View Poll Results: Do you back - probe wiring when doing electrical diagnostics?
Yes, and I don't know if it has caused future problems
1
7.69%
Yes, and it has never caused future problems
7
53.85%
Yes, and it has caused problems
1
7.69%
No, because I believe it will cause future wiring problems
2
15.38%
No, I don't know if it will cause future problems or not
0
0%
No, never had a need to do it
2
15.38%
Voters: 13. You may not vote on this poll
Back Probing Wiring
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Postmaster
Joined: Jan 2003
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From: Durham, NC
Originally Posted by jimdandy
I have more of a clue of what Thevenin's(including how to spell Thevenin) circuit is than you do diagnosing problems with automobile circuits. Since you have so much experience diagnosing problems with the automobile, give me an example where Thevenin would apply, and where you have used it, and where the automotive technician could benefit from it. I'm sure they would appreciate it.
Try studying this URL, it should help your understanding:
http://www.wd5gnr.com/basiccir.htm
And it is spelt Thevinin
You answered your self about an ignition system: "The direct current is changed to some type of waveform/pulse" you can't get a Di/Dt with DC,
which is needed to get the high voltage from an ignition coil.
Another point: "..then changed back to direct current" Simply not true with an ignition coil, or coil pack, there is no rectification off the secondary.....
That's it, I'm taking subford's approach, not wasting any more time with you!!
Last edited by Bob Ayers; Aug 11, 2006 at 06:23 AM.
Lead Driver
Joined: Nov 2002
Posts: 9,557
Likes: 44
From: Concord, NC
You can get a Di/Dt with DC when the current is switched on and off and the current is flowing through a coil, which is what happens with the ignition coils. Yes this wids up as a pulsed current, but it isn't AC.
Also, with the high resistance sinks in the computer....is the signal measured before or after the sink?
I understand what you are saying, but I don't know enough about the basic hardware operation of the computer to understand how the sensor signals are processed physically.
Also, with the high resistance sinks in the computer....is the signal measured before or after the sink?
I understand what you are saying, but I don't know enough about the basic hardware operation of the computer to understand how the sensor signals are processed physically.
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Postmaster
Joined: Jan 2003
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From: Durham, NC
Originally Posted by EPNCSU2006
You can get a Di/Dt with DC when the current is switched on and off and the current is flowing through a coil, which is what happens with the ignition coils. Yes this wids up as a pulsed current, but it isn't AC.
Also, with the high resistance sinks in the computer....is the signal measured before or after the sink?
I understand what you are saying, but I don't know enough about the basic hardware operation of the computer to understand how the sensor signals are processed physically.
Also, with the high resistance sinks in the computer....is the signal measured before or after the sink?
I understand what you are saying, but I don't know enough about the basic hardware operation of the computer to understand how the sensor signals are processed physically.
Posting Guru
Joined: Feb 2006
Posts: 1,448
Likes: 1
Originally Posted by Bob Ayers
If you can comprehend the above posts, a Thevinin's equivalent circuit was used to determine how much wiring series resistance would have to increase to affect the sensor voltage at the PCM, assuming the input resistance at the PCM was meg ohms. Eric had no trouble comprehending this.......I'm a little surprised you would ask for an example, since you claim to understand it!
Try studying this URL, it should help your understanding:
I have no need to go to Bob Ayers training center. If I were ever to have a need for this type of information, I am sitting in front of a huge library.
Jean Charles Thevenin, Telegraph engineer, 1857-1926. There is an accent mark over the e in Jean and the first e in Thevenin.
"A Transformer cannot work with DC at all so this can not be true."
Another point: "..then changed back to direct current" Simply not true with an ignition coil, or coil pack, there is no rectification off the secondary.....
That's it, I'm taking subford's approach, not wasting any more time with you!!
jd
Last edited by jimdandy; Aug 11, 2006 at 07:08 PM.
Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
Originally Posted by EPNCSU2006
You can get a Di/Dt with DC when the current is switched on and off and the current is flowing through a coil, which is what happens with the ignition coils. Yes this wids up as a pulsed current, but it isn't AC.
