Amateur Airplane lighting/electrical

HI all. I joined this forum after reading a thread about running 28V lights on a Jeep. Maybe some of you can help me do just the opposite. I have built an antique style biplane (full size) and have some questions about electrical solutions.

The plane has a 28V/50 amp alternator. For both cost savings and availablitly i would like to use some 12V components...like off shelf lights and light wieght strobes as well as a small servo to drive a trim tab and a light radio.

I would like to use two 12V batteries in series...using one to power a 12V bus and both to power a 28V bus. I"m told this is often done with bass boats...minus the charging system.

Will i have any trouble or need any additional equipment if i choose to proceed in this direction? Will the alternator charge both batteries together?

Thanks,
Dan

I used to have a WWII trainer (Taylor Craft L2M--no electrical system) and worked on WWII (and other planes) in my youth...

The short answer is yes, it will sort of work. However, since you are taking power from one of the series batteries, the other battery will overcharge and probably be quickly damaged/boiled dry if you take any significant current from the other 12 volt battery...

Think of it this way, you want (for example) 10 amps of 12 vdc. You connect to the fully charged battery. It's voltage drops, and the 24 vdc charging system kicks in to supply the makeup power. However, that 12 vdc is provided by the voltage drop of the upstream 12 vdc battery. That battery is now being overcharged with 10 amps at 12 vdc (120 watts) and, if it is an unsealed battery, you are breaking down the water into hydrogen gas. If it is a sealed battery, it is generating gas and heat and cooking the battery internally.

In either case, you have one battery that is acting like a voltage converter with nowhere for its excess power to go. It will probably quickly damage it.

If you needed less than an amp or so of 12 vdc power (depending on the sizes of the battery), I probably would not worry about it as non-commercial aircraft are not flow that much--just a few hours every few weeks (just check the water religiously).

I think you are going to need some other solution (converter, 24vdc units, or something else).

-Bill

Diamgram removed beacuse of my error in the idea.

Ummm Morelite,

Unless I am missing something, you have both batteries shorted--assuming that the colored wires are all copper wire.

And, generally I would not recommend running ungrounded items in an aircraft... You run issues from electrical interference with avionics, to static buildup differentials, and possible lighting path issues...

I could be wrong...

-Bill

BB, your right, the second batt would be shorted, good catch.
I'll remove that diagram before someone trys that.

As long as you did it from one battery, the one that had its - at ground then you would be ok. However I'm betting your not going to be using the airplane body as ground, old airplanes from the biplane era were mostly wood and cloth covering, modern airplanes may have metal but have a lot of fiberglass too. So your probably running grounds to most of the lights. Why not load balance then, run all the lights on the left side across one battery and all the lights on the right side across the other.