Battery switching without tears

At 03:55 13 April 2020, 2G wrote:
snip

Well, today I did measure the inrush current: the peak current was 9A,
very=
close to what I had simulated with Spice. This current is very brief and
t=
otally within the capability of the switch to handle, but a few ohms of
ser=
ies resistance will cut it down to a couple of amps if you are anal about
i=
t.

Tom

A while ago, I asked if anyone else has experienced your problem.
Apparently not.
The LX9000 has (presumably) a capacitance of its own which sustains it over
changing batteries in most cases.
If there is a high load from other devices on the Bus then there may not be
sufficient capacitance in the LX9000 and it need some help.

If we isolate the LX9000 from the other devices on the Bus with a schottky
diode, then other devices on the Bus will not drain the LX9000’s
capacitance during switch-over as the diode will be back-biased. If it
still needs some help, a small capacitance can be added on the LX9000 side
of the diode.
This will also lead to a reduced inrush current as the connected
capacitance will be less.

I see this issue with my S80 in my Ventus Ct with two batteries.

The S80 powers my Flarm as designed.

When switching between my main battery and second battery I often, but not always have the Flarm power cycle and sometimes the S80 as well.

I too was thinking about sourcing a make before break switch but I am going to put in a capacitor.

On Monday, April 13, 2020 at 4:21:35 AM UTC-7, Mike N. wrote:
I see this issue with my S80 in my Ventus Ct with two batteries.

The S80 powers my Flarm as designed.

When switching between my main battery and second battery I often, but not always have the Flarm power cycle and sometimes the S80 as well.

I too was thinking about sourcing a make before break switch but I am going to put in a capacitor.

I have an S10 with an internal battery that is no problem, But I also use XCSoar on a OpenVario computer that I built from a kit. That has a big problem, as I switch batteries a couple of times a flight to keep the main battery as charged as possible for starts. So a year ago, I got with an electronics guy at our local supplier and he recommended a properly sized Capacitor and it has worked great. I don't remember the size or model, but it is hidden in the panel.

I researched true make before break switchs and they tended to be large and expensive. Not all switches that say the make before break really do what they advertise.

Bruce

Bruce

Interesting Mike -

I have a Flarm / S8 / Oudie set up. I never have any issues while switching batteries.

I wonder of the Oudie battery somehow supplies the "make" current while the switch is being thrown?

Lou

On Monday, April 13, 2020 at 3:45:04 AM UTC-7, Tim Newport-Peace wrote:
At 03:55 13 April 2020, 2G wrote:
snip

Well, today I did measure the inrush current: the peak current was 9A,
very=
close to what I had simulated with Spice. This current is very brief and
t=
otally within the capability of the switch to handle, but a few ohms of
ser=
ies resistance will cut it down to a couple of amps if you are anal about
i=
t.

Tom

A while ago, I asked if anyone else has experienced your problem.
Apparently not.
The LX9000 has (presumably) a capacitance of its own which sustains it over
changing batteries in most cases.
If there is a high load from other devices on the Bus then there may not be
sufficient capacitance in the LX9000 and it need some help.

If we isolate the LX9000 from the other devices on the Bus with a schottky
diode, then other devices on the Bus will not drain the LX9000’s
capacitance during switch-over as the diode will be back-biased. If it
still needs some help, a small capacitance can be added on the LX9000 side
of the diode.
This will also lead to a reduced inrush current as the connected
capacitance will be less.

Hell of a lot easier just to add a capacitor to the bus line, and it can be significantly smaller than the 39000μ that I used (10000μ would probably be fine).

I did because I am.

Big old power resistors. I think they were 1-2 ohms. However, after considering battery performance implications of deep discharge I normally fly with the switch set to both batteries.

Andy Blackburn
9B


.... a few ohms of series resistance will cut it down to a couple of amps if you are anal about it.

Tom

That could be a significant voltage drop across the resistors. I'd use
a couple power Schottky diodes instead.



On 4/13/20 1:11 PM, Andy Blackburn wrote:
I did because I am.

Big old power resistors. I think they were 1-2 ohms. However, after considering battery performance implications of deep discharge I normally fly with the switch set to both batteries.

Andy Blackburn
9B


... a few ohms of series resistance will cut it down to a couple of amps if you are anal about it.

Tom

On Monday, April 13, 2020 at 1:08:16 PM UTC-7, kinsell wrote:
That could be a significant voltage drop across the resistors. I'd use
a couple power Schottky diodes instead.



On 4/13/20 1:11 PM, Andy Blackburn wrote:
I did because I am.

