DIY_EFI Digest V2 #328

[Robert Yorke]

Eric:

Thank you for a quite lucid expanation; it's not often that a good baseline
explanation like this shows up...


At 11:20 AM 9/20/97 -0700, you wrote:
>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.
>
>
>>speaking of which, does anyone know how I can identify the optimum voltage
>>of a given injector based on its impedance, and what are some common
>>voltages? i'm dealing strictly with production stuff, for example, bosch
>>LH-jetronic injectors. They are 4 VDC, right? what cars use 12V injectors,
>>and where can i find a good example circuit of how to trigger one?
>>
>>Jake
>>
>>
>Lotsa Luck Eric
>85 GTI with VR6 power
>
>
Riverside, CA