Alternator Question

[Barn1018]

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]

Did you put the diode in the right way?

[Jim Becker]

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.

[radioguy41]

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]

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.

[raystractors]

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]

. . . 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]

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