Electronic ignition wandering spark

[PeteB31]

Does anybody have any theories to the attached picture.

This is a home made electronic ignition system using a Powerspark Halls sensor and a homemade rotor with embedded magnet.

The magnet position in the rotor is indicated by the black dot. The pick up in the red sensor is roughly where the black line is.

I have used a variable speed hand drill to spin the rotor.

At very low revs (hand twiddling speed) the spark seems to be in the right place.

As the speed increases the spark becomes more and more retarded. Approx. 160 degrees in the attached pic.

Slightly higher again and multiple sparks appear, in a regular pattern.

As the speed increases to what is probably a slow tick over speed it seems to settle down to a single spark in the correct position.

Any thoughts anyone. I'm worried my kick over speed could be where the spark is in the wrong place.

Thanks

Pete

[V500]

Interference from the electric drill?

[Allan G]

I'm guessing you're using a strobe light on the rotor to see at what point the spark is firing vs the rotor position.

Assuming also you are using a standard Lucas style 4ohm 12v coil?

The coil dwell time may be altering relative to RPM. Depending on how many degrees it's retarding with increase in speed, this would be a good ignition on a bantam! But for a 4 stroke, it needs to advance. Or better put retard less as revs increase.

Try opening your spark plug gap to a few mm, the spark should easily jump the big gap at atmospheric pressure.

You also want to see what revs your firing at on a 4 stroke your sparking every other revolution. So 4000rpm is sufficient, unless you're running a wasted spark system for a twin with 2 magnets and one sensor? (Or you can use 1 magnet and 2 sensors which can limit the amount of times you need each coil to fire.

[Rog1]

I fitted a Thorspark ignition kit to my M33. The instructions advise that it isn't possible to time the ignition statically. Perhaps your setup is acting the same.

[PeteB31]

Thank you V500, Allan G and Rog1 for your replies.

V500, the motor of the power drill is roughly 12" away from the magneto. A simple matter to lengthen the twiddling stick, so I'll give that a go.

Allen G, I'm not using a strobe yet. The action has been filmed using an iphone in SLO-MO mode. That's 240 frames per second, played back at 30 fps (1/8th speed). This produces an amazing result but a huge file size. The bike is a B33, so single cylinder. The magneto runs at half engine speed, so one spark each time the magnet passes the sensor. The spark in the picture would be as the piston approaches the top of the exhaust stroke! and it delays further from there.

The coil is a standard Lucas type 6v 3ohms. The Halls sensor is supposed to work with 6V.

Rog1, I'm hoping that by spinning the rotor with a hand drill I'm simulating dynamic tuning, but without having the engine running. My initial aim was to get a firing position near enough to enable the engine run, then progress to proper dynamic timing with a strobe light.



Pete 

[rhyatt]

Does the hall sensor "switch" the coil via a module ?
You're switching about 2 amps with a 6v system and 3 ohms primary.

Remember, the collapsing primary magnetic field will itself induce back emf that will go back into the circuit

[PeteB31]

Rhyatt, thank you for your response. There is no module. I shall forward the rest of your comment to my uncle, he's the clever one who made the system for me.

Pete

[rhyatt]

The early vw golf and Vauxhall cavaliers used a hall effect sensor which drove a small module , albeit a 12volt system.
Part of their circuitry was to deal with the collapsing back emf which - on later cars , sent spurious spikes back towards the ecus.
Of course , they all used neg ve earth , whereby the coil had a live and the earth path was switch by the triggering sensor and module, same as with points earth switching.
The diameter of the magnetic, also may have an effect , as there is no finite cutting point of its magnetic field and its relation to the sensor.
The vw had a cutting disc to create the cutting point.
Optical triggers has a light and a photo electric sensor and a solid disc between the 2 , with a tiny hole in the disc at the trigger point
Hope it helps

[PeteB31]

rhyatt, thank you for your further comment.

A bit of background info. We essentially copied a system that a popular bike restorer youtuber chap posted. His system works and seems to be identical to ours. I don't believe an extra bit of kit is required, but you may be on to something with the magnet. As before, I'll forward this on to my Uncle.

Pete

[limeyrob]

Does the Hall effect sensor need a magnet?  Many are just a ferrous toothed wheel.  I could be you are getting a trigger of the front of the ally rotor as well as the magnet.  I appreciate yours is ally, but you may also be getting eddy currents.

[PeteB31]

limeyrob, thank you for your comment.

I didn't know about the ferrous toothed wheel. It seems possible that the sensor is picking up multiple signals from the spinning magnet. Maybe the magnet is too powerful or too close. Currently the system is off the bike and being bench tested.

Pete

[Aquarius]

I think there is a possibility that what you are seeing is to do with the frame rate of the camera (remember wagon wheels rotating the wrong way in old films?).
If so, you will need a strobe light to see what is actually happening.

[Derek996]

I think there is a possibility that what you are seeing is to do with the frame rate of the camera (remember wagon wheels rotating the wrong way in old films?).
If so, you will need a strobe light to see what is actually happening.

I worked with video systems of many years and I think that is probably what's happening.

[Derek996]

I fitted a Thorspark ignition kit to my M33. The instructions advise that it isn't possible to time the ignition statically. Perhaps your setup is acting the same.

It is possible to set the timing statically with a Thorspark, but not accurately.

[limeyrob]

I fitted a Lucas RITA to an A65, it had an inductive (rather than Hall effect) pick up and it had to be timed using a strobe as it continued to advance to 3000 rpm.  But it came with a tool (a 3/16 strip of metal) that you could use to get a good enough static timing to get the engine running safely for the strobe timing. It worked pretty well and was only a few deg out. There clearly is a repeatable relationship between static set up and dynamic timing, the problem is knowing what that is on a bespoke set up.