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PICList Thread
'Car battery power help'
1999\11\04@124318 by Mike M

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i need to connect a pic to my car, using the 12v car battery...umm i assume i ca
n't just wire up the car battery to like a 7805 to control the voltage..or maybe
im wrong...Suggestions?

mikE

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1999\11\04@125119 by Harrison Cooper

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They have a 14V version of one the pics....assume it runs down to 12V as
well.  And, yes, you *can* just use a 7805, but beware of spikes,
noise...etc.  And heat dissipation.  The voltage drop happens someplace and
transfers to heat...

This has had allot of discussion in the past years....someone must have kept
an archive?  Rather than rehash the subject, perhaps someone can just
forward the archive to Mike?

1999\11\04@130815 by Thomas C. Sefranek

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Mike M wrote:

> i need to connect a pic to my car, using the 12v car battery...umm i assume i
can't just wire up the car battery to like a 7805 to control the voltage..or may
be im wrong...Suggestions?
>
> mikE
>
> Send someone a cool Dynamitemail flashcard greeting!! And get rewarded.
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Why do you assume you can't?

I do this all day.  (78L05)
WITH filter caps!

--
Thomas C. Sefranek  WA1RHP
ARRL Instructor, Technical Specialist, VE Contact.
http://www.harvardrepeater.org
http://hamradio.cmcorp.com/inventory/Inventory.html

1999\11\04@134340 by Dave VanHorn

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> > i need to connect a pic to my car, using the 12v car battery...umm i
assume i can't just wire up the car battery to like a 7805 to control the
voltage..or maybe im wrong...Suggestions?


It works for hobby projects.
Add a series fuse before the reg, and a 15V or maybe 18V zener across power
in front of the reg.
This protects you from overvoltage surges, and reverse voltage transients.
If you have more than about 100uF on the 05 output, then add a diode from
input to output on the 05, such that it's normally reverse biased.  Taking
the 78XX or 340-XX reg inputs to ground suddenly (like during an alternator
spike) can kill the reg otherwise. They aren't designed to withstand any
voltage on the output larger than the input.

The auto industry has standards for such things, but this is a practical
minimum.
Don't forget the input and output caps on that 7805 or you may end up with
an AM broadcast station for free!

1999\11\04@135158 by bill

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> i need to connect a pic to my car, using the 12v car battery...umm i
> assume i can't just wire up the car battery to like a 7805 to control the
> voltage..or maybe im wrong...Suggestions?

Linear regulators work fine for automotive use.  Just keep in mind that the
regulator will be dissipating more power than the circuit itself in this
configuration.  There will be 5V accross your circuit, but 7 to 9 volts accross
the regulator with the same current all the way through.  Also, if you want
your device to be really reliable in automotive use, you should design it so
that it can survive supply voltage up to about 20V (not normal, but it can
happen when the car's electrical system is malfunctioning), and down to
about 8V (cranking with very cold or low battery).  Automotive electrical
power is noisy, but it's not too hard to deal with unless your application has
some sensitive analog circuitry.  I typically use a 220uF electrolytic cap on
the input side of the regulator, and a 1000uF electrolytic in parallel with a
0.1uF ceramic on the output side.  Works great for powering PIC's.


---
                                       Peace,
                                       William Kitchen
                                       spam_OUTbillTakeThisOuTspamiglobal.net

The future is ours to create.

1999\11\04@162813 by Dennis Plunkett

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At 13:41 4/11/99 -0500, you wrote:
{Quote hidden}

Delving back into my memory (Most brain cells past on quite a few years
ago). But the Automotive environment is not a nice place to be. A simple
7805 will die in this situation! National Semiconductor had a great app
note no this, as you will find, not all voltages in a car a positive with
respect to ground, and you will find some nasty spikes up to 60V, and then
there is the cranking current voltage drop (GM require operation down to
3V), and the air conditioner etc.
I suggest that you use one of the automotive 5V regs, as it will survive.
There is automotive parts manufacturer that make cruise controllers that
had 7805 in them, many have failed within 5 years of operation.

Dennis

1999\11\04@163649 by King, Jonathan

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Try the LM2931, it is a low dropout regulator specifically designed for the
automotive environment.  It has lots of protection features built in.

{Quote hidden}

1999\11\04@171115 by Tony Nixon
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Mike M wrote:
>
> i need to connect a pic to my car, using the 12v car battery...umm i assume i
can't just wire up the car battery to like a 7805 to control the voltage..or may
be im wrong...Suggestions?
>
> mikE
>
> Send someone a cool Dynamitemail flashcard greeting!! And get rewarded.
> GO AHEAD! http://cards.dynamitemail.com/index.php3?rid=fc-41

Check out http://www.picnpoke.com/projects/ignition.html

1000's of these have been working for years now, so I guess it works ok.

