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'[EE]: Caps & automotive high speed transients'
2004\09\28@151445 by jayhanson

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I am having a hell of a time with coil/points automotive ignition noise in
my power supply.
 
Do high speed transients ( 60v & < 5ns ) damage 50v aluminum capacitors?  If
so, what's the best way to suppress them? The 18v varistor (Digikey #
F2186CT-ND) and 600 ohm ferrite (240-1016-1-ND) can't stop the noise.

Would a new cd ignition generate less noise?

This project is killing me,
Jay


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2004\09\28@164425 by Andrew Warren

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jayhanson <spam_OUTpiclistTakeThisOuTspammit.edu> wrote:

> I am having a hell of a time with coil/points automotive ignition
> noise in my power supply.

Jay:

See Tom Williamson's Intel Appnote AP-125, "Designing Microcontroller
Systems for Electrically Noisy Environments":  

   http://www.intel.com/design/mcs96/applnots/21031302.pdf

-Andy

=== Andrew Warren -- .....aiwKILLspamspam@spam@cypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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2004\09\30@054721 by Peter L. Peres

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On Tue, 28 Sep 2004, jayhanson wrote:

> I am having a hell of a time with coil/points automotive ignition noise in
> my power supply.
>
> Do high speed transients ( 60v & < 5ns ) damage 50v aluminum capacitors?  If
> so, what's the best way to suppress them? The 18v varistor (Digikey #
> F2186CT-ND) and 600 ohm ferrite (240-1016-1-ND) can't stop the noise.
>
> Would a new cd ignition generate less noise?

Simple solution: buy a mains filter (Corcom etc) and put it in the supply
of your circuit, after lifting all grounds from the car ground. It works
for dc at low current. Otherwise a lc filter before the regulator is
usually a good start (use a choke rated inductor, not a normal inductor).

Peter
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2004\09\30@080605 by Morgan Olsson

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Peter L. Peres 04:51 2004-09-30:
>>Do high speed transients ( 60v & < 5ns ) damage 50v aluminum capacitors?  If
>>so, what's the best way to suppress them? The 18v varistor (Digikey #
>>F2186CT-ND) and 600 ohm ferrite (240-1016-1-ND) can't stop the noise.

Where do you get that transients picked up?

Are you sure that noise is real - you don´t get that noise picked up by the test leads?

Inductor, varistor and ceramic cap to GND should be enough on power supply input.
(After them maybe another choke and then alu cap.)

/Morgan
--
Morgan Olsson, Kivik, Sweden


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2004\09\30@090248 by Sascha

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I have built a digital motor and radiator thermometer using DS1820 for my
car and the leads for the sensor are passing right below the high voltage
choke and current generator. I have used just a choke I’ve picked up form an
old device, a current limiting resistor, a 25V zenner diode, a 470uF
aluminum capacitor, a 100n ceramic and the old LM7805 with 22uF and 100nF at
the output. I had no problem what so ever with this setup in more than a
year now.

I have designed and built electronics for big trucks (stone exploitation
Russian trucks and I can tell you there is a lot of noise in there) and
added a linear 15 regulator (a NPN transistor with a 15V zenner and a
100uF/63V in the base o the transistor) and had no problem with this either.
I don’t think you really have noise in the power line. When you are
measuring noise on the supply line pick the GND from the negative lead of
your filtering cap not from the end of the GND trace.


Hope it helps,

Sascha



{Original Message removed}

2004\09\30@092204 by Lawrence Lile

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What is the difference between a choke rated inductor and a normal inductor, (besides, obviously, the words "choke rated" on the datasheet)?

-- Lawrence Lile, P.E.
Electrical and Electronic Solutions
Project Solutions Companies
http://www.projsolco.com

> {Original Message removed}

2004\09\30@093027 by Russell McMahon
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>>>Do high speed transients ( 60v & < 5ns ) damage 50v aluminum capacitors?
>>>If
>>>so, what's the best way to suppress them? The 18v varistor (Digikey #
>>>F2186CT-ND) and 600 ohm ferrite (240-1016-1-ND) can't stop the noise.
>
> Where do you get that transients picked up?
>
> Are you sure that noise is real - you don´t get that noise picked up by
> the test leads?
>
> Inductor, varistor and ceramic cap to GND should be enough on power supply
> input.
> (After them maybe another choke and then alu cap.)


