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Pulse power in
train controllers
A few months ago, I purchased
“14 Model Railway Projects”
which is a most interesting publication. The kit my son is assembling
is from the final article, the “Diesel
Sound Simulator”. We have controllers of both the “pulse” and
“fully rectified waveform” types.
What are the effects of running an
engine with the “pulse” circuit or
a “rectified wave form” type?
I have found the waveform type
produces better results than the
pulse type. The pulse type is a
Hornby R921 putting out 12V DC
at 4VA and the waveform type is a
Bachmann 6607A putting out 17DC
at 0.6 amps (7VA, although I don’t
know how that maths works. 17 x
0.6 = 10.2).
Is amperage the key? It seems
from your articles that 3A is a good
value. This figure contrasts signifi
cantly with the 0.6A maximum
used by a local model railway at
traction (Mike Scott’s Trainworld).
noise. It could be any one of a number
of faults such as loose laminations,
shorted turns, anti-phase primary
connections or who knows what.
Please, please, give it all up as a bad
job before you kill yourself or someone else.
By the way, your letter had no
address on it but was postmarked
“Darwin Mail Centre”. Normally
we do not feature letters in SILICON
CHIP where no address is supplied
but in your case we have made an
exception. We hope you get a chance
to read this!
Millivoltmeter drive
modification
I am interested in constructing your
AC Millivoltmeter as described in
the August & September 1988 issues.
I have a SIFAM meter movement
from an old hybrid AC millivoltmeter which has its scale calibrated
precisely as in your design. Because
this is a very high quality movement I
would like to incorporate it into your
1988 design.
The question is, can the circuit be
94 Silicon Chip
He seems to be able to happi
ly
double-head a very long train (two
Lima class 31s). (J. H., Auckland,
NZ).
• We are not sure about the question you are asking. As described
in the article, the Diesel Sound
Simulator circuit can be made to
work with both pulse or rectified
(waveform) controllers. However,
once set up to work with a particular controller, it will not necessarily
work well with other controllers.
As far as pulse and waveform
controllers are concerned, most
so-called “pulse” controllers do not
use the same system of pulse width
modulation at about 200Hz as used
in the SILICON CHIP controller design. As such, they do not perform
as well as our design and generally
not as well or as reliably as simpler
rectified waveform designs.
Most locos with can motors draw
currents of less than 1A but others
require a lot more and if smoke
and lighting circuits are added,
plus double-heading, then a much
higher current is required.
of IC7b. The accompanying circuit
shows the general scheme and you will
probably need to increase the 6.2kΩ
resistor at pin 3 of IC7b to provide the
appropriate zero offset to the meter.
We must emphasise that we have not
tried either of these ideas but one or
the other should be workable.
A 300V range can be included by
using a 12-position switch and by
splitting the 1.1Ω resistor at the bottom
of the existing input voltage divider.
The two new resistors would be 0.75Ω
and 0.35Ω.
More on battery
capacity meters
I have a suggestion in reply to the
request in “Ask SILICON CHIP” July
1996 for a battery capacity meter. I too
am a regular RC model aircraft flier
and have been using the following
method to determine nicad battery
capacity for several years with suc
cess.
If your nicad battery discharger has
a LED to indicate that discharge is
taking place, it is a simple matter to
connect a single-cell crystal clock in
parallel with the LED. If you set the
hands on 12.00, the clock will begin
ticking when the discharge button is
pressed and stop ticking when the
LED goes out.
It is then just a simple calculation to
work out the battery capacity. For example, if the discharge rate is 200mA
and the clock reads 2.00 (two hours),
then the capacity = 2 x 200 = 400mA.h.
(R. H., Kingston, Tas).
Notes & Errata
modified to accommodate a 5mA meter instead of the 100µA movement
specified and if so how? I had thought
that a simple transistor current amplifier would do the trick, perhaps even
a PNP/NPN push-pull pair but I have
not been able to find any data on such
an idea. I would also like to include a
300V range. (J. L., Yate, UK).
• As far as we can tell, the circuit
should be able to drive a 6mA meter
movement without problems although
the calibration trimpot VR4 will need
to be reduced to 200Ω or 250Ω.
If you find that the LM833 cannot
do the job, you will need an emitter
follower to boost the output current
Stereo Simulator, June 1996: pin 7 of
the M65830P (IC2) is shown connected
to both +5V and GND on the circuit
diagram on page 16; it should only
be connected to +5V. The PC board
overlay diagram on page 19 is correct.
16V 15A Power Supply, Circuit Notebook, July 1996: there are number of
mistakes and omissions in the circuit
on page 17. First, the 56kΩ resistor
from the collector of Q4 should go to
the +25V line instead of to the base
of Q1. Second, D4 should be a LED.
The designer has also suggested that
the 100µF capacitor across the output
terminals be increased to 220µF and
a 1kΩ resistor be connected across
the 10kΩ potentiometer VR3 (Voltage
SC
Max).
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