--
Best regards

Tony

http://www.picnpoke.com
Email .....salesKILLspamspam@spam@picnpoke.com

1999\11\04@172744 by Dave VanHorn

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> Delving back into my memory (Most brain cells past on quite a few years
> ago). But the Automotive environment is not a nice place to be. A simple
> 7805 will die in this situation! National Semiconductor had a great app
> note no this, as you will find, not all voltages in a car a positive with
> respect to ground, and you will find some nasty spikes up to 60V, and then
> there is the cranking current voltage drop (GM require operation down to
> 3V), and the air conditioner etc

That's what the zener is for. Nails the negatives by going into forward
conduction, and the reverse by zenering. The fuse prevents any huge currents
from flowing. As long as you add the diode across the 05, there really isn't
any other way to kill them.

That dosen't mean your project will WORK while cranking at 140F or -20F, but
it won't get nuked.

1999\11\04@175109 by Dennis Plunkett

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At 17:26 4/11/99 -0500, you wrote:
>> Delving back into my memory (Most brain cells past on quite a few years
>> ago). But the Automotive environment is not a nice place to be. A simple
>> 7805 will die in this situation! National Semiconductor had a great app
>> note no this, as you will find, not all voltages in a car a positive with
>> respect to ground, and you will find some nasty spikes up to 60V, and then
>> there is the cranking current voltage drop (GM require operation down to
>> 3V), and the air conditioner etc
>
>That's what the zener is for. Nails the negatives by going into forward
>conduction, and the reverse by zenering. The fuse prevents any huge currents
>from flowing. As long as you add the diode across the 05, there really isn't
>any other way to kill them.
>
>That dosen't mean your project will WORK while cranking at 140F or -20F, but
>it won't get nuked.
>
>


Zeners can be too slow in this case. The fuse is not much use, as it will
alow large current dumps to occur before it blows. Now here is a good one
when it blows:-

V=IR correct?

Assume that V is near 0.6V for conduction purpose
Assume that I is 3 amps
Assume that R is .1 ohms

OK ,so the fuse now blows, and we have infinete R as the fuse is open
circuit! Inductance of wiring stored the enery now needs to dump it, and
into an effective open circuit!
But we has current and a voltage present in this circuit:-
Thus now the voltage will ramp up as the amount of energy flowing at that
point in time causes a large V to be produced (Before the fuse went, and
just after the fuse goes) ,and if the wiring is inductive the spike will be
longer.
I can go into the calculations if you need, but don't wish to

Anyway, the amount of energy in this spike when the fuse blow is often more
than enough to crap all over your nice little ciccuit, and that zener? Now
is just an interesting talking point of "What was that component supposed
to do?" Oh yeh I remember, protect the regualtor that is now craped out.

Making the elctronics world safer by removing zeners. Use a trisil instead,
Tests have not been able to detect the wavefront rise time for these devices.

Dennis

1999\11\04@180945 by Dave VanHorn

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>
> Zeners can be too slow in this case. The fuse is not much use, as it will
> alow large current dumps to occur before it blows. Now here is a good one
> when it blows:-

The fuse is for when the zener has been conducting for a while, and is
intended to limit long-duration events, so that nothing gets permanently
smoked. This basic approach is used in lots of aftermarket equipment, and
works fairly well. I learned it at our contract manufacturer's where they
designed and produced a major aftermarket productline for cars, and quite a
few OEM devices.

I'm talking about a device in a car here, on the end of a few uH of wire,
with an alternator and some large motors and relays as spike sources.  Not a
nS risetime impairment generator..

In any case, SAE has all the notes to do it right. I was suggesting a tested
approach that's somewhere between a bare '05 and a full-bore automotive
industry design.

Also, I can buy the '05, and diodes at any radio-shack.

1999\11\04@182857 by goflo

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I'll bite. What's a "trisil"?

Jack

Dennis Plunkett wrote:
> ...
> Making the elctronics world safer by removing zeners. Use a trisil instead,
> Tests have not been able to detect the wavefront rise time for these devices.
>
> Dennis

1999\11\04@182901 by Russell McMahon

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Mike,

As others have noted, you CAN use standard regulators for this.

HOWEVER,

if this is an automotive environment you are liable to meet noise and other
strange transient conditions (fat noise :-)) which may disrupt circuit
operation or even cause damage. People make regulators especially designed
for use in automotive environments. One such is the National LM2931 series.
There are other brands equally good. The Natsemi parts come in various
packages (TO220, TO92, SMD). Use of such a regulator is well worth
considering. You still have to follow design guidelines (see data sheets)
when using them.



