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Multiple coils for
electronic ignition
I am interested in building the
High Energy Ignition published in
the May and June 1988 issues.
What I wish to do is make an ignition system using a multiple coil
setup similar to the one used on the
VN Commodore. This car uses
microprocessor controlled ignition
but the multi-coil idea could be
adapted to normal electronic ignition if I can find a way of alternating the signal from the ignition
module from one coil to the other.
I intend to use two coils (for a
four cylinder car) and I need either
an electronic or mechanical solution to the problem.
What happens is that one coil
fires two spark plugs simultaneously. One is on the firing stroke and
the other on a harmless exhaust
stroke. I know very little about electronics and was wondering if it
would be possible to build a system
into the SILICON CHIP ignition
High energy ignition
does not start
I have built the High Energy Ignition project featured in the
May 1988 issue of SILICON CHIP
and have a problem.
The unit is fitted to a Toyota
Land cruiser FJ 45 1984 model.
When the engine is being cranked over the unit will not fire but
immediately the key is released,
it will fire. When cranking the
voltage drops to about 10.5 volts
and I am wondering if the unit is
sensitive to low voltage.
The unit was built and fitted
primarily for a better start. I
have replaced the MC3334P IC
and the two transistors (BC337
and MJ10012) but the problem
still persists. Could you please
shed some light on my problem
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SILICON CHIP
module that would alternate the
signal between the two coils.
If you think it would be possible
could I impose on you to do me a
diagram and instructions? There
are alternatives to alternating the
output electronically, so if it is too
complicated, don't worry. Your
help would be greatly appreciated.
(J.K., Ashgrove, Qld).
• There are two drawbacks to the
system you propose. First, where
are you going to obtain the coils
which will fire two spark plugs
simultaneously? As described in
our article on the VN Commodore in
the December 1988 issue of SILICON
CHIP, this car uses special double
ended coils with a high tension output at each end and the coils are integrated with the electronic ignition
module. You might be able to obtain
these coils as spares but that could
be expensive.
Second, there is no easy way of
switching the output of the high
energy ignition from one coil to
another. It would be much easier
and probably cheaper to simply
have two separately controlled ignition modules. Why don't you just try
building the Hall Effect ignition as
described in our June 1988 issue? It
is highly effective and very similar
to that used on many four cylinder
cars today.
Sure, this solution does not get
rid of the distributor as would your
proposed system but it does have
the big advantage that you can do it
without too many hassles.
Needs a Thorn
colour TV circuit
Can you help? I need a circuit
diagram for a 14-inch colour
monitor, model Thorntel PX14TU.
I've been all around the traps and
have come to a dead end. Any
chance that you can assist me? flan
Barrow, PO Box 64, Port Melbourne, Vic 3207).
• We don't have access to commercial circuit diagrams of monitors. If we did, we could solve a
a few problems of our own. Can any
reader help?
and also give a fix for the unit?
(R.K., Darkan, WA).
• In our experience, the High
Energy Ignition will function well
down to quite low voltage.
We suspect that you have
wired the unit up to one of the
fuses coming off the accessory
position of the ignition keyswitch. When cranking, power to
all accessories is removed which
means that your ignition circuit
is not powered up during this
time.
Why are we so sure about
this? Because the writer made
exactly this same mistake some
years ago when installing an
electronic ignition system. It did
the same thing - nothing while
cranking and then it would burst
into life as soon as cranking
stopped.
Optical tachometer
doesn't count
Could you please help me in
regards to your Optical Tachometer [SILICON CHIP, May 1988).
After building it, I first set it up to
6000 RPM as per calibration with a
fluorescent light. I then put a
photostat copy of the strobe pattern
on my turntable but no way would it
pick up any light or show a glimmer
of movement on the meter.
Since I wrote the first part of this
letter I have tried again to get it
working and found that if I put a
finger on the circuit board in the
area of the Q3 & Q4, I get the needle to FSD and in doing this I was
able to set it to 900 RPM using the
strobe.
The electrolytic capacitors may
6V version of the
brake lamp flasher
Could you please tell me if the
"Flasher Circuit for Auxiliary
Brake Lights" featured in the
April 1989 issue of SILICON CHIP
can be modified for 6V operation? I wish to fit this device to
· my 6V motor cycle as a conventional stop light fails to attract
enough attention when stopping.
