Switching Batteries Advice?

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

ContestID67 wrote:
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.

It's a non-issue for me. I use an EW model D which contains a 9v backup
battery that will run it for about 40 hours. Same applies to my GPS, a
Garmin GPS II+ which always has good batteries in it, so a power outage
can't affect the FR: it doesn't see a power break or a loss of GPS signal.

Another solution, of course, is a capacitor that has enough charge
storage to supply the instruments, etc. for the 10-15mS it takes the
switch to change over.

--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot

You can get some slightly lower drop diodes and they can handle plenty
of current. 18 amps forward I think was the max listed for the ones I
used. Great way to go as you never have to think about batteries while
flying. It's always pulling from the best battery and no issues while
changing over if using a switch.

ContestID67 wrote:
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

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.

Brian

Also just two on/off switches working pretty well as also. Then you can
decide if you want to "Make before break" or not. Althought the two
batteries will probably be connected for a longer time. as you switch.

All we need is a PW-5 thread, and we'll know for sure its winter....
See ya, Dave

PS: 1" of snow here last night... So how 'bout them PW-5s ?

I, too, use this system. Turn one on, then turn the other off. No problems
in 6 years so far! I use a panel mounted digital display voltmeter, and
switch when it reads 12.0 v or is decreasing faster than it had been
decreasing. The batteries have 5 A fuses on them. Almost always I get by on
one battery--running a lot of electrics.

--
Hartley Falbaum
ASW27B "KF" USA


"Brian" wrote in message
oups.com...
Also just two on/off switches working pretty well as also. Then you can
decide if you want to "Make before break" or not. Althought the two
batteries will probably be connected for a longer time. as you switch.

I have two master switches, each to its own battery.
Turn on batt 2, turn off batt 1. No problems connecting
them togetther briefly. I can also charge them either
together or one at a time, depending on which masters
are on. Charging independently is best, but a trickle
charge on both doesn't hurt anything.

I know some guys just hook up half their instruments
to each battery. No swithing.



At 02:06 06 January 2006, Hl Falbaum wrote:
I, too, use this system. Turn one on, then turn the
other off. No problems
in 6 years so far! I use a panel mounted digital display
voltmeter, and
switch when it reads 12.0 v or is decreasing faster
than it had been
decreasing. The batteries have 5 A fuses on them. Almost
always I get by on
one battery--running a lot of electrics.

--
Hartley Falbaum
ASW27B 'KF' USA


'Brian' wrote in message
roups.com...
Also just two on/off switches working pretty well
as also. Then you can
decide if you want to 'Make before break' or not.
Althought the two
batteries will probably be connected for a longer
time. as you switch.

I have two master switches, each to its own battery.
Turn on batt 2, turn off batt 1. No problems connecting
them togetther briefly. I can also charge them either
together or one at a time, depending on which masters
are on. Charging independently is best, but a trickle
charge on both doesn't hurt anything.

I know some guys just hook up half their instruments
to each battery. No swithing.



At 02:06 06 January 2006, Hl Falbaum wrote:
I, too, use this system. Turn one on, then turn the
other off. No problems
in 6 years so far! I use a panel mounted digital display
voltmeter, and
switch when it reads 12.0 v or is decreasing faster
than it had been
decreasing. The batteries have 5 A fuses on them. Almost
always I get by on
one battery--running a lot of electrics.

--
Hartley Falbaum
ASW27B 'KF' USA


'Brian' wrote in message
roups.com...
Also just two on/off switches working pretty well
as also. Then you can
decide if you want to 'Make before break' or not.
Althought the two
batteries will probably be connected for a longer
time. as you switch.

I also have a small digital voltmeter which plugs directly
into the charging jack when not used. It records voltage
on whichever battery is switched on.




At 02:06 06 January 2006, Hl Falbaum wrote:
I, too, use this system. Turn one on, then turn the
other off. No problems
in 6 years so far! I use a panel mounted digital display
voltmeter, and
switch when it reads 12.0 v or is decreasing faster
than it had been
decreasing. The batteries have 5 A fuses on them. Almost
always I get by on
one battery--running a lot of electrics.

--
Hartley Falbaum
ASW27B 'KF' USA


'Brian' wrote in message
roups.com...
Also just two on/off switches working pretty well
as also. Then you can
decide if you want to 'Make before break' or not.
Althought the two
batteries will probably be connected for a longer
time. as you switch.