Glider power systems

On Wed, 05 May 2004 13:11:39 GMT, "Bill Daniels"
wrote:

After reading the annual installment of the 12V vs.14V soap opera and the
"We can't power any more electronics" whine, I took a little time to read
the Maxwell Electronics information on their Ultracaps.

See: http://www.maxwell.com/index.html

Maxwell makes a pretty good case for combining a small ultracapcitor with a
NiMH or Lithium-ion battery for use in typical consumer electronics like
computers and cellphones. It seems to me that the devices in our gliders
could use the Maxwell approach. Transmitters place a high demand on the
batteries for short periods and the varios and flight computers place a low
demand for long hours.

The Sealed Lead Acid batteries most of us use are great for short, heavy
amperage demands but not so hot for powering electronics for long hours.
The typical NiMH or increasingly common lithium-Ion are great for low
current devices but not good at high current demands. Maxwell's solution is
to combine a low amperage power source with an Ultracap so the Ultracap
handles the high-current short-duration, demands like transmitters and the
main lithium-ion battery handles the low-current, long-duration demand.

Of course, you still need the same AH's to go the distance but your
transmitter will get the voltage it needs at the end of a long day. We need
our EE's to quit arguing about 14V vs. 12V and whip up a nice circuit for an
Ultracap + Lithium-ion battery.

Bill Daniels



Do we really have a problem that requires this if we use 2 x 7 A-h
sealed lead acid batteries? I use one routinely, keep the other
charged and when #1 dies, switch to # 2 which doesn't have any
charge/discharge cycles on it (you might like to do one to confirm it
is a good battery). After the flight put #2 in the #1 position and put
a new battery in #2.

Automatic chargers for lead acid are cheap and available. Li-ion
batteries are *very* fussy about charging and can be dangerous if this
is done incorrectly.

In many respects our power requirements are lower nowadays. We aren't
running old 360 channel radios full of TTL logic that drew up to 800mA
on standby receive.

Modern radios have standby receive currents of 25 to 100mA.
A B50 vario draws about 100mA
A B40 18mA until you turn the volume up.
GPS receivers are now available that will draw as little as 30Ma from
a 12 volt source.
Our B2000 glide computer draws 50mA.

Allow about 300mA for continuous load and the 7 A-h battery has plenty
of capacity for the whole day even allowing for some reduction with
age and receive/transmit loads.

Add a transponder and you get about another 400mA continuous.

Still likely OK for normal use and you have the other battery at the
end of the day.

What you should do is actually measure what your systems consume. You
may get a surprise.

Also check that you aren't losing volts between the battery and the
systems. Measure the voltage at the battery and at the system. You may
have some unwanted resistance in the circuit.

Use good mil- spec aircraft wire to do your installation. Put a fuse
right on the battery terminal.

We may get a reduction of a few pounds of weight by going to Li
batteries and supercaps and /or some increase in capacity. The
question becomes - how much do you want to pay for this?

Mike Borgelt