Switching Batteries Advice?

Forget PW5's, let's do the aerotow on CG hooks again!

Brian wrote:

I really can't see any drawback to the make before break switch other
than cost and availablity. As long as you have appropiate fuses or
circut breakers in the system fire should not be an issue and 99.99% of
the time you will only be switching from a low battery to a good
battery. and the two batterys are only connected for a few milliseconds
which may not be such a bad thing as it will slightly slow the voltage
transition to your instruments.

Based on my experiments with two 18 amphour batteries, one freshly
charged and the other discharged below 10 volts, the "surge" current
will be less than 10 amps. For the more typical case (two 7 amphour
batteries, one fresh and one discharged to 11 volts or so), the surge
current will be only a few amps. This is well within the capacity of
switches, wires, and fuses commonly used, especially given the short
duration.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

(if the circuit does not show up aligned,
view the message with Courier New Font)

I have in my ASW27 three batteries and two solar
panels on the fuselage for recharging.
Batteries need a certain time to adjust their
chemical process for delivering current and for
receiving current from the panels. The racers for
the solar challenge overcome this problem by using
two batteries: One for driving and the second for
receiving the energy delivered by the panels or
from the motors while braking. Is the second one
full the batteries are exchanged in the circuit:
the second for driving and the first for recharging.

I did the wiring of the rotary main switch the same
way for my ASW27 (example for 2 batteries)
__________________________________________________ _

BATTERIES 7.2Ah 0 A 0 B
¦ ¦
+-----¦------¦---+--- LOGGERS
¦ ¦ DIODES ¦
¦ +------¦---+
¦ ¦
ROTARYSWITCH + +-+ + +-+
ROTARYSWITCH --¦-----¦ 0 A B
ROTARYSWITCH + + + +
¦ ¦ ¦ ¦
+-------+------------- AVIONICS
¦ ¦ ¦
SOLAR-CHARGER -------+---+ = 10000uF
¦
GROUND ------------------+-------------------
__________________________________________________ __


The Cambridge Logger takes the power from the battery
with the highest Voltage.

The capacitor bridges switch over time up to 1sec if
radio is in receiving mode.

I fly with this layout for more than 10 years and never
had a problem with instruments, loggers or palms failing.
I normally fly a complete week until I recharge the
batteries externally.

Additionally I have an override switch which connects the
Solar panels directly to the Avionics, but I never saw
need to use it up to now.

Chris
CH
__________________________________________________ ___

(if the circuit does not show up aligned,
view the message with Courier New Font)

I have in my ASW27 three batteries and two solar
panels on the fuselage for recharging.
Batteries need a certain time to adjust their
chemical process for delivering current and for
receiving current from the panels. The racers for
the solar challenge overcome this problem by using
two batteries: One for driving and the second for
receiving the energy delivered by the panels or
from the motors while braking. Is the second one
full the batteries are exchanged in the circuit:
the second for driving and the first for recharging.

I did the wiring of the rotary main switch the same
way for my ASW27 (example for 2 batteries)
__________________________________________________ _

BATTERIES 7.2Ah 0 A 0 B
¦ ¦
+-----¦------¦---+--- LOGGERS
¦ ¦ DIODES ¦
¦ +------¦---+
¦ ¦
ROTARYSWITCH + +-+ + +-+
ROTARYSWITCH --¦-----¦ 0 A B
ROTARYSWITCH + + + +
¦ ¦ ¦ ¦
+-------+------------- AVIONICS
¦ ¦ ¦
SOLAR-CHARGER -------+---+ = 10000uF
¦
GROUND ------------------+-------------------
__________________________________________________ __


The Cambridge Logger takes the power from the battery
with the highest Voltage.

The capacitor bridges switch over time up to 1sec if
radio is in receiving mode.

I fly with this layout for more than 10 years and never
had a problem with instruments, loggers or palms failing.
I normally fly a complete week until I recharge the
batteries externally.

Additionally I have an override switch which connects the
Solar panels directly to the Avionics, but I never saw
need to use it up to now.

Chris
CH
__________________________________________________ ___

"ContestID67" wrote in message
oups.com...
I would like to ask the rec.aviation.soaring community for comments
about their experiences switching between batteries while in flight.

It seems to be common practice to carry two batteries. There is
usually a master switch and then an A/B switch to toggle between the
batteries. The issue is what will a momentary interruption in power,
when you toggle the A/B switch, do to your flight recorder/computer?
Most important is the integrity of your flight log, less importantly is
your task and other flight data.

PDAs are not suseptible to this issue as they come with their own
internal ("backup") battery. Also, let's not discuss "well I have
this-and-that device as a backup" (handheld GPS, machanical vario,
etc). The issue at hand is competition, record or badge flying and
quarantee that all important flight log by maintaining power to your
flight recorder. I have not seen a ship yet that had two redundant
flight recorders (but I will bet they exist).

A simple double throw A/B switch is commonly used. My measurements
show that this type of switch is completely open (no power) for 10-15ms
but this depends greatly on the quality of the switch. There are
make-before-break switches in which for a brief period of time both
batteries are connected to each other and there is no loss of power.
However even briefly connecting two heafty batteries together, with one
possibly completely failed, has its own drawbacks (like an onboard
fire). This of course all depends on the pilot knowing when to switch.
If (s)he first waits until a failure is noticed, then all may be lost.


