> How does tracy's computer run on 24V? How are the prices of 24V
fuel
> pumps compared to the 12V versions?
>
>
> Matt-
Matt, and others.
I have Tracy's EC-2 unit at the moment and after ground testing the
engine I
will make the decision to use it in flight or not. So far I like
very much
what I see. Changing the input to 24 DC is a relatively easy fix. I
haven't
cracked open his box but I assume it has a step down power conditioner
circuit to bring lower dc power to IC chips that require somewhere
between 3
to 9 vdc.
Makes sense.. Does Tracy's computer still only use one power input?
Fuel pumps, fuel injectors, spark plugs igniters are not something I
have
investigated yet but I can imagine that they must be available
because of
the huge truck market that run on 24vs. I am trying to buy a 24vdc
starter
gen now however and I may have to have a 12v unit rewound.
I think most of those trucks run on diesel, and have engine driven high
pressure fuel pumps. There may be some gasoline 24V systems, but I
doubt that there are many. Not an insurmountable issue, but something
to consider. And something that may unnecessarily raise cost. I don't
know.
Excuse the verbiage but here are my thoughts based on 30 years
playing with
batteries and electrical energy production devices. First up. We
are all
researcher and experimenters. As such IMHO price is not the most
important
criteria upon which to base a safely designed electrically
system. Just as
Paul harps about silicon heater hoses and quality hose clamps a good
electrical system is equally important. Within reason, price reduction
decisions come into play after experience (yours or others) in
successfully
operating a system. This is why prototypes are so bloody expensive
or time
consuming.
Actually, I think prototypes are expensive not because engineers pick
the best of the best at the outset, but because there are so many
iterations in the design process. I have to admit, however, that
sometimes if higher priced materials/components were initially selected,
fewer design iterations would be required to reach an acceptable
product. False economy can be a killer.
Many people are involved in experimental aviation because paying for a
like product from the certificated market is unpalatably expensive.
Our rotary engine happens to be originally designed for an auto but
we are
modifying it for an airplane and as such a different criteria apply.
Is 24 volts better? It depends on your type of flying. You are free
to use
the 12v or 24v and both have their advantages and disadvantages to the
recreational flyer.
I think most of Greg's customers have fast planes that fly
occasionally in
IFR conditions and perhaps depend upon their electrical avionics
systems
more. My plane and type of flying will fall into this category. As the
speed of the plane and the distance to be flown goes up I believe
the 24vdc
system makes more sense.
Lead acid battery is an old, heavily research, technology and is one
item
that you actually get what you pay for. Lead in this case. The
cheapo car
battery you can buy at Wally's are relatively lightweight and start the
engine by delivering a lot of amps for a short amount of time. The
plates in
the batteries are thin, and as such the lead is minimized. This allows
electrons to flow faster. The alternator usually tops off these
batteries
quickly so in operation the battery is just a buffer for the
alternator to
supply juice through. When the alternator goes south, the 12 volt gel
battery (at 13.7 volts in the float charge mode) starts draining down to
become useless around 10volts. this data varies with makers
somewhat. What
doesn't vary is that after you discharge your starter battery to the low
'dead' voltage several times the plates sulfate and no amount of
charging
will bring it back to life. Replacement time. We all know this.
Gel cell??
All of the major airlines use 'Lifeline' deep cycle batteries
however. Why?
Besides the military spec. rating, they are deep cycle batteries and
as such
can be deeply drained down. Translation: You can actually use more
of the
capacity of the battery. Something airlines want with all of their
electronic fail safe modes. True deep cycle batteries are heavier
because
they have thicker plates and hence more lead. They are designed to be
brought down to 20% remaining charge 500 times or so and with the
latest AGM
(Absorbed Glass Mat) construction method do an adequate job of
starting the
engine as well.
I suspect that the main reason that the big boys need deep cycle
batteries is that engine starting on a turbine lasts a much longer time
that it does on a small recip, requiring more total energy. It's just a
matter of the physics. Even with huge deep cycle batteries on a
turbine, self starts are not always a given. Ground power for starts
(or APU starts) are definitely preferred.
If they are only discharged down to 80% full level which is typical in
Telecom. photovoltaic/wind gen. systems, the batteries will last
1500 to
3000 cycles in my experience. One or more engine out situations doesn't
even hurt them. Because of their long life you don't have to change
them out
at every annual either. Some of them at my off the grid workshop are
now due
for a change after 13 years even though they still have some reduced
capacity.
Actually, the engine-out scenario is easy to have enough battery for..
Even at high cruise altitude, it likely won't take 30minutes for you to
land if the engine quits. I think we can keep gyros spun up for that
long with a couple of flashlight batteries.
The hard scenario is where you have 8 hours of fuel on board, and it's 5
hours to a suitable landing site. If your engine needs 10A to keep
running, that's a lot of charge to haul around. I believe for long
distance flight, the highest priority should be placed on redundant
engine driven electrical power. The big boys DO have that.
If the alternator on my single alternator airplane craps out on a long
flight, and I have to deplete the battery in order to make a safe
landing, the least of my concerns is going to be about battery
replacement cost.
One 24v battery or two 12 batteries wired in series? Doesn't
matter. How
do you want to affect your planes CG? and/or wiring runs? I know
some planes
that have the batteries wired so that they be switched either in 12v
parallel or 24v series for starting the engine but that is another
story.
Definitely agree here. This isn't that hard to figure out. I believe
more energy storage per dollar can be had with multiple 12v batteries as
opposed to half the number of 24V units. That's just a market demand
issue.
The future of batteries? Bill Dude is the guy to comment. Perhaps
hundreds
of 2.6 vdc volt LiH rechargeable batteries assembled into a flat battery
pack might make a nice lightweight high density battery for our
homebuilts?
But their goes the alternator regulator design:)
Doug in Japan
Thanks for sharing your thoughts on this Doug.. While we don't totally
agree on everything, it's good to keep the design discussion going in
order to learn and improve..
Regards,
Matt-
Sorry, but embedded reply was the only thing that made sense..
Matt-
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