Big old power resistors. I think they were 1-2 ohms. However, after considering battery performance implications of deep discharge I normally fly with the switch set to both batteries.

Andy Blackburn
9B


... a few ohms of series resistance will cut it down to a couple of amps if you are anal about it.

Tom


Anybody who took EE101 (and most everybody else) can tell you that:
E = I * R
If
I = 1A
R = 1Ω
then
E = 1V

I used Shottky diodes plus power resistors plus capacitors. I'm no EE but I took enough circuits courses to handle this problem. The Shottky diodes keep the batteries from cross-discharging each other, the capacitors keep the instruments powered when the switch is disconnected from battery 1 and before it is connected to battery 2 and the resistors keep the capacitors from drawing too much current when you power them up since they make the circuit (even with the diodes) look like a direct short initially.

Andy

On Monday, April 13, 2020 at 1:08:16 PM UTC-7, kinsell wrote:
That could be a significant voltage drop across the resistors. I'd use
a couple power Schottky diodes instead.

On 4/10/20 3:19 PM, kinsell wrote:
On 4/8/20 10:58 AM, Martin Gregorie wrote:
On Wed, 08 Apr 2020 08:57:43 -0600, kinsell wrote:

Runs an embedded linux, they're not storing any data during normal
operation, so baffling why that's so hard to fix.

When does it commit data to non-volatile memory, i.e. does in
intentionally buffer it and only commit at intervals or as part of
shutting down?
FWIW The same problem occurs with Raspberry Pis.

As you may or may not know, these run a Debian Linux clone as their OS
and use SD cards for non-volatile memory by default. Much of the time
people can get away with simply pulling the plug when the Pi appears to
be idle, but if you do that while the Pi is flushing its caches to its SD
card or, more rarely, the card is in the middle of a wear-levelling
process, then the SD card will become corrupted and possibly permanently
damaged if it was wear-levelling when the power vanished. Which is why
everybody soon learns to shut the Pi down with a 'sudo stop' command
before powering it off. I think its worse with SD cards simply because
their internal controllers and cheap, rather basic and have no power
buffering. Use an SSD instead or, even better, a hard drive and the
problem largely goes away because ext4 is a journalling filesystem, so
has built-in recovery.

I agree this is a tricky problem, and maybe best solved with some sort of
cheap'n cheerful UPS. Here's a suggestion along those lines:

Pimoroni sell the PowerBoost 1000 Charger, a small and fairly cheap UPS
circuit ($US 19.39 from Amazon), which you connect between a 5v power
supply and the device you want to power via a UPS socket. You also
connect a suitable sized 1S (3.7 volt) Lithium-ion battery to it - the
sort used to power small RC models would be fine - and there's a power
buffer for any UPS-powered device that doesn't have an internal battery.
Its good to supply up to 1000mA provided that the battery is rated for
that current. Some soldering is needed.

It comes with a selection of sockets, but they're all sat loosely in
place on the board so you can solder the ones you want on, sling the
others and solder any permanent connections you need.

I have one but haven't used it yet - I'm planning to make a PDA from a 4"
touch screen and a Pi Zero WL and use this Pimoroni plus an RC model 1S
LiPO battery to power it. Add a case made from epoxyboardÂ* and it should
be ready to rock'n roll.



The Stratux project does run on a Rspberry Pi using the micro-SD for
storage.Â* Yes, running other software on that hardware can lead to the
same file system corruption problem.Â* What's interesting is I can load
FlightAware software on the same hardware and never see the problem.Â* In
both applications, there is no user data that needs to be stored to
flash memory, other than a tiny bit of configuration data when they are
first set up.Â* It is possible to run on a read-only file system, if some
provision is made for the configuration data.Â* People have experimented
with this, but the images distributed for Stratux have never had a
solution that I'm aware of.

So many devices these days have a computer with flash memory.Â* If your
smart TV becomes unbootable after a power fail, would that be considered
acceptable?Â* Of course not.Â* But for some reason Stratux doesn't seem to
get fixed.Â* Putting a UPS on a microcomputer seems like an ugly Band-Aid
(rtm) that shouldn't be necessary.Â* Just a simple file system check on
power up might be adequate.Â* There's a Sentry Mini receiver available
now for just $300, I'll bet it doesn't lose its mind if you just pull
power.

-Dave


Looking at a couple lightly-used Stratux boxes, one of then had a
completely full file system, the other was almost full. Seems to be
more of a science fair project than a serious instrument to be used for
navigation.