12/14v vs 24/28v systems

[az_gila]

While I still prefer 12v systems personally, there is one factor for 24v that no-one has mentioned yet.

Used avionics are cheaper in their 24v versions. Just look on e-bay, the price is bid up far faster for a KX-155 that is a 12v version than a similar (and probably newer) 24 volt version.

If you are planning lots of avionics, and like the older King stuff, 24v might save you $$ on avionics...

gil in Tucson

[w1curtis]

Originally Posted by az_gila

While I still prefer 12v systems personally, there is one factor for 24v that no-one has mentioned yet.

Used avionics are cheaper in their 24v versions. Just look on e-bay, the price is bid up far faster for a KX-155 that is a 12v version than a similar (and probably newer) 24 volt version.

If you are planning lots of avionics, and like the older King stuff, 24v might save you $$ on avionics...

gil in Tucson

Sometimes! Anyone planning to use the Grand Rapids system with 24/28 volts, be advised that they charge about $150 more for 24/28 volt unit.

[gmcjetpilot]

Originally Posted by az_gila

While I still prefer 12v systems personally, there is one factor for 24v that no-one has mentioned yet.

Used avionics are cheaper in their 24v versions. Just look on e-bay, the price is bid up far faster for a KX-155 that is a 12v version than a similar (and probably newer) 24 volt version. If you are planning lots of avionics, and like the older King stuff, 24v might save you $$ on avionics...

gil in Tucson

I agree and disagree. Yes used king stuff like the comm 14 v 28, the 28v is a bargain but not by a large margin. On the other hand 28 volts stuff can cost way more.


Another advantage of 28 volts in the avionics/Inst area is an electric attitude gyro. Many of the small electric surplus units are either 28 volts or 115v/400hz. The 115v/400hz inverters only run on 28 volts. Going from 14 to 28 volts is a pain and impractical in cost and weight. So if that is your game plan is to use 28 volt equip, you are justified from that stand point.

Also Whelen only offers a 28v LED lights, not 12v.


28 volt is technically superior, heck 48 volts better from a power (V*I) transfer standpoint. When you have long runs (like on big planes) the saving in wire weight (because you can run lower amps due to higher volts and smaller wires) is significant. On a little RV the savings in little to none by going to 28 volts.

Also RV's are pretty simple with low electrical load systems. If building a Lancair with large electric motors, electric hydraulics 28 volt makes more sense.

14 volt is still the status quo. If you go buy a starter, alternator, battery, relay, avionics, lights you will find 14 volt is more readily available, new and used.

28 volts is technically superior. 14 volts is more practical. No of this is a turn on to me, so I went with a 14 volts system.

[aadamson]

George,

Would your vote differ based upon the kind of avionics you were going to fly behind? Not the brand, but the type and electical circumstances?

For example, if you were flying behind a VFR airplane with 6 pack with vacuum and a single nav/com with VFR GPS, I could see where the strong tendency would be for a 12/14v system - weight savings, avail, etc.

If you were flying behind a full IFR EFIS system with no vacuum, dual electronic ignition and fully redundant alternators, busses, and batteries. I'm curious if you'd still prefer a 12v over a 24v?

I went down the 24v route - mostly because if I do loose the main alt, the backup doesn't have to work so hard providing me "soft" access to the ground .

I find it's interesting as well. Heated pitot tubes are half the price in 24v as they are in 12v.

Just curious, good discussion btw.

[johngoodman]

I've enjoyed this discussion. Lots of good points. I'd like to add another: If you are building an RV-10 and are thinking about air conditioning, the 24/28v makes a lot of sense. You can put an electric compressor aft and not bother with an engine driven compressor. Also, You can run the air conditioning on the ground with a GPU.
John

[gmcjetpilot]

Originally Posted by aadamson

George,

Would your vote differ based upon the kind of avionics you were going to fly behind? Not the brand, but the type and electrical circumstances?

Absolutely, I forgot about the 24 volt pitot, and John's comment about the A/C.

Yes, that was the answer, there is no one answer; no one system voltage is "best". It depends on the equip and mission. Most of the modern avionics run on 10-30 volts anyway.

Also dropping down to 14 volts is easier than going up, so just because you have a 28 v system, does not mean you can't still run a few 14 volt items.

Cars are going to be 42 volts not far down the road. If it was not for inertia (so many cars with 12 volts in service) we would be there. With the Hybrids and the increasing demand of electrical components in cars, the higher voltage makes sense, just like it does in a plane. Some cars have 130 amp alternator! However the inertia issue of 12 volts is real and a consideration.

Cars where 6 volts at one time, right.

[PJSeipel]

Originally Posted by gmcjetpilot

Also dropping down to 14 volts is easier than going up, so just because you have a 28 v system, does not mean you can't still run a few 14 volt items.

This is the route I went. About 95% of my stuff is 28v. For those things that were either really expensive or hard to get in 28v, I've got a small 12v bus. None of the stuff on that bus is critical, so if my converter goes TU, no big deal.

PJ
RV-10 #40032

[aadamson]

Originally Posted by PJSeipel

This is the route I went. About 95% of my stuff is 28v. For those things that were either really expensive or hard to get in 28v, I've got a small 12v bus. None of the stuff on that bus is critical, so if my converter goes TU, no big deal.

PJ
RV-10 #40032

Yup, same with me.... I figure if Cessna can use this convertor, then I can too.... And they are *cheap*.

http://www.radiooutfitter.com/store/124056/N241212.html

[johngoodman]

Originally Posted by gmcjetpilot

Cars are going to be 42 volts not far down the road. If it was not for inertia (so many cars with 12 volts in service) we would be there. With the Hybrids and the increasing demand of electrical components in cars, the higher voltage makes sense, just like it does in a plane. Some cars have 130 amp alternator! However the inertia issue of 12 volts is real and a consideration.

Cars where 6 volts at one time, right.

This talk about cars going to 42 volts is new to me; where is a good site to go for discussions on this?

PS: My first car was a '50 Chevy with 6 volts....

John

[johngoodman]

Well,
I got on the web and answered my own question. You can buy 42 volt cars & trucks right now. You can get a Silverado pickup with hybrid assist that is 42 volt and acts as a generator.
I noticed that some cars/trucks use a 42 volt battery and others use 36 volt, but all the alternators are 42. It looks like it's here to stay. i found numerous articles talking about the problems with 12 volt and on-board computers in cars. The move towards 42 volt is not being driven by hybrids, it's the computers.
John