Master Switch

A while back I was looking at LiFePO4 batteries to solve my electrical
problems and I may still order them as my SLA batteries are getting old and
hold less of a charge.

I did, however, get behind my panel last week and changed out my master
switch for one more substantial in current capability and have experienced a
major improvement in function of my equipment. The switch that was
installed when I bought the glider was adequate for the CAI302 and the
MicroAir 760 but, after installing a Trig transponder, a Dell Steak and a
Zaon MRX, all operated from the same bus, the current capacity of the master
switch was the limiting factor. After two flights with the new master
switch installed it would appear that the problem is solved.

After two flights with the new master
switch installed it would appear that the problem is solved.

Dan, Just for interest what were the symptoms you were experiencing?

Dean

Dean, the radio was cutting out. Initially, other pilots would mention
scratchy and broken transmissions, later the green "Receive" light on my
radio would illuminate but no audio would be forthcoming, finally, the radio
would not function. I'd also see a large voltage drop when keying the
transmitter - sometimes over 1 volt. Switching to a fresh battery would not
solve the problem. I expect switching batteries under load caused pitting
and/or carboning of the switch, making it a high resistance junction.



"Soartech" wrote in message
...
After two flights with the new master
switch installed it would appear that the problem is solved.

Dan, Just for interest what were the symptoms you were experiencing?

Dean

On Wednesday, October 16, 2013 7:26:12 AM UTC-7, Dan Marotta wrote:
A while back I was looking at LiFePO4 batteries to solve my electrical

problems and I may still order them as my SLA batteries are getting old and

hold less of a charge.



I did, however, get behind my panel last week and changed out my master

switch for one more substantial in current capability and have experienced a

major improvement in function of my equipment. The switch that was

installed when I bought the glider was adequate for the CAI302 and the

MicroAir 760 but, after installing a Trig transponder, a Dell Steak and a

Zaon MRX, all operated from the same bus, the current capacity of the master

switch was the limiting factor. After two flights with the new master

switch installed it would appear that the problem is solved.

Ilec is dead set against using a master switch. The SB-7 manual has 22 cautions on the electrical installation page and the first 5 cautions are why it is a bad idea to use a master switch at all.

"MAIN SWITCHES in the electrical system can be a source of serious trouble, in particular where there are radio sets connected to them. When turning on the main switch with the radio on, heavy negative going pulses may be generated on the bus line during the typical 1-ms-bouncing periods of the main switch. They can destroy instruments, if not at once, then in the long run.. We have measured pulses of more than 10 amps".
Ilec goes on and on about what a bad idea a master switch is in a glider. What is the Master Switch really for? To shut off everything in case of an electrical problem.......can you say, smoke in the cockpit? If you do use a master switch (I don't), remember to ALWAYS turn it on FIRST and off LAST to insure these potential 10 amp pulses can't get in your delicate instruments.
Hope this helps,
JJ

On Wednesday, October 16, 2013 9:26:12 AM UTC-5, Dan Marotta wrote:
A while back I was looking at LiFePO4 batteries to solve my electrical

problems and I may still order them as my SLA batteries are getting old and

hold less of a charge.



I did, however, get behind my panel last week and changed out my master

switch for one more substantial in current capability and have experienced a

major improvement in function of my equipment. The switch that was

installed when I bought the glider was adequate for the CAI302 and the

MicroAir 760 but, after installing a Trig transponder, a Dell Steak and a

Zaon MRX, all operated from the same bus, the current capacity of the master

switch was the limiting factor. After two flights with the new master

switch installed it would appear that the problem is solved.

Dan just curious, on the old switch you took out, what was the actual measured voltage drop caused by the faulty switch. Also did you happen to measure the resistance with an Ohm meter? I had a similar voltage drop when I used a riv nut to make a terminal post on a battery. Ironically it was a new LiFePo4 that didn't have the typical attachment connector. FYI I have a master switch and use the First On Last Off sequence that JJ referenced.

Another thing to consider: as the switch is used, over time, the contact surface becomes pitted and corroded due to small arcing as the contact is made and broken. This will lead to less contact area, higher resistance and lower voltage across the switch. It's probably a good idea to replace every few years as a precaution, or at least check the switch for minimal resistance.

Mike

Thanks, JJ. I have always turned the master switch on first and off last
and used the individual switches on the radios and instruments. I guess
it's that switching thing midway through the flight.

