Re: 18g wire good enough?

[ChuckKuecker <ckuecker@mcs.net>]

At 18:31 3/19/97 -0600, you wrote:
>
>Well, it really depends on what the dimmer is. If it is a simple 
>potentiometer (ie, variable resistor), then there is no problem because 
>it simply gets the 12V from the battery and feeds it to the lights. And 
>you can have many-many tiny bulbs, since decent car batteries can provide 
>adequate current to have enough power to all the 12V bulbs (remember the 
>P=VI thingie from high school physics). Problems might arise if the 
>dimmer is not a simple potentiometer but some other structure (hardly 
>doubt it) that cannot feed the full current available from the battery to 
>the bulbs. In that case if one wires up 5 more gauges besides the stock 
>oil temp gauge (a wet dream of many of us in the list :-)) the six light 
>bulbs in the gauges will be dimmer than normal. However, after I wired up 
>my 2 additional gauges I didn't see any drop in brightness, so I think 
>everything is ok. 
>
>
>Ilias (really struggling to find a decent mounting spot for that second 
>3-gauge panel...)

It probably is a potentiometer. A 'rheostat' would work if the extreme 'dim'
end of travel was actually 'off'. This is how some older cars worked. 

The problem is not how much current the battery can supply (hundreds of amps!),
but how much the dimmer can pass. I have not done any tests, but I would be
suprised if it can handle more than an amp. For a pot to supply large amounts of
current, it would need to be a low resistance, and this would get hot. Kinda
like my buddy's Chevy Caprice, where the light switch gets uncomfortably warm

A neat cure, for them who can figure the circuit, would be to use a fairly
large transistor in a heatsink as the actual 'dimmer', while the potentiometer
supplies base current, what is known as an 'emitter follower'. The pot can be
a fairly high resistance in this case. If you send a FAX number, I will send the
circuit.

Chuck Kuecker

ckuecker@mcs.net

'83 Scirocco
'58 Ghia Convert
'67 Bug
'63 Bug
'91 Vanagon


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