On Sat, 02 Feb 2008 08:14:06 -0600, "Pete C."
wrote:

Don Foreman wrote:

On Fri, 01 Feb 2008 20:37:00 -0600, "Martin H. Eastburn"
wrote:

Why not a voltage regulator or better yet - a 12V DC to 6V DC switcher.
There are lots of power supplies like this about the size of a hand
or less.

Martin

Might be a radio noise issue with an AM radio. Some of the "simple
switcher" chips are very easy to use, though. I've built little
switchers by epoxying parts on the back of a wallwart -- no circuit
board at all, just haywire things and then glop 'em good.

AM radio???

Certainly a switching supply would be more efficient than a linear.

It would. Don't know if it matters here or not. It's easy to sink a
few watts in a car.

On Sat, 02 Feb 2008 03:52:18 -0600, Don Foreman
wrote:

On Sat, 02 Feb 2008 01:09:12 -0500, clare at snyder.on.ca wrote:

On Fri, 01 Feb 2008 15:32:02 -0700, Lew Hartswick
wrote:

clare at snyder.on.ca wrote:
A zener does not make a good series regulator Lew.

And why not? It's a perfectly good constant voltage drop
over its operating range. I've use them that way over
the 20+ yrs I've been in the business.
...lew...

Because a Zener only STARTS to conduct above a certain voltage. Zener
regulators are GENERALLY shunt regulators. The load is in series with
a low value, high power resistor, and the zener goes across the load
in such a manner as to short excess voltage to ground, causing the
voltage drop across the resistance to absorb/regulate to the zener
resistance.
Diodes in SERIES are generally used for minor voltage adjustment (not
regulation) with the forward drop of various diodes generally running
in the 0.64 volt range for silicon diodes, Schottky diodes drop
significantly less, Germanium diodes significantly more.

See: http://www.kpsec.freeuk.com/components/diode.htm if you don't
want to take my word for it.

By the way, what business are you in?
25+ in the automotive, and almost as long now in computer electronics.

I'll bet you're very good with autos and computers -- but don't quit
your day job to design power elex!

A Zener would indeed provide a fairly constant drop and they are
sometimes used that way. This wouldn't be a regulator, just a drop
that is fairly constant over a reasonable range of load currents. The
output would not be regulated, but it would be reduced by a fairly
constant amount.


I said exactly the same thing, did I not? Forward drop across a
junction is NOT a regulator.
Then again, nor is a series resistor, which has been used in many
applications over the years to run 6 volt radios, instruments, etc on
12 volt cars. The resistors needed to be the right value for the job
at hand or the voltage would be too high or too low.


I've done design work too. I designed and sold several lines of
equipment for towing 12 volt trailers with 24 volt tow vehicles (in
particular Toyota BJ Cruisers) including units to adapt 12 volt
trailer brakes, using 12 volt Tekonsha brake controllers, on the 24
volt cruiser.
Also built and drove an electric powered Fiat128, with a single
contactor solid state series parallel switching mechanism of my own
design.

I DO understand the issue at hand. Very well.
I have also installed MANY 7805/LM350 replacement instrument
regulators. I like the LM350 best - I used a small trim pot mounted
directly on the terminals of the chip as a voltage devider to set the
output voltage calibration and locked it in place with Hot Glue. The
T03 case unit was mthe one I used most, fastened to a 5 square inch
aluminum heat sink, which was screwed to the back of the instrument
panel mounting brackets (steel)
Never had one fail.
These were installed to eliminate noise in radio equipment caused by
the original equipment thermal/electric instrument regulators used in
the seventies and eighties.

I still have the prototype of that unit floating around my office
somewhere.

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On Sat, 02 Feb 2008 08:12:36 -0600, "Pete C."
wrote:

clare, at, snyder.on.ca wrote:

On Fri, 1 Feb 2008 16:20:55 -0800, "William Noble"
wrote:

consider a 7805 regulator

this will give you nice stable 5VDC at up to 3 amps

With a REAL GOOD heat sink. The common 7805 is considered a ONE AMP
device. Some 7805P devices are rated at 1.5 amps.. This is with
nominal heat sinking. Bare they are a 500ma device. 3 amps is
definitely running the "ragged edge"
A Linear Technologies LT323 is a 3 amp unit.



An LT1003 is a 5 amp unit. It is obsolete.

An obsolete regulator would be appropriate for an obsolete car, no?
Would work just fine if you could find a source!

