Re: 1 Wire Alternator

Posted by docmirror on January 25, 2023 at 20:41:00 from (23.127.217.254):

In Reply to: 1 Wire Alternator posted by super99 on January 24, 2023 at 14:44:45:

Single wire alt: Will charge from idle because it has a voltage path to energize the field. A 3 wire will only charge from idle after the batt voltage exceeds to bias voltage in the regulator and energizes the field. That's why sometimes one needs to rev the engine slightly to get the regulator to engage on an ext regulated 3 wire alt.



Batt drain at rest. First - depends on how the 1 wire alt is wired into the tractor. If it is direct from the charge line to the plus of the battery yes there will be a very slight leakage current backward through the four rectifier diodes onboard the alt. I don't know what the leakage current is for those diodes but it is pretty small. Maybe 50 to 100 microamps? Just a guess.



If the 1 wire is routed through an ignition switch it will have a hot position and a start position. Some tractors only have off and hot. In that case there will be no leakage because when the ignition switch is off, there is no current path from the diodes on the alt to the batt + term.



The best way to do it is to wire the 1 wire alt lead to a 50 amp relay, and then to the plus term of the batt. Run the hot lead from the batt through the ign switch so it will pick or engage the relay AFTER the tractor starts. This requires a 3 pos ignition switch which does not lend itself to some tractor designs with a safety push switch to start.



3 wire alternators are suitable for conditions where there is a large amp draw that is far from the battery, and also far from the alternator. The sense wire on the alt is used to sense the voltage drop of the loads at the battery and adjust the output of the onboard regulator in the alternator to compensate for that voltage drop, and provide a hotter voltage AT the batt + term. In our case on most vintage tractors the elect loads are rarely large, and rarely far from the alt or batt, so the sense wire is not needed, and the default energy from the alt is enough to maintain the batt charge voltage without the distance sense circuit.



This post was edited by docmirror on 01/25/2023 at 08:41 pm.

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