     Russell McMahon
_____________________________

>From another world - http://www.easttimor.com

What can one man* do?
Help the hungry at no cost to yourself!
at  http://www.thehungersite.com/

(* - or woman, child or internet enabled intelligent entity :-))

From: Mike M <elektrikmanspamKILLspamDYNAMITEMAIL.COM>
Date: Friday, 5 November 1999 06:43
Subject: Car battery power help


>i need to connect a pic to my car, using the 12v car battery...umm i assume
i can't just wire up the car battery to like a 7805 to control the
voltage..or maybe im wrong...Suggestions?

1999\11\04@183728 by Mike M

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Well its a simple alarm circuit, once the car is started or anything in the car
activated other then door locks opening and closing it is ASSUMED that the lock
has been disabled.  So i would think that im pretty safe as far as a clean signa
l screwing up the function of the system.  Unless it will damage the chip or reg
ulator?? u think??

As far as the 7805 for some reason i cant get over the idea of currrent.  If any
ones going to reply to this to the group i think i would suggest changing the SU
BJECT line...Tell me if this is correct...It doesnt matter how much current your
batter or what not can supply...it matters how much you are drawing out of it (
?)

MikE

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1999\11\04@190324 by Wagner Lipnharski

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There is no magic, the current your PIC will consume at 5V will come
from the 12V Battery, so the 78?05 will drain *the PIC current* from the
battery, as 12V, and will deliver it as 5V to the PIC. It means that the
78?05 will be wasting 140% of what the PIC will consume, and a little
bit more for the 78?05 internal functions. This solution efficience is
5/12 = around 41%.

To reduce this problem, you have few possibilities;
a) Use of a DC-DC conversion based on capacitors (charge pump
converters).
b) Use of a DC-DC conversion based on coiled step down.

Both systems can be built using a single chip, DIP 8 or SOIC 8, and will
cost you around $5 including the coil or the capacitors.  The coiled
(step-down) is more efficient than the capacitive version (charge pump),
it can goes up to 90% of efficience, it means that if the PIC power
consume is 5Vdc @ 5mA (25mW), the whole conversion system will consume
less than 28mW from the battery, or around 2.5mA!!!

The charge pump solution (capacitors) works pretty well for low
currents, but have not a linear efficience curve along with output
voltage or current.

I use both solutions in my circuits. Each time I take few factors in
considerations to choose one or another.  Normaly I do bench test for
both circuits. Theory here is merely a guidance...

Wagner

Mike M wrote:
>
> Well its a simple alarm circuit, once the car is started or anything in the ca
r activated other then door locks opening and closing it is ASSUMED that the loc
k has been disabled.  So i would think that im pretty safe as far as a clean sig
nal screwing up the function of the system.  Unless it will damage the chip or r
egulator?? u think??
>
> As far as the 7805 for some reason i cant get over the idea of currrent.  If a
nyones going to reply to this to the group i think i would suggest changing the
SUBJECT line...Tell me if this is correct...It doesnt matter how much current yo
ur batter or what not can supply...it matters how much you are drawing out of it
(?)
>
> MikE

1999\11\04@192218 by Brent Brown

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Mike,

I use a regular 7805 in a 12 or 24V automotive environment.  My
design has a 1N4007 series diode, 10ohm 1W series resistor, 33V
1.3W zener to ground, and 1000uF 35V cap to ground on the input
side of the regulator. Adding the resistor here is the key to getting
the most from a simple design:-

1) The resistor limits the peak currents into your zener (during
spikes) helping it do its job and ensuring that it doesn't snuff it on
the first spike.

2) The resistor and capacitor make a low pass filter that helps
reduce noise into (and out of) your circuit.

3) Zeners are a little slow perhaps? - then the low pass filter helps
here too.

I suggest using a 16V zener for a 12V only application. I also noted
that most 7805's have a 35V absolute maximum input voltage
rating, but better than some other regs that have been suggested.

My circuit draws about 40-50mA which makes the regulator get
warm on a 24V supply so I have a small heatsink on it.

The 1N4007 diode in series with the input prevents damage from
reverse supply connection. It also stops the 1000uF cap from
discharging if the supply voltage falls (eg. engine cranking), so if
your circuit doesn't draw too much you have a short term UPS!

Hope these ideas are interesting,

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile: 025 334 069
eMail:  brent.brownspamspam_OUTclear.net.nz

1999\11\04@193047 by Tony Nixon

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Brent Brown wrote:

> The 1N4007 diode in series with the input prevents damage from
> reverse supply connection. It also stops the 1000uF cap from
> discharging if the supply voltage falls (eg. engine cranking), so if
> your circuit doesn't draw too much you have a short term UPS!

