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In Reply to: 2305 John Deere Won't Charge posted by Will on Sunday, June 21, 2009:

Will , this is the stock 20 amp alternator that shows on your tractor, there is an optional 35 amp alternator available and the optional alternator shows a voltage rectifier regulator that is seperate from the alternator itself.
Both of these alternators show to be permanent magnet alternators. This simplifies the system by using permanent magnets for the field instead of electromagnets which requires regulated field voltage to determine the charge rate. So quite simply your alternator simply needs to be rotated to produce ac voltage, the faster it spins the more ac voltage is present at the ac wires coming from the back of the alternator and they are connected inside to the induction coils. If you unplug the alternator at the rectifier regulator the two wires the same color should read ac voltage as the engine is running. The higher the rpm of the engine, the higher the ac voltage at those two wires. Now since we are dealing with ac voltage like what is in your house but lower it needs to be polarized or aligned to go into your battery which is dc, it goes through several diodes and comes out of the regulator rectifier as dc voltage + and - . Now since the ac is rectified the voltage will appear as dc and approximately 1/2 of the ac measurement at any given engine rpm.
When you read a ac voltage of 30 volts and rectify you get about half that in dc when converting it so the regulator should show 15 volts dc to the battery.
Start the tractor and take those measurements, It may be possible something could be drawing current while the tractor is setting. Charge up the battery and hook up the positive lead, then slightly touch the negative terminal to the battery post and see if you can either hear or see any signs of a blue spark indicating something is drawing current with the key off.
I will be more that happy to go deeper into this if you need, don't hesitate to write back and let us know what the problem was.
Dale G. Basgall
- Re: 2305 John Deere Won't Charge Rodney Williams Wednesday, July 22, 2009
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