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I’m building a fairly simple LSA. it will have a Garmin G3X touch screen with remote com, xponder, and EIS but pretty much nothing else. trying to keep it simple and light. To that end, i’ve decided to use a manual master switch rather than an electrically activated master relay. it will go under the seat next to the battery and starter relay. As with everything, there are tradeoffs galore, but here are a few reasons i decided to go this way:
- simplicity. the plane will fly fine with nothing powered so i am not concerned so much about redundancy
- safety. being able to disconnect the battery from the whole plane manually appeals to me. i was used to it when racing sports cars, as it was a requirement.
- weight. this switch is lighter than a master relay.
- power. a master relay pulls a lot of current all the time it’s on. i’m going minimalist on alternator so didn’t want the extra load.
The other choice was to put the battery on the firewall and put all relays right next to it with a very short wire to the starter. this would make the cables a lot shorter. the downside is the heat. I know people put the earthx batteries in insulated boxes forward of the firewall, but i didn’t want to do that. with the starter relay under the seat, the only thing the fat wire going forward does is power the starter. i will do some current measurements to hopefully downsize the starter wire from a #4 to a #6. a much smaller wire will go to the power bus with fuses to run electronics and a few LED lights.
So here is the first cut at packaging. fasteners are all temp, but the position is working out well. it clears everything well and i can reach it from the seat with no problem.
IMG_1287.jpg IMG_1288.jpg
- simplicity. the plane will fly fine with nothing powered so i am not concerned so much about redundancy
- safety. being able to disconnect the battery from the whole plane manually appeals to me. i was used to it when racing sports cars, as it was a requirement.
- weight. this switch is lighter than a master relay.
- power. a master relay pulls a lot of current all the time it’s on. i’m going minimalist on alternator so didn’t want the extra load.
The other choice was to put the battery on the firewall and put all relays right next to it with a very short wire to the starter. this would make the cables a lot shorter. the downside is the heat. I know people put the earthx batteries in insulated boxes forward of the firewall, but i didn’t want to do that. with the starter relay under the seat, the only thing the fat wire going forward does is power the starter. i will do some current measurements to hopefully downsize the starter wire from a #4 to a #6. a much smaller wire will go to the power bus with fuses to run electronics and a few LED lights.
So here is the first cut at packaging. fasteners are all temp, but the position is working out well. it clears everything well and i can reach it from the seat with no problem.
IMG_1287.jpg IMG_1288.jpg
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