Another approach is having two ship's batteries connected to one
another via a "device" which allows each to (safely) supply current and
to automatically switch between the two if one fails. A pair of heafty
diodes is an obvious and simple choice as one battery cannot "charge"
the other but both can supply power. However, you will typically loose
0.6v-0.8v across a silicon power diode.

Ultimately it seems to depend on the manufacturer of the recorder and
how their electronics handle a temporary loss of power. Some
manufacturers support permanent backup batteries which charge from the
ship's main battery. This may be the best overall solution.

Any of your ideas and solutions are very welcome.

Thanks, John

(if the circuit does not show up aligned,
view the message with Courier New Font)
I have in my ASW27 three batteries and two solar
panels on the fuselage for recharging.
Batteries need a certain time to adjust their
chemical process for delivering current and for
receiving current from the panels. The racers for
the solar challenge overcome this problem by using
two batteries: One for driving and the second for
receiving the energy delivered by the panels or
from the motors while braking. Is the second one
full the batteries are exchanged in the circuit:
the second for driving and the first for recharging.

I did the wiring of the rotary main switch the same
way for my ASW27 (example for 2 batteries)
__________________________________________________ _

BATTERIES 7.2Ah 0 A 0 B
¦ ¦
+-----¦------¦---+--- LOGGERS
¦ ¦ DIODES ¦
¦ +------¦---+
¦ ¦
ROTARYSWITCH + +-+ + +-+
ROTARYSWITCH --¦-----¦ 0 A B
ROTARYSWITCH + + + +
¦ ¦ ¦ ¦
+-------+------------- AVIONICS
¦ ¦ ¦
SOLAR-CHARGER -------+---+ = 10000uF
¦
GROUND ------------------+-------------------
__________________________________________________ __


The Cambridge Logger takes the power from the battery
with the highest Voltage.

The capacitor bridges switch over time up to 1sec if
radio is in receiving mode.

I fly with this layout for more than 10 years and never
had a problem with instruments, loggers or palms failing.
I normally fly a complete week until I recharge the
batteries externally.

Additionally I have an override switch which connects the
Solar panels directly to the Avionics, but I never saw
need to use it up to now.

Chris
CH
__________________________________________________ ___

(if the circuit does not show up aligned,
view the message with Courier New Font)
I have in my ASW27 three batteries and two solar
panels on the fuselage for recharging.
Batteries need a certain time to adjust their
chemical process for delivering current and for
receiving current from the panels. The racers for
the solar challenge overcome this problem by using
two batteries: One for driving and the second for
receiving the energy delivered by the panels or
from the motors while braking. Is the second one
full the batteries are exchanged in the circuit:
the second for driving and the first for recharging.

I did the wiring of the rotary main switch the same
way for my ASW27 (example for 2 batteries)
__________________________________________________ _

BATTERIES 7.2Ah 0 A 0 B
¦ ¦
+-----¦------¦---+--- LOGGERS
¦ ¦ DIODES ¦
¦ +------¦---+
¦ ¦
ROTARYSWITCH + +-+ + +-+
ROTARYSWITCH --¦-----¦ 0 A B
ROTARYSWITCH + + + +
¦ ¦ ¦ ¦
+-------+------------- AVIONICS
¦ ¦ ¦
SOLAR-CHARGER -------+---+ = 10000uF
¦
GROUND ------------------+-------------------
__________________________________________________ __


The Cambridge Logger takes the power from the battery
with the highest Voltage.

The capacitor bridges switch over time up to 1sec if
radio is in receiving mode.

I fly with this layout for more than 10 years and never
had a problem with instruments, loggers or palms failing.
I normally fly a complete week until I recharge the
batteries externally.

Additionally I have an override switch which connects the
Solar panels directly to the Avionics, but I never saw
need to use it up to now.

Chris
CH
__________________________________________________ ___

CHo wrote:

(if the circuit does not show up aligned,
view the message with Courier New Font)

I have in my ASW27 three batteries and two solar
panels on the fuselage for recharging.
Batteries need a certain time to adjust their
chemical process for delivering current and for
receiving current from the panels.

How much time are you talking about for glider batteries? I've not seen
any mention of this in the data sheets for our batteries.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

I have received communications from several manufacturers about this
issue and am awaiting information from others. I plan on presenting
this during my speech at the 2006 SSA convention.

Interestingly, I picked up the following from the Volkslogger
manual....

=================
"The VOLKSLOGGER has no internal buffer against momentary power
interruptions. This has the advantage that there is no part, which
deteriorates and would have to be replaced every 2-3 years by the
manufacturer. Therefore, the power supply of the instrument has to be
protected against momentary drops below the minimum voltage. In
particular during switching of batteries such voltage drops can take
place, which will lead to a separated flight record during readout.
This means that the recording of the flight consists of several files,
which is accepted reluctantly or not at all by the evaluator.

The circuit shown is meant as an example for a buffered and fused
installation. Alternately it is recommended to use a separate logger
battery (Gel-Cell, 12V, 1.8 Ah), to which no other power consuming
devices are connected."

=======================

Basically the diagram shows the battery connected to the Volkslogger
via a series 0.5A fuse, a series Shottky diode 1N5817 and a parallel
22,000uF capacitor. You can see the diagram in the manaul available
at the web site http://www.volkslogger.de/en/html/volkslogger.html.

The manual states that the logger can be run as low as 9.5vdc (up to
24vdc). However, Mr Johannes Garrecht (designer) stated in his letter
to me that the Volkslogger will run at 7vdc. Impressive.

After I compile all the information and present it at the convention I
will make it available here. Stay tuned.