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Universal
High Energy
Ignition System
Versatile design accepts inputs from
points, Hall Effect and reluctor distributors
By JOHN CLARKE
18 Silicon Chip
T
HIS HIGH ENERGY electronic ignition
system will boost performance and greatly
reduce the need for tune-ups in cars with points
or it can be used to replace the ignition module
in cars with Hall effect and reluctor distributors.
You could also replace your points with a Hall
effect sensor to forever eliminate ignition timing
adjustments.
Over the past years at SILICON CHIP
we have published a series of ignition
systems all based on the Motorola
MC3334P integrated circuit. This was
first featured in the High Energy Ignition for cars using points in May 1988
and this is still available as a kit 10
years later. In June 1988 we featured
a version for Hall effect distributors
and in May 1990, a version for reluctor
distributors.
Also very popular was the Programmable Ignition system featured
in March 1996. This was used in
conjunction with our High Energy
Ignition circuit to provide electronic
advance. It used a microprocessor to
perform the advance calculations and
there have been several updates to the
program since the publication date.
Because of this Programmable Ignition, there have been many requests
for variations and so we have finally
decided to tie all the versions together
in an update of the original circuit. Accordingly, it has provision for points,
Hall effect or reluctor triggering and
connection terminals for the Programmable Ignition. In addition, the circuit
has been revised to include optional
current limiting for the ignition coil,
has a tachometer output signal and
uses a new high voltage Darlington
output transistor which has a TO-218
plastic package.
The plastic high voltage transistor
is easy to mount and can be fitted
inside the case. In contrast, the TO-3
transistor used in our previous designs needed to be mounted on the
Main Features
•
High energy coil output at
high RPM
•
Operates on reluctor, points
or Hall effect signals
•
Twin points input for twin coil
engines
•
•
Fixed 0.9ms spark duration
Coil current limiting when fully
charged
•
Coil primary voltage limited to
300V
•
•
Separate tachometer output
•
4-22V operating voltage
400mV RMS reluctor circuit
sensitivity
outside of the case. The plastic high
voltage transistor results in a safer
installation.
The full range of features of the new
circuit is shown in an accompanying
panel. Readers who are familiar with
the previous High Energy Ignition
circuits will see that it is quite similar
in overall configuration but with the
refinements listed above.
Current control
The High Energy Ignition is socalled because it provides maximum
The finished High
Energy Ignition module
should be mounted in
a well-ventilated spot
in the engine bay, well
away from the exhaust
manifold. To ensure
good circuit earthing,
the case has a separate
earth lead which should
be bolted to a good earth
point inside the engine
bay.
June 1998 19
Fig.1: the circuit has three alternative input circuits for triggering from points,
Hall effect or magnetic reluctor pickups. Other refinements include current
limiting for the ignition coil and a separate tachometer output.
energy storage in the ignition coil
by including dwell extension. What
this means is that the coil current is
allowed to flow for most of the time
instead of simply while the points
are closed (the dwell time). Dwell
extension means that the high voltage
switching transistor is off for a fixed
0.9ms and this sets the spark duration.
This is particularly important at high
rpm when there is less time for the
coil current to build up.
Most car ignition systems incorporate a ballast resistor which is
connected in series with the coil
primary and limits the maximum
current. In effect, the voltage applied
to the coil is never more than about
7V. During starting, the ballast resistor
is switched out so that the full battery
voltage is applied to the coil. This
20 Silicon Chip
compensates for the drop in battery
voltage when the starter motor is
cranking the engine.
While this is necessary to ensure
an easy start, the battery may not be
particularly low when cranking the engine and, considering that this circuit
also incorporates dwell extension, the
coil current may become excessive.
This can cause the ignition coil to run
considerably hotter than it otherwise
would and also means that the battery
drain is higher than it needs to be.
With these thoughts in mind, we
have incorporated current limiting
to prevent the coil current rising
above 5A.
