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Automotive: Points and Ignition Booster/Amplifiers

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I need electrical help. Some fellow motorcyclists and I are arguing whether ignition boosters, also called amplifiers, really help or not.
The other bikers are great mechanics, but not so good with circuits, so I'm bringing the problem here to the experts.

The ignition amplifier in question is a kit from Velleman. It turns the ignition points into merely a switch for a transistor, and the main current for the spark plug is then handled through the kit, instead of the ignition points.

The question is whether this gives a better spark. The idea is that the electronic "switch" is faster than the mechanical points. A faster switch yields a faster collapse of the coil current, and then a more powerful spark. Especially when starting a machine and the points are moving slowly.

Is this true? Does the ignition booster really give a better spark?

Attached is the manual + diagram for Velleman's kit.
 

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1. Any mechanical contact (points) are subject to bounce. That in itself may mean less spark.
2, The deterioration of the points over time makes it less reliable.

I did convert a points car to optoelectronic ignition and I did convert a lawn mower to electronic as well. They start easier.

I should add that the OEM spark plug wires were not appropriate anymore.

EDIT: plug wires
 
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The electronic switch is faster than the mechanical switch so, in theory, the output voltage would be higher, but only if the capacitor across the transistor is lower than the capacitor across the mechanical points.
The electronic circuit diagram shows a value of 0.22μF which I think is close to the value used with the mechanical system.
If so then both systems would generate about the same voltage.
But, of course, if you have enough voltage to reliably fire the plug, you don't need more.

The other advantage of the electronic switch is that the normal electrical erosion of the points is eliminated with only the wear of the tab on the rotor lob being a factor.
 
Well yes, if all is well there is always enough spark.

But...more spark is better. Because a wire may be loose, a plug fouled, battery/kicker not up to standard, etc.
Especially when starting up, because the points cam is rotating so slowly, the "break" of the circuit will be less abrupt, meaning less of a spark.

Is it right that the spark output is dependent on the capacitor value? That doesn't seem entirely square.

Let me re-phrase the question. So the speed of the electronic switch doesn't offer a real advantage over the points, even when the points are turning slowly (as in starting)?

Is anyone versed in the simulator SPICE, to test the circuit. Sadly, that learning is way about me.
 
My experience says it does. If you replace the "driver", be prepared to upgrade the wires.

Starting is MUCH easier with electronic ignition.
 
If you just replace the points with a transistor then the spark is similar. In fully electronic ignition the transistor is on for a fixed period and off when the spark is needed. It allows the coil to always charge to the exact energy needed for optimal spark. This optimal spark is independent of engine speed or points dwell, it makes the engine easy to start and better run in idle speed.
 
The way to a bigger, hotter spark is a Capacitive Discharge Ignition (CDI) System. If you retain the original coil and capacitor, then all the Vellman kit will do is make the points last longer...
 
..........................

Is it right that the spark output is dependent on the capacitor value? That doesn't seem entirely square.

Let me re-phrase the question. So the speed of the electronic switch doesn't offer a real advantage over the points, even when the points are turning slowly (as in starting)?

Is anyone versed in the simulator SPICE, to test the circuit. Sadly, that learning is way about me.
The capacitor resonates with the coil inductance to generate the spark. The smaller the capacitor, the higher peak of the primary resonant wave and the higher the spark voltage.

The speed of a mechanical is actually quite fast even when the cam is turning slowly as in starting. As soon as the points open even slightly the circuit is totally open so I think the speed of the switch is not that different form a transistor.
Where a transistor could help is if you use a smaller capacitor than can be tolerated with the mechanical switch (too small a capacitor will cause burning and pitting of mechanical points).

The problem with a simulation is how to accurately simulate the opening of a mechanical switch to make it different from a transistor switch. In simulation a switch actually switches faster than a transistor. In real life there is likely a small arc when the mechanical switch opens but that's difficult to model.
 
The capacitor resonates with the coil inductance to generate the spark. The smaller the capacitor, the higher peak of the primary resonant wave and the higher the spark voltage.

The speed of a mechanical is actually quite fast even when the cam is turning slowly as in starting. As soon as the points open even slightly the circuit is totally open so I think the speed of the switch is not that different form a transistor.
Where a transistor could help is if you use a smaller capacitor than can be tolerated with the mechanical switch (too small a capacitor will cause burning and pitting of mechanical points).

