READER-TO-READER TECHFORUM
EasyPIC development board which is
what I recommend for anyone just
getting into PIC programming.
They also sell dozens of add-on
boards that are designed to connect
to their development board. These
can be used to greatly reduce your
development time. Then, if you
later decide you want to build that
component yourself instead of using
an add-on board, they'll even provide
you the schematic.
Their website also has free online
books that are terrific tutorials for the
beginner and a great reference for the
rest of us.
The mikroBasic software itself
comes with templates to demonstrate
just about every feature on a PIC chip.
So, you can quickly jump-start your
new project by building up from their
examples.
Alternatively, there is also
PICBasic, but when I compared it to
the features and cost of mikroBasic,
there was, in my humble opinion, no
contest.
Joe Kissell
Gardner, KS
#3 The Atmel AVR family of microprocessors has long been popular in
professional, education, and hobbyist
circles. As to Basic, arguably the very
best structured Basic, very similar to
Microsoft's Visual Basic 6, is the compiler called ZBasic ( www.zbasic.net,
and the user forum www.zbasic.
net/forum.) This compiler targets the
company's AVR chip based inexpensive microprocessor "stamp" products,
with both byte-code and native code
versions. Another Basic compiler for
eight-bit microprocessors is from
www.mcselec.com; it's an "old school"
Basic which may bring back memories
of spaghetti code! Finally, it's worth
noting the Teensy micros from
www.pjrc.com/teensy/ make a good
target for most any compiler producing standard .hex downloadable files.
The excellent and unrestricted
WinAVR (GNY/GCC) with Atmel's
free AVR Studio is very popular — due
to the price: $0. Of late, the dozens of
Arduino variations have surged in use
by those without a desire to muck
80 September 2010
about in the details of the C language,
at least as a starter.
Steve
San Diego, CA
[#41010 - April 2010]
DC Motors
How does an interpole winding
work in a DC motor?
#1 In a DC motor, as one commutator
segment moves out from under a
brush and another makes contact with
a brush, the result is that sparking can
occur at the commutator. To reduce
the sparking, interpoles can be placed
in the DC motor to help prevent
brush sparking at the commutator.
Interpoles are additional field windings placed on poles located midway
between the field poles. The interpole
coils are connected in series with the
armature; therefore, the current they
carry is proportional to the armature
current. The interpole coils are wound
so as to produce a magnetic field with
a polarity opposite to the polarity of
the magnetic field created by the armature current (thus, the magnetic field
created by the interpoles is opposite to
the magnetic field that is created by the
armature). Interpoles aid the regular
field windings in pulling the armature
coils to and past the magnetic poles of
the field windings.
Ralph J. Kurtz
Old Forge, PA
#2 Irving Gottlieb explains the
operation of interpoles very nicely in
his book Electric Motors And Control
Techniques. A thorough answer is too
long to print here, but to summarize:
Interpoles are small poles (
electromagnets) positioned half way between the
main poles (permanent magnets) in a
brushed DC motor. The interpoles are
wired in series with the commutator
and are "intended to combat the
effects of self-induction and mutual
induction in the armature inductors ...
and improve commutation." If you're
going to dive into motor theory,
this book is worth the $14 on
Amazon.com.
Dan Danknick
Santa Ana, CA
[#5103 - May 2010]
Load Controller, Micro Hydro
I built a 3,000W, 220V, micro
hydro machine and installed it for a
family of five living near a stream. I
need a load controller to offset the
extra power whenever something is
turned off. When the real load goes
down, the frequency and voltage go
up. The design should monitor the
frequency ( 50 Hz) and dump some
load to resistors whenever the frequency starts going up, and dump less of
that load when the frequency goes
down. If there is a better idea please let
me know. Is PWM a good option?
It appears that this is a stand-alone
generator, not connected to any other
power. Throwing a resistive load on to
hold the output voltage and frequency
in spec might be okay if you have a
need for a lot of hot water or steam.
Otherwise, it is wasteful.
My first choice would be to have
a couple of control loops: The first
loop is a speed stabilization loop to
hold the speed relatively constant and
give the desired 50Hz ± a few Hz. This
probably means controlling water
flow/pressure to the turbine. The
second loop involves controlling
excitation of the generator to regulate
voltage. Controlling excitation is very
effective because exciter power is
much lower than the output power of
the generator. Stability and response
time of the loops can be enhanced
by sensing the load current on the
generator and using that information
to alter the loop signals before much
speed or voltage change has actually
occured.
This may sound like a lot of
trouble, but it saves water and will give
better control than the shunt load
responding to actual voltage or speed
changes.
If you insist on the shunt load, the
cheapest load is water itself. Use a
controller to raise and lower a pair of
iron plates in a big drum of water as a
variable load. Use the stream water
flowing through the drum to keep
it cool.
Jon Wexler
Los Angeles, CA
