[Gmecm] High-voltage P&H IDM

[D.Pray]

Saturated means that no further energy can be added to the inductive field
(and that's where the energy goes). As the current passes the point of full
saturation, any increase produces no additional energy but only converts
electrical energy to heat (heat is not our friend). Peak-hold injectors are
designed so that they don't saturate until somewhere around 4 1/2 Amps while
Hi-Z injectors are just under saturation at 1.5 Amps.

You WILL see an improvement in response time but be sure to limit your Peak
current to less than 1.3A. Peak power will be around 25 Watts but only for
longer pulses. Because of the greater inducance of Hi-Z injectors, it will
still take > 2 ms to reach Ipk.

Turn-off time is also important if you expect to see real improvemets.. The
faster we try to stop the current. the higher the voltage spike (V = L
di/dt). As L is of the order of 25mH as opposed to 5 mH in a P-H injector,
your FET will need to handle 80-100 Volts. Again, that is if you want to
REALLY make a difference at idle and low power levels.


----- Original Message ----- 
From: "David Allen" <davida1 at hiwaay.net>
To: <diy_efi at diy-efi.org>; "GM-ECM" <gmecm at diy-efi.org>
Sent: Tuesday, February 28, 2006 10:06 PM
Subject: [Gmecm] High-voltage P&H IDM


>   Has anyone made a stand-alone IDM that will take an injector pulse from
a
> saturated-driver ECM, and create a peak and hold waveform?  I was thinking
> about making one that would operate high-impedance injectors (normally
used
> saturated) in a peak and hold configuration.  The peak voltage would be
30V
> (or thereabout) and the holding duty cycle would be set to create the same
> current flow as the injector at 12VDC. This should improve opening time
and
> result in a more linear low-pulsewidth map. I am thinking of this as a way
> to use big injectors on a small turbo engine without idle issues.
>   This would be fairly easy to do with a microcontroller and some power
> electronics.  I figure this has been done before. The direct-injected
> diesels use high voltage IDM's to get their injectors to work efficiently.
>   Any thoughts?
> David
>
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