Electronic Ignition Help !!!!

[mh121]

Hello all, I have been trying out various electronic ignition systems of late. The problem I am having is that the four systems I have built and tried all seem to blow the hall sensors. I have fit the units to different engines with the same results, blown hall sensor. The sensors are the correct type and cover a range far in excess of the rated voltage of the ignition systems.
I built a small contact unit and this works the ignitions fine.
So could any electrical experts spread a little light on where I may be going wrong.
The units I have tried are:
TIM6 (http://www.jerry-howell.com/IgnitionModules.html)
TIM4
El Cheapo electronic buzz coil.

Cheers,
MartinH

 

[gbritnell]

Martin,
One of two things. Either your ground isn't good or your high voltage spark is too close to the sensor. On a Hall sensor you have 3 wires, from left to right, positive, negative and trigger wire. You can't use the negative wire as your only source of ground for the spark. Hall sensors are also very sensitive to the high voltage from the spark.
gbritnell

 

[stevehuckss396]

I agree with George. Your best bet is to take the negative side of the coil right to the engine block or even better, the head. I have had one blown sensor in 3 years. Usually when a plug fouls out and the spark jumps wildly anywhere it wants.

 

[Lakc]

Rest assured, your not the only one with this problem. Most of the model ignition circuits out there are suitably "Muntzed" http://en.wikipedia.org/wiki/Muntzing and have no protection built in for stray voltages. Since a common ignition coil of olden days can produce 15000 volts in the secondary and 400 volts on the primary, they can have relatively short lives for many different components.
You have to have a good ground for the spark to return to the coil. This is the most important thing.
Avoid hall sensors mounted near any coil or spark plug connections.
Pictures and wiring diagrams would be helpful to go much further.

 

[mh121]

Thanks for the replies, the engine I have been using as a `test bed` is my air cooled associated. The hall sensor picks up from the timing gear. The hall has its own seperate earth from the board and I have the engine earthed at the back corner of the engine block, the coil has its own earth direct from the board.
I may try as suggested in the earlier post and take the engine and coil earths to a bolt on the head. I will try and get some pics up and show what I have now and the mods to it. This may help others who have a problem in future. Failing that I will make up a small pick up plunger and run it from a cam behind the rear flywheel, to see how it performs with that.
I have bought a Rcexl ignition unit to try also, when you read some of the RC forums on this unit they also appear to have problems due to the shielding sleeve over the plug lead and plug cap being the earth for the plug. Some have taken the top off the unit and drilled and fit a seperate small screw in the cover to connect an earth to the engine.

Cheers all,

MartinH

 

[picclock]

I don't know if this will help, but try to think of the Spark circuit and the primary part of the ignition coil ad two separate circuits. Ensure that the spark return path to the coil case is directly through the engine block - absolutely no wires. The reason for this is that when the spark occurs a high speed voltage/current transient occurs. This means that even a small length of wire will drop a lot of volts due to it's inductance. Additionally the transient will induce a voltage by virtue of the rapid change of flux in any wiring close to it - invariably this is enough to destroy sensitive hall devices.

So to summarise, keep the coil casing as near to the plug as cosmetically possible bolting to the metal body of the engine as the spark return. Keep the ignition lead well away from other wiring. If it has a screen on the ignition lead ensure that this is attached to the metal body of the engine.

If the layout of your engine is such that you think induced currents may be causing the failure fit an aluminium screen over the sensor to prevent induced voltages, connecting the screen to the motor body.

Its difficult to offer any further advice without seeing the layout and working out which effect is causing the failure. A few detailed pictures might help if the trouble persists.

Best Regards

picclock