2-Batteries

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.

Steve Paavola 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?

I've been using the 2 toggle switch solution for years. I replace a
battery when it discharges within 5 hours. This means I've always got at
least 10 hours worth of battery (assuming I've recharged the batteries).

It doesn't really matter, when one goes bad, you should replace both.
Not only will a new battery not load share properly with an old one, if
one battery in the set failed, the other can't be far behind.

The same thing goes for your two bulb light fixture at home. If you
only change one bulb at a time, you will just be changing bulbs twice
as often.

On Tue, 26 Dec 2006 01:39:44 +0000, Steve Paavola wrote:

Gary Emerson wrote:

wrote:
Better yet is to use diodes so that both batteries will always be "on"
in parallel and you're always pulling from the best battery with no
fiddling required from the pilot. Relatively low voltage drop diodes
are available with 18 Amp forward capacity.

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?

I used two small diodes to provide a "fail safe" supply to the
Volkslogger, but the radio, vario, transponder etc get theirs via a 2 way
toggle switch.

Then when one battery dies in flight, I will notice and switch to the next
one manually. But in the meantime the logger always draws current from the
highest voltage battery and hence no interruption to the trace.

The diodes are equivalents of IN 5817 "Shottky rectifying diodes". They
are cheap and tiny. At the low currents drawn by the logger, the forward
voltage drop is very small (less than 0.2V). No cooling is required. I
soldered them directly in line with the wires from the fuse holder to the
toggle switch, without a circuit board.

I test the voltage on each battery during my pre-flight by setting the
Volkslogger on its battery voltage function and disconnecting the
batteries one at a time. (If the electric vario had a battery voltage
function, I could switch it between the batteries and measure their
voltage in flight.)

The weak link in this setup is the toggle switch which has to be sized to
handle a significant DC current.

(The u/c warning buzzer is now also running off a 2 diode "fail safe"
supply - but there is another story behind that ...).


Regards


Ian

test
"Ian" wrote in message
news
On Tue, 26 Dec 2006 01:39:44 +0000, Steve Paavola wrote:

Gary Emerson wrote:

wrote:
Better yet is to use diodes so that both batteries will always be "on"
in parallel and you're always pulling from the best battery with no
fiddling required from the pilot. Relatively low voltage drop diodes
are available with 18 Amp forward capacity.

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?

I used two small diodes to provide a "fail safe" supply to the
Volkslogger, but the radio, vario, transponder etc get theirs via a 2 way
toggle switch.

Then when one battery dies in flight, I will notice and switch to the next
one manually. But in the meantime the logger always draws current from the
highest voltage battery and hence no interruption to the trace.

The diodes are equivalents of IN 5817 "Shottky rectifying diodes". They
are cheap and tiny. At the low currents drawn by the logger, the forward
voltage drop is very small (less than 0.2V). No cooling is required. I
soldered them directly in line with the wires from the fuse holder to the
toggle switch, without a circuit board.

I test the voltage on each battery during my pre-flight by setting the
Volkslogger on its battery voltage function and disconnecting the
batteries one at a time. (If the electric vario had a battery voltage
function, I could switch it between the batteries and measure their
voltage in flight.)

The weak link in this setup is the toggle switch which has to be sized to
handle a significant DC current.

(The u/c warning buzzer is now also running off a 2 diode "fail safe"
supply - but there is another story behind that ...).


Regards


Ian

Steve Paavola 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?

You can get fairly inexpensive automatic peak detecting battery
cycler/charger units ($60-$100 at a guess - around GBP 69.00 in the UK)
that will measure the capacity during a discharge cycle. These units
will charge lead-acid, NiCd, NiMH and Li-poly with settable charge and
discharge currents. You can run them off 12v DC (mains or batteries)
they'll charge 12v lead acid and 14 cell NiCd batteries.

