Re: Injectors: P&H and SAT - Part 1

["Swayze" <kswayze@bellsouth.net>]

many,many questions?
is measuring the resistance enough (how do you measure henry's)?
P&H injectors should be wired in parallel so that they drop a full 12V or
does a resistor go in line with them?
I'm sure more will come to mind.

byE
Mike
Swayze
mswayze@truswood.com
kswayze@bellsouth.net
----- Original Message -----
From: "Garfield Willis" <garwillis@msn.com>
To: <gmecm@diy-efi.org>
Sent: Tuesday, May 23, 2000 6:24 PM
Subject: Injectors: P&H and SAT - Part 1


> Ya know, I'm just wondering if it might not be good at this point to
> mention a few pertinents, so everybody's on the same page, regarding
> injectors.
>
> Basically they're just solenoids. They're often spec'd by their DC
> resistance (roughly what you'd see if you meter'd them), but that figure
> alone is misleading. Maybe we should try to pull the cat a little
> further outta the bag?
>
> Peak & Hold:
> Port Injector Size/Style (aka TPI/PI) = 2.4ohms & 4.0mH
> Throttle Body Size/Style (aka TBI) = 1.2ohms & 2.0mH
> Saturated: = 12-16ohms & 18-25mH
>
>
> Now we're all use to dividing ohms into volts to get a current,
> I = V/R, so-called Ohm's law, but when you apply pulses to an inductor,
> the inductance also comes into play; that's what the "mH" means, it's
> "milliHenry" (not a small guy, but a measure of inductance named after
> Mr. Joseph Henry, a self-educated American scientist who later taught at
> Princeton!, and who bribed the judges into giving him credit for the
> idea of inductance :).
>
> So ya know how Farad is the measure of how big a capacitor is ? (as in
> microFarad, named after another lil guy named Faraday :) So Henry is the
> measure of how big an inductor is. Ya know how you have to consider the
> "RC time-constant" because charging up a capacitor takes time, just so
> you have to consider the "L/R time-constant" when charging up an
> inductor. Of course, we don't usually call it "charging up an inductor";
> usually we know the current in the winding has to reach a certain peak
> value for the solenoid's inductor to do the mechanical deed, but it's
> the same thing. Because of this "inductance" phenom in coils, it takes
> them some time to "charge up" to their eventual current level, which
> also relates to how strong a magnet they are.
>
> I know it seems spookie to someone who hasn't had a course or two in
> electrical dynamics, but since most people are familiar sooner with
> capacitors and the idea of a tank taking time to fill up, just think
> about an inductor in a similar way; in a capacitor, it takes time for
> voltage to build up. In an inductor, it takes time for current to build
> up. The higher the charging current, the faster a capacitor charges up
> (voltage rises); the higher the charging voltage, the faster an inductor
> charges up (current rises).
>
> In the case we've just previously seen, two P&H injectors were put in
> series, and we all remember (right?) that voltage divides across things
> in series. OK, well, can you see it now? Putting two inductors in series
> divides their "driving voltage", and we said above that "the higher the
> voltage charging an inductor, the faster the current builds up", and we
> also said "the current in an injector winding has to reach a certain
> peak value" in order to pull in. Or to turn it around to fit this case,
> "the lower the voltage charging an inductor, the SLOWER the current
> builds up".
>
> Generally, while it's expected that multiple SAT injectors will be
> paralleled up, it's NOT usually planned that P&H, especially TBI
> injectors, would be wired in series. They're intended for more
> intelligent, high initial current drivers.
>
> I realize this will sound like talking down to many, and fly over the
> heads of others; if the former, I apologize, if the latter, ask further
> questions.
>
> [Next go-around on this, we'll work thru the L/R time-constants from the
> numbers above for the different sizes; there's an interesting quirk in
> the numbers you might wanna observe].
>
> HTH,
> Gar
>
>
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