Folks,
I hate to burst your bubble, but the zener application for the lamps
will not avoid the use of the voltage-dropping resistor. The difference
between the car's operating voltage, i.e., about 13 volts, and the zener
voltage will have to be dropped across some device, i.e., a resistor, in the
circuit. In reality, the current through the zener diode itself will cause an
even greater amount of power to be dissipated by the dropping resistor. Sorry
about that.
As another poster already said, a readily available voltage regulator
chip is a better device to use than a zener for the regulated 10 volts.
Bud Krueger, OF
ROBERT G. HOWARD wrote:
> Hi Ross,
> Would your Zener Diode idea serve to replace that line voltage
> stabiliser that's supposed to ensure reliable and accurate reports by the
> fuel gauge?
> I ask, because the gauge reads about 3/8 tank low, the stabiliser is
> new, and the WS manual says to test for 10v, with special equipment.
> Would a Zener Diode provide a constant 10v?
> BTW, I estimated that the life of the 7.5v bulb would be about 1/10 of
> the rated-at-7.5v life of 1000 hrs. How does that compare to your
> calculations?
> Bob
>
> On Fri, 21 Nov 1997 19:14:49 -0800 Ross MacPherson
> <arm@unix.infoserve.net> writes:
> >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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