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'14V - 12V'
2000\03\15@004102 by Tony Nixon

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Hi all,

Does anyone know if it's possible to regulate a car battery supply
(usually 14V) to 12V. The video camera I am using expects a 12V 5%
supply, but I need to regulate the power to it from a car battery which
will be fully charged when used.

--
Best regards

Tony

http://www.picnpoke.com
spam_OUTsalesTakeThisOuTspampicnpoke.com

2000\03\15@005320 by Wagner Lipnharski

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Of course it is, you just need to know the camera current consume at
12V, so it will be easy to calculate the 12V regulator.  If you can
ensure the battery will be at least 13V (1V above the 12), then it is
easy to produce a transistor series regulator.  If the battery will stay
around 14V constantly, then probably 3 "robust current" diodes in series
will drop the voltage to the camera to aprox 12.1V... you just need to
know the camera current consume.

Wagner

Tony Nixon wrote:
{Quote hidden}

2000\03\15@005520 by McMeikan, Andrew

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you might want to look at my PSU page on http://www.opendesign.cx

       cya,    Andrew...

PS:I've even got some PIC stuff lurking if you hunt for it.

> {Original Message removed}

2000\03\15@013411 by ND Holmes

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<x-flowed>At 04:05 PM 3/15/2000 +1100, you wrote:
>Hi all,
>
>Does anyone know if it's possible to regulate a car battery supply
>(usually 14V) to 12V. The video camera I am using expects a 12V 5%
>supply, but I need to regulate the power to it from a car battery which
>will be fully charged when used.

My suggestion would be an LM2940-12 - I've been using one of these on a
vehicle-mounted camera for about two years now, and it continues to work
beautifully...  Nice low dropout (1V) allows you to get 12V cleanly from
the 13.6-14.5 that cars usually put out.

ND Holmes
--------------------------------------------------------------------------
 Nathan D. Holmes   maverickspamKILLspamdrgw.net, .....ndholmesKILLspamspam.....iastate.edu
   122 Shepard #3  Box 328  Gilbert, IA 50105  Iowa State University - EE
   http://www.drgw.net/~maverick   PH: 515-663-9368
   "Unless a man has creativity and self-motivation, freedom is an irksome
burden."
-------------------------------------------------------------------------

</x-flowed>

2000\03\22@101658 by Larry G. Nelson Sr.

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If you are just using the battery then no problem.  If the car is running
when you are using this it is another story entirely. The specs allow for
some surges that are very bad news. I bought a cheap inverter and get 110
VAC which I then feed to the standard wall supply brick. Works for
computers and saves expense of buying power supplies or the hassle of
building something.
If you really want to build something you want to block, swamp, and absorb
spikes and surges to protect your equipment. A 7812 will NOT reliably do
the job for you.


At 12:53 AM 3/15/00 -0500, you wrote:
{Quote hidden}

Larry G. Nelson Sr.
L.Nelsonspamspam_OUTieee.org
http://www.ultranet.com/~nr

2000\03\22@102309 by johnny

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So what kind of circuit WILL absorb spikes and other kind of noice in a
car-ish enviroment?
If you want to use a PIC design running at say 10MHz in a car, what kind of
protection do you want to add before (or after) your 7812 regulator?

/Johnny


"Larry G. Nelson Sr." wrote:

> If you are just using the battery then no problem.  If the car is running
> when you are using this it is another story entirely. The specs allow for
> some surges that are very bad news. I bought a cheap inverter and get 110
> VAC which I then feed to the standard wall supply brick. Works for
> computers and saves expense of buying power supplies or the hassle of
> building something.
> If you really want to build something you want to block, swamp, and absorb
> spikes and surges to protect your equipment. A 7812 will NOT reliably do
> the job for you.

<snip></snip>

2000\03\22@102522 by Chris Eddy

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If you want to really do it up, use a flyback transformer in a DC/DC
topology.  The flyback is one of the few solutions that will generate a fixed
output form values above and below the target at the input.  In addition, they
are inherently energy limitted in the case of a short circuit at the output.
Try surfing around at premier magnetics, at http://www.premiermag.com, and see what
might fit your wishes.  You might (cross fingers) get away without a custom
wind.

