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).