12 volt questions for the electric gurus

Lynn Patrick · Apr 25, 2017

1957 960 w/12 volt conversion. This has worked for several years, then recently quit charging. Checking wiring I found a broken wire at the diode. I know either a diode or light may be used. Now my questions: I have a battery disconnect I always turn off when shutting off the tractor. If this is always done, is a diode/light necessary? I understand the diode only allows electricity to flow in one direction, so how does a light keep electricity from flowing the wrong way, or does it only remind you the battery is discharging?
Please forgive my ignorance. Only trying to learn!
Thanks in advance for helping me understand.

Bob · Apr 25, 2017

A diode, resistor, or "idiot light" stops or limits current flowing OUT of the alternator's excite terminal.

This stops the alternator from powering the ignition system when the ignition switch is turned "off", preventing the engine from running on using alternator power, and also protects the alternator form possible internal damage.

A diode stops reverse flow altogether, but lets current flow in the opposite direction to provide "excite" current for the alternator at startup.

A resistor or "idiot light" flows enough current to "excite" the alternator, but limits current to a low enough value there's not enough to fire the ignition system, causing the engine to "run on" or damage the alternator under certain conditions.

You didn't say what alternator you have, the following diagrams are Delco, but other internally-regulated alternators would be similar.

<img src = "http://www.gondtc.com/~blweltin/Bob/DelcoSIA1A.gif">

<img src = "http://www.gondtc.com/~blweltin/Bob/DelcoSIB1A.gif">

souNdguy · Apr 25, 2017

Bob supplied the perfect answer.

Lynn Patrick · Apr 25, 2017

He sure did! Thanks Bob & Soundguy. Even I can understand that! Just what I wanted to know.
Thanks again!
Lynn

David G · Apr 25, 2017

I have never seen the need for battery disconnect, keep wiring in good shape, will never use it

JMOR · Apr 25, 2017

(quoted from post at 17:36:39 04/25/17) I have never seen the need for battery disconnect, keep wiring in good shape, will never use it

f I were you, I wouldn't use it either, but I'm not. Rodents/fire and parasitic (alt reg, radios, other electronics in some instances) drains are all good reasons for some.

old · Apr 25, 2017

By the way if you use the disconnect while the engine is running you can/will fry the alternator because if it is working as it should the alternator will provide the power to keep it running but in doing so it will go to max charge and fry it self in a blink of an eye and even be unsafe to you

budman007 · Apr 27, 2017

(quoted from post at 10:55:18 04/25/17) 1957 960 w/12 volt conversion. This has worked for several years, then recently quit charging. Checking wiring I found a broken wire at the diode. I know either a diode or light may be used. Now my questions: I have a battery disconnect I always turn off when shutting off the tractor. If this is always done, is a diode/light necessary? I understand the diode only allows electricity to flow in one direction, so how does a light keep electricity from flowing the wrong way, or does it only remind you the battery is discharging?
Please forgive my ignorance. Only trying to learn!
Thanks in advance for helping me understand.

need help. Where can I buy a fuse link for my 1710 ford tractor?? It is a small piece of wire coming of the starter solenoid and terminates in a wiring harness. The total length is about 5 inch long. It burned out.

12 volt questions for the electric gurus

Lynn Patrick

Well-known Member

Bob

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souNdguy

Well-known Member

Lynn Patrick

Well-known Member

David G

Well-known Member

JMOR

Well-known Member

old

Well-known Member

budman007

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