Alternator install

[jerry]

Hello I had replaced the gen with an alt long ago.because all the wireing was gone or in disaray for a quick fix I had the exciter wire from the head light switch and had to turn the lights on to charge. Now I have rewired per Stefans post of sept. 19 09. the system works great (Thanks Stefen) except for one thing. I did not use an orginal bulb and socket for the gen light what i used was a 14 volt pre fabed 2 wire unit. now to get it to charge I must excite with 12 volts form the battery then plug in the green gen light and it charges until the next shut down. Could the bulb be the cause. Will a 1 amp in line diode solve this problem. Thanks for any comments Jerry

[Aussie Frank]

Hi Jerry,

Your problem is probably being caused by the light globe being too small and not supplying enough current to get the alternator to start generating power. Many years ago when I was working in the VDO instrument design department it was common design practice to have a 47 ohm 5 watt resistor wired in parralell with the charge light to ensure the alternator always starts charging. We found through testing that unless a 5 watt indicator globe was used alternators would not start charging reliably without the resistor.

Regards, Frank.

[jerry]

Thanks for the reply Frank. Hows the weather down under? I don,t know much on electric circuits. can a 5 watt resistor be installed down line from the light globe just before the excite terminal of the alt? Would an electronics store like (Radio Shack) carry this resistor.
WHAT A GREAT WEB SITE Thanks Jerry

[john.n]

it would need to be in parallel with the bulb or you will reduce the current further.

[Aussie Frank]

Hi Jerry,

John is absolutely right you need to wire the resistor across the globe not in line with it. As far as I know your Radio Shack store does carry 5 watt resistors. The right part will most likely be about an inch long and 1/4 inch square made with a white ceramic case. Don't settle for a tiny part as they can't handle the power. (They get too hot and let the magic electronic smoke out. They stop working after that. )

It has been a great day today weather wise. Perfect for putting the last touches to the Toyota 3K motor I am building for my daughter. It goes in tomorrow, hopefully the weather holds out, the car is stuck at my brother in law's place outside so I don't want any rain. It has been getting colder as we are aproaching winter here so the sun is a welcome sight.

Regards, Frank.

[commander]

Radio shack does carry a line of wirewound resistors in the US......
here is their catalog number for one that will work fine.
Catalog #: 271-133

They get rather warm when the tractor is running, so be careful where you install it. Somewhere out in the air is best, not crammed up in the middle of a jumble of other wires.

[dexta roadless]

One way is to put in a 5w lamp from a parkinglight etc in serial with the warninglamp, and hide it in beside the steeringbox or something.

[russelm]

Remember that the bulb is only there in order to initialy excite the field (note: more modern alternators dont actualy need the bulb), once this is done and juice is being generated then the current through it drops to (almost) nothing.

So a resistor used in its place wont get hot once the engine is running (if wired up correctly).

Heres the circuit diagram for one: