Multi cylinder CDI

[Leucetius]

Good evening guys.

A friend of mine and I have a question regarding CDI on multi cylinder engines. More exactly if it is possible to realize this (in our world) without the usage of a distributor to direct the discharge of the coil to the correct spark plug?

Greeting from Germany
Kevin

 

[Lakc]

To direct the discharge of a coil without a distributor is probably not going to happen. Multiple CDI units with multiple coils are generally the way its done.

 

[Jasonb]

Depends on how many cylinders you have, if not many then the lost spark method is common. eg when the CDI is tripped usually by a hall sensor it will send a charge to each sparkplug only one of which will actually fire.

On say a V8 you could get away with two CDIs and loose the sparks.

J

 

[el gringo]

Roy Scholl at S/S engineering set me up with a two coil CDI for one of my
two cyl engines at a minimal extra charge that allowed me two wire both spark plugs from the same CDI although they were both triggered by the same hall sensor.

 

[Leucetius]

The engine at stake can be seen at the attached pictures. It's from the magazin 'Model Engineer' and my friend is in the planning phase of making it. I've done the CAD files for him and now he wants to change the engine from it's original glow plug system to spark ignited. As you can see on the rear view, a hall sensor can be attached at the camshaft without destroying the overall look. Imagine this beauty with a distributor...

it will send a charge to each sparkplug only one of which will actually fire

So on the 4-cycle, 4-cylinder engine shown, this means all spark plugs fire together every cycle/90° camshaft rotation? Doesn't this especially leads to problems at the end of the intake/begin of compression?

We thought that maybe it's possible with 4 hall sensors but just one magnet. In the manner that there's just one coil which is triggered by each sensor and somehow the circuit routes the discharge to the corresponding spark plug.

 

[mu38&Bg#]

Switching high voltage electronically is not easy or practical. A pair of twin ignitions is the simple answer if you want CDI and no distributor.

Seeing that you're in Germany you may look at http://www.power-spark.de/

Greg

 

[Jasonb]

It will depend on your timing and crank layout but taking a twin or one side of your engine as an example with two magnets on teh end of the cam shaft and one hall sensor.

As one sparkplug fires at the top of the compression stroke the other will get a spark at the top of the exhuast stroke which will have no effect.

The problem starts as you get more cylinders and the sparks get closer together to a stage where you get an early spark in one of the cylinders that tries to make the engine backfire.

J

 

[Leucetius]

Thanks for your answers. We think the lost spark method is interesting as such but he won't use it. My friend will buy
a) one RC-i 400 from Power Spark and
b) two RCexl Twin cylinder from RCXp
when the engine is ready for testing - I will post results and videos.

Greetings and happy weekend
Kevin

 

[Niceonetidy]

BTW,

You can buy these single and Twin Rcxel units at an amazingly low price from Hobby King, Search engine accesories

 

[Leucetius]

That's a nice information! I know HK from my days I was flying several Helicopter and Airplanes, main source of LiPos in this time and scene

 

[Lew Hartswick]

The two coils firing both cyls of a 2 cyl 4cycle engine has been used in regular autos,
at least it was in my NSU Sport Prinz. It used regular points to break the primaries
of the two coils (I believe they were in series) each coil wired to a plug. So one cyl
was at the end of exhaust as the other was ready to fire. If it was good enough for
a car it should be good enough for a model.
...lew...