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On Sat, 02 Feb 2008 08:14:06 -0600, "Pete C."
wrote:

Don Foreman wrote:

On Fri, 01 Feb 2008 20:37:00 -0600, "Martin H. Eastburn"
wrote:

Why not a voltage regulator or better yet - a 12V DC to 6V DC switcher.
There are lots of power supplies like this about the size of a hand
or less.

Martin

Might be a radio noise issue with an AM radio. Some of the "simple
switcher" chips are very easy to use, though. I've built little
switchers by epoxying parts on the back of a wallwart -- no circuit
board at all, just haywire things and then glop 'em good.

AM radio???

Certainly a switching supply would be more efficient than a linear.
Who's worrying about efficiency? We are talking dissipation of
something like 3 watts maximum using a resister, and something less
than that with a linear IC.
POWER efficiency might be better with a switcher, but by the time you
adress the RF implications your total cost/benefit ratio would kinda
outweigh the benefits.


To stay with the "era" of the car, he can go to NAPA and order a
VT6188 or VT6187 Voltage reducer. It is a 1.5 ohm resistor for use on
a 4 amp maximum load. The 6188 is a 6187 with a mounting bracket.

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On Sat, 02 Feb 2008 15:12:48 -0500, clare at snyder.on.ca wrote:

On Sat, 02 Feb 2008 03:52:18 -0600, Don Foreman
wrote:

On Sat, 02 Feb 2008 01:09:12 -0500, clare at snyder.on.ca wrote:

On Fri, 01 Feb 2008 15:32:02 -0700, Lew Hartswick
wrote:

clare at snyder.on.ca wrote:
A zener does not make a good series regulator Lew.

And why not? It's a perfectly good constant voltage drop
over its operating range. I've use them that way over
the 20+ yrs I've been in the business.
...lew...

Because a Zener only STARTS to conduct above a certain voltage. Zener
regulators are GENERALLY shunt regulators. The load is in series with
a low value, high power resistor, and the zener goes across the load
in such a manner as to short excess voltage to ground, causing the
voltage drop across the resistance to absorb/regulate to the zener
resistance.
Diodes in SERIES are generally used for minor voltage adjustment (not
regulation) with the forward drop of various diodes generally running
in the 0.64 volt range for silicon diodes, Schottky diodes drop
significantly less, Germanium diodes significantly more.

See: http://www.kpsec.freeuk.com/components/diode.htm if you don't
want to take my word for it.

By the way, what business are you in?
25+ in the automotive, and almost as long now in computer electronics.

I'll bet you're very good with autos and computers -- but don't quit
your day job to design power elex!

A Zener would indeed provide a fairly constant drop and they are
sometimes used that way. This wouldn't be a regulator, just a drop
that is fairly constant over a reasonable range of load currents. The
output would not be regulated, but it would be reduced by a fairly
constant amount.


I said exactly the same thing, did I not? Forward drop across a
junction is NOT a regulator.

You did say that. A zener has about the same fwd drop as any other
silicon diode, but breaks down at zener voltage in the reverse
direction. So, it can provide a fairly constant drop of Vz (could be
6 volts) if used that way. Power zeners are made, but not nearly as
readily available as 400 mW and 1W units. The reason may be because
it is very easy to "fake" a "power" zener using a small zener and a
power NPN transistor. Zener goes from collector to base. The collector
becomes the cathode (K), emitter becomes the anode.

Fwd junction drop in germaninum is less, not more, than silicon
including Schottky.

On 2008-02-02, Don Foreman wrote:
On Sat, 02 Feb 2008 01:09:12 -0500, clare at snyder.on.ca wrote:

Because a Zener only STARTS to conduct above a certain voltage. Zener
regulators are GENERALLY shunt regulators. The load is in series with
a low value, high power resistor, and the zener goes across the load
in such a manner as to short excess voltage to ground, causing the
voltage drop across the resistance to absorb/regulate to the zener
resistance.
Diodes in SERIES are generally used for minor voltage adjustment (not
regulation) with the forward drop of various diodes generally running
in the 0.64 volt range for silicon diodes, Schottky diodes drop
significantly less, Germanium diodes significantly more.

Actually -- germanium diodes significantly *less* -- as is
supported by the site which you point out below. Germanium diodes at
about 200 mV forward drop, Silicon diodes at about 700 mV forward drop.
(Actually, I had remembered germanium as being closer to 150 mV, but
haven't checked one in years.

See: http://www.kpsec.freeuk.com/components/diode.htm if you don't
want to take my word for it.

By the way, what business are you in?
25+ in the automotive, and almost as long now in computer electronics.

