battery discharge?

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battery discharge?

Postby fstalfire » Mon Feb 20, 2017 11:27 pm

Anyone have any idea why my battery discharged?
just fired up my cub after a rebuild, i have new battery, new hitachi alternator, new volt gauge....i ran it at high rpm for about 15 min, shut it down and later that night checked on it and the battery is dead.....i have the alternator going to the stud on the starter and a jumpr wire from the large alternator stud to the terminal on it, dont have the lights hooked on it so i literally have just the coil and alt hooked to the battery....should the alt have some kind of diode inline or something? not sure why it discharged but something killed it within 6 hours and all thats hooked up is the coil and alt

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Re: battery discharge?

Postby Glen » Tue Feb 21, 2017 2:04 am

Welcome to the website. This might not be the whole problem, but new batteries usually need a charge, they are usually not fully charged. :)

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Re: battery discharge?

Postby Gary Dotson » Tue Feb 21, 2017 7:33 am

I'm not real familiar with the Hitachi, but I'm guessing your jumper wire is keeping the alt. field energized at all time, draining the battery. I would pick up the power for that from the coil, (switched current) with a diode in circuit. I think that will solve the problem.

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Re: battery discharge?

Postby Eugene » Tue Feb 21, 2017 9:32 am

Below is a link to the wiring diagram for a 3 wire alternator. Use diagram #5. ... 0Diagrams/

The wire leading to terminal #1 on the alternator has to be switched and a diode in the wire. Switch is needed to keep from discharging the battery. Diode needed to keep the alternator from back feeding the ignition system.
I have an excuse. CRS.

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Re: battery discharge?

Postby Bus Driver » Tue Feb 21, 2017 9:40 am

I suspect that Gary is correct about the battery drain. Your wiring follows a recognized diagram?
For diagnosing mysterious drains, even very tiny ones, disconnect the negative cable from the battery, connect a voltmeter between the now-empty battery terminal and the just-removed cable. Any voltage reading indicates a current draw. Start disconnecting things one at a time. When the voltmeter goes to zero, the drain has been disconnected. Diagnosed and discovered a soaked insulator on the pull-rod starter switch when a battery drain started after washing the tractor.
I proofread my post and it is correct in stating use of voltmeter.
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