Thorp Air Command - T18.net

Wondering what voltage builders are set up for? I was going to go 12v, but because I am putting in an EFIS I am now considering going 24v as it won't shut off when starting up the engine.

Can I get an inexpensive 24v alternator out there that isn't too heavy?

It seems as though "electrical wise" it is smarter to go with the 24v system....

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Dean Cuke
Visalia, California
N772DM
KVIS

You're better off with the 14v system. In terms of price (24 volt batteries are $$$$) and in terms of availability of components. You loose the ability to use auto components (alternator, starter, volage reg, lights, etc ...) plus the vast majority of general aviation aircraft (the 'little' ones at least) are 14 volt so surplus parts are easy to come by. If you go 28 volt you'll be shopping with the big guys and paying for it dearly ($$$). The only big advantage in going 28 volt is in the weight savings you'll see by using smaller gauge wire but that may be a lb. at best. Certainly not enough to justify the expense.
There are plenty of 14v EFIS products out there, I would not let one component drive the whole aircraft.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

The EFIS can easily run on 12volts. However, when the starter is engaged for that brief moment it will reset the EFIS. takes about 15-20 seconds for the O.S. to reload.

I was going to run the oil pressure gauge through the EFIS, but maybe going traditional analog with the oil pressure would eliminate the need to rely on the computer at startup. I can also put a small backup battery for the EFIS as well (just didn't want the extra weight or expense).

I see your point though, as far as keeping the rest of the project too expensive.

On another note: my original plan was to keep it simple with breakers and wires. On a 24 volt system, I could easily get away with all 10amp breakers (excluding alternator / landing light) with #18 wire. On a 14 volt system, should I be using a different gauge? What is everyone else using?

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Dean Cuke
Visalia, California
N772DM
KVIS

Sounds like the backup battery is the way to go. If you have the EMS ability on the EFIS you might as well use it. What unit is it?

As far as wire gauge goes. I used #4 from the battery to the starter (through the solenoid), #8 to the main bus and shielded #8 from the alternator to the bus. Most everything else was either 18 or 20 gauge depending on the draw.

Here's the chart for that ...

Image Insert:

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

During the start you might get away with a supercap and a shottky diode to hold the EFIS up while the battery is pulled down for start. You have to know the run current on the EFIS and estimate the total time the battery is unavailable to estimate the capacitor size. They are making pretty incredible farad size capacitors these days that are pretty small and weigh less than a spare battery. They aren't cheap though.

Steve

Guys,

We have to remember that these planes fly because of Bernoulli, not Marconi!!


Jim Mantyla

I have a Dynon engine monitor, the last time out flying on a cold day, the bus voltage dropped to 9.5 or so (did I say that it was cold and the engine was very cranky?) and the engine monitor kept on truckin. What is the min voltage of the efis you are considering installing. Most systems will operate with reduced voltage. The people that I know with glass panels are not complaining of them rebooting during engine start, my opinion is it's a non-issue, disclaimer "I may be wrong". [:)]

I don't know of any "cheap" 24/28V alternators or batteries, most at that voltage are stamped "aviation" with an appropriate price tag.

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Bruce Finney
N18JF T-18C #262
Yelm, WA USA

The EFIS is from Blue Mountain Avionics. It is a G4 and uses a maximum of 15 Watts and will operate from 9-32 volts. My concern is that in the installation manual it recommends using an aux battery (12v system) for the start up so that you don't get a restart wait time.

The only reason I started to consider going 24v is because of what this manual was saying and also from reading the engineer's notes on aircraft wiring. The engineer/designer of this EFIS by far believes that 24v is the only way to go. Perhaps the engineer never considered expense for the home builder.

@Lee - I think after reading your post I am swaying back to 12v. I want flying to be affordable now and in the future.

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Dean Cuke
Visalia, California
N772DM
KVIS

Dean,

Sounds like you're leaning towards the 14v system now. Another reason that's a good choice is that you can get a "jump" from any automobile if you ever need it.

John Evens N71JE
Arvada, CO

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE