Hoglet Ignition

[tornitore45]

The magazine article is pretty silent about the ignition. From pictures it looks like there is only one coil and the HV wire appear to split V and feed both plugs IN PARALLEL.

I do not think this arrangement is going to work.
When one cylinder is in compression, the other is exhausting at near atmospheric pressure. The sparking voltage at low pressure is lower, the exhausting cylinder plug will shunt the spark and not much Voltage is left for the compressing cylinder to fire.
In a true wasted spark the plugs are in series, the exhausting cylinder plug subtract a small voltage from the total V available leaving most voltage for the compressing cylinder.

It looks like two coils or two CDI are required, both can be run from the same sensor.

Comments? Opinions? Objections? Like to hear practical experiences before going forward gathering all the parts.

 

[Jasonb]

S/S do a single CDI with twin coil on it so you get the same spark power to each. I have not used it on my Hoglet yet but have a similar unit on my opposed twin 4-stroke and it works fine.

Basic 2tin or complete hoglet setup on this page

http://www.cncengines.com/orderpage.html

 

[gbritnell]

Hi Mauro,
On my home-made V-twin I have a wasted spark ignition and it works fine. I happen to have a Jerry Howell setup but from talking with others the S&S unit should work just fine. My plugs aren't in series but rather each plug fires with full voltage when the coil is triggered.
gbritnell

 

[tornitore45]

GBritnell, just to be clear

Is your system CDI or Kettering?
You have only ONE coil and one HV wire that split to connect to both plugs?

The "wasted" spark is into a cylinder with open valves, and yet both plugs have an arc despite the "expected" lower ionization voltage on the wasted spark side.

I say "expected" because my assumption is based on theory of the ionization voltage at specific gaps and pressure. I never measured what happen at the plug.

In my experience, as electrical circuit designer, I learned that if a design does not work on paper does not work on reality; unless the physic understanding or the model is wrong, in such case a new theory better come out to explain why it works.
In this case, it may be that success depends on some uncontrolled parasitic, such the wire inductance, that tends to isolate one plug from the other so that the common point where the HV wires split is not quite as "shorted" by the low-pressure/low-voltage gap.

I am speculating all over here, it might be that on an opposed cylinders the distance between plugs is higher that on a Vee Twin allowing for more decoupling of the plugs.
CDI give a very sharp V rise time; even small wires inductance can buffer the plugs.
Kettering is current driven, a "shorted" plug should prevent spark on the other.

I have a Upshur twin with the plug in series and it work fine, I hate to get it all dirty but may try to reconfigure to run it with both plug in "parallel" and see what happen.

 

[gbritnell]

It's a Kettering type. The coil has dual outputs and one Hall trigger. Both plugs fire at the same intensity whether under compression or not. The S&S is a similar unit.