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So does this mean I shouldnt finish installing my EC2 cause I may have to send it back to Tracy? Nows the time for me. I'm installing now.
Bob Mears
Supermarine Spitfire
-----Original Message-----
From: Joe Ewen <Jewen@comporium.net>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Sun, 14 Oct 2007 10:28 pm
Subject: [FlyRotary] Re: EC2 20B Injector Power Circuits
Hi Bob,
Don't know if you don't ask. A diode is a device that allows current to flow only in one direction (DC circuit.) Schottky is a particular diode construction. One desirable feature of a Schottky is that it has a low forward voltage drop. All diodes have a drop in voltage (like a small resistor.) In this case, the lower voltage drop allows the injectors to continue firing slightly longer than other diode types in the event of an alternator failure and lowering battery voltage.
On the 20B, the injector control lines are wired together, installing the diodes prevents the current / voltage from back feeding between the primary and secondary circuits and the possible failure modes I noted earlier. Application of diode(s) in this manner is typically referred to as isolation diodes.
Since the EC2 controller internal jumps the 2 controller power feeds, I installed isolation diodes (Schottky) to prevent similar problems between the 2 supply circuits.
You may also find diodes useful in making annunciator press to test circuits. If you have 2 devices such as a transponder and a GPS that both need to share altitude encoder inputs, isolation diodes would be used. Of course with any avionics installations, follow the manufactures guidelines.
Joe
----- Original Message -----
Sent: Sunday, October 14, 2007 10:16 PM
Subject: [FlyRotary] Re: EC2 20B Injector Power Circuits
Al
Hate to continue to display my ignorance but what is a Schottky diodes. When it comes to electronics I’m as dumb as a stump.
Bob K
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Sunday, October 14, 2007 5:42 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: EC2 20B Injector Power Circuits
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?
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