One or more stages of LC filter should do the trick. You can calculate approximate efficacy theoretically.

Depending on what the input and output voltages are and how much power you need, there is a simple trick which may help. We used this with great success long ago in a Telco environment. We simply used two stages of zener plus resistor filtering. ie input R, zener to ground, resistor to next zener to ground. Regulator feeds from second zener. Provided that the voltage drop in the resistors is acceptable to you plus the power in the zeners then this does a good & cheap job of greatly diminishing spikes to the stage where a regulator has no problems with them. If you have eg 12v in and 5v out then you have enough headroom to do this and power loss in resistors is possibly better than in the regulator anyway. Depends muchly on power level.


       RM

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2004\09\30@100347 by Alan B. Pearce

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>What is the difference between a choke rated inductor and
>a normal inductor, (besides, obviously, the words
>"choke rated" on the datasheet)?

I suspect a choke rated one will have a rating for a DC component while
maintaining the inductance value without saturating. An ordinary inductor
may be rated only for an AC component rather than AC+DC.

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2004\09\30@100600 by Russell McMahon

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> What is the difference between a choke rated inductor and a normal
> inductor, (besides, obviously, the words "choke rated" on the datasheet)?

I'd guess he / they mean that it is rated to not saturate at a stated DC
current. (or to have the stated inductance at the rated maximum DC current).

1 Henry is easy and can be small & light.
1 Henry at 1 Ampere, well ... :-)


       RM

>> Simple solution: buy a mains filter (Corcom etc) and put it in the supply
>> of your circuit, after lifting all grounds from the car ground. It works
>> for dc at low current. Otherwise a lc filter before the regulator is
>> usually a good start (use a choke rated inductor, not a normal inductor).

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2004\09\30@133805 by jayhanson

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Peter L. Peres 04:51 2004-09-30:
>>Do high speed transients ( 60v & < 5ns ) damage 50v aluminum
>>capacitors?  If so, what's the best way to suppress them? The 18v
>>varistor (Digikey #
>>F2186CT-ND) and 600 ohm ferrite (240-1016-1-ND) can't stop the noise.
>
>Where do you get that transients picked up?
>
>Are you sure that noise is real - you don´t get that
>noise picked up by the test leads?
>
>Inductor, varistor and ceramic cap to GND should be enough
>on power supply input. (After them maybe another choke and then alu cap.)

I believe the noise is real because my processor board resets every so often
with the motor running (I took out WDT for testing).  
Conceptually, this project is a walk in the park. In reality, I am about to
fall on my sword.

I think the problem is that I have created a special problem in this car.  I
have been screwing around with this car -- on and off -- for three years
now!!

When I designed the latest boards (yes, there have been several versions), I
took the advice of Bob Axtell:  Large varistors on sources, small varistors
on board, optoisolators, 47pf emi filters (P9826CT-ND) and 47pf caps on each
input, current operated (bipolar) transistors to run my high-current relays,
a two inch copper strap down the middle of the car for ground, and a TI
switching regulator for my processor.  ** I even have an totally-isolated
separate 12V battery for my processor board!!!

The car is unusual in that it's a 1973 VW thing.  It was designed to run on
a generator but was converted to alternator.  The noise appears to come from
the spark coil and points (both not original equipment).  I can measure
these 60v spikes on terminals of the car battery AND on the terminals of my
processor board with the separate battery!  Could it be radiating that much
energy through the air?

I measured another newer car and truck and they do not have spikes like this
in their electrical systems.  I am about to install a new capacitive
discharge ignition system (MSD, doing it today).

Jay



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2004\09\30@172621 by Tim ODriscoll

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On Tue, 2004-09-28 at 20:14, jayhanson wrote:
> I am having a hell of a time with coil/points automotive ignition noise in
> my power supply.

I used this circuit in my pick-up: http://www.seetron.com/an_vpwr1.htm

I think I got it from the piclist a year or so ago. It works great on my
pick-up (a diesel).

