Simple injector Drive

[Roberto L. Landrau]

>>>>> "Lusky" == Jonathan R. Lusky writes:

Lusky>> Uhhhhhh, there is a reason why injectors have a minimum
Lusky>> offtime and a maximum duty cycle.  You put a constant 12V
Lusky>> on a Rochestor injector and it will get *HOT*, and melt
Lusky>> the windings, even with fuel flowing through them.  I
Lusky>> toasted a nice 33lb/hr MSD injector this way...

>>>>> "Peter" == Peter Wales <pjwales at magicnet.magicnet.net> replied:

Peter> Now that does surprise me. 3/4 amp and 12v with
Peter> 33lb/hr of cooling fuel going through it and it burnt
Peter> out? So how does an injector survive being on top of
Peter> an engine at 100 degrees and running near 100% duty
Peter> cycles? Has anyone else destroyed injectors by
Peter> running them continuously.

I think your surprise is probably due to a lack of
assumption statements.  You are probably confused about his
experiment and I am certainly confused about the one you
describe below.

Peter> When I was doing flow testing on Bosch and Mitsubishi
Peter> injectors, we just put 12 v across them,

Sorry, I am not trying to pick on you, but I would like to
know more about your setup.  When you say "12 v across them,
I assume you mean "12v across the injector terminals".

Peter> with the ballast resistor in series, and ran them, no
Peter> problems.

This is the part that confuses me.  You said "12 v across
them" and now you mention an ballast resistor.  If you had a
resistor in series, then you must have applied more than 12
volts total to get the injector voltage to 12 v.  I am going
to guess that what you meant was "12 v across the series
combination of the injector AND the resistor".  In that
case, the voltage across the coil is less than 12 v.  In
fact, it is = 12 - I R,  where I is the current flowing and
R is the ballast resistor value.  You can also calculate it
by using  = 12 x Rc/(Rc + R), where Rc is the resistance of
the coil and R is the ballast resistor.

Peter> Maybe I had better not try that with new injectors.

What Jonathan was saying was that a continuous 12v across
the coil will burn it.  What you PROBABLY meant (and I am
just guessing here) was that you can put a continuous 12v as
long as you have a current limiting resistor in series.  In
that case, you no longer have 12v across the coil, which
agrees with what Jonathan said.

--------
Roberto L. Landrau	landrau at mitre.org