exciting alternator

clint s

Member
Finally cut all the old wiring out and replace. It was in bad shape. Rewired it per here: http://www.yesterdaystractors.com/articles/artint195.htm
I did away with the amp meter and light switch as both were broken. Will add a volt meter later
As of now I do not have a wire attached to the 1 terminal on alternator as I did not have an indicator light on hand. Started it up an low and behold the alternator seems to be exciting on its own and charging. Slowly got to 13.5 volts and hung there. Can they self excite?

Can I use a LED type indicator light to excite?
Do I even need to as it seems to be charging now?[/b]
 
They can sure do that. It might take a bit more RPM, but it is not an issue. A 10 ohm resistor with 10 to 20 watts (just
makes it big enough to work with) in a shrink tube hooked from #1 to the ignition, will also excite a little earlier. Jim
 
There are many ways to set one up to excite. My Oliver S88 has a ballast resister in place to do that and be able to shut it off. My W Speed Patrol has it set up so you turn on the lights and that in turn excites the alternator. Or a simple diode will do the same thing. Not sure a LED would have enough resistance to do it since most that I have messed with needed an resister in line for them to work on 12 volts
 

I also think this may solve my charging issue hot coil I had. I think it was wired with #1 to the bat post and # 2 to keyed on. Not letting the regulator work right. Wish I would have paid attention when I took it apart.
Probably will get a regular 12 light or a resistor because it is cheap enough.
It seems to start better with that old crappy wire gone. Best part is that my sisters washing machine crapped out and I robbed all the wire from that.
 
The LED will light up if the polarity is correct, but you need to wire that 10 ohm resistor across the two leads to get it to excite. Jim
 
Well in theory a LED is just a diode that due to the way it is made lights up so if it is like the common diode if wired up the correct way it would do the same things as the old common diode unless electrical theory has changed with the Light emitting diode and it not working like the old common diode
 
It is unlikely that a (typical) 3 to 5 volt maximum forward voltage would operate at 14 volts. Either way they will not pass enough current to excite. Just too tiny to do the exciting or the blocking of reverse current. Too brignt for too short a time, and blown to smoke in the other direction. A resistor of 450 to 500 ohms must be put in line with a LED (typical) to limit current enough to prevent smoke. This prevents use for the purpose unless a 10 ohm resistor is placed aa a shunt across the LED and current limiting resistor. The 10 ohm will conduct enough to excite, and prevent run on. Jim
 
Ok so then your saying the LEDs have a low current ratings so can not handle the amps and volts to excite the alternator so it is more or less the size of it not the fact it does not work like to old say radio shack diode I used hundreds of times in the alternator circuit
 
I have a panel mount LED on my H for the alternator excite, and it excites just fine. The LED goes out and the ammeter kicks over into charge mode when the RPMs get high enough. No resistor needed. Maybe not right, but it works.
 
In the forward bias direction (when it is supposed to conduct) it conducts and makes light. but has pretty high resistance, and flows little current. In the reverse direction it does provide a check valve action, but cannot handle much voltage, maybe 6 volts or a bit more on a typical consumer diode. Their intent is to make light, and are not considered, or used as a rectifier. Jim
 
Ok so not at all like the diodes that we used in years past for the excite circuit. I know the one I used was something like a 6 amp 400 pike voltage diode which was over kill for the excite circuit
 
Yes, even the older 3 wire Delco will self excite itself if turned fast enough. Several times I have forgotten to connect the battery to my alternator test bench and have had a 3 wire Delco self excite, the voltmeter comes up to a normal 14V,but does not indicate any amps charge on the ammeter. I look and yes, I forgot to connect the battery, so they will all self excite. Almost any "1 wire " Delco SI type alternator, made in the last 20+ years, just is an ordinary Delco SI with a regulator that excites the field at very low voltage. That why I constantly beat on the old farmers tale that a "1 wire " alternator will discharge your battery faster than a 3 wire unit. 99% of all those "1 wire" ,alternators built in the last couple decades, are identical to a standard 3 wire alternator in that they have no added connection to the battery and will not discharge your battery any faster than a conventional 3 wire alternator.

I guess I need to resign myself to fact that 2 incorrect old farmers tales will never die 1 Modern ignition coils can have a built in resistor , 2 a modern "1 wire " alternator will discharge your battery faster than a 3 wire model. Both are false, but both will continue to be believed forever. :)
 
I have decided to go with a volt meter that has a separate standard 12v bulb to light the face. I will use the bulb in the excite circuit. If the meter lights up it is not charging. Until then I will just use it as is. I have to get the garden in.
 
Won't work. The meter light is grounded to the panel to light up. The ""idiot light"" needs to be isolated from ground. One lead to the ignition source, one lead to
the #1 spade terminal. The reason it goes out when running is that there is 12v on both leads. Jim
 
The one I am looking at has a black and red wire coming out of an insertable socket. Black end to #1, red to key on. Socket is rubber and gauge back is plastic. Figure that would work.
http://www.amazon.com/AUDEW-Voltmeter-Gauge-Carbon-Yellow/dp/B00S0W9I3K/ref=sr_1_9?ie=UTF8&qid=1461970537&sr=8-9&keywords=volt+gauge
 

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