Joe;
You are
right. We discovered this crossfeed issue some time back. Is
applies only to the 20B version as the 13B has separate drivers for each set.
Install Schottky diodes in the circuits for each injector.
Tracy is aware of this,
and has installed the diodes in his as well.
Al
-----Original
Message-----
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Joe Ewen
Sent: Sunday, October 14, 2007 3:20
PM
To: Rotary motors in
aircraft
Subject: [FlyRotary]
EC2 20B Injector Power Circuits
I have been testing my wiring
harness from the EC2. I found a behavior that I did not expect.
The manual drawing (EC2 manual) show a single injector supply that splits at
the Injector primary and secondary disable switches. On my installation,
I have 2 separate feeder circuits, supply Primary comes from battery 1,
and supply Secondary comes from battery 2. I did this for
redundancy. If I had a failure such as a short to ground in either
circuit, its related overload should trip, but the other circuit should remain
active.
While testing the injector
circuits, I noticed what I would term an abnormality. With both injector
disable switches in the enable position, I turned on the power for the primary
circuit (I have LED indicators on all circuits that annunciate power present)
and the secondary circuit also showed power present even though the power
switch for the secondary circuit was off. The same is true when the
secondary circuit is engaged and the primary is off.
Initially this led me to think I
had miss wired something in the circuit. After checking out the wiring,
I found no issues. So I took a closer look at the wiring diagram in the
manual. It turns out the power was being back feed through the injectors
to the opposite circuit. On the 20B version of the EC2, the injector
control lines for each rotors injectors are junctioned going into the
EC2. For example the Rotor 1 Primary and Secondary control lines are
junctioned into a single input point at the EC2.
I can see several situations where
this may lead to undesirable operation. For example, if the Primary
circuit had a hard short to ground, it would take out the primary circuit's
overload (CB or Fuse.) Since the primary and secondary circuits are
electrically connected on the control line, the other circuit would also
trip. Another situation that could occur is a medium to high resistance
short. Current would then flow uncontrolled through the unaffected
circuit's injector to the affected circuit's injector then to the resistance
short. This could keep both injectors on 100%. While this
situation is unlikely, it seems possible.
I believe the 13B version
uses separate control lines for each injector, so this in not likely to be an
issue on the 13B version.
It appears that isolation diodes
are needed to prevent these possible problems. Before making any changes
I have to look the circuit over more closely, as well as a call to Tracy on
the next service day. My question to the group, especially anyone with a
20B, is am I looking at this wrong?