James,

I'm curious which vehicles are using P&H injectors, as I was recently=20
trying to figure out where to get P&H injectors locally, and all the=20
auto stores can only reference it by the make/year/model of the vehicle.

Oops -- I meant 0.05-ohms (not 0.5-ohms).  It was a quick starting value=20
I chose when working out if the A/D would work for this.  0.05 at up to=20
6 amps (which I'll need periodically at higher rail pressures) =3D 0.3V,=20
which with a 2.5V reference on an 18F would give a 122 A/D steps, so a=20
bit better than 1% adjustability.  But yes, the A/D measurement time is=20
too long, so I'm going to use a comparator instead (with an external DAC=20
to set the trigger level), and probably go lower to 0.03 ohms for the=20
sense resistor.  But that may change again based on noise.

Cheers,
-Neil.


On 10/10/2015 12:35 PM, James Holland wrote:
> I read a lot about PWM being used for Peak-Hold injectors but most=20
> people seem to be quoting the same source without doing any real=20
> research and I've seen articles describing how PWM is used on certain=20
> ECUs that I know use current feedback. I've tinkered with a good few=20
> P&H ECUs and worked on P&H injector designs for an OEM. The PIC A/D is=20
> likely to be too slow, particularly if its servicing a lot of other=20
> channels, a comparator based circuit is the usual method with a single=20
> comparator for the peak detect and a window comparator to maintain the=20
> hold current within fixed limits. 0.5R seems quite high, I was working=20
> on an ECU today that uses a 0.27R resistor and its a 5W ceramic; the=20
> injector on that one is 1.5mH 1R at room temperature. James=20

--=20
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