[rotorwrench]

Generators actually lose efficiency at higher rpm due to brush float. Most old DC automotive generators have a pulley diameter that will keep them within the sweet spot for daily operation but extremes will cause a loss of efficiency.

An electric light bulb that is designed for automotive use will sometimes dim at low rpms due to the lower output but will pick back up to normal as soon as the rpm gets back up to driving speeds. The generator control unit should keep the voltage the same at all rpms withing the normal range of operation. Lights should not get brighter at high rpm. If anything, they can start to dim with extreme rpm. A generator is not like an alternator in that respect. Voltage is usually from 7.0 to 7.4 volts in normal operation but can go as high as 7.6 after everything warms up. If it gets too high then the bulbs will burn out.

Most folks run the 6-volt systems with positive ground. Since this is the normal direction of current flow, it makes the system a tad bit more efficient. It will work on negative ground but it has to be re-polarized for that so that the residual magnetism in the generator will have the polar balance that it should have to generate a proper current flow. The caution of this is if a person has the old voltage step up vibrator replaced in the radio by a newer solid state unit. A change in polarity will kill a solid state unit. 6-volt systems use larger gauge wiring to keep the resistance in the system low. High resistance due to poor grounds or wiring will take its toll.

It's good to know what the three poles are for before adjusting things. The one marked "BAT" is the cutout relay. It's what brings the generator on line after the engine is started. If it sticks closed, it can burn the generator up after shut down due to it trying to reverse motor off the battery. The one marked ARM for armature is the current limiter. It has to be adjusted with an amp meter and an adjustable load so clean it but don't play with it too much unless you have the right equipment to check it. The one marked FLD or field is the voltage regulator. This can be adjusted with a volt meter but it has to be an accurate one. The range of voltage on a 6-volt system is narrow so take care with it. It basically buzzes all the time by rapidly opening and closing the points to maintain voltage. The points have to be clean and in good condition for steady voltage readings. It is sensitive so having the amp meter with the adjustable load and the accurate volt meter is a very good idea.