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Re: MGB Dashboard lights

To: mgs@Autox.Team.Net
Subject: Re: MGB Dashboard lights
From: Ross MacPherson <arm@unix.infoserve.net>
Date: Fri, 21 Nov 1997 19:14:49 -0800
At 07:46 PM 11/21/97 EST, you wrote:
>These bulbs are rated 200 mA at 7.5 volts.
>_ If _    W = A * V,   then W = 1.5A  when .2A * 7.5V
>The 12v bulbs I removed had markings of 2.2 and 3.0 W.
>IF my formula for W = AV is correct, then there isn't much difference in
>current.
>Someone who knows electric theory is invited to participate in this.
>Electricity is not my first love, and I'm trying to perfect a hydraulic
>lightbulb to get away from the stuff entirely.
>Bob
>
>                               
Bob's on the right track here but if you carry Ohm's law a little further
you'll find that the power consumption is doubled  but the life of the lamps
will be reduced exponentially.  If any one wants an explanation e-mail me
privately.  It all boils down to: If you use  the 7.5 V lamps they'll be
brighter but they won't last as long.  We all new that any way, right?

Someone ( I forget who, sorry) mentioned using a resisitor to clamp the
applied voltage to these lamps at @ 10 volts to keep them from burning out
too soon.  DON"T do this! You'll negate any improvement in brightness
because the resistor would be in the circuit at all rheostat settings and
you introduce a very small space heater to the under dash area as the
resistor tries to dissipate the power no longer available at the lamps as
heat . Also the calculated R value will change drastically if a lamp burns
out.  A Zener diode circuit could be bodged together for a couple bucks
that'll do the same thing but without the risk of losing your smoke and will
work with one lamp or ten.

Cheers,

  Ross MacPherson 
 1947 MG-TC 3528
 1966 MGB-GT   


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