Chris Eddy

2000\03\22@104841 by Chris Eddy

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Just a stab at this, there are two well known tests that one must survive.  One
is the double up, where two batteries are attached in series.  In cold areas of
the country, tow truck apes are known to perform this feat of magic on
occasion.  The second is load dump, where the junk car has bad wiring, and the
wire from the laternator somehow becomes intermittent.  When the alternator
comes back on line, the regulator responds slowly, and you can get 60V for a few
seconds.

I would design a front end that can work with 30 to 35VDC (because a 7805 and
most switchers can survive that), and simply add a Polyswitch and a good TVS
diode in front.  Just because you kill the product momentarily at over 3x volts
doesn't mean you failed the survival test.  Use a 1.5KE rated diode, unipolar to
protect from reverse polarity too.

Don't forget to make it work at low (11.0V) levels too.

Chris Eddy

Johnny Lindholm wrote:

> So what kind of circuit WILL absorb spikes and other kind of noice in a
> car-ish enviroment?

2000\03\22@135453 by Mark Willis

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Hmmm.  IIRC, 78xx series regulators have a 3V or so Dropout voltage;
You cannot use one to regulate 14V to 12V.  (Also do want to watch the
upper voltage limit!)

If you put a carefully picked power resistor from car power, to a small
local (motorcycle or gel cell) battery, then regulate down off that with
an LM2941 or other fairly Low Dropout regulator, most any battery
problems become sort of irrelevant (Can anyone tell I have quite a few
gel cells here?  <G>)  A diode in series with that is a GOOD idea,
unless you cart the whole deal off when not using it (You don't want to
drain the small cell when starting the car.)

The small battery will charge on high car power system voltages, acting
like one heck of a power Zener diode, pick the series resistor to have a
1 volt drop or so at the desired load current into the camera.  (BGMicro
sells 4500mAh Gel Cells for $6.95, might have 17000mAh cells for the
same price still.)  Learn about Gel Cell charging first, of course, if
you use one <G>

For safety:  fuse the battery, close to the + terminal as you can manage
that - Under the 1/4" terminal if you can manage it.  Duct tape the lot
for safety, afterwards.  (Digikey sells polyswitches, made by RayChem,
86 cents or so, pp 536-537 in their current catalog.  I'm migrating to
those from regular fuses.)  If you expect to recharge that battery
harder than the fuse will like, parallel a power diode across the
polyswitch, it'll at least charge slowly then while the polyswitch is
open.  Maybe use a Schottky, due to lower voltage drop <G>)

If you want to get "fancy", a switcher is probably a "better" answer, so
long as you somehow handle the possibility of power supply disconnection
- that's why I tend to use a battery.  I've done some field research
where we drove around with 8 or so devices, all sucking power off the
12V accessory power socket.  We found the power connector'd fall part
way out quite regularly, thus the battery - AND, the electrical tape we
used to get it down to just falling out every few days, not daily <G>

Or, just use a "spare" small deep-cycle battery, recharge it as needed
etc.  So many "good", working answers...

 Mark

Larry G. Nelson Sr. wrote:
{Quote hidden}

--
I re-ship for small US & overseas businesses, world-wide.
(For private individuals at cost; ask.)

2000\03\22@154931 by paulb

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Mark Willis wrote:

> For safety:  fuse the battery, close to the + terminal as you can
> manage that - Under the 1/4" terminal if you can manage it.

 Of course, note that this fuse is between the battery and the source
circuit, while the output circuit, with or without another fuse,
connects separately and directly to the same battery terminal.
--
 Cheers,
       Paul B.

2000\03\22@172523 by Mark Willis

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Paul B. Webster VK2BZC wrote:
> Mark Willis wrote:
> > For safety:  fuse the battery, close to the + terminal as you can
> > manage that - Under the 1/4" terminal if you can manage it.
>
>   Of course, note that this fuse is between the battery and the source
> circuit, while the output circuit, with or without another fuse,
> connects separately and directly to the same battery terminal.
> --
>   Cheers,
>         Paul B.

