Re: Alternator troubles

Posted by Owen Aaland on June 20, 2010 at 12:53:08 from (65.165.246.45):

In Reply to: Alternator troubles posted by Zachary Hoyt on June 19, 2010 at 04:50:33:

If your tractor is wired as you posted then you are always going to show the 5 amp discharge even if the alternator is working. You would be charging the battery directly and the ammeter is going to show the total amps being used, not what is coming from the battery.

The following assumes you have the standard regulator and not the self energizing "one wire" regulator.

As long as you have battery voltage at the battery (output) terminal and at terminal # 2 all the time and some voltage at terminal # 1 with the engine running your wiring is good enough for the alternator to work.

The output wire running to the battery terminal meets the electrical requirements but I would rather see it attached to the ammeter on the same side as the lights and ignition wire. That way the ammeter will show the amperage going either to or from the battery. Connecting a small wire directly to the battery is not a good idea because of the corrosion that is likely to occur there.

On these old tractors without much electrical load it is fine to attach the voltage sense wire, the # 2 terminal, to the output terminal on the alternator. On equipment with more electrical loads it is better to run this wire closer to the battery. That way the regulator will compensate for the voltage lose in the system and raise the charging voltage to maintain the correct battery voltage.

Although some alternators will begin to charge without voltage applied to the # 1 terminal it usually doesn't work on tractors. The small amount of residual magnetism in the rotor requires higher RPMs than is available for it to begin charging.

The # 1 terminal wire needs to be switched off when not in use or the field coil in the rotor will draw 4.5 amps draining the battery. Because when the alternator is charging it provides charging voltage on this terminal, if the wire is connected to the ignition coil, it will provide voltage to the coil even though the ignition switch is off. This will keep the engine from stopping when the switch is in the off position.

On your tractor it sounds like you have a simple On/Off switch to accomplish this. It is completely usable like that but it requires some effort on your part to first turn it on and then later to shut it off so that the battery doesn't discharge through the alternator. Five other methods are commonly used, all of which function automatically, requiring no effort on the operators part.

1) A normally open oil pressure switch. Oil pressure closes the switch, when the pressure returns to zero the switch opens. The power to the switch must come from somewhere other than the ignition switch.

2) A resistor between the coil and the alternator. This drops the voltage in the wire enough that the coil will not provide enough spark to run the engine with the switch off. The resistor also drops the voltage going to the alternator but the only difference it would make is the alternator would have to spin at a little higher RPM to start charging. As long as you have 6 volts on the # 1 terminal the alternator should start to charge at idle.

3) An indicator light. This functions the same as the resistor but can give some indication that the alternator is working. An alternator that is charging some may turn out the light but still not work enough to keep the battery charged.

4) Diode. The simplest to install and provides full battery voltage to the alternator and no back feed to the coil.

5) Ignition switch with separate accessory and ignition terminals. Generally not found on farm equipment.

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