electrical terms - motors versus car ignition systems 1

[Tmoose]

On a hot rod engine bulletin board there is a discussion about CDI ignitions reflecting a bunch of Joules back to the battery instead of making spark.

http://speedtalk.com/forum/posting.php?mode=reply&f=1&t=42274

Terms like reactance and real and imaginary power when describing steady state conditions in motors etc are just buzz words to me.

Do they need to be considered for ignition spark evaluation too/

thanks

Dan T

 

[VEBill]

"...battery... ...reactance and real and imaginary..."

Hmmm...

 

[VEBill]

http://en.wikipedia.org/wiki/Capacitor_discharge_ignition#The_basic_principle

The DC side of the CDI (the battery) should be feeding the DC-DC converter within the CDI circuit.

There's not really any mechanism for "joules" to be routed back to the battery.

The secondary circuit path at the point of ignition spark should have nothing to do with the battery as such.

By the way, the link you've provided requires Login.

 

[jraef]

I think you just picked the wrong link, likely while you were posting. Anyone can read the thread here, but you can't see the images without registering.

http://speedtalk.com/forum/viewtopic.php?f=1&t=42274

Still, I imagine this is based on a basic misunderstanding of what the OP in that other forum was looking at.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[MacGyverS2000]

Can't see any images and I'm not going to read the posted thread (other than the OP)... but my mind immediately wanders to a collapsing magnetic field in an inductor and the "lost" energy being stored in said field. Such a thing has confused many a sparky, and getting a non-sparky to comprehend it is an even greater challenge.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

Only half of the maximum energy, like maximum power can be effectively transferred:

http://en.wikipedia.org/wiki/Maximum_power_transfer_theorem

The advantage that I see, for inductors, is that it has a much higher compliance than a capacitor, i.e., if the resistance of the load increases, the capacitor will drop in output current, while the inductor will continue to try and dump its current. That's just seems to be an extra degree of freedom that the capacitive circuit doesn't have.

TTFN
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[Tmoose]

ignition test and discussion, CDI 1

 

[Tmoose]

Ignition test and discussion CDI 2

 

[LionelHutz]

Thanks Tmoose for posting the graphs. Looking at his second graph, he's claiming the purple trace is the energy curve. The energy shouldn't be dropping over time. Based on this flawed data, I don't know what he's really measuring. He did make it clear he simulated the spark voltage so how can he know the spark energy is accurate?

Generally speaking, A CD ignition has a capacitor that is charged and then switched onto the primary coil leads. The charging circuit feeding the capacitor also typically has a transformer with a switching circuit on it's primary side between the battery positive lead and this capacitor. The circuit path when the capacitor is switched across to the coil leads doesn't include the battery so it'd be impossible for energy to be "sent back" to the battery.

The opposite polarity voltage he's seeing on the primary side of the coil after the spark event is likely a snubber circuit that is discharging the remaining magnetic field in the coil so it's ready for the next spark.

 

[MacGyverS2000]

Minor pet peeve, but... if you're talking about amount of current temporarily flowing across a link, I expect to see the graph rise and fall, not fall and then rise. The latter leads me to believe current is always flowing, and then it is interrupted for some period of time.

Dan - Owner

http://www.Hi-TecDesigns.com