A large capacitor would be one way to mitigate that but I'm thinking more of
a "make before break" setup using multiple switches, i.e., turn on the
second battery before turning off the first.

Or I could simply divide my equipment across two (or three) busses and then
rely on the load division to allow the batteries to last an entire flight.

"JJ Sinclair" wrote in message
...
On Wednesday, October 16, 2013 7:26:12 AM UTC-7, Dan Marotta wrote:
A while back I was looking at LiFePO4 batteries to solve my electrical

problems and I may still order them as my SLA batteries are getting old
and

hold less of a charge.



I did, however, get behind my panel last week and changed out my master

switch for one more substantial in current capability and have experienced
a

major improvement in function of my equipment. The switch that was

installed when I bought the glider was adequate for the CAI302 and the

MicroAir 760 but, after installing a Trig transponder, a Dell Steak and a

Zaon MRX, all operated from the same bus, the current capacity of the
master

switch was the limiting factor. After two flights with the new master

switch installed it would appear that the problem is solved.

Ilec is dead set against using a master switch. The SB-7 manual has 22
cautions on the electrical installation page and the first 5 cautions are
why it is a bad idea to use a master switch at all.

"MAIN SWITCHES in the electrical system can be a source of serious trouble,
in particular where there are radio sets connected to them. When turning on
the main switch with the radio on, heavy negative going pulses may be
generated on the bus line during the typical 1-ms-bouncing periods of the
main switch. They can destroy instruments, if not at once, then in the long
run. We have measured pulses of more than 10 amps".
Ilec goes on and on about what a bad idea a master switch is in a glider.
What is the Master Switch really for? To shut off everything in case of an
electrical problem.......can you say, smoke in the cockpit? If you do use a
master switch (I don't), remember to ALWAYS turn it on FIRST and off LAST to
insure these potential 10 amp pulses can't get in your delicate instruments.
Hope this helps,
JJ

Can't say the drop across the switch since I never measured across it.
Neither did I try turning off the transponder, PCAS, and Streak.


"glidergreg" wrote in message
...
On Wednesday, October 16, 2013 9:26:12 AM UTC-5, Dan Marotta wrote:
A while back I was looking at LiFePO4 batteries to solve my electrical

problems and I may still order them as my SLA batteries are getting old
and

hold less of a charge.



I did, however, get behind my panel last week and changed out my master

switch for one more substantial in current capability and have experienced
a

major improvement in function of my equipment. The switch that was

installed when I bought the glider was adequate for the CAI302 and the

MicroAir 760 but, after installing a Trig transponder, a Dell Steak and a

Zaon MRX, all operated from the same bus, the current capacity of the
master

switch was the limiting factor. After two flights with the new master

switch installed it would appear that the problem is solved.

Dan just curious, on the old switch you took out, what was the actual
measured voltage drop caused by the faulty switch. Also did you happen to
measure the resistance with an Ohm meter? I had a similar voltage drop when
I used a riv nut to make a terminal post on a battery. Ironically it was a
new LiFePo4 that didn't have the typical attachment connector. FYI I have a
master switch and use the First On Last Off sequence that JJ referenced.

On Thursday, October 17, 2013 9:10:25 AM UTC-5, Dan Marotta wrote:

Or I could simply divide my equipment across two (or three) busses and then

rely on the load division to allow the batteries to last an entire flight.

Dan, that's how I've had my LS6 setup for over 13 years and it has worked just fine so far.

2 separate busses, one for each battery, with load divided as equally and logically as possible (split varios and loggers, for example).

In addition, the master switch for each buss can also select either battery, so if one battery fails (forgot to charge it?) the essential instruments can be powered by the remaining battery.

Probably WAY over-engineered, but it was fun to wire up and has worked as designed so far (ugly to look at, though - bit of a spaghetti factory behind that small LS6 panel that I want to clean up some day...).

Kirk
66

How about this, diagram below.
Each battery should have its own fuse.
Switches are drawn as -o\-
Vertical line is the Master bus.
Optional PV charge controller charges the active battery, whether avionics are on or off.
I'd suggest locking switches like Alcoswitch MTL106D available from Mouser for $12.60.
Jim

Bat 1 -----o\-----|
Bat 2 -----o\-----|
Bat 3 -----o\-----|
|-----o\----- Avionics
PV Charger -------|