Alternator Question

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Barn1018
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Alternator Question

Postby Barn1018 » Tue Sep 21, 2021 2:34 pm

I thought I had this figured out but no. Installed a Denso mini alternator( actually a cheap chinese copy) on a 49 cub with magneto. it wouldn't charge so ran a wire to the vertical stud on the back side and it started charging. I then installed a diode so stop battery drain or so i thought. Still drained battery. What is the solution? do I need to install a switch to break the connection? or just abandon the idea and start with the crank? Your thoughts please

john2189
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Re: Alternator Question

Postby john2189 » Tue Sep 21, 2021 5:03 pm

Did you put the diode in the right way?
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Jim Becker
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Re: Alternator Question

Postby Jim Becker » Tue Sep 21, 2021 7:45 pm

I don't think a diode will fix that problem whichever way it is installed. A diode is only applicable to a battery ignition system. You need some type of switch to turn off the power to the alternator. Some have used an oil pressure switch. Some have used a manual switch.

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radioguy41
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Re: Alternator Question

Postby radioguy41 » Wed Sep 22, 2021 6:57 am

A diode is only there to prevent backfeeding a battery ignition system. You need a switch of some kind. As mentioned either a manual switch or an oil pressure switch. The nice thing with the oil pressure switch is it's automatic.

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Gary Dotson
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Re: Alternator Question

Postby Gary Dotson » Wed Sep 22, 2021 7:12 am

The oil pressure switch is a very nice way to solve the problem but it can be as simple as a push button momentary switch that you push briefly to excite the alternator.

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raystractors
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Re: Alternator Question

Postby raystractors » Wed Sep 22, 2021 8:16 am

If you have lights on your cub you can use the light switch to send power to the alternator. I have used this method, turn the light switch on for just a second and then back off. If the alternator is charging then the lights will stay on, but with an alternator there will be more than enough power to also charge your battery. Once the engine has stopped the light will go out.

Jim Becker
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Re: Alternator Question

Postby Jim Becker » Wed Sep 22, 2021 10:27 am

raystractors wrote:. . . If the alternator is charging then the lights will stay on . . .

You could add a diode to this method to keep the lights from staying on. It would work just like using a diode to prevent backfeed to an ignition system.

Barn1018
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Tractors Owned: 1949 F Cub,1958 F cub, 1955 Farmall 100, 1968 Int Cub, 1968 Cub Loboy converted to LowRider Parade Tractor
Circle of Safety: Y

Re: Alternator Question

Postby Barn1018 » Wed Sep 22, 2021 6:23 pm

Hey guys thanks for all the input. I think I have a plan now. When I installed the diode I was thinking this doesn’t make sense, I don’t think it will work. Sure enough and I understand why now. I was wanting to use the lights hence the alternator. I will try to use the headlight switch to excite the alternator. That seems most practical in this instance. Thanks again everyone


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