What System Voltage?

[RVG8tor]

I am really early into this build but there are some electrical items I need to decide on soon and don't know which way to go. Do most people build a 12 volt system or are there other options (28v). I am leaning toward the 12v system since I can save weight and some money by using automotive items, though I hear I should use aircraft grade wiring. Thanks for the help. Oh I plan to go glass cockpit, light IFR, leaning toward the Garmin 430.

Cheers

[jdmunzell]

For what it's worth, I recently helped a buddy replace a 28 volt battery in his T-6, and that battery was around 80-90 pounds!! That seems like a lot of extra unnecessary weight to me if you don't require it.

I do know several RV'rs however, that have dual 12volt sysems on their -8s(complete with two independant batteries). Don't how much more or less their extra weight is in comparison to a 28volt system.

What type of equipment would you anticipate putting in that would require a 28volt sys. over a 12 volt one?

[PCHunt]

The weight of a battery has no relationship to its voltage. Some 6v batteries weigh hundreds of pounds, some weigh less than an ounce. 28v batteries come in all shapes and sizes, as do 12v batteries.

The weight of a battery is directly related to its capacity, or energy storing ability.

[Newco7]

A 12 volt system is fine for what you are doing. Dual battery's work just fine.

[John Clark]

There are a couple of technical advantages to a 28 volt system. The wires can be smaller for a weight saving and starter motors are a bit more efficent. BUT the downside is cost. I had a 28 volt Beechcraft Baron and learned a few valuable lessons. 28 volt batteries are more expensive, even at the same weight. The Baron had two 12 volt batteries, but I doubt many RV builders are interested in the extra weight. The real eye-opener is the cost of simple things like light bulbs. The example I recall was a 100w landing light bulb, 12volt $10.00 28volt $26.00. Also, with 28v you can forget about using any automotive bulbs like halogen landing/taxi lights.

John Clark
RV8 N18U "Sunshine"
KSBA

[Jeff R]

I had been contemplating this, too. As an EE, I am well aware of the advantages of higher voltages. However, there are fewer 28 volt systems out there, so a 12 volt system will be less expensive. So, I am going 12 volt. Most of the solid state systems I have seen will work with either 12 or 28 volt systems.

[gmcjetpilot]

There have been several threads on this you can search in this forums archives. Bottom line higher voltage more efficient allowing smaller wire gauges. However we have a small plane with relatively short wire runs and low current devices. A large plane with 1000's of miles of wire can save weight with higher voltage, a RV not so much. As was suggest above the path of least resistance (pun intended) is go 12 volts, its common and most components are readily available. 28v avionics and items by the way cost more and/or will be harder to find, everything, contactor's, pump's, light's, avionics ..... Example given above about battery. The little Odyssey batteries are easy to get, light, small and 12 volts. Go shop for, find, price (size and weigh) a 28 volt battery?

Most likely 28v cost more because they tend to go in larger planes thus they charge more. There is no debate 28v is more "capable", but 12v (more like 14.5 volt) is plenty-good-E-nuff. If you are going to be running hot props, hot windows, heated seats, radar, electric driven A/C compressor.............. yes 28 volts, heck 48 volts and a side of 400Hz AC. Keep it simple and follow the crowd.

[jdmunzell]

Originally Posted by PCHunt

The weight of a battery has no relationship to its voltage. Some 6v batteries weigh hundreds of pounds, some weigh less than an ounce. 28v batteries come in all shapes and sizes, as do 12v batteries.

The weight of a battery is directly related to its capacity, or energy storing ability.

Thank you for pointing that out. I meant to make mention of that but neglected to do so. Granted, I do not know much about 28 volt batteries aside from what goes in a T-6, and I'm sure they do come in various sizes (same as 12 volt batteries). All I know is that battery was a b!@#$ to hoist up and get into it's compartment in the 6. Oh, by the way....the best thing about flying a T-6... is someone else owning it!

For me, 12 volts for my -8 will be all I need for my application.

[asav8tor]

Just get 2 Odyssey batteries wire them in series and you can have a 14v bus and a 28v bus. Some used avionics are cheaper in the 28v version because us RV guys pass them up.