Now let’s have a look at the circuit of
Fig.1. As already indicated, the heart
of the circuit is the Motorola MC3334P
integrated circuit which is especially
designed for this application and has
an operating temperature range up to
125°C. This lets it operate comfortably
inside the engine bay of a car.
Circuit description
Fig.1 shows the MC3334P IC controlling a high voltage transistor Q1.
There are three trigger circuits, catering for cars with points, Hall effect
or magnetic reluctor pickups in the
distributor.
Q1 has a high voltage rating to allow
it to withstand the voltages developed
across the primary winding of the ignition coil and it is a Darlington type
(effectively two transistors in cascade)
to give a high current gain.
When Q1 is turned on to feed current through the ignition coil primary,
its base current is supplied via a 100Ω
5W pullup resistor at pin 7 of IC1. Q1
is turned off when IC1 pulls its output
at pin 7 to ground (0V). The string of
75V zener diodes (ZD1-ZD4) limits the
voltage at Q1’s collector to 300V when
the coil fires. This prevents damage
to the transistor and also prevents
damage to the coil itself if one of the
spark plug leads becomes detached,
allowing the secondary voltage to rise
to an excessive value.
Q1’s emitter connects to ground
via two parallel connected 0.1Ω 5W
resistors. The voltage across them is
monitored by IC1’s pin 8 input via
trimpot VR1 and the 33Ω resistor. The
100Ω resistor from pin 8 to ground
forms a voltage divider with the 33Ω
resistor and VR1, to allow adjustment
of the current limit. This current limit occurs when pin 8 is at +160mV
(nominal). This causes IC1 to reduce
the base drive to Q1 to maintain the
coil current at the set value.
The positive supply for IC1 is fed
via a 330Ω dropping resistor and is
decoupled with a 0.1µF capacitor.
This provides a measure of filtering
for voltage transients. The IC clamps
tran
sient voltages above 90V and
shuts down if the steady-state supply
reaches 30V.
The trigger signal drives the bases of
transistors Q2 & Q3. When the trigger
signal is high, Q2 is switched on and
so its collector is low. This pulls pin
5 of IC1 low via the .01µF capacitor
and causes pin 7 to go low, to turn off
transistor Q1. Pin 7 is an open collector output, meaning that it needs an
external pullup resistor (100Ω 5W in
this case) so that it can go high when
the internal transistor turns off.
The .01µF capacitor at the collector
of Q2 now begins to charge via the
470kΩ resistor and after about 0.9ms,
the voltage at pin 5 reaches the threshold of the comparator inside IC1. This
causes pin 7 of IC1 to go open circuit
again, allowing the 100Ω resistor at
the base of Q1 to turn it on again.
When the trigger signal to Q2 goes
low, the .01µF capacitor at its collector is discharged via the 2.2kΩ and
470kΩ resistors. Thus the .01µF capacitor provides the dwell extension
by turning Q1 on immediately after
the coil has fired. The 0.9ms period
has been set to suit the majority of
ignition coils in cars with single coil
installations.
Transistor Q3 switches on and off
in sympathy with the trigger signal
applied to its base. The resulting 12V
square wave at its collector is suitable
for driving most tachometers. If you
are using an impulse tachometer,
Fig.2: these oscilloscope waveforms show the performance of the ignition circuit
with reluctor triggering. The lower trace is the reluctor signal while the top
trace is the coil primary voltage waveform. The coil primary voltage is limited
to 312V peak-to-peak. Note that the coil is fired on the negative slope of the
reluctor waveform.
then a circuit to drive this is shown
in Fig.8.
Trigger circuits
Fig.1 shows the alternative circuits
for points, Hall effect and reluctor
triggering. Provision for all of these
is included on the PC board.
The points trigger circuit provides
for distributors with one or two sets of
points. Each set of points has current
supplied to it via a 47Ω 5W resistor.
This relatively high current of about
250mA is necessary to keep the points
clean. It acts to burn off oxidation
and oil residues which would otherwise eventually stop the points from
working at all.
Diode D1 provides the trigger signal
for Q2. Each time the points open, its
anode is pulled high via a 47Ω 5W
resistor. This turns on Q2 and IC1
turns Q1 off, as described previously.
