2-Batteries

Thanks Gary for the writeup. I have been thinking of doing the exact
same for a glider I just bought. Can you please add the part number if
you recall them.

I suppose if one really wants to know about the condition of each
individual battery, you could put a voltmeter on a 3-way switch and see
the volatge on the "main" bus, and each of the batteries. This way you
could tell the difference between them.


Gary Emerson wrote:
Nyal Williams wrote:
I'd like to see a full write-up with diagrams, photos,
and names/addresses of places to buy parts. This would
make a good article for Soaring.


Here is a sketch

http://www.mydatabus.com/public/emer...y/e/sketch.JPG

and a pic of my install...

http://www.mydatabus.com/public/emer...y/e/diodes.jpg

There is a aluminum bracket which is lightly mounted to the bulkhead.
The PC board just provides insulation and some support for the wires.

Each diode has a heat sink, but I don't really think it was necessary.

I don't have the part numbers handy, but I'll see if I can't find something.

With 18Amps of forward current capability (each), there isn't really any
"need" for the two diodes in parallel, but for an extra $5 and a few
extra minutes of wiring, if any one diode ever did fail "open" the other
would still provide power. Most likely overkill.

Eric Greenwell wrote:
wrote:
By all means a second battery should be installed in our electrically
driven modern sailplanes. After many years of quickly flipping my
3-position battery switch, and trying not to have my logger to
momentarily dropout,

I thought all loggers just started again after a momentary power loss,
and continued the same flight file. It sounds like yours isn't behaving
properly, or are some brands a bit touchy?

There are some earlier approved flight recorder designs that will start
a new flight data file if the 12V power supply is interrupted
momentarily. The specifications were then changed to eliminate this
behavior from newer designs...

Marc

A quick Google of Schottky Diode and TO-220 yielded some sources.

I just tried the first one and then found this:

http://www.onsemi.com/PowerSolutions...do?id=MBR2515L

looks like even slightly better than what I had bought.

You'd lose about 0.3 volts during normal operation.

Datasheet at:

http://www.onsemi.com/pub/Collateral/MBR2515L-D.PDF

I'm sure some googling will find that someplace like DigiKey will have
these and will take small ordering quantities.

Is Paul Remde out there? Might be a nice "kit" to add to your line.
Kit includes 4 diodes, 4 heat sinks, 4 insulating washers some heat
shrink tubing, etc.??

Good luck.




Gary Emerson wrote:
Nyal Williams wrote:

I'd like to see a full write-up with diagrams, photos,
and names/addresses of places to buy parts. This would
make a good article for Soaring.


Here is a sketch

http://www.mydatabus.com/public/emer...y/e/sketch.JPG

and a pic of my install...

http://www.mydatabus.com/public/emer...y/e/diodes.jpg

There is a aluminum bracket which is lightly mounted to the bulkhead.
The PC board just provides insulation and some support for the wires.

Each diode has a heat sink, but I don't really think it was necessary.

I don't have the part numbers handy, but I'll see if I can't find
something.

With 18Amps of forward current capability (each), there isn't really any
"need" for the two diodes in parallel, but for an extra $5 and a few
extra minutes of wiring, if any one diode ever did fail "open" the other
would still provide power. Most likely overkill.

Noone picking up on Dick Johnson's last paragraph??

http://sinhatech.com/SinhaFCSD-Progress-12132006.asp

John Galloway


At 15:42 25 December 2006, wrote:
By all means a second battery should be installed
in our electrically
driven modern sailplanes. After many years of quickly
flipping my
3-position battery switch, and trying not to have my
logger to
momentarily dropout, I have concluded that is best
to use 2 single-pole
battery switches. That way one can have either or both
batteries
connected at the same time.

I saw the light when Jim Hendrix brought his sailplane
to Caddo Mills
for Wing Deturbulator flight testing, and it was wired
like that. You
will hear much more about that amazing new invention
at the coming SSA
Convention.

Thermally,

Dick Johnson

Testing AH of batteries

Battery capacity is measured using a defined minimum voltage. That voltage
may or may not correspond to the minimum voltage your glider equipment will
operate on. If you use diodes, that minimum voltage will move slightly.
Capacity also depends upon a starting voltage - which is significantly
higher than 12 volts.

I often need to test batterys used in our search and rescue radios and have
found that I can test battery capacity quickly without a full discharge. I
charge the batteries, then let them sit for a day. Then, I put a load on
them and simply watch the decay of voltage over time. In a very short time,
you can make a graph that will indicate the trend of the battery and compare
with a new battery. A battery with reduced capacity will drop voltage much
more quickly.

