DIY_EFI Digest V2 #329

[Jake]

> Hi Jake
> Don't think of injectors, particularly low impedance injectors, as operating
> on a voltage.  Think of them as operating on a current. Their impedance (the
> DC part plus the AC part) varies dramatically with the position of the
> armature in the injector. What this tells us is to drive them with a current
> generator for maximum speed & predictability under varying environmental
> conditions. For a current generator to work properly you need a relatively
> high supply voltage (compliance voltage) to guarantee that you can force the
> required current thru the coil under all conditions. The simplest of current
> generators is a  ON NPN transistor with the base held at a controlled
> voltage, a resistor in the emitter to set current and the injector in the
> collector.  A typical base voltage will be maybe 3 volts. With a 1 ohm
> emitter resistor the "constant current" thru the injector will be
> 3.0-0.7/1=2.3 amps.  This will hold as things vary around, like battery
> voltage.  Motorola has some good stuff on this in their App notes for their
> injector drivers.
> 
> Lotsa Luck Eric
> 85 GTI with VR6 power

hmm.. well, I understand about the current regulation rather than voltage
regulation, and I understand why. The problem is, i still have NO CLUE as
to how i should go about doing this. What's an "ON NPN" and which part
number would you personally suggest? I only need to drive one injector, a
16 ohm style as the example. I assume i would need one current generating
transistor for each injector in my system, since the injectors can fire
one at a time or multiple at once? Also, would 12VDC be a good "compliance
voltage"?  I know i'm asking to be walked through this application, but
this is how I learn new things.. i fully intend to understand the concepts
and parts involved once I have a working injector on my soldering bench.

If you have a good example schematic, or a part number/web site I should
start with, that would be great.. if you can think of radio shack parts
that would do the trick for beginners, that would be good too. This
injector will be triggered by a 555 timer, in one-shot mode (triggered by
a pulse). Thanks for your help in advance. (this goes for everyone)

> All you have to do is use sandys LM1949 injector board
> and drive it with the gm ecm..
> 
> L8tr:peter

where can I find out more about this board? it sounds useful.

> Hi again
> As a more practical answer to answering your original question, just build
> an interface box between the ECU that supports high voltage injectors and
> the kind (low impedance bosch) you want to use.  This would be as simple as
> two sets of connectors and 8 Mot, Siemans or SGS drivers and a few discrete
> parts.
> 
> Lotsa Luck Eric
> 85 GTI with VR6 power

wow.. that was fast. Got an example design yet? I'm new to EFI.

>   Ok, finally time for me to plunk down the money for an inline fuel pump
> for my EFI proj (have been running for short periods of time w/ an in-tank
> type sitting in a big coffee can of gas;)  Anyway, I looked through all of
> my old messages and someone said that pre-85 Nissan's (200SX?) had an
> in-line type, but the guy at the parts store say's nope.  Does anyone know
> of another doner vehicle or where else to get one?  All of the high
> pressure types in the Summit catalog are $200+.  Too rich for my blood (and
> I don't want to double the value of my jeep;)
> 
> Stephen

any volvo 1975-present with FI (mechanical or electronic).
their fuel pumps can exceed 120 PSI easily.. they're designed
for 45-80 PSI constant flow (regulator with return line)
so for lower PSI you might want to use a ballast resistor.

> Just wondering if anyone out there has a simple answer to this question.
> Not exactly EFI, but heading that way.  If I want to use the hall effect
> pickup from a Chrysler 2.2 distributor to fire a simple ignition system
> how do I do it? I understand one of the three wires on the hall effect
> is ground, one is Vcc, and the other is a current sinking output.  Does
> it sink current when the vane is in proximity to the sensor, or when it
> is not?  What would it take to interface the hall effect switch to a HEI
> ignition module? Is there a cheaper, more readily available, and/or
> better module to use for this purpose. I want it small and light, and
> reliable. Will be firing single coil, waste fire system.  TIA

my standard universal answer: volvo.  Many mid 80s volvos (740 and 760
series) used a chryseler ignition with a bosch ignitor box which probably
has the same connector as your distributor (round three pin plug? square?
i dont know.) and this would be your simplest choice, since the
spark on those volvos is completely non-computer controlled. The box very
simply connects to: ground, +12V, tach (coil -), and the hall-effect
pickup. On normal volvos with the bosch distributor, the pickup coil has
two wires and measures around 1300 ohms.. these spark boxes are the most
common, and can be found in ANY volvo 240.. grab the wiring for it too,
it's not very long, and these spark boxes last FOREVER. most setups used
a resistor on the positive side of the coil, which was bypassed during
cranking for full-strength spark. grab that and the coil, it's high
quality high spark-energy stuff. The spark box is located just rear of the
battery (usually) and is black plastic, and about 5"x5"x2". Its the only
box on the car fitting that description. The spark coil ballast (resistor)
is by the passenger side hood hinge, in the corner of the engine bay.

Jake