The second set of points (Points 2)
is used with 2-stroke twin cylinder
engines where the two plugs can be
fired simultaneously.
The Hall effect trigger circuit is
based on a Siemens HKZ101 ignition
sensor. Power is fed to the sensor via a
100Ω resistor. This limits the transient
current which is clamped by the Hall
effect sensor’s internal circuitry. The
820Ω resistor is the pullup for the
internal open collector transistor. Its
output drives the base of Q2.
The reluctor trigger circuit employs
a 10kΩ load across the reluctor coil
and a 470pF noise suppression capacitor. From there, the reluctor signal
is fed via 10kΩ and 47kΩ resistors
to the base of Q4. This transistor is
initially biased on using a 5.1V zener
which supplies a stable offset even if
the battery supply varies. The circuit
is designed to trigger each time the
reluctor signal swings negative. The
2.2kΩ pullup resistor at Q4’s collector provides the trigger signal to the
base of Q2.
The oscilloscope waveforms of
Fig.2 show the performance of the
reluctor trigger circuit. The lower
trace is the reluctor signal while the
top trace is the coil primary voltage
waveform. The peak-to-peak coil primary voltage is limited to 312V. Note
that the coil is fired on the negative
slope of the reluctor waveform.
Construction
The High Energy Ignition system
is constructed on a PC board which
measures 102 x 82mm and is coded
05305981. It is housed in a diecast
aluminium case measuring 119 x 93 x
57mm. The case must not have internal ribbing, to allow the high voltage
June 1998 21
Fig.3: the component overlay for the points version. Note that while provision is made for two sets of
points, this will only be required on twin-cylinder motors where the plugs can be fired simultaneously.
Fig.4: the component overlay for Hall effect triggering.
Darlington transistor to be mounted
inside it.
Before you install any parts on the
PC board, check it thoroughly against
the published pattern of Fig.10 and
make sure that all holes have been
drilled. There should not be any
shorts or breaks between tracks. If
there are, repair these as necessary.
There are several component overlays for the PC board and you should
22 Silicon Chip
choose the one which applies to the
version you wish to build. Fig.3 shows
the component overlay for the points
version, Fig.4 is the version for Hall
effect triggering while Fig.5 is for reluctor triggering. Fig.6 shows how to
connect up the Programmable Ignition
described in March 1996.
Start construction by inserting the
PC stakes at the external wiring connection points on the PC board and the
link (for the Hall effect version). This
done, install the resistors. You can use
the accompanying table (Table 2) as a
guide to the colour codes.
When inserting the diodes and
zeners, take care with their orientation
and be sure to place each type in its
correct place. Once these are in, install
the IC and transistors, taking care to
orient them as shown. Transistor Q1 is
oriented with its metal flange towards
Fig.5: the component overlay for reluctor triggering.
Fig.6: this component layout shows how to connect the Programmable Ignition described in March 1996.
the edge of the PC board. Do not cut its
leads short as you will need the full
length to enable the tab to be bolted
to the case.
The capacitors can be installed
next. The accompanying capacitor table can be used as a guide to the codes.
Insert the PC board into the case
and mark out the positions for the four
3mm corner mounting holes. Drill
these out and then fit 9mm standoffs
using 15mm long 3mm screws.
Place the PC board onto the screws
and hard down on the standoffs. Now
Table 1: Capacitor Codes
❏
❏
❏
Value
0.1µF
470pF
IEC Code EIA code
100nF 104
470p 471
June 1998 23
Fig.7: this diagram shows how to mount the
high voltage Darlington transistor.
Fig.8: this circuit uses the primary winding
of a small 12VAC transformer (type 2851 or
equivalent) to produce a high voltage pulse to
drive impulse tachometers.
mark out the mounting hole positions
for Q1, the earth screw on the side of
the case and two holes at each end for
the cordgrip grommets. Remove the
PC board and drill and file these out
to shape. The hole for Q1’s mounting
must be deburred with a larger drill
to prevent punch-through of the insulating washer.
