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There was a discussion a while ago to the effect that the transformer is a
ferro-resonant one, i.e., the external capacitor and the special winding it's
connected to make up a 60 Hz tuned circuit. This causes the magnetic field
to saturate the iron core, which in turn makes the output square-ish wave
instead of the usual sine wave, and to have a constant output voltage since the
saturation happens well below the peak of the input since wave.
This is doubly good since it means the charging voltage is somewhat
regulated, and rectified square-wave is almost pure DC, which is easier on the
batteries than unfiltered sine-wave.
So when the cap is open, the tuned circuit doesn't work, the magnetic field
isn't strong enough to saturate the core, and the output voltage is low.
>>> Paul and Sue Abendroth <pabendro gemair com> 2/5/2004 6:41:37 PM >>> At 07:06 AM 2/5/04 , Jeff wrote: Does anyone have a link to a site the explains how this thing works? (in simple terms.) I am at loss in understanding why the transformer will not work when the capacitor dies. Thanks Here is an excerpt from the following site http://www.allaboutcircuits.com/vol_2/chpt_9/6.html "Ferroresonance" is a phenomenon associated with the behavior of iron cores while operating near a point of magnetic saturation (where the core is so strongly magnetized that further increases in winding current results in little or no increase in magnetic flux). While being somewhat difficult to describe without going deep into electromagnetic theory, the ferroresonant transformer is a power transformer engineered to operate in a condition of persistent core saturation. That is, its iron core is "stuffed full" of magnetic lines of flux for a large portion of the AC cycle so that variations in supply voltage (primary winding current) have little effect on the core's magnetic flux density, which means the secondary winding outputs a nearly constant voltage despite significant variations in supply (primary winding) voltage. Normally, core saturation in a transformer results in distortion of the sinewave shape, and the ferroresonant transformer is no exception. To combat this side effect, ferroresonant transformers have an auxiliary secondary winding paralleled with one or more capacitors, forming a resonant circuit tuned to the power supply frequency. This "tank circuit" serves as a filter to reject harmonics created by the core saturation, and provides the added benefit of storing energy in the form of AC oscillations, which is available for sustaining output winding voltage for brief periods of input voltage loss (milliseconds' worth of time, but certainly better than nothing). Unfortunately, these devices have equally noteworthy disadvantages: they waste a lot of energy (due to hysteresis losses in the saturated core), generating significant heat in the process, and are intolerant of frequency variations, which means they don't work very well when powered by small engine-driven generators having poor speed regulation. Voltages produced in the resonant winding/capacitor circuit tend to be very high, necessitating expensive capacitors and presenting the service technician with very dangerous working voltages. Paul Abendroth pabendroth dma org "I think that wind is a species of air." Adelard of Bath, A.D. 1120 _______________________________________________ Elec-trak mailing list Elec-trak cosmos phy tufts edu https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak |