Re: Re: Re: Re: Re: Re: Re: Light Switch on M

Posted by Dan from PA on July 27, 2000 at 02:15:48 from (151.201.75.234):

In Reply to: Re: Re: Re: Re: Re: Re: Light Switch on M posted by marvin on July 26, 2000 at 08:30:44:

It's true that a 12V bulb carries half the current of a 6V bulb of the same wattage, but this is only helpful when discussing a circuit where the bulb is the only load.
When you activate the dim circuit, you now have a circuit with two loads, the bulb and the resistor. You converted the bulb to 12V (doubling its resistance if you choose to maintain the same current in the wire, or quadrupling the resistance if you chose to maintain the same bulb wattage), but the resistor's value was unchanged.
The following example assumes that the dim setting cuts the wattage output of the bulb in half, and that you chose new bulbs of twice the resistance. All resistances are chosen for easy arithmetic, and are for comparison purposes only. I don't know what the actual values are.
Imagine instead of a resistor and a bulb, you would have had (originally) two 3V bulbs. These bulbs have a resistance of 3ohms each for a total resistance of 6ohms. Apply 6V and you have a current of 6V/6ohms=1amp (current=voltage/resistance). Now change to 12V, using a pair of 6V bulbs (of resistance 6ohms each for a total resistance of 12ohms). Current is now 12V/12ohms=1amp, still the same. What you have done is put 12V across a 6V bulb and a 3v bulb (total resistance=6ohms+3ohms=9ohms). Current now is 12V/9ohms=1.333amps which is higher than 1amp. Smaller resistance=higher curent.
So yes, you now have a higher current through the dimmer resistor. Wheather or not this will actually cause a problem is debatable.
So far, the resistor on my Super C is doing fine, and I use the dim circuit all the time because I never bothered to swap my light bulbs to 12V. I just never run them on bright. This actually results in an even higher resistor current than you have. As long as the resistor doesn't burn out, if you keep wires and such away from it and maybe provide a bit of ventilation, you should be fine.
If someone wants to see the actual math, post the real values for the original 6V dimmer resistor, and either the bulb wattages or resistances (both old and new).

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