They can be the same fuse, really - I did neglect to mention the fuse in
the Auto Plug-in connector, though with the existing fuses in the car's
fusebox and the diode & power resistor there as well, that fuse *is*
optional <G>

Power path is Car system - Diode - Resistor - Fuse terminal to battery,
possibly paralleled with a diode - Voltage Regulator to camera;  As most
everything runs off the car battery, the battery's just there to prevent
power dropouts (i.e. when you start the car or if the power connection
falls out of the socket), the battery sits there in "Float" charge
usually, not fast charge, due to the diode drop & resistor.

A second fuse is redundant, really, IMO (so far.)  Maybe you can
convince me, though?  <G>

The idea is to make sure this battery (which is around humans and thus
can have wrenches dropped on it, etc.) doesn't get shorted by accident,
causing burns or other problems.  If you put a fuse holder in line and
then take the fuse holder apart, or remove the fuse entirely, the parts
*can* short to something else or just direct connect to each other,
either causes "Spitzensparken" (in the second case, if something is
across the output leads, even when not plugged in to the car.)  If all
load current's handled by current from the car system, why a second
fuse?

Also, good idea to make a safe place to store the Auto Plug-In connector
when carrying this rig indoors after use, if you don't store the lot in
the car (we didn't, we dragged it inside & trickle charged it at
night.)  Yeah, the diode "should" protect it from shorting - but not
from being stepped on, which can happen.

 Mark

--
I re-ship for small US & overseas businesses, world-wide.
(For private individuals at cost; ask.)

2000\03\22@184518 by paulb

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Mark Willis wrote:

> A second fuse is redundant, really, IMO (so far.)  Maybe you can
> convince me, though?  <G>

 I thought the battery was there as a glorified Zener?  If the fuse or
Polyswitch opens because it happens to be subjected to a ridiculous
over-voltage (60V or 100V) and you have the regulator connected to the
source side of the fuse, does not the regulator and possibly your
circuit-to-be-protected begin to develop smoke enuresis ever-so-shortly
afterward?
--
 Cheers,
       Paul B.

2000\03\22@213506 by Mark Willis

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Paul B. Webster VK2BZC wrote:
> Mark Willis wrote:
> > A second fuse is redundant, really, IMO (so far.)  Maybe you can
> > convince me, though?  <G>
>
>   I thought the battery was there as a glorified Zener?  If the fuse or
> Polyswitch opens because it happens to be subjected to a ridiculous
> over-voltage (60V or 100V) and you have the regulator connected to the
> source side of the fuse, does not the regulator and possibly your
> circuit-to-be-protected begin to develop smoke enuresis ever-so-shortly
> afterward?
> --
>   Cheers,
>         Paul B.

"smoke enuresis"?  Wazzat?  =)

Aah.  I omitted my reasoning (or something) there I guess?!

I size that PolyFuse at the maximum capacity allowed for the battery -
say 7A, for a 4500mAh battery.

Most likely cause of it's opening when set up for a 1A digital camera,
let's look:

We size the series resistor for 1 ohm as that drops one amp / one volt,
so it's a say 2W resistor.  Make it 5W, for luck <G>

We use a 5 Amp or so diode, probably.  And thus size the fuse in the
auto power connector at 5A (can install a polyswitch there, maybe!)  If
we use one.  If not and we get a spike, what happens, though?

We start off with the small battery basically charged fully, and the
connections are Auto power - 5A fuse - wires with inductance and
resistance - blocking diode - far terminal of the battery polyswitch, a
7A unit (RGE700) - wires with inductance and resistance - regulator with
bypass capacitor.

Say we get a 100V spike on the car power bus;  the battery charges like
this, assuming that we have a half ohm of wire & joint resistance (in
practice, the auto power connector tends to be a little higher
resistance unless you buy a higher quality one <G>:

E = IR so (100V-14V-0.7V) = I (1.5) so I = about 56.866 A, for how long,
though?  The Polyswitch will take 100A maximum, and trips at somewhere
between 7A and 11.9A, *sustained* - it has a Rmin of 0.006 ohms.  If
tripped, it'll still let 7A through, max.  It has to melt, remember, to
trip - that phase change, takes TIME, and some energy.

