alternator draw

ken house · Oct 9, 2013

farmall c with 12 v conversion.

i understand that alternator needs excitement to be able to charge. however, battery cable spark seems to be excessive. how much draw is normal?

Bob M · Oct 9, 2013

It depends...

A Delco 10SI "3 wire" alternator draws just a few milliamps when shut down. This is normally less than a battery's internal self-discharge rate.

So called "one wire" alternators can draw anywhere from about 10 to 200+ millamps at idle. At the high end this will flatten a fully charged battery in a couple weeks.

However even 200 milliamps is too small to create an observable spark when connecting/disconnecting battery cables. So if you are getting sparks at the battery cables when you connect you've got a serious current drain going on - either a defective alternator or a load left on (lights, ignition, etc.)

ken house · Oct 9, 2013

i forgot about points. maybe i will turn the engine a bit and look again.

thanks

Janicholson · Oct 9, 2013

a little chunk of plastic between the points assures they do not conduct. Jim

charlieu · Oct 9, 2013

If the ignition switch is off there should be no current flowing to the points so it makes no difference if the points are open or closed.

There are very few electrical wires on a Farmall M, it would not be that hard to start to disconnect wires untill you find the one that is doing the sparking

Jon Hagen · Oct 9, 2013

Is it more than a little blue spark when you connect the cable. There is a capacitor in a Delco alternator that charges when you connect the battery cable. It will produce a tiny blue spark when you connect the cable and will stop drawing power an instant later when the capacitor is charged. Perfectly normal and will not discharge your battery.

ken house · Oct 9, 2013

sounds like the spark that you describe. never noticed it being so intense, before. thanks.

Raner · Oct 10, 2013

Easy way to test for a draw...
Disconnect positive battery cable...
Connect a test light, wire lead to cable and the test light point to battery...
If there is no draw the test light will show no light...
If there is a draw the brighter the test light bulb is the bigger the draw...
If you want to check your test light connection connect it as described above and
turn on any kind of electrical component and the test light will turn on...
Note...If you have the test light connected for a long while just touch the cable
to the battery before you continue checking...
If you don't have a test light any light assembly with two wires and a blub will
work...

alternator draw

ken house

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Bob M

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ken house

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Janicholson

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charlieu

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Jon Hagen

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ken house

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Raner

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