Also, with the high resistance sinks in the computer....is the signal measured before or after the sink?
I understand what you are saying, but I don't know enough about the basic hardware operation of the computer to understand how the sensor signals are processed physically.
Also, with the high resistance sinks in the computer....is the signal measured before or after the sink?
I understand what you are saying, but I don't know enough about the basic hardware operation of the computer to understand how the sensor signals are processed physically.
Here is the thread:
https://www.ford-trucks.com/forums/4...hlight=coil+DC
FTE Leadership Emeritus
Joined: Jan 2003
Posts: 161,999
Likes: 75
From: 3rd Rock
jimdandy, I purposely left out that I was now back to talking about the DC/DC converter. I knew you would jump on it with both feet.
Last edited by IB Tim; Aug 12, 2006 at 05:24 AM.
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Brett Foote
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From: Lake Tahoe, Nevada
Originally Posted by EPNCSU2006
Plusating DC does not equal AC, and I think that was covered in the coil thread that subford linked to...
As Subford points out, the "pulsating dc" is seen as a waveform, pulsating on the high side of the zero line on the scope.
Move the zero line up and it is ac.
But in fact the current flow in pulsating dc is in one direction only. The capacitor and the coil complicate things in an ignition circuit because the induced current caused by the collapsing field of the coil actually does flow the other way! So call it ac or call it dc, you have a good case either way.
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From: Durham, NC
Originally Posted by Bdox
This gets down to a language/definition problem.
As Subford points out, the "pulsating dc" is seen as a waveform, pulsating on the high side of the zero line on the scope.
Move the zero line up and it is ac.
But in fact the current flow in pulsating dc is in one direction only. The capacitor and the coil complicate things in an ignition circuit because the induced current caused by the collapsing field of the coil actually does flow the other way! So call it ac or call it dc, you have a good case either way.
As Subford points out, the "pulsating dc" is seen as a waveform, pulsating on the high side of the zero line on the scope.
Move the zero line up and it is ac.
But in fact the current flow in pulsating dc is in one direction only. The capacitor and the coil complicate things in an ignition circuit because the induced current caused by the collapsing field of the coil actually does flow the other way! So call it ac or call it dc, you have a good case either way.
http://www.automotivetestsolutions.c...oblem_idle.jpg
Fleet Owner
Joined: Sep 2005
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From: Lake Tahoe, Nevada
In the seventies, I wrote the technical manual used it the "Insta-tune" tuneup chain. They were all equipped with scopes so I had to provide the images and the explainations for all the waveforms. Points systems, no problem. This was when electronic ignition systems were just becoming common and I had to work my tail off researching all the scope patterns availble. What I learned was, the various manufacturers were all developing their own systems, but the waveforms were nearly the same even though they used different techniques to achieve them. Of course I didn't know that when I started.
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Pulsating direct current is not ac current, no matter how you cut it.
Transformer "ringing" is an after effect of the intitial drive force, not a driving force itself.
Subford's statement was that dc current could in no way be used to drive a transformer. It was simply my opinion that his statement was wrong in the way it was worded. I think Subford is knowledgable enough to know transformers work with dc, but would the reader know this from his statement? He could have clarified, but chose not to do so. So that leaves the rest of us to do our own interpreting.
We can get into ringing and all sorts of transformer phenomina, circuit design, moving baselines, etc., but it is very dull and boring. jd
Transformer "ringing" is an after effect of the intitial drive force, not a driving force itself.
Subford's statement was that dc current could in no way be used to drive a transformer. It was simply my opinion that his statement was wrong in the way it was worded. I think Subford is knowledgable enough to know transformers work with dc, but would the reader know this from his statement? He could have clarified, but chose not to do so. So that leaves the rest of us to do our own interpreting.
We can get into ringing and all sorts of transformer phenomina, circuit design, moving baselines, etc., but it is very dull and boring. jd
