Light bulb as Diode

[Sawatch 8N]

I have been reading over K LaRue's 12volt conversion pg & am using the late 8n wiring diagram for my 52 8n side mount dist set-up [has existing alt conversion]

Was wondering how the use of a reccomended 50v, 1.0amp, 3-5watt incondesant bulb works in place of a inline diode on the field/#1 alt wire?

 

[souNdguy]

a low wattaqge lamp like a 194 or the diode.. if you start getting too high a wattage lamp it will still allow the ignition to run on.

if it's too high a voltage lamp.. it will never light up.. thus killing your idiot light scheme.

stick to the correct lamp or use a diode.

soundguy

 

[Sawatch 8N]

Thx Soundguy, I'm going to use a recommended diode, was wondering how the lite works as a diode? can see that the voltage is of concern.

 

[Cliff(VA)]

The light bulb does NOT function as a diode. It provides resistive isolation. The diode limits the direction the current can flow. The light bulb limits how MUCH current can flow, a different way of getting the same effect.

Either works. Take your pick.

Cliff (VA)

 

[souNdguy]

it doesn't work as a diode.

a diode is a 1 way switch for electrons. it allows current to flow to the alt to excite it, but does not allow current to flow back to power the ignition.

a lamp is a current limiter .. just like a resistor. it also allows some current thru to allow the alt to excite... and it limits the current enough that the ignition can't stay running when you turn it off.

a proper wattage/voltage lamp will glow with key on and engine off, and go out with key on and engine running and alt charging. classic idiot lamp.

soundguy

 

[Sawatch 8N]

Thx guys, now I see what's happenin'.

 

[Bob]

A 50 Volt, 1 Amp diode is too wimpy to function reliably in this environment and will occasionally fail.

Get a 3 Amp diode with a 600 or 1000 Volts PIV rating, 1N5404, 1N5408, for example.

...Bob, alternator guy who has probably done more alternator repair and conversions than 95% of the board membership put together.

 

[Sawatch 8N]

Thx Bob, that's great info not to be found in the archives [at least as far back as I went]

 

[Bob]

Here's a photo that I've posted here quite a few times.

<img src = "http://i167.photobucket.com/albums/u125/27Grainfield/424IH/Alternator%20Stuff/AlternatorHarness31.jpg?t=1291655203">

 

[Hec In Omaha]

I used a miniature marking light that has a #194 bulb in it. I picked it up at a truck stop for $2.00. I mounted next to the battery on the right side of the tractor. It does the trick nicely. Been there for over 5 years and no problems. Another nice thing is that the light will stay lit if you forget to turn the key off. I can take a peek at the ride side of the tractor and see if there is a red glowing light. If there is then I left it the key on. I have caught myself doing that a few times. This may save your ignition system one day.

Good luck

 

[old]

Radio shack part #276-1661 works well and cost about $2.50 for a pack of 4. It is a tad bit bigger then the one Bob says to use at 6amp but in my area it is the easier one to find also

 

[Sawatch 8N]

Thx Bob, that pic is worth a thousand words!!

 

[souNdguy]

as far as i saw he mentioned a 50v 1 a light bulb.. at least that's what i read his post as saying.

soundguy