False Magneto

[TonyM]

I have been working on trying to make a false magneto for hit and miss engines. About 1/4 scale(depending on engine.) The case is designed to hold the coil, the electronics, a suitable capacitor, and the battery either 1.5V AA or 3.5V 14250.
I have the first set of cases printed and made(modified) the first circuit . While testing the circuit I noticed a blip in the spark at 600 RPM (magneto) this looks like it disappears at higher RPM. I would appreciate any thoughts on what might be happening at the lower RPM. There is a blank in the video between 36 and 44 secs. After 44 seconds the revs are increased. Sorry for the quality of the video. I haven't got round to testing the complete assembly because I want to sort this our first.


Thanks.

 

[minh-thanh]

Hi TonyM !
Maybe I'm wrong.... but it's hard for people to comment without a schematic of the circuit .

 

[TonyM]

Hi TonyM !
Maybe I'm wrong.... but it's hard for people to comment without a schematic of the circuit .

You're right. I should have said it's based on this by Mr Ridders. Only difference is a newer version with smaller components.

 

[minh-thanh]

If you use a reed switch, replace it with another reed switch - as far as I can remember there are different types of reed switches. Maybe the reed switch you are using is not suitable for opening and closing with that frequency

 

[Vietti]

Maybe consider an actual magneto.

 

[TonyM]

I haven't tried an alternative but the reed switch should be OK at that low frequency. I have had it up to 2500 RPM but at the higher speeds it does not look like it is missing as in the lower speed. This vid is at 2500 RPM and does not look like it is missing when played at 1/4 speed

 

[TonyM]

Maybe consider an actual magneto.

I have been looking into that but can't see a way to get it too look the part and be functional.

 

[willray]

I have been working on trying to make a false magneto for hit and miss engines... While testing the circuit I noticed a blip in the spark at 600 RPM (magneto) this looks like it disappears at higher RPM...

Are you sure you have a blip in the spark at ~600 RPM, or, are you basing that conclusion on looking at the video?

I ask, because sparks are really short, and stuff happens between the frames that are captured in video. It's really easy for a video to miss stuff. It's rather suggestive that your problem appears to happen at 600RPM, as the video you're shooting is likely to be either 30 or 60 frames per second. Right around 600RPM is going to be one of the speeds where the exact timing of the spark is going to slowly move "into sync" and back out of sync with the (digital) shutter, resulting in the possibility of the spark disappearing and reappearing in a regular pattern...

 

[minh-thanh]

Are you sure you have a blip in the spark at ~600 RPM, or, are you basing that conclusion on looking at the video?

I ask, because sparks are really short, and stuff happens between the frames that are captured in video. It's really easy for a video to miss stuff. It's rather suggestive that your problem appears to happen at 600RPM, as the video you're shooting is likely to be either 30 or 60 frames per second. Right around 600RPM is going to be one of the speeds where the exact timing of the spark is going to slowly move "into sync" and back out of sync with the (digital) shutter, resulting in the possibility of the spark disappearing and reappearing in a regular pattern...

Maybe that's also a reason ,


Actually I know it and but only used it 2 or 3 times so experience is zero....maybe...with slow speed, battery voltage/current is still high so sometimes reed switch is shorted , and at high speed, the voltage / current is dropped because the circuit behind it consumes too much, so there is no shorting.
maybe.. use a different reed switch or replace the resistor R 470 with a higher one

 

[Gedeon Spilett]

the problem with reed switches lays not only in the frequency (which may be quite high enough) but in the position of the sensor in front of the magnet with could be very critical : in my own tests...you may have 0 to 2 sparks per rotation according to their orientation...
moreover, in one my engine with exactly the same ignition you're using, closing the tin plate bonnet over the engine completely extinguishes the spark, so I have replaced the reed switch by a plain "contact breaker", but without high voltage !
Or I suggest you may use either a Hall sensor with a slightly modified circuit as in this video, a circuit less prone to interference (not tested myself).
And yes, I agree that capturing short lived sparks in video is not reliable as you explain.

 

[TonyM]

Are you sure you have a blip in the spark at ~600 RPM, or, are you basing that conclusion on looking at the video?

I ask, because sparks are really short, and stuff happens between the frames that are captured in video. It's really easy for a video to miss stuff. It's rather suggestive that your problem appears to happen at 600RPM, as the video you're shooting is likely to be either 30 or 60 frames per second. Right around 600RPM is going to be one of the speeds where the exact timing of the spark is going to slowly move "into sync" and back out of sync with the (digital) shutter, resulting in the possibility of the spark disappearing and reappearing in a regular pattern...

I take your point. I Have just got back to this project after a long break and can't remember if I first noticed it on the video. I think I did!
I guess I need to go back and check at various rev ranges. I will set everything up more firmly and retry.