On Jul 2, 1:49 pm, Sjouke Burry <burrynulnulf...@[EMAIL PROTECTED]
>
wrote:
> Mike H wrote:
> > On Jun 30, 2:07 pm, Sjouke Burry <burrynulnulf...@[EMAIL PROTECTED]
>
> > wrote:
> >> Mike H wrote:
> >>> I would like to data log commanded spark events for my vehicle. It
> >>> uses a Distributorless Ignition System which consists of a engine
> >>> control computer, a control module, and a coil pack. The coil pack
is
> >>> fed 12v and has control wires. When a control wire is brought to
> >>> ground by the control module, current can flow through a coil
primary
> >>> winding. The control module holds the ground for a ECC demanded
dwell
> >>> at which time the ground is raised, causing the coil to discharge.
> >>> I want to monitor when each control wire is being held to ground.
> >>> My monitoring device can take a 0-5v DC input.
> >>> Do I need to be concerned with the current in the primary circuit
that
> >>> I will monitor voltage on?
> >>> Is there a circuit design, or a discrete component that will scale
the
> >>> 12v on/off signal into a 0-5vDC output I can push into my DC input?
> >>> This will need to operate fairly quickly.
> >>> Other suggestions?
> >>> Thanks
> >> You have to deal with very high voltages(hundreds), when the ground
> >> connection opens.
> >> I would advice 100k to 1 megohm in series with two 4 volt zenerdiodes
> >> anti parallel, to clamp voltage to 4 volts.
> >> to make more of a divider, shunt 30k accross the diodes and a small
> >> capacitor of 200 pf.(the last to stop capacitive coupling accross the
> >> 100k to your input).
> >> Then maybe your electronics will stay alive :)
>
> > Perhaps I didn't describe my intention fully or am understanding what
> > I see incorrectly.
>
> > In the case of my ignition system, an electronic control module
> > receives 12v. A pack of 3 coils receives 12v (6 cylinder motor,
> > wasted spark system). Each coil primary thus has 12v but the
> > primaries are not grounded. Ground is achieved by a switch inside the
> > electronic control module which provides a ground to the primary of
> > each coil as necessary.
>
> > Note that these are ignition events, thus such events occur in
> > hundreds of microseconds.
>
> > My understanding is that
> > When the electronic control module brings a coil primary to ground,
> > current will flow through the primary. When the ECM lifts the ground,
> > an electrical field in the primary will collapse creating a large
> > induced voltage in the secondary winding of the coil.
>
> > If I just want to monitor when the ECM drops a line to ground, and
> > then lifts it again, will the voltage not be limited always to 12v at
> > the primary?
>
> > My idea.. thus far is to create a voltage divider that sits in
> > parallel on the control line. When the ECM drops the control line to
> > ground, my voltage divider will output 4.5v. When the ECM raises the
> > ground, my voltage divider will output 0v.
>
> > New idea, that I used aaCircuit to show.
>
> > Could I not use a 5vdc power source for my input to my data logger.
> > Then have the sensor ground for that input be tied to the ground on
> > the primary control wire to the Coil? Thus when that becomes grounded
> > my 5vdc flows through my other circuit?
>
> > '-----------.
.----------------------------o----------------
> > o
> > | | | | 12v DC
> > |Spark Plug | | .---------------. |
> > .'. | Coil | ' .-----'
> > | | | | | ECM |
> > | | C.---12v DC- '--' |
> > | | C| | '-------o-------'
> > | | C| | |
> > '.' |'-------o-----' |
> > | | ECM Switched Ground |
> > '-----------' | |
> > | | |
> > | | |
> > | | ===
> > === '-----' GND
> > GND |
> > |
> > |
> > |
> > VCC |
> > + _ |
> > | 5v DC / \ |
> > '------------------(_/_)-'
> > \_/
> > (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)
>
> As soon as the ecm line gets diconnected from ground, a huge
> induction voltage is sitting on your device, blowing it to pieces.
> You need the protected divider I spoke of.
> The ignition coil acts as an auto transformer, and as soon as you
> break the current, you get a big volage across the 12volt winding.
> Not as bad as at the spark plug(thousands of volts), but bad enough.
> Thats why they use ~800 volt transistors to do the switching in the
> ecm unit.
If possible, could you use aacircuit to diagram this for me? I'm not
certain how to create what you described.
VCC
+
12v DC |
|.-------------------------------------------------'
C|
C|
C|
|. .-----------.
| | |
| | ECM |
'----------------------------' |
Switched Ground '---o-------'
|
|
|
|
|
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
|
