Possible design idea for HF gap issues

So, I'm sure that it's been considered, but I want input from those in our forum about it. It seems that if there was a single issue that affects new owners, and, based on the level of discussion it receives here, current owners as well. is HF spark gap. We see machines that new owners are having issues with right out of the box, and typically, among the first things suggested in the troubleshooting process is to check/adjust the HF spark gap. I've even seen a post or two suggesting that the new EXT isn't a "true digital" machine, since it has a component that requires a mechanical setting (the air gap, and yes, it is all digital, this don't count). Of course reading this got me thinking about the modern day ignition systems for the internal combustion engine (not diesel). Even though many automobiles, my v10 powered f250 included, have ignition systems with NO moving parts. They sense crank position and timing via an array of sensors, etc. to generate a signal, which in turn fires the spark at the appropriate time. That being said, instead of having a pair of points that need to be adjusted, why not retrofit, or design into the new models, to use a standard spark plug, or pair of plugs when necessary, to perform the duty of the points. This would have the benefits of not only eliminating the need to manufacture special components for the new machines, but also, in the unlikely event they ever needed to be replaces, it would be as simple as a trip to the local auto parts store. Anyone know if this would work?

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Originally Posted by kenwhite

....A more robust point gap design might be better solution.

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Yes.

Like the points in the new 250EXT.
Which I'm told cannot be retrofitted to my PP256.

Points are points, but then what do I know. ;)

Cheers,
rivets

Quote:

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Originally Posted by kenwhite

EDIT: It looks like there are some home brew kits that have successfully used a spark plug, so it might be possible.

But I don't really see an advantage to setting the plug gap versus a set of points.

The HF point gap is used to reduce the voltage across the resonant capacitor in the output circuit. Once the plasma arc starts to flow, the resonant voltage is maintained at a safe level so the points are acting as an open.

A more robust point gap design might be better solution.

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Ken is right. The spark gap is not like a traditional set of points in an ignition system. The points in an ignition system break the current in the coil to collapse the magnetic field inside it, causing a huge voltage spike (inductors like to keep constant current, and will generate huge voltage spikes trying to achieve it). Once this happens, the large voltage generated will spark.

The hf system in a welder is more complicated than this. Generally they actually resemble a tesla coil. The voltage from the mains is stepped up through a transformer and fed to the tank circuit. Once it reaches a high enough voltage to jump the spark gap, it jumps, and starts a very fast oscillation between the resonant capacitor and inductance in the circuit. This very fast oscillation is then coupled (usually through and air core transformer) to the welding circuit. This circuit has two advantages in that it has both high frequency and high voltage, both of which help ionize the air and arc.

The reason the spark gap causes so much issue is that it has much to do with the resonance of that tank circuit and it can totally mess with the circuit if it's off. If the gap is too narrow, the resonance will happen too soon, and may not produce enough voltage to make a nice arc. If it's too wide, it resonance will never start, and no arc happens. Not to mention, the arcing can oxidize the surface, and over time cause the circuit to not function as well.

IIRC, many spark gaps are made from tungsten to help with longevity. I haven't had a reason to dig into my welder yet to look at it.

So is the problem that they come set wrong from the factory, or that they go out over time?

I think the current setup is fine but if I could change anything, it would be the location. When looking at mine the first time they looked fine and the drag on the guages felt perfect. After finally seeing a black mark on another component, I really started looking into it and found that looking from one position they were slightly mis-aligned and not straight. My guess would be the arc was bouncing off the dome shape from not being aligned right. I think that any change should make them more accessible.