Check your local friendly RC model supply shop if you're interested in
this type of charger.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Gary,

I developed a circuit card with isolation diodes for two batteries and
a pair of efficient voltage regulators, one for high current devices
(radio and transponder) and the other for the rest. As Dick indicated
the panel has two SPST switches for two batteries. The diodes drop .3
Volts, but the regulators operate down to low voltages. There is a
price to pay for operating the regulators. But, I felt that
considering that I use 12 Ah batteries, I had plenty of capacity and I
was more interested in supplying regulated power to my instruments.

The problem was that the large regulator couldn't handle the start up
load from the transponder. So, my quick fix was to bypass that
regulator with the second switch. I expect to revisit the project some
day and finish it properly.

Jim Hendrix


Gary Emerson 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 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

Better yet is to use diodes so that both batteries will always be "on"
in parallel and you're always pulling from the best battery with no
fiddling required from the pilot. Relatively low voltage drop diodes
are available with 18 Amp forward capacity. For redundancy, I used two
in parallel on each battery. The diodes are available in the TO-220
package and it's easy to incorporate a small heat sink, but I have no
reason to believe they ever attained any temperature at all.

With two batteries connected with switches, if one battery does really
"die" then any time spent with both switches in the "on" position causes
the good battery to attempt to charge the "dead" battery to no avail, so
ultimately you're wasting what power you do have during this time. The
diodes eliminate any chance for cross charging...or discharging. Used
this system for several years, never experienced a single power issue.

OxAero wrote:

The problem was that the large regulator couldn't handle the start up
load from the transponder. So, my quick fix was to bypass that
regulator with the second switch. I expect to revisit the project some
day and finish it properly.

If you are using a transponder like the Becker ATC 4401, the bypass is
the best setup. The Becker, like many other modern transponders and
radios, has a wide range input voltage regulator (9-32 volts for the
Becker), so regulating it's input voltage has no advantage. As you
discovered, it may even prevent the equipment from working properly, as
it is designed to operate from a battery, not a regulated supply.

I suggest you determine exactly which instrument(s) really benefit from
input voltage regulation and put only those on the regulator. Most of
the newer equipment we use was specifically designed for battery use, so
adding a regulator just increases the things that can fail.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

OxAero wrote:
Gary,

I developed a circuit card with isolation diodes for two batteries and
a pair of efficient voltage regulators, one for high current devices
(radio and transponder) and the other for the rest. As Dick indicated
the panel has two SPST switches for two batteries. The diodes drop .3
Volts, but the regulators operate down to low voltages. There is a
price to pay for operating the regulators. But, I felt that
considering that I use 12 Ah batteries, I had plenty of capacity and I
was more interested in supplying regulated power to my instruments.

The problem was that the large regulator couldn't handle the start up
load from the transponder. So, my quick fix was to bypass that
regulator with the second switch. I expect to revisit the project some
day and finish it properly.

Jim Hendrix


Gary Emerson 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 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


Better yet is to use diodes so that both batteries will always be "on"
in parallel and you're always pulling from the best battery with no
fiddling required from the pilot. Relatively low voltage drop diodes
are available with 18 Amp forward capacity. For redundancy, I used two
in parallel on each battery. The diodes are available in the TO-220
package and it's easy to incorporate a small heat sink, but I have no
reason to believe they ever attained any temperature at all.

With two batteries connected with switches, if one battery does really
"die" then any time spent with both switches in the "on" position causes
the good battery to attempt to charge the "dead" battery to no avail, so
ultimately you're wasting what power you do have during this time. The
diodes eliminate any chance for cross charging...or discharging. Used
this system for several years, never experienced a single power issue.



Just curious what made you want to add a regulator? Pulling off a
battery should be pretty regulated supply in the first place. Shouldn't it?

