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emuyshondt

Well Known Member
I'm helping a friend build an RV6A. I believe the plans call out for a 12V electrical system. However there seem to be a number of components that use a 24V supply. Is there an advantage to implementing one voltage level over the other? If we build a 12V system per plans, is it acceptable to use some sort of DC to DC converter to supply those devices that require 24V? For example, we are looking at a 24V used heated Pitot tube. There may be other components that require one or the other voltage level. In case it makes a difference, we intend the plane to be certified for IFR even if we don't intend on flying in severe weather conditions.

I'd appreciate any thoughts on this subject. While we have engineering degrees to understand the flow of electrons, we don't know what the trade-offs are in terms of availability of components, safety, and practicality in an aviation environment.

Henry
 
Forget 24V

Everything is available in 12V, unless your going with second hand equipment. Plus then you either have to get a 24V batt, or two 12v batts in series, plus a lot of the cool experimental stuff is either not available in 24V or you have to install dropping resistors etc.

Yes the cable runs weigh less but on a small airplane like this one the weight savings add up to ounces at best.

Really its not worth the advantages in my mind
 
True stuff above. Additional thought: For those building the -10 or otherwise putting the battery in the back, a 24V has the advantage of being able to push a starter from a distance better. Also, if you are stuck with 24V, it's easier to step down than to step up. Ray Allen, for example, sells a cheap regulator for their servos.
 
Why 24V in the first place

It is my understanding that the reason aircraft moved from 12 to 24 volts was as more and more equipment was added, aircraft electrical systems had to put out more power and one way to save weight was to increase the voltage, which reduced the required wire sizes.

With modern electronics using much less power, there is no longer a driving need to install a 24 volt system. As for the starter issue, the new SkyTec starters are much more efficient than the old units, thus more than offsetting any weight penalty a slightly larger starter wire might require.

Again, that is my understanding. Someone please correct, if I've misspoken.

As an aside, the auto makers were close to installing 48 volt systems in cars to power all the options expected in even a "cheep" car but they have elected to stay with 12 volts because they were able to reduce the power requirements due to more efficient components.
 
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At this point we just happen to have access to a couple of 24V components but can put in whatever we decide on.

Any recommendations if we have a used component or two that require 24V in an otherwise 12V electrical system?
 
From a technical perspective, 24V is better. Smaller wires, etc.

From a practical standpoint, 12V is better because you can purchase components (instruments, batteries, etc) at any auto parts store in addition to the aviation supply houses. Shoot, you can even use your automobile to jump start your airplane.

Would I go to the trouble to mix and match 24v items into a 12v system? Not unless the 24v items I had were expensive items. Otherwise, it would just be complicating things...
 
flion said:
True stuff above. Additional thought: For those building the -10 or otherwise putting the battery in the back, a 24V has the advantage of being able to push a starter from a distance better. Also, if you are stuck with 24V, it's easier to step down than to step up. Ray Allen, for example, sells a cheap regulator for their servos.
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Pat,

Will you be installing a 24V system in your -10 for the above advantages? 24V is pushing the starter better because you are using twice the power (two 12 V batteries wired in series) to push the starter. Over a large scale, the extra potential (V) helps, but in the size of our aircraft, the advantages are not worth the drawbacks.

RVnoob said:
I think radio is the only component that requires 24V.
I guess the voltage is needed for transmission?
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Which radio are you referring? Most modern radios will operate on 10-32 volts. You will find a lot of 28 volt KX-155s on eBay however. The 12 volt models sell quicker and command more $ than the 28 volt units. For Garmins, only the early model GNS-430s required 28 volts for their COMM sections. ALL current Garmins will operate on 10-32 volts.
 
emuyshondt said:
I'm helping a friend build an RV6A. I believe the plans call out for a 12V electrical system. However there seem to be a number of components that use a 24V supply. Is there an advantage to implementing one voltage level over the other? If we build a 12V system per plans, is it acceptable to use some sort of DC to DC converter to supply those devices that require 24V? For example, we are looking at a 24V used heated Pitot tube. There may be other components that require one or the other voltage level. In case it makes a difference, we intend the plane to be certified for IFR even if we don't intend on flying in severe weather conditions.

I'd appreciate any thoughts on this subject. While we have engineering degrees to understand the flow of electrons, we don't know what the trade-offs are in terms of availability of components, safety, and practicality in an aviation environment.

Henry
Click to expand...

Henry:

To answer your original post ?

