Subject: Best Tracy schematic
From: rotaryeng
Date: 6/17/2014, 2:48 AM
To: AAA-rotaryeng



I notice that Tracy uses a separate ground for the injectors. He is
not fooling. If you connect the battery ground to the injector ground
it wont work. He should have mentioned that. It is an attempt to keep
the injector spikes out of the computer. IMHO a few chokes here and
there would also have worked without the uncertainties :)


Paul Lamar

Not necessarily -- putting the currents where you want them, where
they don't share common impedance paths, is a better approach.
"Chokes here and there" doesn't work very well unless you have a lot
of energy storage in the power supply so it never sees the spikes
anyway. Otherwise you will always be fighting the voltage spikes on
the computer power that follow the current spikes from the injectors.
Strongly recommend Henry Ott's book "Electromagnetic Compatibility
Engineering." It's mostly about meeting EMC requirements but the
issues are the same. His earlier version "Noise Reduction Techniques
in Electronic Systems" is just as good for this problem.

David Josephson


True! Capacitors are needed. A 1000 Uf and a small choke on each
injector would work well I suspect. Worth a try.  Of course the
computer is well grounded to the engine.

Even better is mount the switching transistor on the injector like a
smart coil.


Thanks for the book tip. I'll get it.

Paul Lamar
## Manual quote starts here ##
-- 
Maybe this discussion should be offline, but having wrestled this
particular demon for decades in the audio and instrumentation biz I can
assure you that "I suspect" approaches (even mine, or especially mine)
are often a waste of time. It is tedious engineering but it is doable
without too much exertion. Your number one question, for every instant
of time for a given injector pulse, is "where does the current flow?"
From battery + back to battery -, figure out the resistance of each
path and see how the current through an injector gets there and back.

I am not sure that putting the switching transistor at the injector
would help. I would rather have the switching transistor where the
source impedance for power feeding it was lowest. Yes, the loop area for
radiated EMI would be reduced, but then you have another handful of
connections that are more subject to engine vibration. What is a "small
choke" and what function does it serve? Why 1000 uF and where would you
put it?

David Josephson


What ever happens please put your response at the bottom of the thread
and sign it so it makes it easier to read and follow.

Smart coils have no problems with ground loops nor does tracy use a
separate ground for the smart coils. The switching transistor is in the
coil.


Paul Lamar
## Manual quote ends here ##

Oh, by the way David, when you are editing your email response please
delete the double dash "--" that you included in your response to Paul's
comment above.  See the double dash above right after the
"## Manual quote starts here ##" line.  Many email programs interpret
that double dash at the beginning of the line as the end of the body and
the beginning of the signature.  When you reply to such a message, as I
did here, the quote ends at the double dash.  Notice how the quote,
preceded by the "" symbol, ends at the double dash.  I had to copy and
paste in the rest of the quote separately to include it in this email.

Also, all text following the double dash is presented as under
intensified gray text that is much more difficult to read.  Perhaps your
email tool presents the signature that way.  You can tell by looking at
my signature which is preceded by the double dash at the beginning of
the line below.

If it was you, Paul, that included the double dash then I owe David an
apology.  I hate it when that happens. ;-)

-- 
   _
  °v°
 /(_)\
  ^ ^  Mark LaPierre
Registered Linux user No #267004
https://linuxcounter.net/
****


Could be me. Sorry Mark I will look for it in the future.
I suspect the NSA is using hidden characters to identify certain
class's of email users. It would be great if everybody used plain text.
We get a wide variety of html messages. Especially from cell phones,
tablets and Apple products. There is no effective standards in html.
Every email editor program and cell phone manufacture wants to be different.

David, Tracy uses separate grounds but the same 12 volt supply, He has had a lot
of trouble over the years with glitches from the injectors despite the separate ground.

A built in transistor switch with a large capacitor and small choke would suppress
the spike  on the 12 volt supply. The choke need not carry the full 2 amps as the capacitor will handle the high peak currents. The choke will block the out going  spike.
If I ever do an EFI that is the approach I will take. The injectors used to be shock
and hold and now they are mostly just plain high current. It is when they turn off
that causes the spike.  They are not designed for a 100% duty cycle.

Paul Lamar

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