2-Batteries

The previous poster was making measuremnts that disproved the argument
that there is a loss while temporarilly having both masters on while
switching batteries.Whichever way you slice that it is just not an
issue that causes any significant power loss, It is totally
insignificant, you lose much more power though ohmic loses in fuses
and circuit breakers.

Of course that relies on the operator not to accidently leave two
master switches both on all the time (without taking the diode
approach).

Darryl

Gary Emerson wrote:
Tinwings wrote:
Being the incurably curious type, I decided to test this theory. I
took two known good 7Ah 12V SLA batteries and discharged one to 8 volts
(resting) with a 12V light bulb. The other battery I topped off with a
charger to 13.6 volts. I connected the two using less than two feet of
18 gauge wire and a ordinary toggle switch. Using a 60 Mhz bandwith
oscilloscope and a hall-effect type current probe I looked at the
resulting waveform when I closed the switch; a nice square edged rise
to about 3 amps, tapering down to 2.5 amps in a few seconds. Because I
didn't know what the frequency response of this current probe was, I
inserted a precision .001 ohm current shunt in line (very high
frequency response) and used the scope to watch the voltage drop across
it. The results were identical; no current spike, no inrush of current
- just a nice square edged waveform rising to about 3 amps. This simply
isn't going to weld contacts, burn out switches or blow (properly
sized) fuses. As for "wasting energy" by dumping from the good battery
into the dead battery when switching over - just do the math. Even if
the two batteries were connected for as much as 5 seconds while
switching from one to the other (two switch or "make before break"
switch arrangement), you will be using less than one thousanth of the
good battery's capacity to charge the "dead" battery.

If the batteries are both "good", but not charged equally, then the last
part is true. If a battery happens to go "bad" and won't take a charge
then the situation is different. Then the "bad" battery will just suck
down the extra power from the good battery and that power will not be
recovered.

wrote:

The Filsner is unlikely to have a problem through the diode setup you
have now. (not that I like the diode setup but it should work - BTW you
should be able to find lower voltage drop diodes).

Thanks for that advice.

For the Microair I would not read too much into a nominal voltage spec.
It is hard to tell wether the manufacturer is quoting a real absolute
voltage range or the nominal voltage. On the other hand I'd not want to
inflict anybody with a Microair radio (oops I can feel the flames
already).

I'd noticed that they get generally slagged off and have a reputation
for low output and intolerance for depleted batteries. I tend to think
there must be something behind those stories except that I've never seen
one being flogged off second hand.

Are they really so bad that folks are slinging them in the garbage
rather than risking their reputation by selling them on? ;-)

If you are goigg to install a transponder, have lots of avionics toys,
expect long cold flights it may well be you need to look at moving up
to larger capacity batteries or installing solar panels.

That's not an option. I fly a Standard Libelle and already have two 7 AH
gel cells installed: there's not a cat's chance in hell of fitting
anything significantly bigger.


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

Gary Emerson wrote:
Martin Gregorie wrote:
wrote:

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.

That should be easy enough to do with a pair of suitable power MOSFETs
and an LM358 dual op-amp to control the MOSFETs. If I don't split my
supply (see earlier post) I'm thinking about making this type of
circuit this because the voltage drop in the MOSFET will be very small.

Size isn't an issue - suitable MOSFETs are in TO-220 type packages and
the LM358 is an 8 pin DIP package.


How much lower thatn 0.3V drop will the MOSFETs get you?

The forward resistance is around 0.015 ohms (HUF75337P3, 62A, 55V, TO220
package), so at 5amps that's a 75 mV drop. That looks like a worthwhile
improvement.

The MBR1035 was the lowest drop type (0.6v drop) I could find at RS
Components or Maplins, the only two decent retail outlets in the UK.


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

I have had a Microair 760 Rev N, radio in my glider for two years with
no problems. I believe that the key is the Rev N or later. There are
tech notes and fixes on the problems you detailed with earlier
revisions. For those with the earlier revs, Erie Aviation is a
Microair Service Center and may be able to help.

I sell Microair and also Becker for an addtional $450.

Richard
www.craggyaero.com

wrote:
The Filsner is unlikely to have a problem through the diode setup you
have now. (not that I like the diode setup but it should work - BTW you
should be able to find lower voltage drop diodes).

For the Microair I would not read too much into a nominal voltage spec.
It is hard to tell wether the manufacturer is quoting a real absolute
voltage range or the nominal voltage. On the other hand I'd not want to
inflict anybody with a Microair radio (oops I can feel the flames
already). They have a very bad reputation where I fly. The several I've
seen installed have had problems, especially apparent heat related
problems with the displays getting garbled and then finally the whole
radio going out to lunch (and I'm not talking really hot days). Other
brands seems to be much more reliable. Why not go with Becker?

