Spark Gap Source or Replacement

On a sunny day (Thu, 4 Feb 2016 11:27:21 -0800 (PST)) it happened Wanderer wrote in :

Car spark plug? :-)

I remember seeing these in an old television. From the schematic I was able to figure out what they were. They looked like a small block of plastic with a notch down the middle. I assume the idea is that the gap is controlled so the breakdown voltage is controlled limiting the voltage to levels that can't arc across protective barriers.

I don't know where to buy them though.

Octoparts says north star micro has some

George H.

Yes that's what it is. I can see the little short in the gap. It's 25 years old.

I'm looking to buy one part. I'm thinking of replacing it with this

Or maybe I'll live dangerously and leave it out.

I assume this is in your meter because it can measure very high voltages and this is part of the safety circuit? As long as you don't connect the meter to >2000 volts it shouldn't matter, no?

Yes. The meter has a 1000 volt scale. I believe it is to protect the meter from spikes when looking at high voltage inductive loads. I don't think it was supposed to short.

Digikey has hundreds of thousands of them. Search for GAS DISCHARGE TUBE.

Cheers

Phil Hobbs

So, it's a kerf-cut loop of wire. The short is some kind of dirt in the gap; just clean it out. Shim stock fished through the gap won't change the spacing.

Try Mouser: spark gap Gas Discharge Tubes - GDTs / Gas Plasma Arrestors; 17 two-electrode unit variants in stock.

Quicker to make your own than search for a new one. copper wire, blob of epoxy, snip snip.

NT

It's a spark gap CAPACITOR. If it's just a DMM, probably any small capacitor is good enough. Let's see, I just saw these last week.

Aha, Elect. Goldmine

This seems implausible. A spark gap may look like a capacitor until it sees enough volts for the gap to break down

but it's not there to provide capacitance.

Yes. That's the search term I needed, though the packages don't look anything like this part. When I reduce the search by the specs I only end up with three with 2000 volts that might fit in the meter.

My first Google search came up with hits calling it a capacitor too but when you read the actual data sheet, it brags about having a very small capacitance. The data sheet calls it a spark gap.

There are spark gap capacitors, just disk ceramics with an added slit.

Subtracted slit?

--sp

Hmmm, does one add a hole to a part, or subtract one? I'll have to ask a machinist.

If you add a spark gap by subtracting material, then presumably one subtracts features by adding material. Yes it works... one can remove a diode volt limit by adding a diode in series.

NT