>I have an 0-320D2G engine with 28V Alternator & Starter. Many of the
>electrical items I already have purchased use 12V (nose lift, mac servo's).
>I have the option of trading for a 12V Alternator & Starter at no additional
>cost.
Please consider taking advantage of this option . . .
I understand that 2X the voltage = 1/2 the current, meaning the wire
>size going from the battery to the engine is much small for the 28V system
>(less weight).
The 28v option made sense when we were building B-29's and B-52's with
as much as several hundred miles of wire in them . . . the weight savings
was significant. Further, the builders of these machines had pretty deep
pockets to reach into (yours and mine) to finance the miliatary aviation
specialty hardware items unique to their task.
Later on, folks who built DC-6's and 707's knew that the return on
investment for a revenue generating machine was a function of how
many pounds of pax/bags could carried. The airplanes were still pretty
complex and again, the cash to pay for them would continue to come
from the same pockets . . .
Now, your airplane isn't going to make you a dime. In fact, it's
going to COST you a lot of dollars. Further, money isn't going
to come from any pockets but your own to finance the task. While
one might successfully argue a small weight savings it will be quite
small. In a simple single it's not over a couple of pounds.
However, locking yourself down to aviation specific, 28V hardware
shuts you out of all the opportunities to exploit automotive and
consumer products that are widely available, high volume, and
competitively priced.
One exception to consider in this reasoning is unique to canard-pushers.
Cabin heat. If you're going to insist on flying in cold weather and/or
high altitudes, electric toe warmers might help you survive the
experience with a minimum of discomfort. I've had several builders
go for 28V, 60A systems. While the weight of the altenrator
and battery needed are about the same as for 14V, 60A . . . the energy
you can get out of the 28V alternator is twice that of the 14V . . .
all of which you will need and wish for more if you're considering
electric cabin heat.
> . . . . Also, If you mix your loads, what is the best solution? A
>converter or two batteries or something else? Or does someone make a 28V
>battery with the cell poles exposed with 12V tapping capability? Any
>suggestions greatly appreciated.
Mixed voltages in a small airplane are almost never practical.
The size, weight, and cost of voltage conversion equipment clobbers
an otherwise elegant design. Further, you're often forced
to run multiple accessories from the voltage converter meaning
that it becomes a single point of failure for all the goodies
it powers.
Tapping down on half of a 28v battery to get 14v is about the
best way I know of to kill off an otherwise perfectly good
battery.
Bob . . .
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( Knowing about a thing is different than )
( understanding it. One can know a lot )
( and still understand nothing. )
( C.F. Kettering )
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