Link to schematic: http://www.oxaero.com/GliderPowerBoard-Hendrix.pdf
Jim Hendrix

On Dec 29, 7:02 pm, "OxAero" wrote:
Gary,

I developed a circuit card with isolation diodes for two batteries and
a pair of efficient voltage regulators, one for high current devices
(radio and transponder) and the other for the rest. As Dick indicated
the panel has two SPST switches for two batteries. The diodes drop .3
Volts, but the regulators operate down to low voltages. There is a
price to pay for operating the regulators. But, I felt that
considering that I use 12 Ah batteries, I had plenty of capacity and I
was more interested in supplying regulated power to my instruments.

The problem was that the large regulator couldn't handle the start up
load from the transponder. So, my quick fix was to bypass that
regulator with the second switch. I expect to revisit the project some
day and finish it properly.

Jim Hendrix



Gary Emerson 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 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

Better yet is to use diodes so that both batteries will always be "on"
in parallel and you're always pulling from the best battery with no
fiddling required from the pilot. Relatively low voltage drop diodes
are available with 18 Amp forward capacity. For redundancy, I used two
in parallel on each battery. The diodes are available in the TO-220
package and it's easy to incorporate a small heat sink, but I have no
reason to believe they ever attained any temperature at all.

With two batteries connected with switches, if one battery does really
"die" then any time spent with both switches in the "on" position causes
the good battery to attempt to charge the "dead" battery to no avail, so
ultimately you're wasting what power you do have during this time. The
diodes eliminate any chance for cross charging...or discharging. Used
this system for several years, never experienced a single power issue.- Hide quoted text -- Show quoted text -

I just don't get it. Why do you need the extra stage of regulation -
what device is having problems running at typical "12 volt" battery
voltages?

I have the same compuer (C302) as you, fly often in a club ships with
B40 varios and I've never noticed any problems with either at during
battery discharge. I've not heard of problems with the TruTrack T&B
either. Are you doing this because the Microair 760 is voltage
sensitive?

If you believe the efficiency figures for the regulators you quote you
are paying a cost around a 20% reduction in capactity for something I'm
not sure you need. I expect it may be less than this but still it seems
like an unneeded throwing away of capacity and increase in complexity
for no real benefit. It might be interesting to measure the actual
capacity penalty you are paying.

Though I don't use diodes with my two main batteries/master switches, I
do understand the why/how/advantages and disadvantages for doing so. I
do not get the why/how/advantages for adding voltage regulation.


Darryl Ramm


OxAero wrote:
Link to schematic: http://www.oxaero.com/GliderPowerBoard-Hendrix.pdf
Jim Hendrix

On Dec 29, 7:02 pm, "OxAero" wrote:
Gary,

I developed a circuit card with isolation diodes for two batteries and
a pair of efficient voltage regulators, one for high current devices
(radio and transponder) and the other for the rest. As Dick indicated
the panel has two SPST switches for two batteries. The diodes drop .3
Volts, but the regulators operate down to low voltages. There is a
price to pay for operating the regulators. But, I felt that
considering that I use 12 Ah batteries, I had plenty of capacity and I
was more interested in supplying regulated power to my instruments.

The problem was that the large regulator couldn't handle the start up
load from the transponder. So, my quick fix was to bypass that
regulator with the second switch. I expect to revisit the project some
day and finish it properly.

Jim Hendrix



Gary Emerson 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 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

Better yet is to use diodes so that both batteries will always be "on"
in parallel and you're always pulling from the best battery with no
fiddling required from the pilot. Relatively low voltage drop diodes
are available with 18 Amp forward capacity. For redundancy, I used two
in parallel on each battery. The diodes are available in the TO-220
package and it's easy to incorporate a small heat sink, but I have no
reason to believe they ever attained any temperature at all.

With two batteries connected with switches, if one battery does really
"die" then any time spent with both switches in the "on" position causes
the good battery to attempt to charge the "dead" battery to no avail, so
ultimately you're wasting what power you do have during this time. The
diodes eliminate any chance for cross charging...or discharging. Used
this system for several years, never experienced a single power issue.- Hide quoted text -- Show quoted text -