papamike
Well Known Member
I apologize if this has been asked before. What is the consensus on whether to go 12V or 24V? I've been reading Aircraft Wiring for Smart People and he brings up some good points about using 24V.
Thanks
Thanks
Van's Air Force
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12V or 24V?
- Thread starter papamike
- Start date
Wayne Gillispie
Well Known Member
I would say 12 Volts for 99% of us. Yep it has been discussed, but not like primer. I am very happy with my 12 V system.
GusBiz
Well Known Member
Weight
Its about weight mainly, that's not the only consideration but it's what the main argument is about. 24v allows you to use thinner wire. So it is less mass, but the battery is alot heavier. What does that all mean in the end? Well for a small plane where wire does not fun for 10s of metres, small batteries and thicker wire is better.
Its about weight mainly, that's not the only consideration but it's what the main argument is about. 24v allows you to use thinner wire. So it is less mass, but the battery is alot heavier. What does that all mean in the end? Well for a small plane where wire does not fun for 10s of metres, small batteries and thicker wire is better.
The next major consideration (perhaps primary for some of us) is the price. Almost universally, where there is a price difference, 24-volt components are more expensive.
John Clark
Well Known Member
In a small aircraft the weight issue is not worth the cost increase. I owned a 24v Baron for many years and the difference in price for things as basic as light bulbs was breathtaking, not to mention batteries, alternators, regulators and starters.
John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
Try buying a 24V alternator from Autozone!...
"Ummm, yeah, I think it's a Suzuki Samurai..."
Before putting all your faith in that document, consider the alternative viewpoint from Bob Nuckolls:
http://www.aeroelectric.com/articles/richter/richter.html
Make sure to read the pdf files linked as first and second pass reviews.
Note: I am not saying that Bob is more right than Greg, but one should always consider both sides to every story.
http://www.aeroelectric.com/articles/richter/richter.html
Make sure to read the pdf files linked as first and second pass reviews.
Note: I am not saying that Bob is more right than Greg, but one should always consider both sides to every story.
N395V
Well Known Member
Has anyone ever calculated exactly how much weight would be saved in a typical RV by going to 28V as opposed to 14 V?
I gotta believe it is so insignificant as to be un-measurable.
Ultimately you are going to want to put something into the plane that is 14 v and not available in 28V. Now you add a converter, weight, and complexity.
Simple and cheap are better.
I gotta believe it is so insignificant as to be un-measurable.
Ultimately you are going to want to put something into the plane that is 14 v and not available in 28V. Now you add a converter, weight, and complexity.
Simple and cheap are better.
jdeas
Well Known Member
Weight savings
I do like to additional 'reserve' voltage that is proposed but given the discharge characteristics of modern batteries and operation of new EFIS systems I really don't see this as much of an issue.
I did the calculations based on my CANaerospace design. The weight savings is very very low. Most of the heavy wire (coax, starter cable, Shielded cable etc) are not impacted by the change to 24v. In cost per weight savings I saw it as a bust.
I do like to additional 'reserve' voltage that is proposed but given the discharge characteristics of modern batteries and operation of new EFIS systems I really don't see this as much of an issue.
I can't imagine saving any weight by going to 24V in aircraft like ours. The weight savings of wire would be in the ounces. The weight penalty of the 24V battery would be in lbs.
And that doesn't even get into the extra cost of 24V starters, alternators, light bulbs, etc.
There is no good reason to use anything other than 12/14V in 99% of these RV's (and most homebuilts for that matter). If you were running lots of wire between multiple engines across huge distances, then it makes sense (but then we move up to AC and very high voltages/hertz anyway). I can count on my modified hand how many RV's I've seen go 24V and it was only due to things like air conditioners, etc..
Also note that the weight savings would be minimal and on top of that it's 99% likely you'll still end up needing a 12V buss in the airplane anyway. Lastly, as others have mentioned it's difficult and expensive to find some of the stuff in a 24V version anyway (trim, flaps, some lights, some fuel pumps, alternators, batteries) so it just makes more sense all the way around to stick with 12V. I believe that Greg Richter did a calculation some years on weight savings and it was insignificant.
My 2 cents as usual.
Cheers,
Stein
Also note that the weight savings would be minimal and on top of that it's 99% likely you'll still end up needing a 12V buss in the airplane anyway. Lastly, as others have mentioned it's difficult and expensive to find some of the stuff in a 24V version anyway (trim, flaps, some lights, some fuel pumps, alternators, batteries) so it just makes more sense all the way around to stick with 12V. I believe that Greg Richter did a calculation some years on weight savings and it was insignificant.
My 2 cents as usual.
Cheers,
Stein
fstringham7a
Well Known Member
REitto
Stein I would suggest your modified hand is more accurate than those of us that have choosen, for now, not to upgrade to a better hand.
I ditto your observations on this subject!!!
ittoStein I would suggest your modified hand is more accurate than those of us that have choosen, for now, not to upgrade to a better hand.
I ditto your observations on this subject!!!
delusional
Well Known Member
I might be "speaking" out of turn here, never having built one, but taking a historical perspective, could I modify the op to "12v or 24v yet?" The number of items unavailable 28v shrinks daily, and tso'd converters are readily available. No, I doubt you would save much weight on cables, but in some cases you might be able to get away with a smaller alternator, which, even given the converter and associated wiring could save a little weight.
And consider this; just as those with 28v eventually want something 12v, those with 12v might find some day they want some gadget that needs, or prefers, 28v, in which case, it's easier to go down than up. You can get a converter for either, but check the prices, size and weight.
