12v or 24v?

It turns out that I need to start making some decisions about my little project early on and this may be one of them. Is there any benefit of choosing one over the other and is there any particular engine layout that would proclude me from choosing either one? Are there any benefits of 12v or 24v over the other? How did you decide?

Thanks as always,

Will
#91056

12 Volt

I fly both 172's and 152's for work. The 172's all have a 12 volt system and it makes life much easier. Need to plug in a PDA, computer, or cell set, no problem in the 172. Battery needs a charge, everyone has a 12 volt charger. Need a jump start, just use your car. Now, try any of the above in the 152. The 152 needs a converter to use your 12 volt plug in accessories and I bet that you don't have a 24 volt battery charger laying around either. Forget the jump start. Most of the avionics,engine gauges, lights, starters, and alternators are cheaper and more plentiful in the 12 (14) volt version. IMHO 12 volt is the only way to go.

Jim

Current

For well designed equipment, the current required for a 24V item should be nearly half of that required for the identical 12V item.

The thing I don't know is if most avionics are 'well designed', the could very well use linear regulators and therefore require the same current regardless of input voltage.

Anyways, the advantage here is that you could use lighter guage wire, thus saving (however little) weight...

The only disadvantage I can think of off the top of my head, is that the majority of non-aircraft specific electronics runs off of 12V, so you'd have to buy aircraft specific (read, expensive) things like CD players, etc, if you want that kind of stuff...

Greg Richter on the Blue Mountain site is a proponent of 24 volt systems, but his main argument is that if a 12 volt battery goes low, it will be dead almost immediately, whereas he says that if a 24 volt battery goes low, it will still drive all the radios down to below 10 volts.

I'm afraid I don't buy the logic in that (a dead battery is a dead battery, and a 24 volt battery may produce voltage below it's design rating, but I can't imagine that it's putting out any amperage worth a flip. Somebody please correct me if I'm wrong about that.)
I'd much rather have a 12 volt system that incorporates a standby alternator than a system that depended on the final throes of a dying 24 volt battery.

Bob Nuchol's of AeroElectric Connection suggest's a system (his "Z-13" drawing with two alternators and one battery) that seems to offer more backup redundancy than any single alternator system could even with a second battery.

As far as being able to use smaller wire in a 24 volt system, I don't think that would make much difference in an RV. Now in an AeroStar or Lear, you could be looking at a couple of hundred pounds difference