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12v conversion questions

S

sflem849

Well-known Member
05-12vAlternatorConv-rev4_22_08.gif


In Bob M's diagram he calls for a warning light or a diode. What is the purpose of this?

On my neighbors VAC and my B there is a switch that is rigged into the 3 wire alternator system. What is the purpose of the switch? IIRC it is rigged into the Bat connection on the VAC alternator. Where should you run the switch? I would go check where it is tied in, but it is dark and there are skunks out there! :lol:

On my MD there is no switch, but there is a thing tied into the oil pressure gauge. This leads me to believe that it is there to excite the alternator. This also leads me to believe that the switch is possibly a manual alternator exciter.

Why don't I see a ballast resistor on the VAC or the B? I doubt I need one on the MD because it was originally 12 volts from the factory.
 
The light is the supply for exciting voltage.
One lead of the light to the ignition, and one to the #1 terminal on the alternator.
A diode will work here, as will a 10 ohm resistor.
The purpose is to allow excitement of the alt, while preventing the tractor from continuing to run when shut off.
The alternator (when turned on by this voltage, then puts out charging voltage to this terminal. (because both sides of the light, diode, or resistor have system voltage the light goes out.
If the tractor is shut off with no light diode or resistor, the alternator voltage keeps feeding the ignition.)
The switch does this job OK (as on the neighbors tractor) but requires remembering all the time.
Th oil pressure unit is an automatic exciting method as well, but sense the diesel is shut off with fuel, the oil pressure shuts off the alt.
The coils in the other tractors are probably 12 volt designed with no resistor required. Hoping this helps, Jim
 
The purpose of the warning light is to: 1 - Warn if the ignition is "on" and the alternator is NOT charging, and 2 - Limit the backflow current from the alternator when the alternator is charging and the ignition switch is opened. (Without the lamp the backflow current is sufficient to continue to fire the coil when the ign is switch opened. End result is the engine will continue to run after you shut the ignition off.)

The diode serves the same purpose as #2 - it prevents backflow current from the alternator to the coil when the ignition switch is opened. On the VAC the manual switch accomplishes the same thing.

On your MD the oil pressure switch together with the manifold serves a surrogate for ignition switch on a gas tractor.

A ballast resistor is not required if the coil is a "self-ballasted" (ie. 12 volt) coil. It has the required resistance incorporated within the coil primary winding.
 
The diode or the light "get 'er done" without any input from the "blem" operator either forgetting to switch the charging system "on" and causing a "no charge" condition OR forgetting to switch the charging system "off" causing a drained battery by tomorrow morning!
 
Hmm, niether tractor will keep running if the switch is in the on position. Is this a problem or possible because they won't always have that problem of backfeeding?

So you could either leave the switch on for a second or run with it on until you shut the tractor down? The real question is do you only need to excite the alt once or continuously?

Did anybody ever see a generic ALT warning lamp? I might as well do it up right and get a red light housing for the lamp. If it says ALT or something like that all the better.
 
The switches on the other tractors might be excite switches only, and not be connected to the ignition "on" switch. Thus not allowing it to run on. (but allowing it to discharge the battery if left on.) Once the alt starts charging it stays charging, no issue. Thus a momentary contact switch will make it start to charge, and can then be ignored. Jim
 
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