Multiple Battery Setup

You don't need to use an ideal diode part like LTC4358.
You can use a reverse-connected MOSFET as an ideal
diode for battery paralleling and/or reverse-polarity
protection. Here's an explanation:
http://www.geofex.com/article_folder.../mosswitch.htm

In my never-ending quest to make glider-pilot-proof
equipment, I'm using FDC610PZ in a new project.
I've recently noticed this part featured in some
LTC appnotes so apparently others think this a
suitable part for this application.

Choosing MOSFETs, watch the body diode max current on
inrush current (not specified for all MOSFETs).

Remember to keep the smoke inside the chips,
Best Regards, Dave "YO electric"

PS: This configuration is not an ideal diode;
does not prevent crossfeed as an ideal would...

On Feb 6, 8:38*am, Dave Nadler wrote:
PS: This configuration is not an ideal diode;
does not prevent crossfeed as an ideal would...

Question, if you want to keep it pretty simple and just have two
batteries, for example a big 12 volt 15AH like a 12150 and a smaller
back-up like a 4AH Li-Ion. Then this is wired to an A B switch and
you only use the Li-Ion for emergencies. OK, finally the question.
When you switch from A to B doesn't the computer restart? I have
heard of a capacitor you can connect somehow to provide enough voltage
to keep everything from dropping off like, but now we aren't keeping
it simple anymore.

Cheers,
Brian

On Monday, February 6, 2012 1:25:06 PM UTC-5, brianDG303 wrote:
When you switch from A to B doesn't the computer restart?
If you have an ILEC SN10 this is not a problem
(if the power cycles off and on, no information is lost).

I have
heard of a capacitor you can connect somehow to provide enough voltage
to keep everything from dropping off like, but now we aren't keeping
it simple anymore.

And you will get big inrush current when you connect the
battery to charge the capacitor, and maybe you will blow
fuses and/or damage our switch...

Hope that helps,
Best Regards, Dave "YO electric"

I vote for simplicity - a fuse at each battery, a panel switch for
each battery, a fuse for each instrument, a switch for each
instrument, and a voltmeter (discrete or in an instrument). If its a
long flight for a badge or record, use a separate flight data logger
powered from an independent battery, and turn off instruments you
don't need. No circuit breakers, no diodes, no FETs - save that energy
for the avionics.

Fly with one battery until its voltage goes below 11.0, then switch to
the other battery. Switch the battery you fly with first the beginning
of next flight. You'll then know the performance ability of each
battery during the season, because you'll know how long it supplied
your exact flight needs, at what temperature, at most one flight ago.
And of course, charge the overnight batteries after the flight.

Automation is fine, but battery management is so simple why waste
electrical energy? I bet there isn't a glider pilot out there who
doesn't look at his battery voltage at least several times during each
flight, and who doesn't understand switches...

-John

On Feb 6, 11:10*am, jcarlyle wrote:
I vote for simplicity - a fuse at each battery, a panel switch for
each battery, a fuse for each instrument, a switch for each
instrument, and a voltmeter (discrete or in an instrument). If its a
long flight for a badge or record, use a separate flight data logger
powered from an independent battery, and turn off instruments you
don't need. No circuit breakers, no diodes, no FETs - save that energy
for the avionics.

Fly with one battery until its voltage goes below 11.0, then switch to
the other battery. Switch the battery you fly with first the beginning
of next flight. You'll then know the performance ability of each
battery during the season, because you'll know how long it supplied
your exact flight needs, at what temperature, at most one flight ago.
And of course, charge the overnight batteries after the flight.

Automation is fine, but battery management is so simple why waste
electrical energy? I bet there isn't a glider pilot out there who
doesn't look at his battery voltage at least several times during each
flight, and who doesn't understand switches...

-John

I agree John. One switch for each battery. During switch over to the
stronger battery, both switches are "on" for a brief moment. No loss
of power to the flight recorder and no loss of capacity.

