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-   -   12V or 24V? (https://vansairforce.net/community/showthread.php?t=80767)

hydroguy2 01-04-2012 06:39 AM

220, 221 volts...what ever it takes :D

jdeas 01-04-2012 08:03 AM

Weight savings
 
Quote:

Originally Posted by N395V (Post 613091)
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 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.

Mel 01-04-2012 08:05 AM

Quote:

Originally Posted by N395V (Post 613091)
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 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.

SteinAir 01-04-2012 03:41 PM

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

fstringham7a 01-04-2012 04:32 PM

RE:Ditto
 
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!!!


Quote:

Originally Posted by SteinAir (Post 613322)
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


delusional 03-09-2012 07:09 AM

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.

N941WR 03-09-2012 07:34 AM

Quote:

Originally Posted by delusional (Post 637837)
...
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.

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 03-09-2012 08:47 PM

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....

roee 03-10-2012 01:19 AM

Quote:

Originally Posted by delusional (Post 638099)
... Since we agree that avionics can do either voltage,

Most modern avionics, yes.

Quote:

Originally Posted by delusional (Post 638099)
... lights, alternators, battery, and starter, no problem;

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.

Quote:

Originally Posted by delusional (Post 638099)
so what's left? Servos? It all come downs to just servos?

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.

Quote:

Originally Posted by delusional (Post 637837)
The number of items unavailable 28v shrinks daily, ...

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.

Quote:

Originally Posted by delusional (Post 637837)
... and tso'd converters are readily available.

Another box. More $$$, more complexity, another failure point. Run a common 12V system and you'll have no need for a converter.

Quote:

Originally Posted by delusional (Post 637837)
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 ...

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.

Quote:

Originally Posted by delusional (Post 637837)
... could I modify the op to "12v or 24v yet?"

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 03-10-2012 09:15 AM

Quote:

Originally Posted by airguy (Post 612700)
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.

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...:)


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