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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