Diode Question

I am installing a 3 wire 10 si alternator on a 340 and wanted to follow Bob M's wiring diagram. Went to Radio Shack to buy the IN145408 diode for on the exciter wire and they did not have one. Ended up buying a pack of assorted diodes, labled IN14001,IN14002,IN14003,IN14007. Would any of these work just as well?? (I know I could use a small light bulb but I wanted to use a diode if available.)

Pete

I"m not sure about the radio shack diodes. Some gm (I think) cars used a push in diode for the ac clutch. This diode pushes in the fuse block and looks like a fuse except it is marked "diode". These should be available in most auto stores. They have blade terminals so you can use crimp terminals and they are pretty rugged.

Another option is if your starter or relay has a "I" terminal. This terminal is energized only when cranking and is seperate from everything else. I"ve used this method successfully several times.

Yet another option is a single wire alternator. This is my personal preference. They can be usually be found at Autozone for about $50. I have these on two of my tractors and they work greatand are easy to wire, 1 wire from alternator to battery is all you need.

Hope this helps, Jon

i have used several different styles of diodes to control 10 si alternators the cheapest priced ones came from radio shack they worked fine if the ones you have can't handle the load, which is small it will fail causing the alt.not to excite until replaced not much to loose. be sure to install in the proper direction so elec.flows to alt. when switched on

Radio shack part #276-1661 works very well for that diode and I have been using them for decade or more and never had one go bad yet

What's your reason for the diode. Are you trying to prevent reverse flow of power that stops you from turning the ignition off?

Sounds like the diodes in that pack are the cheap 1 amp diodes. The field-exciter circuit can run up to 3 amps, and can blow those little diodes.

Doesn't your Radio Shack store have their diodes listed by amperage or wattage? Mine does, and they have plenty in the 3 amp and 5 amp range. The 278-1661 that the other poster mentioned is a 5 amp diode.

Any alternator or motor repair shop will have boxes full of them.

If you want to use them up, now that you have them, just take 2 or 3 of them and hook all in parallel. Three cheap 1 amp diodes hooked together in parallel will be equals to one 3 amp diode.

Any diode/rectifier will work as long as it permits current one way, stops the other, and is big enough to carry the current.

If you use an automotive type ignition switch, you don't need any diode to block reverse current. Just hook the IGN terminal to your ignition (assuming you've got battery ignition), and hook the ACC terminal to the exciter wire to the alternator. This way, the exciter is totally isolated from the IGN when turned off.

GM 1-wire, no problems, no diodes... Simple... Why mess with a 10si 3 wire?

CT

(quoted from post at 19:57:33 10/15/09) GM 1-wire, no problems, no diodes... Simple... Why mess with a 10si 3 wire?

CT

Click to expand...

This is a long answer and it's from a hot rod site, but it points out some advantages of the 3-wire setup.

http://www.madelectrical.com/electricaltech/onewire-threewire3.shtml

Mark W. in MI

If the truth be known, what you perceive as a "GM one-wire alternator is an AFTERMARKET abomination.

The 10 SI and 12 SI alternators, as designed and built by GM, were "three-wire" units.

I recommend instead of a diode to use a 10 ohm resistor (or even a small incandescent idiot light charge indicator) because it serves dual purposes... (and its cheap n easier to wire with no polarity concerns)


1) It provides at least some degree of safety current limiting........A much larger (higher ohms) resistor will work even provided theres still enough curent to excite the alternator at start up BUTTTTTTT if you use an idiot light use a small incandescent as an LED is too high resistance

2) It prevents "run on" if the tractor doesnt die when you turn off the ignition. Thats the purpose of those diodes to prevent reverse current flow out of the alternators lil No 1 terminal from powering the coil (if wired as most do) even if the ignition is turned off...Likewise the resistor can prevent run on

OKAY Ive seen them work fine with a diode,,,,,,,,with no diode,,,,,,,with a 10 ohm and much larger current limiting resistor,,,,,,,with an idiot light,,,,,, SO TAKE YOUR CHOICE

Im talking about GM 10 SI 3 wire alternator wiring here ya know

John T

And the question is would any of these work. The answer is YES.

I am aware that they were created as an aftermarket item. Made from GM 10SI's. I have seen them used on A LOT of things from off-road vehicles, tractors, to boats. They are USUALLY trouble free, but as anything can, fail. There are advantages to the 3-wire. I know this. But I like the 1-wire and I accept its quirks. Such as you have to rev the motor to "excite". Everyone to their own.

I read the webpage describing the 1-wire vs 3-wire. "Terminal Illness" is common with shoddy wiring. I solder all splices and heat shrink them. I also solder all stake-on terminals and heat shrink them. I have a 1979 C20 farm truck and if I plug into someone elses trailer and the lights or brakes do not work, its their trailer... No Exceptions. Why?? I solder all my joints.

As to the original post. I'd use a diode. That is how most OEM were wired. Any electronics store can provide them cheaply. Also MOUSER.COM has about anything you can imagine. But shipping would suck for 1 diode.

CT

Thanks guys, I appreciate the help. Bought a bigger diode today and finished the job. New ( rebuilt) alt works great. I used 3 wire alt because it was half the price ($34) of a 1 wire alt ($69) at Auto Zone. I put the alt on a Farmall 340 that I just picked up, so I'm kind of excited to get out and use it now.
Pete

I make my own diode,(no, I don't actually make the diode) knock them out of a rectifier bridge from most any S series delco alternators, solder a wire on each side, slip some heat shrik over it, and throw a couple in the electric supply tool chest for spare parts. .

I noticed this website is pushing their wiring harnesses to upgrade charging systems in "classic" vehicles. I can understand why they are biased towards a 3-wire in an existing harness.

Congrats on the diode on your 340. I hope it works out. I know how dealing with these old tractors and their wiring harnesses.

I had a mangled and burnt wiring harness on my 504. I gutted ALL WIRES and started over. A 1-wire is perfect for a custom made wiring harness. All connections are crimped, soldered, and heat shrink tube installed. It takes a little more time, but worth it. I also use silicone grease on all terminals to minimize corrosion.

I made my own harness for the dash gauges and installed a ATO size fuse block with 6 circuits. I have auxilliary lighting on my loader and have them wired to relays switched by the original light switch. In total I have almost 300 watts of lights. 2-55W high mounted side lights, 2-55W front lights, 2-35W OEM headlights and 1-35W OEM rear light. I have a 63A or 80A alternator charging a group 31 battery. This is also a diesel, so my electrical is stricly starting, charging, and lights/instrumentation.

Once again, congrats PETE7.

CT