12v to 24v Conversion

[rubixcube2k3]

I haven't been able to find this covered anywhere, and since I have nothing to fly while my avionics are being installed, I apparently keep coming up with ways to keep it in the avionics shop with "While you're in there" tasks.   I'm really trying to break this trend, but little things keep occurring to me....

 

Anyhow, my question is: With all the added avionics I am getting, (Very much power dependent stuff) is there any way and/or any benefit to convert a 12v to a 24v system. IE: add a second battery...

 

I have a C model, so I'm sure if it could be done, it would require a new alternator, revised weight and balance along with placement of the second battery if it is even possible. What about my Gear actuator, flap motor, and fuel pump...can they support 24v? 

 

If Yes, then the next question then becomes - is it worthwhile? If  I lose the alternator, do I have any longer on avionics before critical power is reached? 

 

Just soundboading and know that I can depend on you guys and gals to give me personal thoughts and experiences. 

Thanks in advance!
Abe

[Mooneymite]

Abe, I'm no electrical engineer, but I do own a 12V Mooney 'C'.  So without answering your questions, I would like to understand what benefits you would get from converting to a 24 volt system.

 

In many cases, new avionics draw less than the boxes they replace, and if you go for the new LED lights, etc, the up-dated plane will not really need addtional capacity.  12 V should work very well.

 

A second battery?  If you want the cost/expense/weight of an extra battery, it seems like adding a 12 volt battery in parallel might be a much simpler way to go, but even then, I'm not sure what the advantages.  Help me here.

 

One of the things I like about my "Classic" is that it IS 12 volt, but maybe I'm missing something here?

[N601RX]

The only real advantage is the few pounds saved by using smaller wire.

[rubixcube2k3]

 

One of the things I like about my "Classic" is that it IS 12 volt, but maybe I'm missing something here?

 

I'm no electrical engineer either, but as I understand it, from what I recall of current vs voltage, is that based on an ideal source, they exhibit inversely proportional drain characteristics. (IE a device typically draining 1 ampere at 12v would operate on 24v at 500 milliamperes) In my fuzzy logic that means that the (albeit anemic in terms of usage) requirements of the new tech installed in my plane I would essentially double my time in the event of an alternator or charging failure in flight. 

 

Again, this is not something that I am bent on making happen, I'm just asking the questions if it has been done or can be done. There may be absolutely -0- benefit from it, and if that's the case I'm just hoping to get that info out in front of me. 

 

As a side note, I think avionics shops should be required to loan out planes when doing massive upgrades that take weeks to complete. It would curb people like me from having idle time to think of things to do to make their jobs more difficult. 

[HRM]

Well, I am an electrical engineer and I can tell you that converting an aircraft that old from 12 to 24 would not be worth the cost. As was pointed out, the newer avionics draw far less power than their predecessors and if you went through your plane and replaced all of the incandescents with LEDs (where you can), then that would be a significant improvement in lowering current draw.

 

What you are really looking at is loss of the alternator and the question "How long will I have before the battery is exhausted?"

 

Well, the quickest and easiest fix would be to, again as someone mentioned, put a second battery in parallel with the current battery. There are issues with parallel battery systems, but they are well known and there are switches and electronics to manage them (this has been done fro years in cars and RVs). Keep in mind that the cost would be high and you would need to find a very "understanding" A&P.

 

Before doing the second battery thing, why not do a power survey? Very, very easy to do. List everything in the AC that draws power. This should include the nominal operating voltage, which should be around 12 and the current. When everything is on the sum of currents will yield the amp-hour draw and batteries are rated in CCA (cold cranking amps, for starting) and in sustained amp-hour draw.

 

Let's say you start her up, taxi out, fly up into the soup and buzz along until your battery is recharged. Suddenly, the alternator gives out. Now everything is on the battery. You quickly shut off all non-essential electrical stuff and at that point you know you are drawing 10 amps because you did your homework. Your battery, at full charge, is good for 30 amp-hours. You have 3 hours to get on the ground.

 

Of course, you'll garner extra credit by taking account for the fact that every time you key the mic on your radio the amount of current draw jumps significantly 

[N601RX]

Yes you are correct that with all other things equal, the current draw at 24 volts will be half of what it is at 12. This is why you can user smaller wire for the given device at 24 volts. The problem to the question is the battery. Assume the same physical size battery. To get a 24 volt battery you will have to use 2 times as many cells to get 24 volts vs 12. The only way to manufacture this in the same physical package that is make the cells 1/2 as big, so you will only have 1/2 as much as capacity. Now you have a battery with 1/2 the capacity and avionics that draw 1/2 the current so your right back where you started.

