What about MOV's?  Typical transient response time measured in nanoseconds...

   <Marv>  




"Steven Boese" <sboese@uwyo.edu> wrote:

Ed and Joe,

The diode in the EC2 allows the current from the collapse of the
injector magnetic field to flow to the positive supply rail (~14V); it
doesn't oppose this. A resistor allowing this current to flow would
also result in a close delay since the current flowing is what maintains
the magnetic field during this delay. What is needed is a way to
decrease the rate of voltage rise just after the EC2 pulse ends so
arcing in the A/B selection relay is suppressed. After the relay
contacts open enough that an arc is no longer possible (which shouldn't
take long) an open circuit condition now would allow the injector to
close quickly. The arcing may or may not be a problem any given time
the relay is opened since the timing of the end of the EC2 pulse and the
opening of the relay are independent and arbitrary. One possible
solution is a RC snubber rather than the resistor that Joe proposed. I
think Tracy is working on checking this out. I have installed this in
my plane and it works. Tracy, however can do a much more thorough job
of evaluating this and be sure the change is reliable. Let's give him a
chance to do this before we do something we wish we hadn't.

Steve


-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Sunday, March 11, 2007 9:16 AM
To: Rotary motors in aircraft
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