Hi folks,
I'm setting up my airplane with one magneto and one Lightspeed Plasma III ignition. The airplane has one Odyssey PC680 for its main battery, plus another ~4.5 Ah battery under the baggage floor that's there to keep the most important avionics alive during engine cranking (similar to the setup described in this recent thread). Since I have this second battery already, I wanted to find a way to let the LSE ignition also get power from the aux battery during engine cranking. I don't want to use a separate "power select" switch as described in the Lightspeed manual, since I already have my panel cut for a single switch. I've read the Lightspeed documentation and all the various threads about wiring the LSE ignition, and I haven't come up with a solution that I find totally satisfactory. Here's what I have sketched so far:
I know the ignition will certainly get power from both batteries if I hook it up this way. However, I find all those extra shield connections to carry around the ground side of the circuit to be worrisome. So I guess my main question is: For those who are flying with Lightspeed ignitions, did you follow the instructions to use the power wire's shield for ground? If so, or if not, have you experienced any problems with comm, nav, or audio interference from the ignition?
thanks,
mcb
I'm setting up my airplane with one magneto and one Lightspeed Plasma III ignition. The airplane has one Odyssey PC680 for its main battery, plus another ~4.5 Ah battery under the baggage floor that's there to keep the most important avionics alive during engine cranking (similar to the setup described in this recent thread). Since I have this second battery already, I wanted to find a way to let the LSE ignition also get power from the aux battery during engine cranking. I don't want to use a separate "power select" switch as described in the Lightspeed manual, since I already have my panel cut for a single switch. I've read the Lightspeed documentation and all the various threads about wiring the LSE ignition, and I haven't come up with a solution that I find totally satisfactory. Here's what I have sketched so far:
- A pair of diodes (or half a bridge rectifier) is used to let the ignition draw power from either battery.
- As per the LSE instructions, I've drawn this using the ignition power wire's shield to provide the ground connection. Obviously you wouldn't want to ground the shield at both batteries (ground loop) so I show it grounded next to the main battery only. This part of the LSE documentation seems like voodoo to me, but I'm trying to follow it as best I can. That's going to be a lot of shield connections, though!
- I don't like unfused conductors attached to batteries, so power from the main battery comes from the always-hot battery bus fuse block on the firewall, right next to the main battery. Power from the aux battery comes from a similar fuse block next to the small aux battery.
- I drew provisions for a filter capacitor next to the ignition box, per this thread.
I know the ignition will certainly get power from both batteries if I hook it up this way. However, I find all those extra shield connections to carry around the ground side of the circuit to be worrisome. So I guess my main question is: For those who are flying with Lightspeed ignitions, did you follow the instructions to use the power wire's shield for ground? If so, or if not, have you experienced any problems with comm, nav, or audio interference from the ignition?
thanks,
mcb