I'm not an EE, nor do I claim to be. I've done technician work and know the business end of an oscilloscope when I see it. I'm pretty well schooled on the basics, I get a little out of my comfort zone when we get into more complicated things.
In the scope of these forums, I think I can safely say an amp is an amp is an amp.
Power consumption in a simple resistive load, will be the same from 10 AC amps, as 10 DC amps. Same is true for AC voltage and DC voltage dropped across a simple resistor -- a filament bulb on 12VDC will draw similar power as it would from a a 12VAC source.
Now for a good counterexapmle that is well within the scope of CPF:
Try doing the same thing with an LED (nonlinear load) instead of a incan lamp (more or less a simple resistor), and the results will be very different.
There the RMS value of voltage or current are completely irrelevant, as an LED will tend to draw a huge current when the sinusoidal voltage is close to its peak value, then close to zero current when the value of the sine wave is less than the Vf of the LED, or negative.
Or, let me put it this way -- let's say you are driving some LED christmas lights directly from AC. You design your circuit so that over one full period, the root mean square current, or AC current, is 20mA. I design a circuit where my LEDs are driven by a constant DC current of 20mA. If you compare the two circuits, The AC circuit (with the same number of amps) will be overdriving the LEDs mercilessly for about ~20% of the cycle, and they will suffer from a highly annoying 60Hz flicker. The DC setup will be running within spec, and will substantially brighter, more power efficient, and longer-living.
jaygrant said:
Which means I'm looking for a 20amp rotary 3 position switch that will fit in a Mag D body.... Simple......
Do you mind ellaborating on your proposed setup, eg. what are you trying to do -- incan light? LED? Soemthing with multiple levels? If I know this I might be able to offer some specific suggestions. A light which involves multiple levels, and also 20 amps (of any kind) sounds very interesting...
LukeA said:
Alternatively, you may want to consider a switch with a lower amp rating and FETs, which is explained for the mag's stock switch
here. (explained for one position, you would need 3 of the explained setups.
Good idea on the MOSFET. However, rather than using three mosfets, a better soltion if the idea is just to get different output levels, is to simple use a rotary switch or even a continuously variable potentiometer, to adjust the biasing of a MOSFET -- and make it more or less resistive. Note that this will require heatsinking the FET to the body of the light as the transistor will dissipate significant power if used this way.
A "lossless" way to dim an incan, would be to actually use a MOSFET as a switch, and control it using a PWM driver (in a D-cell maglite you could probably fit a homebrew circuit based on a 555 timer) -- which will basically switch the lamp off and on very rapidly. This will effectively reduce the RMS voltage delivered to the bulb, without wasting power.