Well for starters, like most
people who lack a machine shop for
metal work, I did it the slow way. For
bending the sheet metal, I jury-rigged
Continued on Page 35
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