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Alternator Won't Charge

K

kscycler

New User
1949 8n, side distributor, converted to 12V.



My new-to-me 8n has been converted to 12V and won't start charging on its own. If I take a screw driver and short between the #1 and #2 terminals, the alternator will start charging.

Read through the forums, consulted the wiring diagrams, and thought I had a solution.

I ran a wire from the switched side of the ignition switch to a small warning light and then to the alternator #1 terminal. When the switch is turned ON, the warning light illuminates, as I believe it should. However, when I start the tractor, the warning light does not extinguish. If I (again) short between the #1 and #2 terminal, the warning light extinguishes.

Can't figure out what I'm forgetting or omitting. Any help would be appreciated.

Photos:
#1 Terminal Block. The blue wires are for the ignition switch. The brown wire runs to the warning light and then on to #1 terminal.
44417.jpg

#2 Warning Light in series coming from terminal block and going to terminal #1
44418.jpg

#3 Connections at alternator. Jumper from Bat + to #2. Brown wire from warning light.
44419.jpg

#4 Warning Light package
44420.jpg
 
Likely, the little warning light doesn't draw enough current to "excite" the alternator.

If you want to retain the light, options are to put a resistor across it, or replace it with a warning light that draws more current.
 

Hadn't considered current draw, hmmmm. I thought the point of the warning light was to transmit 12v to terminal #1 and once excited, 12v would flow back to the warning light, balancing the voltage and extinguishing it. Now I'm really confused....
 
The field current needed to start the alternator charging at startup is supplied through the circuit to the #1 terminal.

Once the alternator begins to charge the field current is supplied by the stator windings though the diode trio.

At that point, there's no current draw through the warning lamp, so it no longer lights.

Typical values for a resistor in the excite circuit are 10 Ohms, 15 Watts WITHOUT a warning lamp in parallel, so a resistor of considerably more resistance ACROSS your warning light should do the job.
 

Thanks, Bob. I wish I understood it better, but I have something to try. I'll look for a resistor...thanks.
 
Or to verify that the low current draw of your little pilot lamp is the problem, temporarily connect up a #194 lamp with clip test leads in place of the small pilot lamp, start it up and see if the alternator will excite.
 
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