>>>READER-TO-READER QUESTIONS AND ANSWERS
over the power line. They can also control loads, turn your
electric off and on, and determine precise power outage
maps over the power line. You can read more about
TWACS on their website at www.aclaratech.com.
It uses a zero-crossing modulation scheme and is
neither fast nor efficient. In fact, remember back in the days
of the Commodore 64 when you could read a text file as
it downloaded at 1200 bps? Yeah, that is lightning speed
compared to power line communication.
Saint Louis, MO
[#8082 - August 2008]
I need info on refurbishing or building custom solar
yard lights. I currently have a Lighthouse lawn ornament that
has a solar light that doesn't recharge the replaceable
rechargeable battery. Information on troubleshooting would
be helpful for what I assume to be a fairly common circut. I
would also like to illuminate the lantern of a Lawn Jockey and
a Pagoda. Adding multiple LEDs with changing colors and
blinking patterns could also be a take off.
Shown is a suitable charging circuit which consists of a
string of solar cells producing a voltage high enough to
charge the NiMH or NiCd batteries through a Schottky
diode. The diode prevents discharge through the solar cells
with insufficient sunlight. In our latitudes, significant current
is produced from about 9 am to 3 pm and the solar cells
should be sized to produce about 0.2-0.25 It (cell capacity
in mAhr nominal conditions). Further information can
be found in rechargeable battery literature; SANYO has
probably one of the best explanations up on their website.
A circuit for a pattern generator is also shown,
consisting of an oscillator driving a four-bit up counter
connected to the lower addresses of a 2K x 8 EEPROM. This
circuit simply reads consecutively the contents of the
EEPROM, and you can either store the desired patterns or
use an already programmed (recycled) one; you may be
surprised by the patterns you get. Other EEPROMS can also
be used at either more or less patterns depending upon the
size of the EEPROM. The 2K x 8 has space for 64 different
patterns, which are adjusted through SW1 through SW6.
[#9083 - September 2008]
I have several Maytag Neptune washing machine motors
with the driver board.
I would like to make an adjustable speed generator so
that I could use these motors on wood working tools. I was
thinking that a 555 series chip would be the basis, but I don't
know how to get the three phase output. Also, would I drive
one or two phases of the motor at the same time?
One thought was to use the 555 to cut the power to
one winding at a time sequentially and leave power on the
other phases. I don't know how Maytag did this. I don't want
to use a microprocessor chip if I can avoid it.
#1 Appliance manufacturers have switched in the last
few years to three phase motors connected to a variable
frequency drive, especially on applications requiring several
speeds, such as washing machines. It also frequently
includes power factor correction ahead of the DC intermediate loop to present an almost purely "resistive load" to the
power grid in order to get high efficiency. For this particular
application, Microchip Technology makes several boards
using either their digital signal processors or their microcontrollers with power modules (three half bridges) from
International Rectifier. This will give you some insights and
the software is completely open. You can also hack the VFD
board; usually there is a connector to a controller. As an
alternate, you can use three phase motors connected
through a few capacitors to a single phase system at higher
efficiency than even connected to a three phase system.
There is an excellent report by Dr. Otto Smith, High
Efficiency Air-Conditioner on Single-Phase Electricity, Energy
Innovations Small Grant, State of California (in public
domain, on the Internet), revealing some interesting results.
This is, however, a single speed application and you may
use variable pulleys to change the speed.
#2 The key to success here would be a working schematic for the Maytag designed controller; without it you are
guessing in the dark. The board is readily available as a
spare part (for under $200), but the schematic was not
found by Google search and may be proprietary. The
hook-up diagram (found inside the washer rear door) does
not specify the voltages and signals needed to operate the
motor controller module and doesn’t help here.
It would be worth “reverse-engineering” a motor
control module and using a DMM and oscilloscope to
examine the signals on a working appliance before making
any homebrew modifications. At this point, it is not possible
to understand how the motor operates, as it could be a true
stepper motor with multiple phase windings or a modified
induction motor that only requires phase angle control
using the AC power line frequency and one or two triac
Frequent mention of replacing over-stressed components on that module was found in the on-line forums for
appliance repair. Perhaps that Maytag repairman has less
free time on his hands than in the old days!
October 2008 95