>>>READER-TO-READER QUESTIONS AND ANSWERS
circuit diagram, I would appreciate it.
#3095 David Luther
Los Angeles, CA
Digital Multimeter Input
Impedance
I have purchased an inexpensive
DMM which appears to work satisfactorily. Is there a method to measure
the input impedance of the meter?
#3096 Doug Poray
Jackson, NJ
>>> ANSWERS
[#1099 - January 2009]
Electronic Simulation Software
I see simulations of circuits in
many articles. I used to have a copy of
Electronic Workbench 12 years ago,
but found it to be unreliable in switch
mode designs. I would like to know
what package you recommend for
mixed signal and switch mode design
simulation that is easy to use and
under $1,000. Also, I have been out of
electronics for six years and need a single source for info on SMT packaging.
#1 Surprisingly, there are a couple
of free circuit simulation software
packages available. I like Linear
Technology’s LT SPICE IV (Switcher
CADIII), which is a general SPICE
program, but uses a specific algorithm
to do switch mode simulation
extremely well. It excels at start-up and
transient events, and rarely fails to find
the operating point or hangs. The
program updates frequently and other
SPICE models are easily added.
Almost all of their products are
supported. Also, there is TINA-Ti
(Texas Instruments) and National
Semiconductor has a web-based
solution. The best sources for SMT
information are the manufacturers
themselves, since most of them have
extensive tutorials and PDF files
available. Other good sources are
the PCB manufacturers and many of
them have free layout software. I
recommend expresspcb.com; they
have an excellent, brief (on-line)
manual and CAD software to get you
going quickly. Other good sources
right now are the solder manufacturers, parts, and equipment makers, due
to RoHS (Restriction of Hazardous
Substances).
Walter Heissenberger
Hancock, NH
#2 You probably sent this SPICE
question in a few days before the
December 2008 issue of Nuts & Volts
was published. The most inexpensive
SPICE for the MS Windows OS is
described in " A Touch of SPICE" by
Peter Stonard in the December 2008
and January 2009 issues. This superb
introduction to LT SPICE (Linear
Technology SPICE) will get you
started on a package with a schematic
capture front end. LT SPICE is
probably the best answer.
If you have a rich employer to buy
Electronic Workbench, the schematic
capture is much improved. Back when
you were using EW, I used Penzar
TopSPICE to good effect when it was
half today's $500 price. If your
employer provides OrCAD schematic
capture, consider PSPICE. Most of the
published SPICE netlists are based on
PSPICE. There is a free student version
of OrCAD/PSPICE.
I got a lof of mileage out of the
PSPICE student edition before it had
schematic capture in the early 80s
because my "fortune 100" employer
wouldn't buy it. I actually learned
SPICE from Intusoft newsletters and
books. They sell IsSPICE. They are very
good at providing models of exotic
devices.
These days, I am Linux OS based
using Xcircuit schematic capture and a
patched version of Berkeley SPICE
3f5. I don't recommend this approach
for casual users. See Kuphaldt,
"Lessons in Electric Circuits" AC,
Chapter 6 on the web for examples.
Dennis Crunkilton
Abilene,TX
[#12086 - December 2008]
Power Tool Batteries
Does anyone have information on
how to recell/rebuild power tool
batteries? Procedures and suppliers of
equipment needed to do it properly?
I have rebuilt numerous powertool batteries, generally upgrading
them as far as capacity (ma/hrs) and
reliability as I did. I have discovered
that about 90% of all common tool
batteries are made up of sub C size
NiCds or NiMh cells. A few older ones
were actually full size D cells (not the
Eveready, etc., D cells with a 1/3 D
tucked in one end that they sold as
rechargeables for home use to replace
dry cells). Those D cells were very
powerful and heavy. There is also a
smattering of AA, AAA, AAAA, and
"coin cell" stacks out there now. Then
there are lead-acid, lithiums, and
nickle-iron Edison cells, and even
some alkalines.
The most important thing is that
the cells you rebuild with need to be
as identical as possible to each other
in capacity, internal resistance and
charge and discharge rates, as your
battery pack can only perform as well
as its weakest link.
Another consideration is operating temperature (there are high temp
versions) and the temperature
tolerance of the insulation around the
cells — some of the plastics used on
China imports melt and short the cells
together — a common failure in
"liquidation store," weak, low priced
drills and saws. I have found the blue
plastic thin insulation on available high
capacity cells and the old standby
"cardboard" or pasteboard paper-like
insulation to perform well. The non-oil
or non-plastic soaked pasteboard
insulation's only flaw is that continual
repeated exposure to moisture and/or
salt water can cause a high resistance
short between cells due to either salt
or mineral build-up and residual
moisture or iron oxide (rust) from the
cell's outer case permeating the material. Use the plastic or soaked "paper"
insulated cells for tools, RC toys , etc.,
used in rain or underwater cameras,
for example. I have soaked paper ones
in varnish or polyurethane when desperate, and have also seen wax used.
I now go on the Internet Googling
NiCds or NiMH or batteries, etc., to
find good ones at a good price —
2,250 ma/hr is easy to come up with
and close to that in sub C NiCds, but I
don't remember the site. They were
cheaper than the 1,250 ma/hr ones.
Over 5,000 ma/hr units have been
located. There appears to be a
March 2009 95