A little gotcha with this idea.

Make sure you have some sort of brownout detect on the PIC or some weird
things may crop up.

--
Best regards

Tony

http://www.picnpoke.com
Email @spam@salesKILLspamspampicnpoke.com

1999\11\04@195004 by Mike M

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>
>A little gotcha with this idea.
>
>Make sure you have some sort of brownout detect on the PIC or some weird
>things may crop up.


weird things?? such as?

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1999\11\04@200250 by l.allen

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>
> >
> >A little gotcha with this idea.
> >
> >Make sure you have some sort of brownout detect on the PIC or some weird
> >things may crop up.
>
>
> weird things?? such as?
>

The programme will "go off into the weeds".
That is...
Random data is inserted at inconvenient times and a general
malfunction results, a watch-dog reset MIGHT save the application but
I wouldn't count on it.
Another potentially nasty result is a driven device like a mosfet
might only partially turn its channel on will insufficient gate
voltage and excessive heat might be generated in the channel.
I lost 12 P channel power mosfets this way a while ago.
Brown-outs are bad.
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

1999\11\04@200857 by Tony Nixon

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Mike M wrote:
>
> >
> >A little gotcha with this idea.
> >
> >Make sure you have some sort of brownout detect on the PIC or some weird
> >things may crop up.
>
> weird things?? such as?
>
> Send someone a cool Dynamitemail flashcard greeting!! And get rewarded.
> GO AHEAD! http://cards.dynamitemail.com/index.php3?rid=fc-41

Who knows. Hence the word 'wierd'. Put a PIC in a circuit without a
brownout circuit and turn the supply down. Wierd things may start
happening or they may not. The PIC may lock up or maybe it won't. etc
etc.

The point is, you don't want to risk the PIC losing control.

At one time the segments on the led display on my Ignition controller
started rotating in a circle and then it stopped. That's pretty wierd
considering the display is fed by a serial to parallel decoder. It's
amazing the PIC sent out the signals to do this in an uncontrolled
state.

--
Best regards

Tony

http://www.picnpoke.com
Email KILLspamsalesKILLspamspampicnpoke.com

1999\11\04@210313 by Dave VanHorn

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> > weird things?? such as?

Program execution in non-deterministic mode.
Bad Juju

1999\11\04@210749 by Gennette Bruce

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If you use the power supply circuit shown on the page listed below make sure
the first 2 components can handle the FULL POWER demand of the rest of the
circuit.  For example, the protection diode and 22R resistor probably need
to be able to continuously pass 2 watts if your circuit draws 400mA @ 5V.  A
1N4004 diode can just take it, but you'll need 2 x 47R @ 1w resistors in
parallel to create a 2w 23R resistor.

Do some calculations, then give yourself a good safety margin in any power
supply design.  Personally I'd add an inductor ahead of the protection diode
in an automotiver environment to keep ALL electrical noise to a managable
level.

Bye.

> {Original Message removed}

1999\11\04@214546 by Brent Brown

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Yes, there should be at least a voltage sensitive reset circuit on
any micro in just about any practical application, particularly
automotive. Watchdog is next on the list of most important things.

The circuit I described uses an Atmel AT89C2051 (shame on me!)
and a Dallas DS1833 econo-reset chip with a threshold of 4.375V. I
could have used a PIC (too late now) with internal brownout detect
and watchdog, but the above circuit behaves very reliably - so far...

{Quote hidden}

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile: 025 334 069
eMail:  spamBeGonebrent.brownspamBeGonespamclear.net.nz

1999\11\05@105224 by Larry G. Nelson Sr.

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You can but in a car environment it is possible to get voltage spikes that
exceed the max input voltage by a large amount. You may want to put a
series resistor in front of the regulator with a 12 volt zener to clip
spikes. Calculate the current needs and voltage drop to be sure you don't
have too much power dissipation in the regulator, zener, or resistor. Be
sure to put caps on both sides of the regulator.
Good luck and have fun.
Larry



At 12:36 PM 11/4/99 -0500, you wrote:
>i need to connect a pic to my car, using the 12v car battery...umm i
assume i can't just wire up the car battery to like a 7805 to control the
voltage..or maybe im wrong...Suggestions?
>
>mikE
>
>Send someone a cool Dynamitemail flashcard greeting!! And get rewarded.
>GO AHEAD! http://cards.dynamitemail.com/index.php3?rid=fc-41
>
>
Larry G. Nelson Sr.
TakeThisOuTL.NelsonEraseMEspamspam_OUTieee.org
http://www.ultranet.com/~nr

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