[ ... ]

A Zener would indeed provide a fairly constant drop and they are
sometimes used that way. This wouldn't be a regulator, just a drop
that is fairly constant over a reasonable range of load currents. The
output would not be regulated, but it would be reduced by a fairly
constant amount.

The problem here is that a 12V automotive system goes through a
wider voltage swing than a 6V one does, and if you are using a zener in
series, (assuming that the load draws enough to get past the knee of the
zener's curve) you will wind up with more voltage swing at the 6V load,
by subtracting something approaching a constant from the 12-14V swing of
the charging system and battery.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Sat, 02 Feb 2008 15:21:28 -0500, clare at snyder.on.ca wrote:

snip


POWER efficiency might be better with a switcher, but by the time you
adress the RF implications your total cost/benefit ratio would kinda
outweigh the benefits.



Surely that will be a small effect compared with the noise from the ignition
and the noise from the vibrator for the HT supply for the radio?



BG)



Mark Rand
RTFM

On Sat, 02 Feb 2008 17:42:35 -0600, Don Foreman
wrote:

On Sat, 02 Feb 2008 15:12:48 -0500, clare at snyder.on.ca wrote:

On Sat, 02 Feb 2008 03:52:18 -0600, Don Foreman
wrote:

On Sat, 02 Feb 2008 01:09:12 -0500, clare at snyder.on.ca wrote:

On Fri, 01 Feb 2008 15:32:02 -0700, Lew Hartswick
wrote:

clare at snyder.on.ca wrote:
A zener does not make a good series regulator Lew.

And why not? It's a perfectly good constant voltage drop
over its operating range. I've use them that way over
the 20+ yrs I've been in the business.
...lew...

Because a Zener only STARTS to conduct above a certain voltage. Zener
regulators are GENERALLY shunt regulators. The load is in series with
a low value, high power resistor, and the zener goes across the load
in such a manner as to short excess voltage to ground, causing the
voltage drop across the resistance to absorb/regulate to the zener
resistance.
Diodes in SERIES are generally used for minor voltage adjustment (not
regulation) with the forward drop of various diodes generally running
in the 0.64 volt range for silicon diodes, Schottky diodes drop
significantly less, Germanium diodes significantly more.

See: http://www.kpsec.freeuk.com/components/diode.htm if you don't
want to take my word for it.

By the way, what business are you in?
25+ in the automotive, and almost as long now in computer electronics.

I'll bet you're very good with autos and computers -- but don't quit
your day job to design power elex!

A Zener would indeed provide a fairly constant drop and they are
sometimes used that way. This wouldn't be a regulator, just a drop
that is fairly constant over a reasonable range of load currents. The
output would not be regulated, but it would be reduced by a fairly
constant amount.


I said exactly the same thing, did I not? Forward drop across a
junction is NOT a regulator.

You did say that. A zener has about the same fwd drop as any other
silicon diode, but breaks down at zener voltage in the reverse
direction. So, it can provide a fairly constant drop of Vz (could be
6 volts) if used that way. Power zeners are made, but not nearly as
readily available as 400 mW and 1W units. The reason may be because
it is very easy to "fake" a "power" zener using a small zener and a
power NPN transistor. Zener goes from collector to base. The collector
becomes the cathode (K), emitter becomes the anode.

Fwd junction drop in germaninum is less, not more, than silicon
including Schottky.

You are correct - Germanium is about .3 volts. Gallium Arsenide is
about 3.5 Schottky are generally figured as .2 to .3 volt.
Selenium stacks are much higher, and increase with age.
It's been a while since I worked with anything with germanium
transistors - but the lower forward drop makes germanium diodes
superior to silicon diodes af RD detectors (think crystal radios)

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On Sun, 03 Feb 2008 01:16:15 +0000, Mark Rand
wrote:

On Sat, 02 Feb 2008 15:21:28 -0500, clare at snyder.on.ca wrote:

snip


POWER efficiency might be better with a switcher, but by the time you
adress the RF implications your total cost/benefit ratio would kinda
outweigh the benefits.



Surely that will be a small effect compared with the noise from the ignition
and the noise from the vibrator for the HT supply for the radio?



BG)



Mark Rand
RTFM
Not necessarily. The vibrator supply is well filtered and so is the
ignition. And on the vehicles where I was using the regulators the
radios were not vibrator units (they were solid state 12 volt units)
and with proper snubber caps on the coil and good RF Suppression plug
wires, the instrument regulators were the only thing causing problems.
Except for the odd vehicle where we had to put suppression caps across
blower moors and wiper motors.

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