Fig.9: this diagram shows how the
Siemens Hall sensor should be
installed to provide reliable triggering.
The vane needs to penetrate the sensor
by between 8mm and 11.5mm. The
triggering point is between 0.1mm and
1.8mm from the centre line of the unit.
Secure the PC board to the case with
star washers and nuts. Q1 is mounted
as shown in Fig.7. Secure Q1 to the
case with a screw, nut, insulating
washer and insulating bush. If you
are using mica washer insulators we
recommend using two to obtain an
adequate voltage rating. You should
also apply a smear of heatsink com-
pound to the mating surfaces before
assembly. The silicone impregnated
glass fibre washers do not require
heatsink compound. Check that the
metal tab of Q1 is indeed isolated from
the case by measuring the resistance
with a multimeter.
Attach the wires for the +12V supply and trigger input connections
Table 2: Resistor Colour Codes
❏
No.
❏ 1
❏ 1
❏ 2
❏ 1
❏ 4
❏ 1
❏ 3
❏ 1
❏ 1
❏ 1
❏ 2
❏ 1
24 Silicon Chip
Value
470kΩ
56kΩ
47kΩ
22kΩ
10kΩ
4.7kΩ
2.2kΩ
820Ω
390Ω
330Ω
100Ω
33Ω
4-Band Code (1%)
yellow violet yellow brown
green blue orange brown
yellow violet orange brown
red red orange brown
brown black orange brown
yellow violet red brown
red red red brown
grey red brown gold
orange white brown gold
orange orange brown brown
brown black brown brown
orange orange black brown
5-Band Code (1%)
yellow violet black orange brown
green blue black red brown
yellow violet black red brown
red red black red brown
brown black black red brown
yellow violet black brown brown
red red black brown brown
(NA)
(NA)
orange orange black black brown
brown black black black brown
orange orange black gold brown
The PC board caters for points, Hall
effect or reluctor triggering. Note the
plastic high voltage Darlington
transistor which is easy to mount.
and tachometer output, if used, and
secure with the cordgrip grommet.
The coil output has its own cordgrip
grommet to separate this wire from
the trigger inputs. Wire up the earth
connection to the solder lug and secure to the case. Note that a second
solder lug attaches to the outside of
the case and is attached with the same
screw. The wire from this is secured to
the car chassis with another lug and
self-tapping screw.
Installation
If you are using the existing points
or reluctor trigger, the ignition unit
can be installed directly into the car’s
engine bay. Locate the case in a position where air flows over it and away
from the exhaust side of the engine. It
can be secured in the engine bay with
angle brackets attached to the side of
the case and secured with self-tapping
screws to the chassis.
Wire up the positive connection to
the positive 12V ignition, the negative
wire to the chassis and the trigger
input to the points or reluctor. The
High Energy Ignition Or CDI?
Some readers will be wondering about the pros and cons of this circuit
versus the Multi-Spark CDI system published in the September 1997
issue of SILICON CHIP. Briefly, we recommend this revised High Energy
Ignition circuit for most cars, including those with Hall effect reluctor
distributors, when the existing ignition module has failed and is very
expensive to replace.
We do not recommend using this system to replace or modify the
ignition system in any unmodified car with fuel injection and electronic
engine management. We take the view that the car manufacturers do know
best, having spent many millions of dollars in optimising their systems.
On the other hand, if you have a highly modified late model car which
has been supercharged or turbocharged, you may require an ignition
which delivers more spark energy than the existing original equipment.
In this case, you may want to consider the Multi-Spark CDI system. Su
percharged and turbocharged engines have considerably higher cylinder
pressures, meaning that the existing ignition system may not have enough
energy to reliably fire the spark plugs.
Of course, we also recommend the Multi-Spark CDI design for 2-stroke
and 4-stroke engines in motorbikes, outboards and Go-karts, in racing
applications and in older cars (pre-1975) which do not have lean mixtures.
