On Aug 24, 7:08*pm, brianDG303 wrote:
More about Glider Batteries:

My club's gliders use Gel batteries, probably because they fit the
mounts so well, but mostly the private gliders use a battery type with
many names, I guess it's an SLA (Sealed Lead Acid) except it's not
really sealed. I started to call it an AGM (Acid Glass Matt) which it
has, but suddenly it started to be called a VRLA (Valve Regulated Lead
Acid). Anyway they are very interestingly made. Although they look
sealed many of these have a separate and tightly fitting top which is
glued on only at the short sides, (the Valve Regulated gas being
allowed to escape through the unglued long sides) and this cap can be
pulled off pretty easily exposing the sub-assembly consisting of small
recessed nipples rising from the center of little 'moats' that have a
fabric packing in them, I guess to absorb any acid that gets out of
the valve. Each of these little nipples has a rubber cap which forms a
one way valve. Pictures of this can be found he

http://picasaweb.google.com/BrianDG3...laneBatteries#

As far as I can tell the battery exhausts gas (and/or liquid) whenever
the internal pressure rises very much beyond the ambient, but seals
tightly when the internal pressure is lower than ambient. When the top
is removed the caps are dished down into the nipple from negative
pressure and when you pull the cap off there is a considerable hiss of
air flow into the battery. So, although they are valve regulated I
don't think they 'breathe' much, at least not in.

Also in that group of photos is a housing I've made, different from
but based on an example I saw Darryl Ramm make, that forms a handle,
protects the battery terminals, holds a Klixon aircraft rated circuit
breaker and two Anderson Powerpole connector sets. Using clear Lexan
for the top is a trick from hospitals, they will sometimes make
electrical devices out of clear polycarbonate- you can inspect the
terminals that way and see a failure developing. Also makes it easier
to work on. Having two outputs is very useful as well.

Brian

SLA == VRLA == AGM it is all the same stuff.

But why use a TLA when you can use a LFLA :-)

Some VRLA batteries are also referred to technically as recombinant,
or valve regulated lead acid recombinant, or lead acid recombinant
batteries. All basically the same stuff.

Most situations where glider pilots are referring to "gell cell" they
turn out to be VRLA batteries.

There really is no benefit of the old gel cell technology (electrolyte
gelled with a silica powder) and some disadvantages, including
repeated deep cycling and rapid charging causing gas pockets in the
gel. VRLA construction tends to be a bit more robust against
misshandling - with the plates really solidly packed in a compressed
sandwich that gel cells, but both are pretty robust.

The neoprene valves that Brian describes hold a slight over pressure
of the battery and prevent gas escaping under normal charge
situations. The valves will vent if the battery gets hot and/or is
overcharged. This why its normally OK to operate a VRLA battery in any
orientation but just don't charge them when upside down or they can
blow out a few drops of acid with the venting gas (even if they have
absorber designed to catch that acid).

Darryl