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.
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.
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.
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.
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.
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.
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.
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
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