alternator feedback diode

Could someone give me a part number(radio shack or ?) for a diode to prevent feedback to ignition switch so switch will stop the engine from running with key off.  Thx , donm

Radio Shack  276-1101   50V/1 Amp diode. Make sure you face the grey stripe toward the Alternator.
Steve@B&B.

That's called - makin money- to folks who gotta have the parts and don't kno!

The assembly is probably a lot sturdier than the RS diode with wires soldered on and held together with black tape. I just bought some 1 amp diodes on epay for 6.5 cents each good for more voltage than 50 volts that but doesn't hurt them in this application. What hurts is that the diode package is about the diameter of the insulation on 18 gauge wire. I'd recommend a 3 amp diode just for its sturdier structure. Like at RS, a 276-1141, 276-1143, or 276-1144. Then I'd encase the diode and the wire connections with heat shrink tubing followed by a couple layers of Scotch #33, 33+, or 88, no substitutes.

Gerald J.

The switch works. Another way to make the switch automatic is to use a switch that closes on oil pressure rise.

Gerald J.

Some data indicates the 1N4007 has a different junction for the higher voltage. A PIN junction instead of simpler PN junction. The I means intrinsic material, that's not doped for either P or N semiconductor. Sometimes that PIN junction is used for radio frequency switching, but diodes made for RF switching perform better than 1N4007s though the 1N4007 have been proven to perform better for RF switching than high speed switching diodes, because of the PIN junction vs a PN junction.

There is a lot of selection in resistor and diode production. There always has been for resistors other than wire wound. The process produces a broad range of values and they are selected for the bins. Turns out the standard number series for each tolerance of resistors overlaps, so there are no discards whether selecting for 5%, 10% or 20% values. E.g. 10% larger of a nominal value just happens to be 10% lower than the next standard value when selecting for 10% resistors. Sometimes when checking 20% resistors it seemed the same batch had 5 and 10% resistors taken out first and the left overs were always more than 10% away from the marked value, but within 20%. Good enough for some circuits or I'd have paid for tighter tolerance.

And there is nothing wrong in a diode operated at lower than its rated Peak Inverse Voltage rating, so the test bins are minimum values all the way up to the next voltage rating.

This week I replenished my supply of 1 amp diodes on line. I bought 50 1N4007 for $3.25 delivered. Had I anticipated a need for 100 I could have gotten them even cheaper per diode. At Mouser (http://www.mouser.com/ProductDetail/Rectron/1N4007-B/?qs=sGAEpiMZZMt9EC5K82p3ylQUF%252buG6cB8) the lowest price vendor is 3 cents each in small lots, 2 cents in 100s, and 1.5 cents for a 1000 diodes, but I would have had to have paid shipping on top of the price, probably at least $6 so I'm satisfied with my on line auction purchase.

Gerald J.

Just curious , whats the whole point of this ? I kno nothing about diodes etc, just curious on what the problem is to start with , and whats an exciter wire from the alt ? Never heard of this stuff

Doug, a stock 10SI Delco Remy needs a shot of power to excite it so that it charges. If you hook the exciter wire to your ignition, it will work, but when you go to turn the engine off, the alt will "backfeed" power to the coil and the engine will keep running. Installing a "dummy" light or diode in series does not allow the alt to do this by breaking the circuit, the engine shuts down. I'm no electrical wizard but this is my understanding and experience, Trev.

You are very welcome. I had learned this about 15 years ago when I installed an alt on a 1949 gmc truck, in place of the genny. Unfortunately, I had to "relearn" all this last week when I gave up on the genny in my 1946 chevy 2 ton, and installed an alt I had...Had forgotten the whole affair...getting old and still not so smart, Trev.

There are multiple solutions. Using the accessory contact on the ignition switch works. It not connected to the ignition when its off so there's no back feed.A typical original tractor ignition switch doesn't have the accessory connection, only comes with universal replacement switches.

As discussed above from three years ago, a 1 amp diode is electrically adequate, but a 3 amp diode will stand up to being wired better. The cathode side (bar) goes to the alternator.

Leaving that circuit open also often works putting the alternator into one wire mode where it has to be spun to a couple thousand RPM to begin charging. Once it starts charging it will charge at idle until the battery is charged or the engine is shut down.

Gerald J.

Hay Fred..
https://www.sparkfun.com/products/8589
They have them for 15 cents US, though you'll have to figure out shipping....
Too bad you're not on this side of the boarder..easier to hand deliver !!
I take it Radio Shack is closed ?? If not ,easy just to walk in there....

Sad thing is I have 10s of thousand of $$ in 'old' electronic parts here..

Jay

I was just kidding .I do a lot 12v change over systems have everything I need for them.