If you're using the Concorde 35 AXC that is in good condition, You can fly a long time before it is drained. I know that after an 1 hr it still has enough to crank my engine.

You can't always divide the amp hrs by current to see how long a battery will last at a given load. A battery that is rated at 30 amp hrs may be based on a load of 1 amp and lasting 30 hrs. If you put a 30 amp load on it it may very well be completely discharged in 30 minutes.

[1964-M20E]

Power requirements are still the same for 24V or 12V just 1/2 the current at 24V and you could use smaller wire.  As for converting I have not seen this and myself I like the 12V system.  If for some reason I need a boost any automobile around can be of assistance not so with 24V system.

I'd save my money and efforts for some other modification.

[carusoam]

We have a winner!

24V is nice to have, so is a second battery and a second alternator.

The back up systems gain value when flying IFR, often.

You may want to check if there are STCs in place for each of the alternator, controller and battery combinations.

You can use this logic with your financial advisor to look into a J because it has this modern system already?

[fantom]

You can use this logic with your financial advisor to look into a J because it has this modern system already?

IOS 8 gave me emoticons,

 

 

You're lucky...all it gave me was a headache

[bonal]

What I would like to do if it were allowed would be to install an automotive battery the dry cell type. I would install it in the back where the modern Mooney's have them. The problem is not the voltage but the capacity of the current bats we can install in our early birds. Modern automotive bats have well over twice the output and capacity . Installing in the back would move my CG further back might even pick up a bit more speed. It would also open up a lot of space in the engine area making service on the motor more accessible. One of the problems with certified aircraft is we can't install things that would improve them. Not to mention costs. I am planning on installing a fuel flow meter and the options for experimental are greater and cheaper. When I browse aircraft spruce and see all the things I could afford for my plane that are not certified it makes me angry cause I can't afford the ones that are.

[jetdriven]

[quote name="HRM" post="175018" timestamp="1414876367"

What you are really looking at is loss of the alternator and the question "How long will I have before the battery is exhausted?"

Let's say you start her up, taxi out, fly up into the soup and buzz along until your battery is recharged. Suddenly, the alternator gives out. Now everything is on the battery. You quickly shut off all non-essential electrical stuff and at that point you know you are drawing 10 amps because you did your homework. Your battery, at full charge, is good for 30 amp-hours. You have 3 hours to get on the ground.

Of course, you'll garner extra credit by taking account for the fact that every time you key the mic on your radio the amount of current draw jumps significantly

[Mooneymite]

Bonal, I have a certified plane and an experimental. I can tell you there's not much savings with an experimental because you'll be like a kid in the candy store buying stuff for it. 1/3 the cost, but you buy 3 times more.

Sad.

[bonal]

Mooneymite you speak the truth.

[rdav]

Rather than converting the entire system, have you considered creating a 24 volt bus using a converter off of the main bus? Something like http://www.kgselectronics.com/products/dc-power-converters-tsod/rh28.html. It would certainly be cheaper than trying to recertify a new alternator, adding a battery, etc.. And would allow you to run any existing equipment off of the existing 12 volt bus without a change. Of course, there is an efficiency loss with the converter.

Are 24 volt avionics less expensive?

[jetdriven]

Then you also introduce one more item into the chain for a "single point failure"

[carusoam]

Byron is always the logical one!

If you follow his logic, be sure to add one thing. It requires knowledge of the alternator failure to have best known battery capacity.

If you find out by having instrument panel lights wavering on you, the battery is very discharged already.

Modern voltage regulators have outputs for warning of the alternator failure. A light on the instrument panel is easy to see and can warn of the situation.

Best regards,

-a-

[drbob]

M20C<Aft battery repositioning C,D,G 

      is covered by STC SA 00941AT (unfortunately a dead STC)

So: would anyone have access to that paper work, 

I and my DER would like to see whats involved,

prob.not much as Mooney relocated the battery aft in the '64  M20E models(SNs 26101-469)

they also relocated the oil cooler but thats another story.  Helps with changing the CG.           

                                                                                                            drbob