By the way, if you wish to use the High Energy Ignition with a rotary
engine, you will need to build two complete systems; one to fire the first
set of plugs and one to fire the second set.
June 1998 25
This photo shows how the high-voltage Darlington transistor is mounted on the
end of the case with a silicone heatsink washer (see also Fig.7).
reluctor requires the correct polari
ty connection in order to fire at the
correct position. However, this is best
determined by testing the engine. If it
does not fire immediately, reverse the
reluctor leads and try again.
Hall effect trigger
While readers may prefer to use
the existing points in their initial
installation, Hall effect triggering is
a far better proposition since it has
no contacts and is unaffected by dirt.
It also does not bounce and cause
erratic triggering nor does it require
constant readjustment for correct
engine timing. The Hall effect sensor
recommended is the Siemens HKZ101
(available from Jaycar Electronics).
You must also obtain a rotating vane
assembly to suit your distributor.
These are available from automotive
aftermarket retailers selling Bosch
ignition systems (eg, Repco). Make
sure that you have one of these before
purchasing the Hall sensor.
Fig.10: this is the full-size etching pattern for the PC board.
26 Silicon Chip
Fig.9 shows how the Siemens Hall
sensor should be installed to provide
reliable triggering. The vane needs to
penetrate the sensor by between 8mm
and 11.5mm. The triggering point is
between 0.1mm and 1.8mm from the
centre line of the unit.
To install the sensor, you must remove the distributor from the vehicle.
To do this, rotate the engine until cylinder number 1 is at the firing point
and this is seen by the rotor button
roughly lining up with the number 1
firing position, usually marked with
a notch on the edge of the distributor
housing. You should also note the
direction of distributor rotation as the
engine is rotated.
With the distributor out of the
engine, find the position where the
points just open for the number 1
cylinder and mark the position on
the distributor where the centre of the
rotor is now positioned. This is the
point where the Hall Effect sensors’
output should go high.
Now remove the rotor, points and
capacitor. The Hall sensor should be
mounted near where the points were
located so that there is sufficient lead
length to exit from the distributor. The
exact location for the Hall sensor can
be determined as follows.
Fit the vane assembly to the distributor and align the rotor with the firing
point marked. The Hall effect sensor
should now be positioned so that the
leading edge of one of the metal vanes
is about halfway through the slot.
Mark the position for the sensor
taking care to ensure that the vane
will pass through the gap without
fouling.
Note that Fig.9 shows the configuration for a counter clockwise rotating
distributor. Clockwise rotating distributors are timed as the vane enters
the Hall sensor from the other side.
A suitable mounting plate can
now be made to fit the Hall sensor to
the distributor advance plate. This
mounting plate must be positioned so
that the vane penetrates by 8-11.5mm,
as stated above. The Hall sensor
should be pop riveted to the adaptor
plate through 3.5mm holes which are
countersunk beneath the plate. The
adaptor plate can then be secured
to the advance plate using machine
screws, nuts and washers. Try to take
advantage of any existing holes left
when the points were removed.
The leads from the Hall effect sen-
sor should pass through the existing
points lead grommet. Check that the
vanes pass through the gap in the
sensor without fouling and that the
lead dress allows the full movement
of the distributor advance plate.
Reinstall the distributor in the engine, with the rotor pointing towards
the number 1 cylinder firing point.
Do a static timing check so that the
engine is set to fire when the vane is
central to the Hall sensor.
Connect the Hall sensor leads to
the ignition unit using suitable automotive connectors. Finally, start the
engine and correctly tune it with a
timing light.
Current limit adjustment
The current limit adjustment is
done by measuring the voltage across
the 0.1Ω resistors and adjusting VR1
for a reading of 250mV when the
engine is stationary. Connect your
multimeter (set to read 0-2V) across
the 0.1Ω resistor and set trimpot
VR1 fully clockwise. Now short out
the ballast resistor and switch on
the ignition. Adjust VR1 for a meter
reading of 0.25V. This will give current limiting at 5A. Switch off the
ignition.