While there are DC-to-DC converters available that can change 12VDC to 24VDC, I really do not think that the use of the device would be all that beneficial.

You seem to be primarily concerned about the costs in that you have some used 24VDC items available, therefore I would think that after factoring the cost of the converter, the installation of the converter, and the maintenance of the converter, I doubt that you would really be saving all that much.

So, in my opinion, I think it would be better just to keep it simple and keep everything to 12VDC instead of trying to mix and match components. And if cost is still an important issue, then perhaps you could sell the 24VDC items (perhaps on ?VAF? or ?e-Bay?) and use the money to buy used 12VDC items instead.

Thanks much!
 
Do not put 24V stuff in a 12V system. Well you can if you want to waste a lot of money and weight! We made that mistake and in the long run it cost a lot more. Converters to bump up are expensive and heavy. Save yourself from a big hassle and go 12V. If you want to buy my 24V radios and converter I would more than likely pull them out and sell you them.
 
w1curtis said:
Pat,

Will you be installing a 24V system in your -10 for the above advantages? 24V is pushing the starter better because you are using twice the power (two 12 V batteries wired in series) to push the starter. Over a large scale, the extra potential (V) helps, but in the size of our aircraft, the advantages are not worth the drawbacks.
Click to expand...

It's more than just the size of our aircraft. In my -6A, the battery is on the firewall, close to the starter. In the -10, it will be behind the baggage compartment, which is a significantly longer run. Mainly, I'm going on the advice of Aerotronics and they're not stuck on 24V; they did the 12V system in my -6A. Also, I'm going with a Concorde RG-24-15 to avoid having to wire two batteries in series; less complexity and not as much extra weight for the equivalent power. I still have to modify the battery mount, though. Other than that, I don't see any drawbacks.

But I'm not saying a 12V system in a -10 is wrong and I'd stick with a 12V system in the smaller RV models. What I would avoid as much as possible is mixing voltages. My advice to the original poster would be to sell or trade the 24V components he has and build a strictly 12V system.
 
I am mixing it up on my -10 with 12 & 24 volt. Two Odyssey batteries with an equalizer. The equalizer took care of the problems my friend has had with the Cozy MKIV. He's had no problems of one battery going dead since the equalizer was installed.
 
We typically see 24v only in experimental aircraft that have air conditioning or a hydraulic pump. Otherwise, 12v works fine for most aircraft, based on the load planning worksheets we've seen. A typical RV will draw about 30 to 45 amps with everything on, depending on configuration, which is well within the limits of a common alternator.

Just FYI... the flap motor on an RV-10 is not readily available in a 24v version. And the trim motors will need a box from Ray Allen. And the contactors Van's includes in the kit are 12v. And... (just more stuff to plan around) :)
 
w1curtis said:
... 24V is pushing the starter better because you are using twice the power (two 12 V batteries wired in series) to push the starter.
Click to expand...
Power is independent of the voltage applied ... W = V x I
Double the voltage and the current is half. The power remains the same.
(neglecting any changes in the internal resistance due to heating etc.)
 
Thanks for all the perspectives. While the higher voltage means lower power losses in the wires, it sounds like most modern equipment is OK to run at 12V and the plans are designed for that voltage. 12V it is ...

Dave & Trina: You hang out on TUG too, don't you? I Luv Maui too!
 
I just flew and had the landing lights and strobes on and was somewhere around 10 amps (12V). I don't know who uses 35-40 amps but it isn't me.
 
The total draw for everything is in that range. If you have LED lights, no pitot heater, etc. it will be lower. YMMV.

Conventional strobes are about 9A (at 14v), 75W halogen landing lights about 6A each, pitot heat is about 8 amps, big screen EFIS about 1 to 3A each, incandescent nav lights about 2A each, radios about 2A each. Master contactor is .7A.
 
more pros and cons

This pro-24v info is from Greg Richter at Blue Mountain Avionics:
1. You can use smaller wire because a given load draws half the current at 24v than it does at 12v. #18 wire weighs less than #14.
2. Engine start will drop a 12v system to 9v possibly causing EFIS systems to reboot and fuel totalizers to restart.
3. A 24v system has a LOT more reserve energy available for use.

This pro-12v statement is from the Nov 2009 issue of Light Plane Maintenance:
"Unfortunately, the 24v system has a number of basic shortcomings, such as much higher costs for the batteries and components, as well as shorter lives based on our experience and feedback by hundreds of reader questionaires."
 
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