Quote:
Originally Posted by Lynn Eades
Tony W. the difference in the field windings has to be the number of windings, and therefore the strength of the magnetic field. How this converts to voltage I am not sure (I remember less than I've forgotten) but my guess is that the stronger the magnetic field the higher the voltage at any given armature speed.
The problem unregulated, is the overheating and melt down. (melting and throwing of the commutator solder? etc.)
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Yes but you're forgetting current Lynn, since magnetic field strength = current x number of windings. What I'm thinking is the 12V field coils have more windings, and therefore more resistance, so they draw less current. The net result is the same, ie. same magnetic field strength, because the lower current cancels out the extra windings. Conversely, if you put 12V through a 6V field coil, let's say a Ford 6V field coil rated at 3 ohms, it will draw twice the current it was designed to carry, and potentially overheat like you say. Evidently they can handle it, because some of the rodders leave the 6V field coils in and report no problems, but you wouldn't put 12V through a 6V globe and expect it to last as long, so why expect it from a 6V field coil? Correct practice in theory would be to match the field coil to the voltage it will operate at, so I'm thinking the use of 12V field coils is IDEAL practice, although not necessarily ESSENTIAL practice. For example I notice the professionally converted 6V gennys all have 12V field coils fitted, possibly because they have to give a warranty...?
The same doesn't apply to the armature, because the situation is reversed. That is, the 6V armature is designed to carry more current than the 12V armature, because you need twice the current at 6V to produce the same wattage. Which means the 6V Ford armature running a 12V system is operating well BELOW its designed current load. Which would explain why no one changes them, including the professional genny converters.
On the question of magnetic field strength - like you I'm a little hazy on some of the complexities of generators, but I know they operate fundamentally under Faraday's Law, which dictates that voltage output is proportional to the number of armature windings x the speed they move through the magnetic field. In other words - RPM. Which means voltage has nothing to do with magnetic field strength, that just determines the potential current output at a given RPM. And of course if you draw more current you need more power to drive it, eg. when you turn on the headlights at idle you can hear the motor being loaded up. So what I'm wondering is if you run 6V field coils on 12V, which doubles the current through them, and therefore doubles the field strength, does it double the potential current output? And is that a good thing or a bad thing? Maybe it's a reason to change the field coils....?
Anyway I'm thinking a lot of this genny theory has more to do with current than voltage, which is simply the job of the regulator. Like you said earlier the 6V Lucas genny will put out 50V if you let it, so they're really not a voltage critical device - it's only the field coils which are voltage rated, because they're fixed resistance.
My brain is hurting now so I might get back to something mechanical!