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Has anyone ever used an Auburn "igniter" as a vacuum high voltage feedthrough?

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jpsmith123

Thu Jan 31 2019, 07:18PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

I see where some people have used various Champion spark plugs as electrical feedthroughs in vacuum systems, apparently successfully, but I'm wondering: Are all "spark plugs" similar enough in design and construction that if one works they all will?

This is the "igniter" I'm thinking about:

Nik

Sat Feb 02 2019, 03:25AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

There are igniters that are meant for low pressure combustion chambers (low in comparison to a car engine), they will not hold up to any kind of useful vacuum. However I don't know if the model you have linked is one of those, they are generally for boilers/heaters.

Conundrum

Sat Feb 02 2019, 06:05AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

Yup, the best one for that is designed for a small lawnmower engine with an unusually high combustion temperature.
I have a picture on my phone somewhere.

What you want is one with a specific throw and ideally a central electrode which is copper.
Don't forget that you can operate it "backwards" if you need the extra length for some reason eg for a fusor and then make your own custom gap.
-A

johnf

Sat Feb 02 2019, 08:26PM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

Not all plugs are equal
Some have series resistors built in
I did post on another site how to use ordinary sparkplugs up to 20kV as vacuum feedthroughs

Conundrum

Sun Feb 03 2019, 06:38AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

May yet put my 400Hz variac to good use.
Tried to sell it on but alas it was too heavy.
Incidentally these do work at lower frequencies if you derate them accordingly.
I believe the factor is F/x A where F is the start frequency and x is the new frequency, A is the current.
So at 50 Hz it would be 1/8 of the rated current due to the thinner wires.

You can however use a very old trick invented in the 1930s which uses mains transformers arranged
as a magnetic amplifier so that the (low current) 400Hz signal modulates a larger input current.
Also useful:

Have some electric bike motors I can probably repurpose if not some units from a broken tape drive.

Ash Small

Wed Feb 27 2019, 08:50PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

No they are not.

What you want is an unsuppressed plug, as used in Model T Fords, many racing applications and some other applications.

Modern spark plugs have considerable resistance for EMI suppression.

Any specialist supplier should know which ones, I do have some part numbers, but I'd have to dig them out.

They were common in the days before cars had radios fitted.

jpsmith123

Mon Mar 11 2019, 12:23AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

The Auburn OJ-21-4 igniter doesn't have a resistor. (I got one and measured its resistance to be about 0.1 ohms or something like that).

(Also, I measured the resistance of a Champion J99 599 plug and it was about 1.7 ohms, which I think is due to the alloy used).

Ash Small wrote ...

No they are not.

What you want is an unsuppressed plug, as used in Model T Fords, many racing applications and some other applications.

Modern spark plugs have considerable resistance for EMI suppression.

Any specialist supplier should know which ones, I do have some part numbers, but I'd have to dig them out.

They were common in the days before cars had radios fitted.

Sulaiman

Mon Mar 11 2019, 01:16AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

From memory, most spark plugs are not suppressed,
there was a period ('70's) when spark plugs had internal supression,
but it proved unreliable due to temperature so supression was instead done by using resistive h.t. wires.
Supressed spark plugs usually had an 'R' in the part number.
Coil-on-plug would not need supression.
I do not know what current trends are.

I doubt that a military igniter would be supressed for reliabiity reasons.
=============================
"I believe the factor is F/x A where F is the start frequency and x is the new frequency, A is the current.
So at 50 Hz it would be 1/8 of the rated current due to the thinner wires."

... No, it is the voltage that is de-rated.
The wire and brush don't change so neither does the current rating.

johnf

Mon Mar 11 2019, 08:49AM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

about 85% of plugs are resistive to meet the emi guidelines in most modern countries
Hence my warning!!!

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