If I lower the value of the Darlington transistor and halve the
value of the resistors could 6V
then drive the unit?
Keep up the very good articles
and information in your magazine. I'm teaching myself electronics and find your publication
very helpful. (G.W., Ocean
Shores, NSW).
• The circuit itself will work
quite happily from 6V without
modification but the voltage drop
across the BD645, typically
about lV, will reduce the
brightness of the brake lamp.
not all be new but are the ones
stated. As the unit works perfectly
when tested with a fluorescent
light, I am wondering what could be
wrong. (R.W., Stuarts Point, NSW).
• There is a quick and dirty test to
see if the Optical Tachometer is
working. Just point it at a light
source or open window and then
rapidly flick your fingers back and
forth in front of the sensor, to
simulate a light interrupter. If the
circuit is workir..g, the pointer will
move part way up the scale.
From what you have said with
regard to calibration from the
fluorescent light source, we think
the circuit is probably working correctly. When you are testing from
the strobe pattern on the turntable,
you need to hold the sensor very
close to the platter - within just a
few millimetres - otherwise there
is too much light reflected from adjacent parts of the pattern.
That is probably why you've
managed to get the unit going by
putting your fingers on the board.
By doing this you have altered the
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5A CONTACTS
In a 12V system you can live
with the slight reduction in
brightness but in a 6V system a
1V reduction will mean that the
lamp will be too dull. In daylight,
you might not be able to see it at
all.
The only way to overcome this
problem is to use a relay to do
the switching, as shown in the
accompanying circuit. The relay
should be fast enough to flash the
lamp but if it is not, you may
want to reduce the flash rate.
This can be done by increasing
the 0.15µF capacitor at pin 6 of
IC2.
The only problem which re-
bias on the preamp stage and
thereby made it a little more sensitive. However, we don't think the
circuit needs modifying to increase
its sensitivity.
Info wanted on
gate turn-off SCRs
Do you have any information on
the operation, application and
availability of gate turn-off SCRs,
as referred to by Bryan Maher in
the August issue of SILICON CHIP?
My reason for asking is that I am interested in building a chopper type
speed control for an electric golf
buggy.
I have seen a commercial speed
control which uses two MJl 1016
transistors but it seems to me that a
gate turn-off SCR could offer a better solution. (J.E., Bull Creek, WA).
• We do have limited information
on GTO (gate turn-off) SCRs as
made by Philips but no applications
circuitry. They are not simple to
design into circuitry, for two
This circuit will let
you adapt the
auxiliary brake
lamp flasher for 6V
operation. It uses a
6V relay to switch
the brake lamp
instead of a
Darlington power
transistor.
mains is where to get 6V relays.
Most kitset and parts suppliers
do not stock 6V relays with a
contact rating of 5 amps more.
You may get one as a motorcycle
accessory. Alternatively, you
can obtain them from Farnell
Electronic Components Ltd, 72
Ferndell Street, Chester Hill,
NSW 2162. Phone (02) 645 8888.
Their relay Cat 176-696 or
170-191 will do the trick.
Alternatively, you could try
the Perth branch of Radiospares
at 28-30 Northwood Street, West
Leederville, 6008. Phone (09) 381
4799. Their 6V 16A relay, Cat
346-025, would be suitable.
reasons. First, they have no reverse
blocking capability as does a normal SCR and so series diodes need
to be added for reverse blocking or
parallel diodes added for reverse
conduction.
Second, the big disadvantage of
GTOs is that their turnoff gain is
not very high and can be as low as
unity. This means that you need a
pulse of current, as high as the load
current, fed into the gate to turn it
off.
When first introduced, GTOs
were touted as being suitable for
high frequency inverters, power
supplies and motor control. These
days though, these applications
seem to have been largely taken
over by Mosfets.
For really high power applications, such as motor control in rolling mills and locomotives, GTOs are
still used although they are very
large devices indeed. For lower
power motors, high power Mosfets
and IGBTs (insulated gate bipolar
transistors) have largely taken
over.
1§:;l
DECEMBER1989
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