Master Switches

On 4/26/2013 8:38 AM, Evan Ludeman wrote:
On Friday, April 26, 2013 11:28:31 AM UTC-4,


http://www.amazon.com/dp/B005KLOYO2/..._M3T1_ST1_dp_1



http://www.amazon.com/BALLISTIC-PERF...=pd_sim_auto_1

These are both Lifepo4 batteries that would be well suited for
glider usage. Note that the higher capacity battery has 8 cells
but still 13.2V nominal voltage. Obviously, inside are two of the
first kind batteries connected in parallel. This has to do with
the standard cell (3.3V, 7,000mah) they are using, makes sense to
me.



Herb

Herb: No! Much better off with a battery pack that includes current
limiting protection. These are starting batteries. There are
several good looking 9 - 12 AH LFP battery packs available now that
include in-the-pack battery management. Over charge protection,
under charge protection, cell balancing and over current protection
(all somewhere between "really good ideas" and "essential" for safe
LFP use). It remains to be seen how well these systems work over the
long haul. Technology is still a little young to say for certain
imo. Vendors include K2, Bioenno, Starck. If you choose to go any
of these routes, get the spec sheets, ask questions, do some
diligence.

I agree with Evan: these are totally unsuited for glider use. In
addition to the concerns he noted, also note that this particular 4-cell
unit has only 2.3 Amp hours! Beware of Li batteries offered for
"powersports" use: they often are rated by _equivalent_ lead-acid
numbers batteries, but they are ration only the cranking amps ability,
no the actual low current amp hour capacity.


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what
you need to know tinyurl.com/yfs7tnz

On 4/26/2013 7:09 AM, Tom Gardner wrote:
rk wrote:

Let me repeat: there is no good reason for parallel connection, do not
use it.

Precisely.

I haven't yet seen anybody articulate any significant advantages of
direct parallel connection, let alone why they overwhelm the
disadvantages.

I parallel the two 12 volt, 18 AH batteries in my ASH 26 E. The
advantages for me:

* Triple the effective starting capacity of a single battery, especially
useful in cold conditions.
* Simplicity when charging, whether by solar on the trailer or at the
tiedowns, with an AC charger, or a DC/DC charger.
* Wiring simplicity - just two 8" cables from the front battery to the
rear battery.
* Simplicity when using: glance at the volt meter ocasionally.

I've been doing this for 12 years, and haven't had any reason to change.

There are other methods used by ASH 26 E pilots that keep the batteries
separate: one for the engine starter, charged by the alternator; one for
the instruments, charged by the on-board solar panels. I think most of
these can switch the instruments to use the engine battery, but not the
reverse.

Disadvantages: the only one that is significant to me is the potential
to inadvertently leave an instrument (such as the radio) AND the master
switch on. The trailer/tiedown solar panel charging overcomes that drain
easily.

I do capacity tests on the batteries once a year, and replace them as
needed.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl

On 4/27/2013 3:42 PM, Eric Greenwell wrote:

I agree with Evan: these are totally unsuited for glider use. In
addition to the concerns he noted, also note that this particular 4-cell
unit has only 2.3 Amp hours! Beware of Li batteries offered for
"powersports" use: they often are rated by _equivalent_ lead-acid
numbers batteries, but they are ration only the cranking amps ability,
no the actual low current amp hour capacity.

That should be "they are _rating_ only the..."

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)