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Re: Ford NAA Voltage Regulator problems

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Author  [Modern View]

07-28-2013 16:12:58

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The VR does 3 things, 1)connects/disconnects battery to generator armature terminal when Armature voltage exceeds a preset value (high enough to charge a battery. This is so that it does not connect if so low that battery would discharge back into generator. 2)Senses voltage of battery and controls generator output by modulating field current, such as to apply only enough charge current to maintain a specified battery voltage. 3) senses generator current so as to not exceed the rated generator output & thus damage generator AND also senses a reverse current as when battery is discharging into the generator & disconnects gen to battery accordingly. SO, to answer your questions, a VR failure could result in keeping battery connected after shutdown of engine (cut out contacts fail to open/stuck closed) & this will discharge battery & heat generator in minutes. It might never connect batt to gen so all charging/discharging by generator does not exists...just as though you removed gen from tractor. If field contacts remain closed/stuck & never open regardless of voltage, then in time battery will overcharge, excess voltage & excess current will heat battery and generator, sometimes to destruction. If field contacts never close, then generator output will be very minimal to zero.

You can "temporarily" remove the VR from consideration & prove generator working, by placing a jumper wire on generator between ARM and FIELD terminals AND a second jumper wire between the gen ARM terminal and that side of ammeter which is not connected to the battery. Should see charging amperes as well as an increase in battery voltage. Be sure ti remove ARM to ammeter jumper when engine is turned off. Suit yourself as to whether or not you leave present wiring on generator ARM & FIELD terminals..if all is wired correctly it doesn't matter, but one more step toward removing more things from circuit would be to disconnect them.

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