The problem with a simulation is how to accurately simulate the opening of a mechanical switch to make it different from a transistor switch. In simulation a switch actually switches faster than a transistor. In real life there is likely a small arc when the mechanical switch opens but that's difficult to model.

I'm surprised the capacitor plays such an important role. Does a smaller capacitor maximize spark, or a capacitor that matches (resonates well) with the coil?

So you think the mechanical switch is comparable to the speed of the transistor? If that's the case, then the points booster does nothing to increase spark intensity. A pity. A disappointment, really.
 
The mechanical switch (points) is still in the circuit. The transistor can't work any faster than the points opening. The transistor is just handling the current, instead of the points.
 
I'm surprised the capacitor plays such an important role. Does a smaller capacitor maximize spark, or a capacitor that matches (resonates well) with the coil?
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As I stated, if you can go with a smaller capacitor, then the peak voltage will increase.
Not sure what "resonates well with the coil" means.
The coil will resonant with a wide range of capacitors. The smaller the capacitor, the higher the resonant frequency, and the higher the peak resonant voltage.
 
The mechanical switch (points) is still in the circuit. The transistor can't work any faster than the points opening. The transistor is just handling the current, instead of the points.

Take another look. The voltage of the spark is dependent on the rapid collapse of the coil current. This is why a quick switch is needed for the coil current. With the points booster, the points are simply a switch for the transistor. It's the transistor's rapid switching that makes the spark powerful (or not).
 
Take another look. The voltage of the spark is dependent on the rapid collapse of the coil current. This is why a quick switch is needed for the coil current. With the points booster, the points are simply a switch for the transistor. It's the transistor's rapid switching that makes the spark powerful (or not).
Due to the capacitor in parallel with the coil inductance, the field collapse is much slower than either the transistor or the mechanical switch. It's a moot point which is faster.
 
Due to the capacitor in parallel with the coil inductance, the field collapse is much slower than either the transistor or the mechanical switch. It's a moot point which is faster.

In the transistorized (boosted) ignition circuit, the capacitor is disconnected.
 
Capture1.gif

crutschow will probably back me up on this, Velleman circuit isn't very clever. When T1 is on the current to the base of T2 stops. The collector current of T2 collapses slowly because of the high Cbc (collector base capacitance), the proper way to switch T2 off fast is to pull down the base to ground or to negative bias. This means that the transistor in this circuit is slower than the breakers.
 
I recall the nominal value for Points Cap is 0.22uF which is now across the transistor. THe slew rate of coil current is limited by this cap and not the switch speed. Resistance wiring to plugs will reduce the level of AM radio interference.

THis design will prevent points wear to improve long term performance only for most cars older than 1980
 
I recall the nominal value for Points Cap is 0.22uF which is now across the transistor. THe slew rate of coil current is limited by this cap and not the switch speed. Resistance wiring to plugs will reduce the level of AM radio interference.

THis design will prevent points wear to improve long term performance only for most cars older than 1980
Your claim that only the cap and not the transistor limits the slew rate of coil current could be based on experience with this circuit or similar circuits, it could also be a guess. My claim that the transistor in this circuit is slower than breakers is a safer guess.
 
In either case the rise time needs to be controlled well above 2 us to reduce AM interference at 500kHz. Otherwise AM radios will not work very well in the country with weak signals.
 
Your amplifier will perform as good as a new set of points, the advantage is that this performance unlike points alone degrades much slower (the points still mechanically degrade), if the kit is a good design reliability will be increased as the points will last much longer.
Its important to maintain a minimum 'wetting current' on the points, if they run with nearly no load they wont last as long, a minimum current through them keeps the contacts in good condition, from memory the velleman kit has a loading resistor for this purpose.
 
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I'm surprised the capacitor plays such an important role. Does a smaller capacitor maximize spark, or a capacitor that matches (resonates well) with the coil?

Yes matching the capacitor to the coil makes a huge difference. I have played around with ignition systems on old equipment for most of my life and I know for a fact there is an optimal condenser size to coil inductance ratio that gives very good high voltage high current sparks but there is a upper and lower limit to the two values which as long as you are withing those limits will just work well enough which is what most systems are set up at by people who just don't know any better.
 
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