How to build a Capacitor Discharge Ignition for a early CX500
These Ignition systems were used on the CX500 from 1978 to about
1982 or so. They can be identified by a single box unit that included
a 8 pin connector and a 2 pin connector that supplies power. The more
modern ignition used a transistor ignition and was mounted in 2 boxes.
Note pictures show old style slide pots. new one uses round
pots as listed on parts list.
HOW IT WORKS
IGNITION SYSTEM
Thge spark is developed by special coils on the alternator charging
a capacitor and then other coils trigging a SCR to discharge the capacitor
through the primary of the coil. The spark plug voltage is taken
from the secondary of this coil.
ALTERNATOR
As the engine turns it is connected to the alternator. This
is a set of magnets which rotate inside a stator. Three
seperate sets of windings on the stator develope a three phase output.
This output is fed to a three phase bridge rectifier and a current
regulator. This is the battery charging system.
CDI CAPACITOR CHARGING SYSTEM
In addition to the charging coils on the stator there is a seperate
set of two coils. their function is to develope two sets of six
pulses. With each revolution of the motor the white wire
sends out 6 pulses to charge the capacitor. The blue wire
places a sine wave ( both positive and negative) on the capacitor
and the SCR. The function of this blue wire seems to be to apply
a short negative pulse to be sure the SCR is turned off after the last
fireing pluse. The blue and white wires together develop
a charge of 150 volts on each of two ( 2.2 uF ) capacitors.
SCR TRIGGERING SYSTEM
The SCR's are triggered from the outputs of 3 seperate coils.
These pulses occur at correct times to advance the spark as required.
The first pulse to occur is the orange red wire. This is a negative pulse
and prevents the SCR from turning on. It's function is to limit the extent
that the advance pulse can fire. This avoids damage to the engine.
At low speeds there is no effect from this pulse.
The second pulse to occur is the orange/white wire. The pulse
on the orange white wire is a triangle waveform. It is too
small to trigger the SCR.
The next pulse is the orange wire. This pulse triggers the SCR
at low speeds. As the engine speed increases to 2000 RPM
the amplitude of the orange / white wire increases and it begins to trigger
the SCR at a earler time.
As the engine speed increases even more the triangle waveform of
the orange white wire gets bigger and it triggers the SCR even sooner.
This causes the spark to advance more and more until at 4500 RPM
it is limited by the negative pulse from the orange / red wire.
When this negative pulse occurs it prevents any more spark advance from
taking place. This is done to avoid engine damage.
One difficulty is that the trigger voltage of the SCR is dependent
upon temperature. This is compensated for by a thermister. It is
difficult to duplicate the thermister Honda used.
My design is different from that of Honda. The advance pulse in
my design triggers a comparator. The is followed by a transistor and
which then triggers the SCR. This design has no temperature dependence
but 12 volt power is required for the comparator. In the event of
a power failure the engine will still run but it will have no spark advance.
COIL DATA
The following resistance measurements were made:
LEFT
Orange White Trigger 200 ohms to ground
Orange / Red Negative pluse 93 ohms to ground
Orange / Left Advance pluse 100 ohms to ground
Coil wire = yellow
RIGHT
Blue White Trig 200 Ohms to ground
Blue / Red negative pluse 90 ohms to ground
Blue Right advance pluse 100 ohms to ground
Coil wire = Peach
Coil secondary high tension ( connector unscrewed from cable
cable to ground 7.4 K ohms.