Failing that, rip out the petrol engine and stick a diesel engine in. :)

Cheers,

Tim

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'[EE]: Caps & automotive high speed transients'
2004\10\01@093247 by Support - KF4HAZ
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----- From: "Tim ODriscoll" <tim@
> On Tue, 2004-09-28 at 20:14, jayhanson wrote:
> > I am having a hell of a time with coil/points automotive ignition noise in
> > my power supply.
>
> I used this circuit in my pick-up:
http://www.seetron.com/an_vpwr1.htm

Add a 5 ohm 10W resistor in series with D1 and a cap to gnd. after it and
maybe a 0.1uf  to gnd on each side of D1 and you should be able to use the 7805 up to 1 amp.
The RC combination will reduce the voltage dropped across the 7805 and reduce noise on the 5V.
KF4HAZ - Lonnie

> I think I got it from the piclist a year or so ago. It works great on my
> pick-up (a diesel).
>
> Failing that, rip out the petrol engine and stick a diesel engine in. :)
>
> Cheers,
>
> Tim

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2004\10\01@112840 by Peter L. Peres

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On Thu, 30 Sep 2004, Lawrence Lile wrote:

> What is the difference between a choke rated inductor and a normal
> inductor, (besides, obviously, the words "choke rated" on the
> datasheet)?

It works with dc through it and it has a low Q factor. This prevents it
from ringing too much with large but fast spikes. A high quality inductor
followed by a high quality capacitor used as a filter would cause enough
ringing at the LC resonant frequency, when subjected to a spike or step
pulse, to disturb downstream circuits. The low Q is usually obtained by
winding it in a certain way so it has a large stray capacitance vs.
ground. There are also hybrid chokes that use other methods to kill
pulses (transmission line like).

Peter

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2004\10\02@090041 by Peter L. Peres

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On Thu, 30 Sep 2004, jayhanson wrote:

> I think the problem is that I have created a special problem in this car.  I
> have been screwing around with this car -- on and off -- for three years
> now!!

If it still runs it's ok. Try to put a 100pF cap between Vdd and MCLR
directly at the chip (regardless of what else is there). The MCLR spec
has the lowest noise margin on pics afaik. 0.5V below Vdd and you're reset
afair.

> The car is unusual in that it's a 1973 VW thing.  It was designed to run on
> a generator but was converted to alternator.  The noise appears to come from
> the spark coil and points (both not original equipment).  I can measure
> these 60v spikes on terminals of the car battery AND on the terminals of my
> processor board with the separate battery!  Could it be radiating that much
> energy through the air?

Yes and no. Cables in harnesses that live in the same metal compartment
couple into each other strongly. Also old cars do not have 'grounds' they
have something that is most of the time below +12V. Unless you turn the
headlights on or something ;-)

> I measured another newer car and truck and they do not have spikes like this
> in their electrical systems.  I am about to install a new capacitive
> discharge ignition system (MSD, doing it today).

The spikes are not supposed to be there at all. Poor wiring to the voltage
regulator and/or generator can cause them, as well as picking power for
the ignition from an arbitrary point in the system and grounding things
arbitrarily. F.ex. check if the engine block still has a good ground (<0.2
ohms to battery - including meter wires).

Peter
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2004\10\03@170239 by jayhanson

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I am happy to report the problem has been fixed.  I was experiencing 60v,
<5ns spikes occurring at about (I think) 100 mhz.  I had an old coil,
points, and copper wire spark plug wire ignition system.  I had a cap on the
distributor but not one on the coil.

I fixed the problem by replacing the old ignition system with a new
capacitive discharge system from the MSD company.  I put in a new control
unit, coil, distributor, and resistor spark plug wires from MSD.  I am still
getting some 20V noise from the alternator but my circuits can handle that
just fine.

My advice to anyone who wants to put a PIC project into an old/modified car
would be to FIRST upgrade the ignition system to a modern capacitive
discharge system.

Thanks for all the help from all of you,
Jay


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2004\10\03@173939 by Bob Axtell

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Thanks for sharing, Jay. This is a continuing problem for all of us.
Every bit of sucess is cherished.

--Bob


jayhanson wrote:

{Quote hidden}

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