Cheers,
Craig

On Feb 6, 1:10*pm, jcarlyle wrote:
I vote for simplicity - a fuse at each battery, a panel switch for
each battery, a fuse for each instrument, a switch for each
instrument, and a voltmeter (discrete or in an instrument). If its a
long flight for a badge or record, use a separate flight data logger
powered from an independent battery, and turn off instruments you
don't need. No circuit breakers, no diodes, no FETs - save that energy
for the avionics.

Fly with one battery until its voltage goes below 11.0, then switch to
the other battery. Switch the battery you fly with first the beginning
of next flight. You'll then know the performance ability of each
battery during the season, because you'll know how long it supplied
your exact flight needs, at what temperature, at most one flight ago.
And of course, charge the overnight batteries after the flight.

Automation is fine, but battery management is so simple why waste
electrical energy? I bet there isn't a glider pilot out there who
doesn't look at his battery voltage at least several times during each
flight, and who doesn't understand switches...

-John

John Carlyle is right and it pains me to say this but the whole
parallel battery business is nonsense. In the first place, select
batteries that last by themselves over a long day of flying. Have two
of those installed and follow John C's advice above. Except, you
don't have to switch since you don't run your primary battery down.
In fact, I only charge my battery #1 before each flight and top off
the reserve every couple of weeks (all NiMH batteries). I carry a
third large battery that only drives my transponder.

On Feb 6, 12:10*pm, jcarlyle wrote:
I bet there isn't a glider pilot out there who
doesn't look at his battery voltage at least several times during each
flight, and who doesn't understand switches...


I'll take your bet on understanding switches. How many glider pilots
do you think understand the difference between the AC and DC rating of
a switch and select one with an approprate DC rating? How many know
why the ratings are very different? How many glider pilots know the
inrush current of their installed avionics? How many know if the the
load has a significant inductive component?

It's only a switch after all.

Andy

Andy wrote:
On Feb 6, 12:10 pm, jcarlyle wrote:
I bet there isn't a glider pilot out there who
doesn't look at his battery voltage at least several times during each
flight, and who doesn't understand switches...


I'll take your bet on understanding switches. How many glider pilots
do you think understand the difference between the AC and DC rating of
a switch and select one with an approprate DC rating? How many know
why the ratings are very different? How many glider pilots know the
inrush current of their installed avionics? How many know if the the
load has a significant inductive component?

It's only a switch after all.

Andy

Andy,

Mea culpa - in my attempt to tread a fine line between brevity and
excruciating detail I omitted the phrase "how to use" between the
words "understand" and "switches" in the last sentence of my post. I
also omitted giving precise instructions on how to switch over from
the supplying battery to the unused battery, and I didn't explain the
need to size the batteries to avionics current draw, expected
temperatures, battery age, etc.

Others kindly added some of the information I omitted regarding the
last two points, thus furthering the conversation. It would have been
nice if you'd done the same, rather than attempt to pick a fight. But,
I guess you're not one of those people who share.

I'm not going to provide answers the questions you raised, even though
I could. I'll just say that for those who are interested in this
topic, if you don't understand the questions Andy raised, then don't
attempt to select components and wire your glider yourself. Rather,
use this thread as a rough guide, get professional advice (Radio Shack
doesn't count, spend a few bucks at an avionics firm), and avoid the
horror of fire in the air.

-John

On Feb 6, 8:23*am, Dave Nadler wrote:
You don't need to use an ideal diode part like LTC4358.
You can use a reverse-connected MOSFET as an ideal
diode for battery paralleling and/or reverse-polarity
protection. Here's an explanation:http://www.geofex.com/article_folder.../mosswitch.htm

I get the "reverse polarity" part. But how is it supposed to help with
connecting batteries in parallel? The weaker battery will still pull
the strong one down - at least SPICE says so.

On an unrelated note, I enjoyed your presentation in Reno.

Bart