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300U 12 Volt Conversion

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Bob Jr from MN

09-21-2002 19:36:45

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I just converted my 300U to 12 volts and I replaced all the old wiring. Starts OK but won't shut off. Do I need a diode for the exciter lead? Exactly how would it go in the circuit?
Thanks in advance

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Doug in OR

09-22-2002 11:15:36

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 Re: 300U 12 Volt Conversion in reply to Bob Jr from MN, 09-21-2002 19:36:45  
As Bob M said, you can install a diode. Use a 1N4001 or equivelent, available at most Radio Shack stores. Install it with the band (cathode) facing toward the alternator. I always recommend using a 47 ohm, 2 watt resistor in series - as overcurrent protection. While not necessary, it does protect the diode.

The lamp works well too - and shows if the alternator is working.

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Bob M

09-22-2002 08:26:00

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 Re: 300U 12 Volt Conversion in reply to Bob Jr from MN, 09-21-2002 19:36:45  
Bob - You can install a diode in the line to the exiter (#1 terminal) connection. Use a diode rated at least 50 PRV and 1 amp or greater. I forget whether the diode's cathode or anode goes to alternator side. Try installing the diode one way - if the alternator doesn't work, simply reverse the diode connections.

Alternatively you can put an indicator lamp or a resistor in the line. A lamp rated at about 200 ma at 12 volts is good - like a auto instrument panel or side marker light bulb (#168, etc). Or use a resistor rated between 12 and 40 ohms.

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