Fattening-up an HT spark

It's a 1952 Fl (they call it a panhead). The timing is fixed -- no advance mechanism. That's how they did it back then. The bikes came with a twist grip you could use to fiddle with the timing, but with a bike that old the twist grip is likely to be missing or broken and a lot of owners just use a spring to hold the timer in place. You basically ride with it at full advance all the time. Although before you start the bike you twist the plate to bump the timing back a little.

Yeah, I know the device you mean. I had a later model, a 1200FLH shovelhead (Electraglide) that used to disassemble itself through its own vibration. I bought it with a blueprinted engine, but after about 250 miles and a trail of chrome, domed-nuts strewn up and down the roads of southern England, the torque settings were irrelevant to say the least. :-(

BTW, why do you have this earth wire taped to an HT lead and connected to the 'pan' in such an unsightly and impractical manner?

I assume you must have a good reason, but can't figure out WTF it might be!

"Impractical?" "Unsightly?" Easy there, big fella.

The word of the day: capacitance.

Try hooking up an ignition coil and a driver circuit of some sort on the bench. Add capacitance to the high voltage side, and see what happens to the spark.

After seeing some stuff on the web about a product that does just that (a thing that screws onto the spark plug) and claims to increase spark intensity greatly, I though I'd check it out on my own. I did bench test the idea with a spare ignition coil driven by a 555 timer, and I used a capacitor made from plastic soft drink bottles.

With a cap in parallel with the spark gap, the spark got a lot brighter.

A company called Nology makes a spark-boosting cap device that gave me the idea. Instead of shelling out bux for the Nology product, I just wrapped aluminum foil around my spark plug wires and taped a bit of wire down onto it, which I grounded. I made a rough estimate of the length of foil I would need for a certain capacitance, based on the dielectric constant and diameter of my spark plug wires.. Google or go to Nology's web site and read the marketing material about this product (of course they puff it up; they are selling something) -- it has the capacitance figure. Also, I noticed that Electronic Goldmine has 3nF 35,000 volt capacitors for sale. If you try adding capacitance to the ignition secondary, start another thread and let us know how it goes.

Do they also have Monster Cables for your battery ?:-)

I just LOVE the science we have here at sci.electronics.design

...Jim Thompson

You're such a sly one, Jim. Monster Cables. I took those things off my bike a while back just because I didn't like the look of them, and what the hell difference does it make. The bike runs pretty good without them. But capacitance does make the spark brighter in the bench test. Quite noticeably. Not hard to understand why. By the way, I love the brevity of your responses. Soul of wet.

When you have designed as many ignition systems as I, please come back and tell me about it.... "brighter" doesn't mean s*it... you need to evaluate the spark under compression conditions... I have.... have you?

...Jim Thompson

One of my CD ignition designs had such a hot spark that I used to demo it by sawing plexiglass with the spark ;-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

Yeah, that's true enough, but surely a brighter spark at 1000mmHg (or whatever it is) means a brighter spark at 100psi generally speaking? I've been using these transparent 'spark-plugs' that are intended to be used for tuning the air/fuel ratio by the colour of the explosion set off; but they're also purty good for evaluating the strength of a spark under compression. One can just about make it out with practice.

The basics are shown in...

"Self-Inverting-CD-Ignition.pdf"

on the S.E.D/Schematics page of my website.

The subtleties are in the beta-independent current sensing in the emitter of the HV device (notorious for having low beta).

...Jim Thompson

Oooo, got a schematic? I wanna try that.

Al

Inductor charges to 5A and is then dumped into the capacitor, producing 350V. When transistor turns on again primary coil current is 11A peak.... 62.5mJ energy.

...Jim Thompson

Hmmm. The CD system I used in the 60's on my 140HP horizontally opposed

How much current is generated by the inductor in your circuit?

Al