Batteries (again) - 2 Main Batts plus Tail Fin Batt wiring/switching

[Neil Allison]

Hi,

Time to dust off a perennial topic ;)

I looked through the archives and read Darryl Ramm's battery
presentation. Not an exhaustive search but I didn't find an answer to
my question.

At present we have two (fused) 12V 7Ah "main batteries" connected to
the Master switch via an SPDT "changeover" switch. We are adding a
smaller capacity tail fin battery as a "reserve".

Without using diode switching and keeping it as simple as possible for
multiple club pilots, I can see 3 possibilities that I've illustrated
here:
http://www.avon-tech-solutions.co.nz/images/GliderBattery.pdf
- select 1 of the three batteries using two SPDT "changeover" switches
in "series"
- separately isolate the tail battery in parallel to the currently
selected master
- separately isolate the tail battery in parallel to the master switch

Each has its advantages and disadvantages. No doubt there are more
possibilities. I expect to add the recommended Volkslogger "hold up"
circuit separately (or power the logger and possibly a PDA from a
dedicated battery, much like the self contained battery/logger systems
previously discussed here on r.a.s.).

What wiring / switching schemes are you using for this 3 battery
arrangement?

Thanks for your suggestions.
Neil

[HL Falbaum]

Schleicher uses a rotary switch
Batt 1, Batt 2, Batt 3, Off.
If you can get one of these, it reduces to one switch.
--
Hartley Falbaum

"Neil Allison" > wrote in message
...
> Hi,
>
> Time to dust off a perennial topic ;)
>
> I looked through the archives and read Darryl Ramm's battery
> presentation. Not an exhaustive search but I didn't find an answer to
> my question.
>
> At present we have two (fused) 12V 7Ah "main batteries" connected to
> the Master switch via an SPDT "changeover" switch. We are adding a
> smaller capacity tail fin battery as a "reserve".
>
> Without using diode switching and keeping it as simple as possible for
> multiple club pilots, I can see 3 possibilities that I've illustrated
> here:
> http://www.avon-tech-solutions.co.nz/images/GliderBattery.pdf
> - select 1 of the three batteries using two SPDT "changeover" switches
> in "series"
> - separately isolate the tail battery in parallel to the currently
> selected master
> - separately isolate the tail battery in parallel to the master switch
>
> Each has its advantages and disadvantages. No doubt there are more
> possibilities. I expect to add the recommended Volkslogger "hold up"
> circuit separately (or power the logger and possibly a PDA from a
> dedicated battery, much like the self contained battery/logger systems
> previously discussed here on r.a.s.).
>
> What wiring / switching schemes are you using for this 3 battery
> arrangement?
>
> Thanks for your suggestions.
> Neil
>

[JJ Sinclair]

> Paralleling batteries is Bad Bad Bad.

Its OK to parallel 2 batteries for the brief moment it takes to turn
on battery 2, just before turning off battery 1 (or tail battery on/
off) This way you don't interrupt current flow to your flight
recorder. I have used this method for 30 years. Please don't tell me
it will cause a voltage spike. I have tested it by hooking a dead
battery directly to a freshly charged one...........................no
spike, didn't blow a 3A fuse all that happened was 220 m/a current
flow as the good battery tried to charge the dead battery. While we're
speaking of voltage spikes, you can get one coming out of your radio
when the power is interupted and this can cause trouble with other
units in the system ....................see Ilec manual warning about
this.
JJ

[Martin Gregorie[_1_]]

HL Falbaum wrote:
> Schleicher uses a rotary switch
> Batt 1, Batt 2, Batt 3, Off.
> If you can get one of these, it reduces to one switch.
>
I just checked the Maplins online catalog (Maplins is the UK equivalent
of Radio Shack) for their standard range of panel mount rotary switches.
These are 1,2,3 and 4 pole types (12,6,4 and 3 positions). They have a
movable stop so you can blank off unwanted positions. Something like
these is available pretty much anywhere.

They are rated at up to 5 amps, so should be OK in a glider panel.


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

[Ian[_2_]]

On Mon, 19 Nov 2007 12:45:57 +0000, Tim Newport-Peace wrote:

> Not using diodes is good.

I use two diodes to provide a "fail safe" supply to the equipment that
draws low current but requires high availability, like the Volkslogger.

Two very small cheap rectifying diodes do a very effective job with
negligible voltage drop (about 0.1V), no heat sinks etc.

The high current equipment (radio, transponder etc) is powered directly
from alternate batteries via change over switches. But these normally
don't mind a short duration interruption.


Ian