Coil primary resistance to ground 1 ohm
CAPACITOR POWER WIRES
Blue to White = 80 Ohms
White to Gnd = 350 TO 400 OHMS
Kill wire = black with white stripe
SPARK ADVANCE
start @ 15 degrees = 2000 RPM
end @ 37 degrees = 5500 RPM
PARTS LIST
CDI PARTS
ALLIED ELECTRONICS ( http://www.alliedelec.com)
SCR NTE 5465 # 70215791 X3
C2 = Pulse capacitor 2.2uF 600 volts # 70103271 X2 ( metalized
polypropylene )
MOUSER ELECTRONICS (http://www.mouser.com)
prototype board board $ 20.77 # 574-169P44WE
523-L77-DE09S connector socket $5.43
523-L77-DE09P connector pins $ 4.25
512-LM7805ACT 5 volt power supply
511- LM339N comparator
72-T7RYB-1K X 4 Potentiometer 1K
72-T7RYB-2K X1 Potentiometer 2K
Capacitors .047 600V # 667-ECQ-E6473KF X8
Box Mouser # 563-CU-3006A
OTHER PARTS
LEDs 2 red 2 green
Q1 Q2 2N2222
Diode N4005 X 16
Resistors 1/4 watt (see schematic )
EASTERN BEAVER (http://www.easternbeaver.com)
Connectors 8 pin female = # 8P250-CNA-TL
3.5 mm bullet connectors 3 - 5BCS - 10 need 3 female
The unit was built on two perforated boards. The first one contained
the SCRs and the capacitors. The second contained the 6 timing inputs
and the adjustment circuits.
CAPACITOR BOARD
The second was also built on a piece of vectorboard and held the timing
components.
THE BOX
Here is a drawing of the box
Pictures
Box
Top Board
Bottom board
Bottom of lower board
This shown the bottom of one of the boards. all grounds are connected
here.
Above is finished assemply
The above two pictures show the pulser waveform on the bottom. The
top waveform is the 5 degree BTDC idle pluse . Only 1/4 of the pulser
waveform is used. it is the rising edge in box 9.
This also shows the idle pluse on top and the max advance pulse on
the bottom. Note that the large peaks are not used it is the small step
on the top trace that is clipped by the input diode which triggers the
idle pluse. On the bottom trace it is the first negative pluse that stops
the advance. The positive pluse is not used. Magnetic pickups produce
both positive and negative pluses.
Here is a test procedure
CDI TEST PROCEDURE
Materials to test CDI board
clip leads from Radio Shack .
2 push button switches.
5 AA batteries.
Two 9 volt batteries and with two battery clips with leads
radio speaker
Wire and solder and electrical tape.
Connect 5 AA batteries together in series to give + 7.5 Volts.
use tape and solder
Add a wire to the first battery to give +1.5 volts. and a wire to
the last battery to supply+ 7.5 volts.
Connect leads with alligator clips to the neon indicator light
STEPS
1) Connect 9 volt battery to 12 volt input.
1A) connect both 9 volt batteries ground to board ground. Input
on 8 pin connector
2) check for 5 volts .with voltmeter
3) check for vreff changes with pot. with voltmeter vreff should
go from .9 v to 2.9 volt.
3A) check for Vmax should be 2,9 volts with no adjustment.
4) connect 2nd 9 volt battery to blue lead Through push button switch.
7) Connect ground wire to 5 AA battery set.
7A) Connect 1.5 volt lead to blue input through push button switch.
8) connect speaker to right coil output other end of speaker should
be ground
9) Push and release first push button switch to charge capacitor.
check with meter .
12) Discharge right capacitor by pushing second button . speaker
should click.
13) Set both left and right potentiometers to minimum .
14) Connect 7.5 volt battery through push button switch to blue white
wire.
15) push and release first switch to charge cap. push 2nd to
discharge through speaker speaker should click
16) repeat above for other circuit.
16) Note that the third input, the blue/red and orange/red wires
cannot be tested. Review circuit to be sure they are correct.
CDI MATCH TO MOTORCYCLE
Note it may be necessary for a 2nd person to maintain the RPM of the
engine as it will change with the pot adjustment .
1) Run engine at 4000 RPM.
2) Adjust orange pot to flicker red LED at 4000 RPM
3) Adjust blue pot to flicker red LED at 4000 RPM
4) Run engine at 2000 RPM
5) Adjust green pot to flicker both green LEDs at 2000 RPM.
Repeat if necessary
To check performance of motorcycle find a empty road, place engine
in 4th gear and use a stopwatch to measure acceleration from 30 MPH to
50 MPH with no gear changes.
My early data
Stock CDI from honda 30 MPH to 50 MPH = 4 sec
First try with CDI 30 MPH to 60 MPH = 6 sec
RETURN