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 04/19/05 www.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.
|
