Knife Switches

[Corwin C]

I ran into an old sheep camp being hauled away for restoration/rebuild and noticed that they used old fashioned knife switches for electrical lights with old paper covered dry cells. It was inspiring with the ceramic fixtures and exposed fabric covered wiring and still worked (albeit dimly) despite its obvious age. Sorry, it was a quick look and I didn't have a camera so no pictures.

This is the type of hardware that I'm talking about:


I'm definitely going for a somewhat "antique" look to my build and am considering using some form of (probably homemade) knife switch on the 12v. I've used these as a battery disconnect before, but it was in a "protected" location where it wouldn't get casual contact. I'm slightly concerned about the safety aspect and would like some constructive feedback concerning the use of this type of switch. I am going to be using leds so the current will be limited.

If using these could cause a safety issue, my first thought is to put the switch on the "return" leg of the wiring so that the full current of the battery will not be available to cause problems. Otherwise I could hide a microswitch in the knife switch that would actually handle the power. Another potential option would be to use "touch light" circuitry where the knife switch is the "touch" to safely turn everything on and off.

Obviously this is not safe on AC and I have no delusions that it could be made so. Conventional switches will be the rule for that part of the system.

[Shadow Catcher]

Some one will correct me if I am wrong but I can see no reason not to use a knife switch in your 12V. You can also find period fabric warped modern wire for specific look.

[bobhenry]

By switching the negative (ground) side of the circuit you will eliminate any possibility of a short from hot to ground. This has been done on almost every auto door to control the courtesy ( dome ) light since the dawn of time. I kinda like the idea, myself

[gregp136]

I do not think you need to worry about casual contact with the 12 V. Even if someone did bump it, I cannot imagine much of a shock. I think it is an excelent idea. Good Luck.

Greg(and Laurie)

[eamarquardt]

Fuses or circuit breakers will also help protect from an unintentional short to ground.

Cheers,

Gus

[angib]

The great thing about knife switches is their 'wiping' action. For 12 volt switches what is needed is low resistance and the wiping action helps maintain good conduct. In contrast the resistance in a 110 volt switch matters little and they are designed not to spark when making or breaking contact. That's why 110 volt switches are very substandard products to use with 12 volt circuits - don't get fooled by the big voltage number, it's not a measure of quality.

Unless you're going to build an all-metal trailer with one side of the 12 volts grounded, it doesn't matter which side of the load you put the switch. Either way you will have exposed terminals with up to 12 volts between them, so you wouldn't want to have unsupervised children playing in the trailer. Other than that, I don't see a serious safety issue.

[LarryJ]

This is probably too big for your needs, but what about something like an outdoor power outlet cover for simple protection.

[H.A.]

..

[H.A.]

)

[Corwin C]

Love the knife switch !
I say go for the whole Steampunk or Frankenstein theme !

Now you've got me thinkin' ... stirling engine driven whimshurst machine and a jacob's ladder ... HAHAHAHAHA .... IT'S ALIVE!!!!
Nothing like the smell of ozone in the campground.

I'm encouraged to hear agreement with my thoughts. Time to pull out some sheet brass or copper (or both) and see what I can come up with. If I don't get started on my tear soon, I'll have too many ideas to fit inside ... contemplating build "umpteen" before starting "one."

[Engineer Guy]

See some nice items here. Perhaps one or a few would be affordable as a working showcase Component:

Porcelain Antiquities

Of course, there's a good selection now on eBay. I just Searched for some stuff out of China, as I've seen during Tech Biz visits to there. It takes some dedication to find such stuff. I recently have bought a Box of round Porcelain Insulators used for Electric Fences, as found at Farm and Ranch Stores.

I just visited the fantastic AZ Mining Town of Jerome. The Mine Owner's Mansion on a Hilltop had this lovely Switch that controlled the Vacuum Cleaner power. No problem sourcing Copper, since they pulled a stupendous amount out of the Mine.

Jerome AZ



The Whole House Vacuum Cleaner:



One of many Custom Transformers fabricated out of need:



A full Trip Report, including the Quartzsite Show[s], is still a few weeks out...