Under those conditions, the Polyswitch will open in about 1/2 second
(give or take);  If you have 100V on a car power bus, for over 1/100
second or so, something is **WRONG**!  <G>  (Yep, we see quick tiny
spikes all the time, if those were Battery Killers, what's happening to
your car battery right now, as it's sitting there without any fuse?  <G>

Also, within less than a quarter second at 56.866A (or so), I'd expect
the auto power connector, the series diode, and the wires from the auto
connector to the small battery terminal, so do the "smoke enuresis"
thing <G>

Read http://circuitprotection.raychem.com/pdf/p17_28.pdf and
http://circuitprotection.raychem.com/pdf/p129_139.pdf, for good info <G>

 Mark

--
I re-ship for small US & overseas businesses, world-wide.
(For private individuals at cost; ask.)

2000\03\22@220337 by nkett

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-----Original Message-----
From:   Paul B. Webster VK2BZC [SMTP:RemoveMEpaulbTakeThisOuTspamMIDCOAST.COM.AU]
Sent:   Thursday, 23 March 2000 10:44
To:     spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU
Subject:        Re: 14V - 12V

Mark Willis wrote:

> A second fuse is redundant, really, IMO (so far.)  Maybe you can
> convince me, though?  <G>

>  I thought the battery was there as a glorified Zener?
Not in Aust where there is a common ground line. In Europe a mecca ground is used, somewhat better!

If the fuse or>
>Polyswitch opens because it happens to be subjected to a ridiculous
>over-voltage (60V or 100V)


??? since when do fuses and polyswitches go open on a highish voltage?


and you have the regulator connected to the
source side of the fuse, does not the regulator and possibly your
circuit-to-be-protected begin to develop smoke enuresis ever-so-shortly
afterward?

Connectus to sameus spotus and nous useus!

--
 Cheers,
       Paul B.


Dennis :)

2000\03\22@220954 by nkett

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-----Original Message-----
From:   Mark Willis [SMTP:TakeThisOuTmwillisEraseMEspamspam_OUTFOXINTERNET.NET]
Sent:   Thursday, 23 March 2000 13:33
To:     RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU
Subject:        Re: 14V - 12V

Paul B. Webster VK2BZC wrote:
{Quote hidden}

"smoke enuresis"?  Wazzat?  =)

Aah.  I omitted my reasoning (or something) there I guess?!

I size that PolyFuse at the maximum capacity allowed for the battery -
say 7A, for a 4500mAh battery.

Most likely cause of it's opening when set up for a 1A digital camera,
let's look:

We size the series resistor for 1 ohm as that drops one amp / one volt,
so it's a say 2W resistor.  Make it 5W, for luck <G>

We use a 5 Amp or so diode, probably.  And thus size the fuse in the
auto power connector at 5A (can install a polyswitch there, maybe!)  If
we use one.  If not and we get a spike, what happens, though?

We start off with the small battery basically charged fully, and the
connections are Auto power - 5A fuse - wires with inductance and
resistance - blocking diode - far terminal of the battery polyswitch, a
7A unit (RGE700) - wires with inductance and resistance - regulator with
bypass capacitor.

Say we get a 100V spike on the car power bus;  the battery charges like
this, assuming that we have a half ohm of wire & joint resistance (in
practice, the auto power connector tends to be a little higher
resistance unless you buy a higher quality one <G>:

                       No such beast exists, but one can argue that the quality is high, as it
meets the requirements!


E = IR so (100V-14V-0.7V) = I (1.5) so I = about 56.866 A, for how long,
though?  The Polyswitch will take 100A maximum, and trips at somewhere
between 7A and 11.9A, *sustained* - it has a Rmin of 0.006 ohms.  If
tripped, it'll still let 7A through, max.  It has to melt, remember, to
trip - that phase change, takes TIME, and some energy.

