How do Atom Computer Ignition modules work?

[legendre]

quote mercuryman:

Is this a valid test for the D1071’s Hooked 14 volt dc supply to a auto tail light , light to collector and Emitter to negative. Connected 300 ohm resistor from collector to base( had .7 volt on base). The light burned dim and 8.1 volts was across the D1071. Should the light burn bright in the test.

Add ammeter in series between the supply + terminal and the light bulb, then take all of the same voltage measurements as well as the current reading and we’ll know for sure, BUT..

Take a look at the 2SD1071 datasheet. The saturation voltage of 2.0V is reached at a base current of 15mA. Your base current is 27mA (8.1V / 300 = 0.027) which is way higher than the 15mA required to saturate.

But you still read a 8.1V drop across the D1071 – it is +not+ saturated, and it +is+ a fake. Put an accurate DC ammeter in series with the bulb, I bet you measure about 595mA – or just over 1/2 amp.. right? That would be an hfe of ~22 as in my fakes.

Get your money back, I did.

[legendre]

Here’s something to try.. Use your existing test setup to measure each of the parts you have, one at at time, and select the two with the lowest voltage drops from E to C (or the highest drops across the bulb). Then take those two and wire them in Darlington, and plug them into the circuit as if they were a proper D1071

Or just be lazy and grab two at random – whatever.. 😉

If you get two with a beta of 22-24, that would give you an hfe of 500 or better in Darlington. That meets the min. of the D1071 spec.. and unless they are just total crap that can’t take a couple hundred volts, I bet your module starts working..

[debe]

Mercuryman, Theres something wrong with your transistor, its not turning on fully. I tried your test using 12V & a tail light bulb on one of my 2SD1071 transistor & the bulb was almost full brightness. Theres 1.2V betwean collector & emitter with bulb lit up.

[legendre]

quote debe:

Mercuryman, Theres something wrong with your transistor, its not turning on fully.

That’s because it’s a dirty little fake, lol. Same as I have, and from the same source.

In other news, I moved my breadboard module to a real motor, and the results are interesting. It works – that is, it fires the plug – irrespective of "polarity" (phase, really). But it definitely +prefers+ one phase as it produces more energetic sparks and at lower RPM in one configuration. In the better config, the spark from the module is the equal of that produced by the original points & condenser (it’s a two-cylinder motor, same-old "won’t run right" 1949 TD20 – at least it’s doing something useful).

I’m guessing that the commercial modules (and debe’s) are absolutely phase-sensitive due to the diode present within the transistor package – and if not, due to the snubber diode added externally. Recall my setup still lacks any sort of diode, internal or external, as well as the capacitor. Resistor values are still 1K3 and 470R.

ETA: Changed 470R to 360R, which increased the spark energy. The module trips at a higher coil voltage with that change.

[debe]

Just curious, does these fake transistors markings look the same as the ones ive used? The picture is 3rd down on page 1 posted by Mumbles.

[legendre]

quote debe:

Just curious, does these fake transistors markings look the same as the ones ive used? The picture is 3rd down on page 1 posted by Mumbles.

Yep, for all practical purposes they are identical. The cases do have some minor molding differences, though..

Then again, what self-respecting Willy-Wong fake wouldn’t have a convincing manufacturer’s logo..?

[ken-w]

After sample testing in a working module, 4 out the ten purchased 2SD1071 failed to produce any spark, so I have determined that these are fakes or factory rejects that did not meet requirements. I did purchase the BD649 big brother the BD651 its voltage rating is 120v CE and produces nice bright snap when I flip the Flywheel. I have also mounted the 200v transzorb. I was wondering if this transzord could be dropped to 150v to better match the Darlington output, I think that at 200v the higher voltage will kill the device? And from the scope images on page 8 it looks to be about a 300v spike produce by the coil induction, I think that we need to find a device rated at 300-400v that can handle this. so I have ordered some BU931T to test.

[debe]

Ken, Transorbs come in any voltage you want. I picked the 200V to match the 2SD1071. Its worth trying one nearer to the voltage of the transistor you are using.

[legendre]

Why is the transorb / snubber diode needed in the first place? Why is a simple flyback diode (which is already part of the D1071 package) inadequate?

That’s why it’s there, isn’t it?

BTW as the voltage is clamped at progressively lower levels (like moving from 200V to 150V) doesn’t that start to harm the spark power? When the diode clamps down, it reestablishes current in the primary, which retards field collapse, doesn’t it?

[ken-w]

I had a brain pop and was wondering if the voltage or current levels at the base of the 2SD1071 were not high enough to turn it on? I know that Q2 is working in my circuit with the BD651, so it must be working. Maybe the Q1 is not turning on? And I need to change the value of R1 to maybe 1k?

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