Personally I'd stay away from trying to get too fancy with regulators
etc. I want the supply to be as dumb and simple as possible. Just
batteries and circuit breaker or fuse and master switches. As few
connectors or solder joints as possible. And I personally I like
running one battery at a time - I want to see the health of each
battery and know about how much capacity I have in both batteries and
know I can switch in a reserve if I run a battery down -- which I may
not notice until it is too late. Like many of us in the Western USA I
fly over pretty desolate areas and I really want to know roughly what
battery capacity in reserve.

If you are goigg to install a transponder, have lots of avionics toys,
expect long cold flights it may well be you need to look at moving up
to larger capacity batteries or installing solar panels.

Darryl Ramm


Martin Gregorie wrote:
COLIN LAMB wrote:
Most diodes have about a .6 volt drop, which may be significant. Therefore,
you will need diodes with a low threshold. Schottky diodes should be about
.3 volts drop. You can measure the actual drop using a digital
volt-ohmmeter. There is a diode test range and it will show the voltage
drop.

I'm flying with the diode setup. The best diodes I was able to find in
the UK were Fairchild MBR1035 Schottky diodes. These handle 35 amps and
come in TO-220 packages. Their spec quotes a 0.57 v drop, which seems
about right: with 2 x GPS II+, EW-D logger, SDI C4 and B.40 varios all
on the C4's internal voltmeter shows 11.6 v on two fully charged 7 AH cells.

I need to fit a radio and am thinking of fitting a Filser ATR-500. Can
anybody tell me if that will be OK on the end of the diodes or would I
be better to discard the diodes and use one battery to drive the ATR-500
and the other to run the GPS, logger, and varios?

Another reason I'm wondering about rewiring to separate the batteries is
that if we get landed with transponders I assume I'd be better off using
one for radio and transponder and reserving the other for the
GPS/logger/vario setup. Comments?

The other choice of radio would be a Microair 760. I assume that, as its
rated for 12-14v it would be quite unhappy on the end of the diodes and
just barely usable on a separate battery. I see that Maxim sell a range
of solid state voltage boosters (there is a model that can output 14v at
2 amps). Has anybody tried using one of these to drive a Microair radio?
If so, how well did it work?




Colin Lamb




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

This setup does not allow both batteries to be connected to the same
"bus" at the same time. On the rare time I've had to switch due to old
or insufficiently charged batteries, I've had no trouble with the
races from the loggers.

My question is, is this better, equal, or worse (from the standpoint of
battery usage/efficiency) than the more common "use one batt until it
dies, then switch" 2-battery setup.


I think you have a simple, efficient method of using your batteries.

The only time having both batteries on at the same time is an advantage is
when they are both so depleted that neither one alone will operate the
equipment, or the current draw is so great that the capacity will increase
by dividing the work. Your system has the advantage that it works and you
have specific information from the work performed by each battery.

There is a slight potential problem with having two batteries in parallel.
That is if one has a shorted cell. In that case, the good battery will try
to charge the bad battery, wasting energy. That could be solved by the
diodes, but they waste energy, also.

There is a great deal of merit to keeping something as simple as possible
and remembering that if it works, don't fix it.

Colin

Mike,

The web link gives my interpretation of Dick's preliminary data. He
will speak for himself in Memphis.

Many will not agree with my methods. I'll be more specific soon.
possibly before Memphis, but using my data from two years of flying
deturbulated wings, not Dick's data. I'll give my interpretation of
his data after the convention. I'm not an aerodynamicist, so you will
be excused for not believing me. On the other hand, new things often
don't fit in old boxes, so an open mind may be required for
understanding the true potential of this new technology.

Jim Hendrix
(The Johnson deturbulator flight tests were sponsored by Dallas Glider
Association.)

On Dec 26, 11:41 am, "Mike" wrote:
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.- Hide quoted text -- Show quoted text -

John,

You use what you have.

Jim Hendrix
(The Johnson deturbulator flight tests were sponsored by Dallas Glider
Association.)

On Dec 26, 11:01 am, wrote:
John Galloway wrote:
Noone picking up on Dick Johnson's last paragraph??

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

John GallowayThe 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.

Nyal,

You can get a PDF of a schmatic I used for my Standard Cirrus panel at
http://www.oxaero.com/GliderPowerBoard-Hendrix.pdf.

It's a bit over the top, but you may get some ideas. If you run a
transponder and use a voltage regulator, you will need more than 1.25 A
capacity.

Jim Hendrix

On Dec 25, 2:09 pm, 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.

At 19:48 25 December 2006, Udo 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. For redundancy,
I used two
in parallel on each battery.

If it is always drawing from the best battery, what
is the time
interval between switching.
What controls the switching. Please advise.
Udo- Hide quoted text -- Show quoted text -

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 -