This time with the attachment.
Ed,
I think you did understand what I was
saying. I have attached a circuit sketch to make certain my
suggestion is correctly understood. There may be couple of other
factors to consider in selecting the pull down resistor. Normally the
current to energize the injector coil and make the pintle move is greater than
the current required to hold the pintle in the open state, so if the pull down
resistor value is too low the current may not drop low enough to allow the
pintle to close (like gating an SCR.) Without putting calculations to it,
my gut feeling would be a higher resistance value say 1KΩ, it would give more margin to the
closing current (or lack of.)
On the safety side of things:
* Does it add a failure point to the system?
I don't think it would. if the pull down looses its smoke, the circuit would
still operate but probably richer.
* After a change like this, I would also do ground
testing to see if this has affected the minimum voltage requirement for
operating the system. (Min Bat voltage.)
If you get this all sorted, I would
appreciate feedback as well as your formula for fuel flow based on the EC2
data. As you can see in the following screen shot from my AC CPU, I don't
have a formula yet for calculation from EC2 Value to Engineering
Units.
Hope this helps,
Joe
----- Original Message -----
Sent: Sunday, March 11, 2007 11:16
AM
Subject: [FlyRotary] A solution? was :
The truth??? / Injector flow rate mystery solved
Sounds like a reasonable approach to me
Joe. A pull-down resistor would be relatively easy for me
to install - I have the resistor pack required for the peak-hold
type injectors. So I could easily place four
additional resistors in that box.
If I understand you (please correct me if I don't), the
pull down resistor should go between the injector and the EC2 sinking
terminals. That way the current induced when the intended pulse
terminates and the magnetic field collapses will have a path to ground rather
than being opposed by the diode in the Ec2.
The value of said resistor could be around 100
ohms. Since the induced voltage could reach from 50 - 100+ volts an 100
ohm resistor could flow from
0.5 - 1 Amp (for a very short duration). As far as
affecting the 12 Volt signal it would only draw 12/100 = 0.12 amp or 120
milliamps. That would be pulled through the injectors at all
times. The injector resistance is probably (peak and hold case)
around 3 ohms. So the injector would draw 12/3 = 4 amps (DC case - its
undoubtedly less due to the A/C impedance of the coil). It make take
some experimenting - but 100 ohm looks like a good place to
start.
The wattage should probably be around 5 - 10 watts just
to be on the safe side.
So certainly looks like a suggestion that would work,
Joe.
Ed
----- Original Message -----
Sent: Sunday, March 11, 2007 10:54
AM
Subject: [FlyRotary] Re: The truth??? /
Injector flow rate mystery solved
ED, George, Steve,
A strong contributor to this may lie in the
fundamental design of the EC2. It's output control is sinking rather
than sourcing. If it were sourcing the positive EMF would be switched
and the other side of the could would always be grounded, leaving a
place for the coil breakdown current to go. Well the controller is
what it is, so the question become what can we do to work around the
problem? Encoders are used often in industrial applications,
these are generally connected in a sinking fashion just as the EC2. In
high frequency (encoder pulses) applications the impedance of the input
electronics is often to slow to bleed of the leading edge of the encoder on
voltage before the next pulse cycle. End result is that the input does
not detect tithe state change. The solution is very simple for the
described situation is very simple. Installing a pull down resistor
between the sensor signal line and ground. This technique is used with
standard input electronics with pulse trains up to 50kHz, which translates
to a cycle period of 20µS.
How does this translate to our
application? If we were to add a pull down resistor in injector signal
line, which may very well be a simple method to reducing the off delay
time. This would of course add a small increase in the current for the
injector circuits, but that increase would likely be minimal. The
value of the resistor would certainly need to be determined using factors
such as Injector turn on voltage, turn off voltage, device current,
etc. IMO this may be a simple solution to the delay
issue.
In the end I defer final recommendations to
Tracy, who certainly knows the characteristics of his controller system
better than I.
Joe
----- Original Message -----
Sent: Saturday, March 10, 2007 11:44
PM
Subject: [FlyRotary] Re: The truth???
/ Injector flow rate mystery solved
Ed and
George,
In my plane, at
least, injector open times need to be less than 2 ms at idle and just
above the staging point. This
is not possible with a minimum open time of 2 ms due to the delay on
closing. You can program the
EC2 for less than 2 ms but the hardware is unable to do this. That means that the problem can’t
be fixed with software or programming different values in the map
table. A shorter close delay
time is required unless you lower the flow rate of the injectors by
changing the injector itself or lower the fuel pressure. The injector open time is at least
2 ms or it doesn’t open at all.
Steve Boese