re; p&h injector driver

[Garfield Willis]

On Mon, 22 May 2000 18:47:18 EDT, KasaRyan at aol.com wrote:

>My guess is that 
>they supply a driver module to do the dirty work.

Or they supply eight SAT injectors, four each easily driven in parallel
by a driver that could originally pull open 1 TBI.

>In my case I have 2 TBI 
>injectors just wired in series from each injector driver on a 747 ECM for 
>four total injectors.  The driver would not handle the current required for 
>putting them in series.  They can't possibly take very much power though, as 
>I can fire them easily for testing with a 9 volt battery.

This is interesting from a DC analysis standpoint. You've got the
equivalent of roughly 2.4ohms total series resistance, assuming you have
all day to wait for the injector solenoids to pull in. By that I mean,
we're ignoring the very real inductance of the injectors, that will
considerably delay reaching that impedance when operated with real
pulses.

OK, but you've got a battery, and you apply it across these TBIs in
series; lemme see, 9V/2.4ohms = 3.75A. Yeah, you just got real lucky
with that battery. A TBI (or ten of em in series, doesn't matter)
requires about 4A nominal peak current to reliably pull in. If you had
applied a 12V battery to the two in series, that would still only give
you 5A, but that's only EVENTUALLY. The current rises exponentially in
an injector's solenoid/inductor; the 1.2ohm is only the resistive
component of the injector winding. Even with the best drivers in the
world, you don't have the voltage headroom required, with the two in
series, to get the current up quickly enough to pull in the injectors in
the real world of short-duration pulses. This is an inductor we're
dealing with here.

>Thanks for listening to my electroyappin!
>Ryan Hampl - a K-State Grad!    kasaryan at aol.com
>139 Hoover Ct.                  Controls Engineer (tubes rule!)

Hmmm. Careful, those kinda signatures can raise expectations! :) 

Gar


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