Power Distribution and Buses

[lakespookie]

That's a handy graphic to refer to. None of your instruments have trouble with that drop to like less than 8.5 volts? I'll have to dig through the Garmin encyclopedia later and see if there's a specified minimum.

I looked through the G3X manual but I couldn't find an actual min voltage spec. Just this note on page 27-1:

14. TO MINIMIZE THE CHANCE OF THE SYSTEM RESETTING DURING ENGINE CRANKING, THE OPTIONAL REDUNDANT (DIODE OR'D) POWER INPUTS MAY BE CONNECTED TO AN AUXILIARY BATTERY (SUCH AS THE TCW TECHNOLOGIES INTEGRATED BACK-UP BATTERY SYSTEM) OR STABILIZED POWER INPUT (SUCH AS THE TCW TECHNOLOGIES INTELLIGENT POWER STABILIZER IPS-12V-8A) TO MAINTAIN THE NECESSARY LRU MINIMUM INPUT VOLTAGE. HAVING A STABLIZED SOURCE OF POWER DURING ENGINE CRANKING SHOULD ALLOW THE SYSTEM TO PROVIDE CONTINUOUS ENGINE INDICATING SYSTEM (EIS) OPERATION DURING ENGINE START AND MAINTAIN ANY DESIRED PRE-FLIGHT SYSTEM SETUP OR FLIGHT PLANNING THAT WAS ACCOMPLISHED PRIOR TO ENGINE START. VISIT
http://WWW.TCWTECH.COM

So this actually says to connect the optional power inputs to the power stabilzer... I'll have to figure out if what I was planning will work or maybe I need to change some stuff!!

you can either use the stabalizer or a battery the way the dioed or module works is basically like having a convergence of two inputs with one output with a check valve so if you think of it in terms of water. You have two independent sources of water but the one with the higher pressure, will feed the line and the check valve (The dioed) will prevent backflow to the lower pressure line. so if your voltage were to drop during cranking or become unstable the dip will be covered by the other source of water (Electricity). Thats why you want to connect it to the second input line so that the dioed cuircuit can prevent any electrical back flow without complicating the rest of the aircraft wiring.

[Spaceman]

OK I was thinking more about that power stabilizer and how best to use it to get my setup to work the way I want it. What I had in version 1.3 was pretty much what's shown on page 5 of the IPS instructions: https://www.tcwtech.com/Installation%20 ... %20IPS.pdf ... which is the simplest way but it puts all the avionics in series with the IPS. So if the IPS failed somehow I suppose I would lose power to all those items.

So here is version 1.4-A. This is pretty much the same as version 1.3 except I'm powering the avionics bus directly from the main bus and also with the IPS in parallel. Does that work? Maybe I need to put a diode between the IPS and the main bus to prevent the main bus power from flowing the wrong way back down the IPS like you're talking about lakespookie, since in this instance I'm not taking advantage of the internal diodes of any of the Garmin components....

I think I'd either need to add a diode to this setup, or use the dual power inputs of the Garmin stuff instead. I am sketching that up now so I'll post it next.

[Spaceman]

Here's version 1.4-B. I started drawing this as soon as I had the diode realization looking at 1.4-A. I think this is a more correct answer than the previous version.

So now I have all the Garmin avionics powered from the main bus to each power input #1. Then I ran the IPS, also from the main bus, to another sub-bus, which then feeds all the #2 power inputs. I'd lose stabilization for the ELT and fuel probe in this case but I don't think that'll matter. Everything else would be the same as 1.3-A so I didn't fill in all the details of the other systems.

I think this closely resembles page 12 of the IPS instructions (https://www.tcwtech.com/Installation%20 ... %20IPS.pdf), with the exception that I don't have an avionics master switch.

I really don't see the point of putting these items on a switch downstream of the master switch... I can't think of many situations I'd put power on the plane and not want the display to turn on, and at that point I might as well spin up the GPS, ADAHRS, etc for how small their loads are. I only put the radio and transponder on their own switched bus because their power consumption is too high for the stabilizer... I'm trying to minimize unnecessary switches on the panel... What do you guys think?

[lakespookie]

Last one looks pretty good =). of course its 1am so my eyes might not be working great lol

[Spaceman]

of course its 1am so my eyes might not be working great lol

Haha that's where I was at last night drawing these out. Just noticed I put the comm and utility buses In series again with the main bus for no reason. Disregard that part!!