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After doing a search for alternater conversions I'd like to know what size or kind of diode I need or where to buy the pig tail with the built in diode.
Thanks Tony

I used an old diode from an alternator and bolted it right to the coil and clipper off the terminals I wasn't using. Worked great!

Tony,

I had the diode part number...but I sure can't find it now! I have a eBay item number (170269243310) of a ready made DA harness for a 10SI alternator, complete with diode.

A small dash lamp can be installed in series and it will supposedly give enough resistance to negate any run-on problems when DA #1 is attached to the coil +.

I have heard that farm stores sometimes carry this little DA plug with the diode shrink wrapped in the #1 wire. It's used on old tractors that are upgraded to a alternator charging system.

Sorry I couldn't give you exact info!

Stuart

I use a diode I got from Radio Shack. They call it a rectifier. It is about 3/8" diameter and you get 2 or 3 in a package for something like $5.

Tony,

This is what you want. Solder it in the DA#1 wire that you will run to coil or any other source that won't be switched from the ignition when the key is turned OFF. This device is directional and has to be installed correctly to properly function.

http://www.radioshack.com/product/i...amp;currentTab=summary&tab=techSpecs

Stuart

Thanks guys Off to Radio shack tommarow.

Tony

Guess I'm missing something big here, I've read this thread several times but still can't figure out what you guys are talking about.
I thought the rectifier was built into or integral to an alternator. For what reason do you need a diode or rectifier external of the alternator????
Back in the early 80's I built a bi-plane and used a I0-360 Lycoming engine in it. Since it would be licensed Experimental, when it came to the electrical system I simply went to my good buddy at the Chevy parts counter and bought a brand new Chevy alternator and installed that, all the rectification and regulation was built into the unit. Worked great for the three hundred hours that I got to fly the plane.
Denny Graham
Sandwich, IL

Denny Graham,

If you were to install a GM 10SI alternator on your 'big old truck' and happened to tap off the coil for a handy source of switched power to excite the alternator, then there is a chance that when you turned your 'big old truck' off, it would refuse to shut down.

After the alternator gets up and running, DA#1 creates voltage that can power the coil even when the key is turned OFF resulting in engine run-on. The diode prevents this from happening.

Some folks don't want to crawl through the firewall to the ignition switch for power...the coil location is handy. Remember, don't shoot the messenger!


Stuart

No, I can see that Stu, now when have I ever taken aim at you? Interestint debate even if it will never see the underside of my truck, it might come in handy on someone elses that I'm working on. It would be a little clearer if I could see this type of a modification inserted in to a schematic.
With out seeing a schematic of the alternator it's not exactly clear to me why the alternator would feed back a voltage. By cutting off the DC to the coil with the ignition there would be no power applied to the field and the alternator would not be capable of generating any power would it? Again, a schematic would probably clear this up.

I'm assuming that the old voltage regulator is completely out of the circuit and just left to plug a hole or for decoration when using an alternator, is that correct?? In other words you're not running anything through the old regulator at all with the modification are you?

Denny Graham
Sandwich, IL

Denny Graham,

There is no external regulator. This stuff pertains to a system that has been changed to a internally regulated Delco 10SI alternator.

On a three wire setup, the internal regulator has two connections to the outside world through a external plug..the DA plug. These two connections allow the regulator so see system voltage and allow it to be energized with voltage from a outside source when the engine is started so as to get the whole enchilada charging.

Through some mysterious circuitry, the #1 wire completes a circuit to ground which energized the field and allows the charging process to begin. When the alternator starts creating power, this ground (#1) changes to a positive source of voltage and the wire now produces power...enough to power the ignition on its own, which would preclude turning off the engine if it were wired directly to the coil. The diode prevents the reverse flow of voltage to the coil.

After the alternator starts charging, #1 is powered as long as the engine is running. If you turn the key OFF but #1 is supplying the coil then it's as if you didn't turn the key OFF.. does that make sense? This is what this little diode thing is all about.

I flunked electronics so this is merely a shade tree explanation of how it works, and it's my shade tree explanation to boot! Caveat emptor!

Stuart

Good enough Stu, thanks.
Denny G

"Some folks don't want to crawl through the firewall to the ignition switch for power...the coil location is handy."

Why not just run it from the switch and save yourself the trouble of installing a diode? Seems to me wiring it to the coil is just cutting one corner and diving into some extra work.

"A small dash lamp can be installed in series and it will supposedly give enough resistance to negate any run-on problems when DA #1 is attached to the coil +."

I don't think the resistance of a dash lamp will stop power to the coil. A dash lamp can be installed in the wire from the ignition switch to the alternator. When the switch is turned on, the lamp will illuminate because it is grounded at the alternator. When the alternator kicks in there is 12V coming from both directions and no ground, thus the light goes out. When the ignition is turned off the engine dies.

If you wired the alternator to the switch you don't need the lamp but one can be handy as an instant notification that you've thrown a belt.

You'll need to diode, because the alt will backfeed through the ignition. It'll run on even though ignition switch is off.

Whitedog,

Interesting point. Tony doesn't indicate what kind of rig he is working on so most of this is a guess. I thought it was determined that the AD ignition switch had three terminals. One terminal was BATT and the other two were NO and switched together when the key was turned to ON. Wouldn't this mean that when ON, they are both common with BATT but when OFF they are not common with BATT or with each other.

If this is true, and the alternator was attached to the terminal not connected to the coil, when the key was turned OFF, that wire going to the alternator (#1) wouldn't have BATT power and wouldn't be common with the coil. Does this theory hold water!

Cletis,

I wasn't advocating connecting DA #1 to the coil, I was only trying to explain how folks that have done it in the past have addressed the run-on problem.

Stuart

That's how I have my 53 3100 wired.
I also have an alternator light in the excitation wire (DA 1).
One or the other is preventing run-on.
I don't know if Tony's vehicle is an AD, so this may not apply.

regards,
Leon

The vehicle is 46 Chevy of my own making. It has a simple key to balin to coil ignition. The alt. has 10 ga. wire from plug to bat. terminal on the alt to battery, the smaller wire is used as a exciter wire heated up with a push button. The problem I'm having is battery drainage if left unused for several days. I have one main lead from the battery terminal on the starter to power all of the other accessories, with this unhooked i still have drainage so this leaves only the charging system to blame for the discharge. I'v tried two different alts. same results. Would the diode on the exciter wire solve this problem?

ttodd,

No, the diode discussed above wouldn't solve the problem. Your battery drain sounds like a typical shorted diode in the alternator...other than the fact you said you tried another alternator and it did the same thing. Was it a known good alternator?

I'm not clear from your post how you have this thing wired, but it still shouldn't discharge the battery. A shorted cell can self discharge a battery so do keep that it mind. If you are sure you are disconnecting all the other loads on the battery other than the alternator, then it's either a faulty alternator, a high resistance short to somewhere between the alternator and battery, or the battery itself. This is how I see it.

It sounds like the alternator isn't wired in a conventional fashion, could this have something to do with the problem.

Stuart

"...... the smaller wire is used as a exciter wire heated up with a push button."

HUH?

I just converted my 261 to an alternator.I had a problem with the battery draining.The problem was my pigtail that plugs into the internal regulator.The red and white wires were in the wrong position in the plug.After switching them to their correct position,problem solved.

Automarc has posted good instructions as to the position of the wires.