>>>READER-TO-READER QUESTIONS AND ANSWERS
GPS units are fairly accurate at
computing altitude. Are directional
accelerometers or GPS units sufficiently quick and accurate to produce
such a signal? I have also seen digital
levels that must produce an off level
signal to send to a readout or display.
How might these devices be used?
#12066 Robert Fisher
I'm having a hard time clearing up
excessive static on my AM radio
reception, and I want to do time shift
recording on my computer. I've
purchased an external antenna, but
the radio has to be close to this
interference source, and even worse,
it needs to be connected to it (limiting
the distance I can move it). Anywhere
in the room is going to have the same
problem because of the amount of
electronics ranging from flourescent
lights to an office fridge.
Is there an easy way to build a
Faraday cage around the radio, so that
the interference generated within the
room isn't a factor? Then if I use a
shielded cable to bring in the external
antenna signal from outside and use a
ferrite core on the USB cable to the
radio, will that stop the RF noise from
feeding in through the signal/USB
Unfortunately, I don't understand
a lot of the technical aspects of
Faraday cages and/or ferrite rings. If
there is a good reference for this type
of project to help me construct the
cage (i.e., materials required as far as
composition and structure) and/or
select the ferrite ring (diameter, thickness, etc.) then I'd be happy to refer to
it if someone could point the way.
I'd hate to spend a lot more time
and money chasing a fundamentally
flawed hypothesis, so I would appreciate any direction.
San Diego, CA
[#10064 - October 2006]
I need an alternator regulator circuit that will allow me
to charge a 36-volt and a 72-volt battery bank using a
standard automobile alternator ( 75-100 amp type
alternator). Any ideas?
#1 You need to read Alternator Secrets by T. J. Lindsay,
available at www.lindsaybks.com. For $3, you will have all
you need to know about how to modify an alternator
output to the voltage you need. The quick summary of
about 20 pages of information is that you need to add
resistance between the zener diode and the resistance
bridge in the regulator circuit to raise the voltage.
New Castle, IN
#2 Shown in Figure 1 is a way to charge higher voltage
batteries using an old style alternator with an external
regulator. The regulator adjusts the field to cause the
voltage at the I input of the regulator to be 14. 4 volts. The
potentiometer is used to divide the charging voltage down
to 14. 4 volts. I do not know what the current requirements
of an old Chrysler regulator would be, so I have not
indicated a value for the potentiometer. You would have to
measure the current and choose a reasonable value. Of
course, fixed resistors can be used. The diode pack in the
alternator should be good for 40 to 50 volts, maybe even
higher. I have seen an old Chrysler alternator put out 300
volts and the diodes did not blow. All you can do is try it.
The RPM will have to be quite high to get any current
at high voltages. Do not expect to get 80 amps out of an
These same modifications can be made to an
alternator with an internal regulator. It would have to
hacked to find the equivalent of the I and F terminals to the
#3 Figure 2 is a modification of a design I did for my
tractor alternator. The alternator will put out 72 volts with
12 volts on the field if you turn it fast enough. It is only
necessary to change R1 to change the regulated voltage.
You could install them with a three-position switch.
December 2006 101