Your right, and that maintained a constant voltage to the load over a range
of input voltages and load currents. However a series zener with a
relatively constant supply voltage (14.3v when running, remember, not 12v)
and a relatively fixed load (n * lamps) will still give a relatively fixed
voltage across the load e.g. 14.3 - 5.1 = 9.2.
Auto bulbs may well be labelled '12v' but they are in fact rated at 14v.
Which is why non-auto 12v bulbs give a brighter light than auto 12v bulbs,
but they will also suffer from a shortened life, greatly shortened as users
of 7.5v non-auto lamps have found, and also draw double the current of a set
of auto bulbs shortening the life of the, very expensive, rheostat.
I can't really see the point of putting lower voltage, same wattage lamp in
and then having to drop the voltage. For a similar technology bulb isn't
the end result the same? Can't speak for halogen instrument lamps as
Halford's don't seem to stock them. But if the theory is that that give
more light and less heat for the same electrical power then they really
should be an improvement.
Beats me why anyone should need to read the numbers anyway. They're
analogue instruments, can't you tell what's happening by the angle of the
needle? Do you all have watches with numbers round the outside so you can
tell what time it is?
But then, I'm just an old fart who bought two new rheostats for his two cars
and has never had them off max. I'd also need a set of arc lamps to be able
to focus on the figures at night anyway.
PaulH.
-----Original Message-----
From: Arnold Molloy <a.j.molloy@worldnet.att.net>
To: Tim Economu <economu@whidbey.com>
Cc: MG List <mgs@autox.team.net>; mgbob@juno.com <mgbob@juno.com>
Date: 09 November 1999 02:02
Subject: Re: Halogen dash lights
>Tim;
>Maybe modern electronics is similar to modern math????? But back in the
50's
>when I went to school a series resistor was used to drop the excess
voltage,
>(5-6V) and the zener (in this case 7.5V) was placed across the load
(parallel)
>to determine the voltage applied. IMHO
>
>Arnie Molloy 53 TD
>
>
>Tim Economu wrote:
>
>> Dear Bob, Jay, et al:
>>
>> If you want to use your 7.5V bulbs and have them last a long life, just
add
>> a 5.1V zener diode in series with the bulb to drop the other few volts.
The
>> bulbs will last the normal 2000 operating hours (their rating) and you
will
>> still get a nice bright bulb. The zener can also be purchased at Radio
>> Schlock (misspelling on purpose!) and will be soldered into the circuit
with
>> the band end (cathode) toward the plus side of the battery on neg ground
>> systems.
>>
>> But really, isn't the dim instrument good for all of us? And some LBC's
have
>> REOSTATS!! Wow modern technology!!
>>
>> Kind regards,
>>
>> Tim Economu
>> '69 BGT mona
>> email: economu@whidbey.com
>>
>> > It was previously said....
>>
>> Date: Sun, 7 Nov 1999 17:34:24 -0500
>> From: Bob Howard <mgbob@juno.com>
>> Subject: Re: Halogen dash lights
>>
>> Jay,
>> I was one of the guys who contributed to the Radio Shack bulb
>> correspondence.
>> Experimentation with the 7.5 volt bulb (#50) demonstrated great
>> illumination, so bright that the rheostat could be turned down almost to
>> the miniumum
>
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