Note that some cars have the ballast
incorporated as resistance wire into
the main wiring harness. In this case,
the easiest way to bypass the ballast
is to take the +12V feed to the circuit
directly from the battery via a 10A
fuse or from a convenient point on
the fuse panel.
Tachometer connection
The tachometer output signal is a
12V square wave which should be
sufficient to trigger most electronic
tachometers. For example, the digital
tachometers featured in the August
1991 and October 1997 issues of SILICON CHIP can be directly triggered
without modification.
Impulse type tachometers will require a much higher voltage. You may
find that the tachometer will operate
when connected to the collector (coil)
connection of Q1 but if not, the auxiliary circuit shown in Fig.8 should
solve the problem.
As shown, this uses the primary
winding of a small 12VAC transformer
(type 2851 or equivalent) to produce
a high voltage pulse when switched
via transistors Q1 and Q2. The coil
voltage is limited by the .033µF ca-
Parts List
1 PC board, code 05305981, 102
x 82mm
1 diecast aluminium case, 119 x
93 x 57mm (with no internal
ribs)
2 cordgrip grommets
1 transistor insulating bush
1 TO-218 insulating washer
(silicone type rated at 3kV)
2 solder lugs
4 3mm x 15mm screws
2 3mm x 9mm screws
4 9mm tapped brass spacers
6 3mm nuts
6 3mm star washers
5 PC stakes
1 2m length of red automotive
wire
1 2m length of black or green
automotive wire
1 100Ω horizontal trimpot (VR1)
Semiconductors
1 MC3334P electronic ignition
(IC1)
1 MJH10012 TO-218 10A 400V
Darlington transistor (Q1)
2 BC337 NPN transistors (Q2,
Q3)
4 75V 3W zener diodes (ZD1ZD4)
1 1N4004 1A 400V diode (D3)
Capacitors
2 0.1µF 63VW MKT polyester
1 .01µF 63VW MKT polyester
Resistors (0.25W, 1%)
1 470kΩ
1 330Ω
1 56kΩ
1 100Ω 5W
1 22kΩ
1 100Ω
2 10kΩ
1 33Ω
1 4.7kΩ
2 0.1Ω 5W
2 2.2kΩ
Miscellaneous
Angle brackets and screws for
pacitor connected between collector
and emitter of Q2.
Programmable ignition connection
If you are building the Programmable Ignition system described in
March 1996 (or its later variants),
mounting case, automotive
connectors, cable ties, solder
Reluctor trigger circuit
1 5.1V 1W zener diode (ZD5)
1 BC337 NPN transistor (Q4)
1 .0022µF 63VW MKT polyester
capacitor
1 470pF 63VW MKT polyester
capacitor or 100°C rated
ceramic
2 47kΩ 0.25W 1% resistors
2 10kΩ 0.25W 1% resistors
1 2.2kΩ 0.25W 1% resistor
1 390Ω 1W 5% resistor
1 PC stake
Points trigger circuit
1 1N4004 1A 400V diode
(D1)
1 1N4004 1A 400V diode (D2)
(optional; see text)
1 .01µF 63VW MKT polyester
capacitor
1 47Ω 5W resistor
1 47Ω 5W resistor (optional; see
text)
1 PC stake (optional; see text)
Hall effect trigger circuit
1 Bosch rotating vane assembly
to suit distributor
1 Siemens HKZ101 Hall effect
sensor (available from Jaycar
Electronics)
1 820Ω 0.5W 5% resistor
1 100Ω 0.25W 1% resistor
2 PC stakes
Programmable Ignition
interface
5 PC stakes
Delete 1 0.01µF 63VW MKT
polyester capacitor
1 470kΩ 0.25W 1% resistor
1 22kΩ 0.25W 1% resistor
1 330Ω 0.25W 1% resistor
the circuit of Fig.1 shows asterisks at
the connection points for the +12V,
ground and points input and the +5V
and coil output. The compon
ents
marked with a cross are to be removed.
This is shown in the overlay diagram for the Programmable Ignition
installation – see Fig.6.
SC
June 1998 27
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