Under those conditions, the Polyswitch will open in about 1/2 second
(give or take)

Take quite alot and give quite alot, unless you use the pre tripped ones
this can vary all over  the place like a drunken sailor, infact if you know
what your doing these things can be convinced not to tirp until 4 to 5x the
ratted current!

;  If you have 100V on a car power bus, for over 1/100
second or so, something is **WRONG**!  <G>

No not at all! This is to be expected! See the Ford and GM spect ETITM 92
for this one! 60V wave fronts and 80V too!


 (Yep, we see quick tiny
spikes all the time, if those were Battery Killers, what's happening to
your car battery right now, as it's sitting there without any fuse?  <G>

Also, within less than a quarter second at 56.866A (or so), I'd expect
the auto power connector, the series diode, and the wires from the auto
connector to the small battery terminal, so do the "smoke enuresis"
thing <G>

Only id you use hair for your connections!


Read http://circuitprotection.raychem.com/pdf/p17_28.pdf and
http://circuitprotection.raychem.com/pdf/p129_139.pdf, for good info <G>

 Mark

--
I re-ship for small US & overseas businesses, world-wide.
(For private individuals at cost; ask.)




Dennis

2000\03\23@012712 by Graeme Zimmer

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> Just a stab at this, there are two well known tests that one must survive.
One
> is the double up, where two batteries are attached in series.

> The second is load dump..........and you can get 60V for a few
> seconds.

Also short spikes to (say) 200 Volts..

And also reverse 12 Volt for indefinite period.

.................... Zim

2000\03\23@013957 by nkett

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-----Original Message-----
From:   Graeme Zimmer [SMTP:gzimmerEraseMEspam.....BIGPOND.COM]
Sent:   Thursday, 23 March 2000 17:27
To:     EraseMEPICLISTspamMITVMA.MIT.EDU
Subject:        Re: 14V - 12V

> Just a stab at this, there are two well known tests that one must
survive.
One
> is the double up, where two batteries are attached in series.

> The second is load dump..........and you can get 60V for a few
> seconds.

Also short spikes to (say) 200 Volts..

And also reverse 12 Volt for indefinite period.

.................... Zim

Now my bit on reverse,
and on any connection to tbe body harness and any point where your item
internconnects to other modules (there are some exceptions but not many).
And get this, it is perferable that no fust is blown and the item MUST
function to specification after the removal


Dennis

2000\03\23@024636 by Mark Willis

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Dennis Plunkett wrote:
{Quote hidden}

A blocking diode handles reverse connection quite well;  Adding a TVS
(1.5KE20 or so) across the power leads after the resistor or at the
battery terminals, or so, would do good things when over-voltages hit.
Those are a whopping 44 cents apiece in onesies <VBG>

 Mark

--
I re-ship for small US & overseas businesses, world-wide.
(For private individuals at cost; ask.)

2000\03\23@155423 by nkett

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Oh boy,


Dennis Plunkett wrote:
{Quote hidden}

A blocking diode handles reverse connection quite well;  Adding a TVS
(1.5KE20 or so) across the power leads after the resistor or at the
battery terminals, or so, would do good things when over-voltages hit.
Those are a whopping 44 cents apiece in onesies <VBG>


A blocking diode hey, well that may be ok but try to find one that will
handle 40Amps or so, also when you start to look at the numberos in the
100k+ area a cost of a diode is EXPENSIVE.
On the other side we have the droput problem in that a controller in a car
"must" operate down to 9V without fail, and then also resume operation if
the voltage falls below  3V (Cranking) after  the voltage returns to above
9V

The TVS is interesting in that a 30V TVS will allow a wavefront of 59V to
enter the device, this is often over the 40V limit that most semiconductors
operate at (Can not use a 24V as this is a doubled battery limit), so one
could say that these devices are almost useless in this environment. The
idea is not to clamp the voltage as this will ring the cct (I*R type stuff
and generaly highish ohmic distrobution), also hitting this device will
cause a current clamp (Possibly a fuse to blow, this is not a good option)
and then you may fail emmissions at the high frequency end.

Gess life is not easy in the automotive market!

Dennis


 Mark

--
I re-ship for small US & overseas businesses, world-wide.
(For private individuals at cost; ask.)

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