Re: Testing timing of Red Atom Modules

[oldfogeyuk]

Further tests: still basically a ‘Brown’ module with changes..

C1=47pF disc ceramic
R2 is a composite consisting of 100K Pot with a series 2K7 all in parallel with a 3K3. This gives a range of adjustment from 1400 to 3120 ohms without the sporadic noise of a just using a potentiometer on its own (which killed the engine as soon as I moved it).
By the way I’m using a TIP162 for Q1. It’s designed for exactly this kind of job.

Results as follows: ( using timing Strobe. ‘Scope pictures are not readable. I’ll try again another time)
R2 at 3210 18 degrees advance
R2 at 2720 22 degrees advance
If R2 is less than 2700 the engine will not run. The adjustment is not linear, and this part of the range is more sensitive, so there’s a bit of leeway here. Mark it down for further testing.

These timings remain the same at all speeds. This is a significant point. We expect that peak coil voltage increases with speed, and hence the trigger point should occur earlier.

From the above we can get the trigger voltage:
With R2=3210 the Pot Div ratio is 0.2427 and the voltage required to trigger is 2.884V. This occurs at 18 degrees BTDC
With R2=2720 the Pot Div ratio is 0.2688 and the voltage required to trigger is 2.604V. This occurs at 22 degrees BTDC

We don’t know the coil characteristic (bad ‘scope), but we can deduce that:
– It is only around 2.6 volts at 23 degrees BTDC, the point at which the module ceases to operate as the trigger point voltage is reduced.
– Any earlier than this point it seems there is not enough energy in the coil to create a spark when the module triggers.

From this I have learned:
I can make the module timing adjustable up to a maximum advance of 22 degrees with this magneto.
This engine improves it’s mid and full throttle performance with more advance than the present static timing of 15 degrees.
The engine will chug along at idle with the timing at 22 degrees advance, but it is much smoother with it at 15 degrees.
If I want any more advance than 22 degrees, I’ll need to move the magneto plate, the module can’t be pushed any further.
The magneto plate is already at maximum advance adjustment, plus the holes are elongated by an extra 2mm to get it where it is.

So my options are:
Stick with what I’ve got and just tidy it all up. Retain the contacts and the Normal/Electronic changeover switch as a fallback system.
Fix the module timing at 22 degrees, and just switch to contacts when idling.
Or
Completely rebuild the magneto plate mounting to allow further adjustment. This isn’t as difficult as it might sound. The plate is quite flat on the underside and mounts on two raised posts, so the posts could be machined lower and an intermediate rotator plate fitted to provide a mechanical advance adjustment like my old Johnson 10. If I went down this route, then I could lose the contacts and go electronic.

I’ll still continue with the ‘scope and try to get some usuable pictures, and I’ll test the effect of a small inductor in series with R3 to see if it will provide automatic advance.