You can determine the capacity of the battery during charge, too. Capacity
is the ability of the battery to resist change. That applies either way.
it means the battery will drop in voltage or charge more slowly. So, you
can simply time the charge of two batteries and learn the comparative
capacity of each.

Colin

Gary Emerson wrote:

With 18Amps of forward current capability (each), there isn't really any
"need" for the two diodes in parallel, but for an extra $5 and a few
extra minutes of wiring, if any one diode ever did fail "open" the other
would still provide power. Most likely overkill.
Yes because most often (probably at least 90% of the time) a diode
fails "short"
Therefore you may be reducing the reliability. :-)
...lew...

John Galloway wrote:
Noone picking up on Dick Johnson's last paragraph??

http://sinhatech.com/SinhaFCSD-Progress-12132006.asp

John Galloway


The results are interesting, but way do the testing on a Std. Cirrus?
To be taken seriously put them on a modern ship and test them. I
can't believe Dick did the testing on the Std. Cirrus and did not at
least put them on his Ventus for some additional comparisons.

If the numbers are real, that Standard Cirrus is now a 41-1+
sailplane-and that IS a serious improvement. $16K for a 41-1sailplane
is great, and a boon for a lot of people that do not have $40K-60K for
that type of sailplane performance. Looks like some older sailplanes
could be hanging out with a new crowd.

Mike



wrote:
John Galloway wrote:
Noone picking up on Dick Johnson's last paragraph??

http://sinhatech.com/SinhaFCSD-Progress-12132006.asp

John Galloway


The results are interesting, but way do the testing on a Std. Cirrus?
To be taken seriously put them on a modern ship and test them. I
can't believe Dick did the testing on the Std. Cirrus and did not at
least put them on his Ventus for some additional comparisons.

With the diode solution, when the system is turned on the battery with
the highest voltage will provide the current. As the battery draws
down the second battery will come on line. From that time on both
batteries will be providing power to the circuits. The strongest
battery will provide the most current but both batteries will be
stabilized at a common voltage. Therefore BOTH batteries will require
re-charging after being used for any substantial period of time.

Regarding the 3 position switch. The simple solution is to put a
capacitor between ground and the output side of the switch. The
capacitor must be large enought to provide the current needed during
the switch switching time. This should not be a very large capacitor
for our purposes.

Brian Utley
Gary Emerson wrote:
COLIN LAMB wrote:
"If both batteries are on-line all the time, how do you know when one is
getting weak and needs to be replaced? Or do you replace both batteries
when voltage is marginal at the end of a flight?"

Well, that is a problem. You do not know. Everything is automatic. If you
have one battery that has lost most of it's capacity, the good battery will
do all the work. The only way you will know is when the total capacity of
both batteries has been reduced. And, then, you will not know whether one
battery has done 50% of the work and they are both down in storage ability,
or one battery is still 90% and the other one is 10%.

So, you will have to determine the capacity of each battery separately. You
could test the battery capacity by switching either off during discharge, or
even by using 2 ammeters - but it is becoming more complex once we try to
extract more information. You can also determine the capacity during
charge.

Colin



During any one flight, you don't need to know. What is a good idea is
to test the batteries if you think you are losing capacity. During the
week charge them up Monday and Tuesday, and Wednesday put a load on each
one and see how long it lasts. Ideally, you'd like the load to test the
batteries for as long as you'd normally fly. Say 4-6 hours unless you
are typically flying for longer. If either one can't go the 4-6 hour
distance and mainain a suitable voltage, then it's due for replacement.
After the Wednesday test, charge them back up so you're ready for the
weekend assuming they pass. I'd certainly do this in the spring and
before any big contest during the year. 7Ah batteries are cheap in the
grand scheme of things.

This is great discussion. I was doing a bit of research myself (it has
been over 10 years since I did any HW design, so am pretty rusty).

Another option that sounds even better is to use the new chips designed
for exactly this to control DirectFETs. That way the voltage drop and
power waste will be significantly reduced with very little additional
cost. The chips I were looking at were IR5001S:
http://www.irf.com/product-info/data...ta/ir5001s.pdf or LT4351:
http://www.linear.com/pc/productDeta...,C1079,P21 73


I have used DirectFET stuff in robotics and found them to be very
reliable and very simple to design with.

My biggest problem is all these components are only available in
surface mount these days and I have never tried to build a circuit
using them.