And consider this; just as those with 28v eventually want something 12v, those with 12v might find some day they want some gadget that needs, or prefers, 28v, in which case, it's easier to go down than up. You can get a converter for either, but check the prices, size and weight.
N941WR
Legacy Member
Having co-designed and built a small electronic instrument for the Experimental market, it does not add cost or weight to include a 12 to 24 volt voltage regulator. Thus I doubt you will find instruments that can?t run on both.
Besides, we are lucky in the E-AB world in that we are now the largest producers of aircraft and the manufactures are taking us into account when they design new instruments, which means 12 volts.
Stay with 12 volts, it is a lot easier.
delusional
Well Known Member
Bill, I am reluctant to discard your advice, so please help me see the piece I'm missing here. Since we agree that avionics can do either voltage, lights, alternators, battery, and starter, no problem; so what's left? Servos? It all come downs to just servos?
Easy for me to be so skeptical, since I haven't purchased one single electrical item yet....
Easy for me to be so skeptical, since I haven't purchased one single electrical item yet....
Most modern avionics, yes.
Well...
Lights: 24V lights available, pricey specialty aircraft item. Inexpensive automotive lights are typically 12V only.
Alternator: 24V alternators available, but not standard in the kit, less common. Pricey specialty aircraft item.
Battery: 24V batteries available, but not standard in the kit, less common. Pricey specialty aircraft item. Also typically bigger and heavier than 12V Odyssey batteries typically used in RV's.
Starter: Yes, 24V available, likely no difference from 12V, or configurable for either.
Ray Allen trim servos: 12V only.
Van's flap actuator motor: 12V only.
Fuel pump: Van's standard fuel pumps are 12V only. Equivalent 24V pumps may be available from other sources. Don't know.
Master and starter solenoids: Van's standard solenoids are 12V only. 24V solenoids available from other sources, but less common, and typically more expensive.
Heated pitot: Brands commonly used in RV's are 12V only. 24V pitot tubes available from more limited sources that are typically more expensive.
Just a few off the top of my head. There may be others.
That may be, but 12V is still far more common, and 12V items are not disappearing. Most modern avionics will continue to support both into the foreseeable future. And anything with roots in the automotive world is still also firmly planted in 12V.
Another box. More $$$, more complexity, another failure point. Run a common 12V system and you'll have no need for a converter.
Yes, hypothetically that could happen. But in reality, it just doesn't very often. Most of the fleet is 12V, and you will hardly ever find one with a converter to 24V. It's still a 12V world, and will likely remain so for the foreseeable future.
The "yet" might be a bad assumption.
An RV could certainly be built with a 24V electrical system if you're determined to do so. But it would entail significant extra work and cost associated with deviating from standard and commonly used parts, and ultimately all this is for dubious benefit that's marginal at best.
I don't think you're going to see many RV's with 24V systems any time soon, simply because, again, the extra work and cost is significant, and for most of the fleet there just isn't a very compelling reason to do it.
az_gila
Well Known Member
I'm not sure if that is true if you are buying used avionics.
A quick review of items like the KX-155 which come in either 12v or 24v versions shows cheaper prices for the 24v units - probably due to a smaller market...
Listen to those who are giving you the advice and just move on from the 28V thought process for an RV9. It's a waste of usefull time to continue thinking about it when you could be building instead!
Roee's list is only a start. I could go on and on, but again it's a waste of perfectly good time to discuss it for an RV9 so just trust these folks already.
Cheers,
stein
N941WR
Legacy Member
Good advice. Look up SteinAir, if you don't already know who he is.Listen to those who are giving you the advice and just move on from the 28V thought process for an RV9. It's a waste of usefull time to continue thinking about it when you could be building instead!
Roee's list is only a start. I could go on and on, but again it's a waste of perfectly good time to discuss it for an RV9 so just trust these folks already.
Cheers,
stein
Keep this bit of advice in mind whenever you think of deviating from the plans, "There is thousands of RV's flying in the stock configuration for a reason."
While going down your own path is fun and has its own rewards, bushwhacking usually adds a lot of time and money to any project.
delusional
Well Known Member
Bill, thanks for your thoughtful and detailed response. Okay, you sold me. The toughest hurdle seems to be the flap motor (though, I suppose that is optional), servos and heated aoa probes seem tricky, too.
Regarding availability of reasonably-priced devices, just from supplier web sites:
I see no real difference with regard to lights. Anyone starting a project today is going to use LED lights if they have any sense and those are pretty voltage agnostic.
Battery is no big difference; two smaller batteries will do just as well, possibly better, and weigh the same. Little more money, I guess.
Relays, heated pitot and pumps; no problem unless you want one from Vans.
So a couple key items and the ability to use unanticipated, non-aviation type devices is the real difference.
I predict the gap continues to narrow....
Regarding availability of reasonably-priced devices, just from supplier web sites:
I see no real difference with regard to lights. Anyone starting a project today is going to use LED lights if they have any sense and those are pretty voltage agnostic.
Battery is no big difference; two smaller batteries will do just as well, possibly better, and weigh the same. Little more money, I guess.
Relays, heated pitot and pumps; no problem unless you want one from Vans.
So a couple key items and the ability to use unanticipated, non-aviation type devices is the real difference.
I predict the gap continues to narrow....
P
paul mosher
A/C Voltage
Why not just use A/C? Boeing likes it.
Why not just use A/C? Boeing likes it.
