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Re: 300 alternator troubleshooting

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Author  [Modern View]

11-13-2012 11:55:41

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In most cases the alternator will tend the battery so well that (if it starts quiclkly) the needle will stay in the middle most of the time. Use an analog meter to assess the real voltage. Turn on the lights if they are bright (as much as they can be) and the needle stays in the center all is well. Jim

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Zachary Hoyt

11-13-2012 12:33:16

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 Re: 300 alternator troubleshooting in reply to Janicholson, 11-13-2012 11:55:41  
Thank you, that is how it did work up until Saturday. I tried the lights at the time and showed about 15 amps discharge, vs about 3 with just the distributor drawing current. Before Saturday it would jump over to about 5-10 amps charge right after the engine started and then after a minute or less it would go right back to 0 and stay there for the rest of the time the tractor was running.

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Bob M

11-13-2012 14:57:40

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 Re: 300 alternator troubleshooting in reply to Zachary Hoyt, 11-13-2012 12:33:16  

Assuming the wiring is OK, could be the diode has failed open. Try shorting across the diode and see if it now charges. If so, replace the diode.

If it still does not charge, bypass the internal regulator by shorting the test tab inside the D-shaped opening in the rear of the alternator to ground (photo). If it charges hard with the tab grounded, the VR has failed - a new VR or replacing the alternator is the fix.

However if it doesn't charge with the tab grounded there's something else wrong with the alternator. Best solution is replace with a rebuilt alternator.

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