Q&A
■ WITH RUSSELL KINCAID
In this column, I answer questions about all
aspects of electronics, including computer
hardware, software, circuits, electronic theory,
troubleshooting, and anything else of interest
to the hobbyist. Feel free to participate with
your questions, comments, or suggestions.
Send all questions and comments to:
Q&A@nutsvolts.com
WHAT’S UP:
Join us as we delve into the
basics of electronics as applied
to every day problems, like:
✓Electric Car Battery Charger
●✓How to Monitor Series Cells
✓Audio Amplifiers
X- 10 PROBLEM
QThe X- 10 appliance module
is great for in-house control.
The problem I have is with
the new compact fluorescent
lights. When you turn off the X- 10, there
is enough leakage current that the CFL
will flash once or twice a second. Not
a complete lighting of the whole tube,
but enough that it is distracting and a
waste of energy. (True for units with or
without the sense line cut.)
A couple of tests show that a
small (4W) incandescent night light
in parallel with the CFL takes care of
the leakage current and the CFL won’t
flicker, and there is not enough current
so the incandescent doesn’t light. (Still
wasting energy, but oh well.) Great! But
... when you turn the CFL on, the night
light also comes on — another unneeded light, expense, and waste of energy.
What I need is a circuit that is small,
cheap, and safe that I could put under
the socket of a table lamp with a CFL,
or in a dummy plug to be plugged in
alongside the lamp into the X- 10 that
■ FIGURE 1
26
March 2008
would take care of the leakage current
when the X- 10 is off so the CFL doesn’t flicker, but doesn’t “turn on” (light,
heat, etc.) when the X- 10 is turned on.
— V. Alan Mode
AYour X- 10 unit must be
defective or poorly designed.
At any rate, since the four
watt lamp works, try a 0.1 μF,
600V capacitor (Mouser part #75-
MKT1813410635 should work) in parallel with the compact fluorescent lamp.
The capacitor will not use any power
and will help correct your power factor.
ELECTRIC CAR BATTERY
CHARGER
QI am building an electric, plug-in car using 12 deep cycle 12
volt batteries for the 144 volts
to drive the motor. Chargers
for 144 volts are expensive so I would
like to build my own if possible, that will
run off 120 VAC so that I can recharge
anywhere there is an outlet. Any ideas
for a circuit would be welcome along with
cautions about how not to damage the
batteries during charging and how to do
it fairly efficiently. There are some “bad
boy” chargers I have seen that are
simply a transformer and rectifying bridge.
Should these be used, for example?
— David Abineri
AThe transformer/rectifier system works okay, you just need
some way to limit the current.
Most battery chargers have a
circuit breaker if the current is too high,
but I used a one ohm, 100 watt resistor
to limit the current when the battery is
in a low charge state (see Figure 1). The
transformer is 1:1 when the primary
windings are connected in parallel and
the secondary windings are connected
in series. The peak voltage is 165 volts
which is needed to fully charge the 144
volt battery. The tolerance of components and line voltage is such that I would
not recommend leaving the charger on
the battery for more than a few days. So,
there is a switch to disconnect the one
ohm resistor, but leaving a 200Ω in place
to provide a trickle charge. The switch is
double pole, single throw with the
contacts connected in parallel. You can
leave the trickle charge on indefinitely.
CIRCUIT TO PROTECT
GPS UNIT
QI have a little problem with
my new Garmin C550 GPS
navigation unit. The issue
seems to be related to when