The Household Light Dimmer Switch

This is a device that varies amperage without varying voltage. (A reostat varies voltage.) A dimmer is useful in lab contexts as an inexpensive component of a device to regulate the speed by which electrophoresis is carried out. Electrophoresis has a major limitation in that the passage of electricity through a gel generates a lot of heat. Too much and enzymes denature, and if hotter still, the system begins to boil. The gels may melt. Since it is amperage that is the dynamic component of electricity that generates heat, the regulation of amperage is of overriding importance. (High speed electrophoresis is done in a system that dissipates heat rapidly and is done at very high voltages - 1,000 or more VDC.) Here is how the dimmer works, so that you will not be surprised that your system will be running at 110 to 120 VDC no matter where you set the dial.

Electricity comes into your home or lab as alternating current ("AC"). While you would expect a sine-wave, it instead gives a boxy graph because in the slow 1/120th of a second for each half wave, the voltage reaches its extremes so fast that a right angle is formed.

What the wave cutter does is momentarily break the circuit allowing the voltage to drop to zero for the remainder of the half-phase. You see that the boxes become of shorter duration. Obviously, while the voltage is zero, there is no current (i.e.: no amperage). Thus the amps come in spirts, and the average amps over time is lower.

When the output of the dimmer is passed onwards to a "push-pull" rectifier,* that rectifier in effect folds the lower part upwards and superimposes it on the pre-existing upper portion of the wave. Since all the voltage is on one side of the base line, it is now a direct current ("DC")

* A "push-pull" device makes use of both the upper and lower parts of the full wave of the alternating current.

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