Glider Batteries and Chargers

For what it's worth, I've used a Battery Tender Plus ($60), a Battery
Minder Plus($60), and a Xenotronic HPX-10 charger ($40) on my 9AH and
14AH SLA glider batteries. All are multi-stage chargers, and frankly,
I never saw a bit of difference between these chargers in my useage.
That useage is simple - I put the battery on charge about 9pm when I
get home from the airport, and I take it off the following morning.

My experience also agrees with Andy (GY) in a previous thread - SLA
batteries work fine, losing a little capacity every time you charge
them, until suddenly they go bad. I keep an eye on the end of flight
voltage to get a feel for capacity problems, and buy new batteries
every two years.

-John

On Aug 24, 11:17*am, Grider Pirate wrote:
On Aug 24, 7:59*am, T8 wrote:



On Aug 24, 10:03*am, Grider Pirate wrote:

VSLA? A123? Cycling chargers?? *I think this subject should have it's
own thread. *Unlike transponders, we almost all need them.

Powersonic batteries. *Battery Tender Plus charger. *Bullet proof,
inexpensive. *Excellent technical info available at both
manufacturers' websites.

I like the Battery Tender Plus because it is a reasonable size
capacity three mode charger that also includes a 6 hour limit on
absorption mode. If you read the tech info on those two sites, you'll
understand why that might be a good thing. *That charger will safely
and correctly charge almost any 12V AGM battery from about 5 AH up.
The Powersonic chargers also work great, but need to be matched to
battery capacity, making them less universal.

More exotic and expensive solutions work also, but unless you need
more than 14 AH capacity or have weight or space constraints I don't
see it as worth the bother. *Of course, some people just like
exotica... nothing wrong with that.

-Evan Ludeman / T8

Hmm, that's EXACTLY what I use in my motorcycle! I'll have to see if
the Battery tender will deal with my 14v (10ah) glider battery.

No, it's completely unsuitable for 14V.

As it happens, I have a 14V "Super Charger" from the 1980s I'm no
longer using -- I converted to 12V earlier this season. It's not
quite as good as the modern three mode guys, but it's close. Email me
if you want it.

Evan Ludeman / T8

On Aug 24, 9:03*am, Grider Pirate wrote:
VSLA? A123? Cycling chargers?? *I think this subject should have it's
own thread. *Unlike transponders, we almost all need them.

I went to the local Interstate Battery store. Picked up a 12V Sealed
Lead Acid battery, 7 amp hour I think but maybe 10. Either way plenty
of juice to run my Microair radio and Cambridge FR. I also bought a
charger from them with a float mode. Usually I plug it in before I go
to bed the night before a flight and take it off in the morning and
its charged up real good.

On Tue, 24 Aug 2010 08:03:48 -0700, Tony wrote:

I went to the local Interstate Battery store. Picked up a 12V Sealed
Lead Acid battery, 7 amp hour I think but maybe 10. Either way plenty
of juice to run my Microair radio and Cambridge FR. I also bought a
charger from them with a float mode. Usually I plug it in before I go
to bed the night before a flight and take it off in the morning and its
charged up real good.

SLAs in good condition have a very low self-discharge rate, so IMO its
better for the battery to put it on charge as soon as you get home and
then put it back in your flight kit when the charger says its done or
next morning if red light is still on when you go to bed.

Example of holding charge: yesterday when I ran the discharge rate test
Eric asked about I used one of my flight batteries to power the charger
while it discharged my other flight battery. Pulled 22 mAh out of the
test target and (probably) less from the other one. After the test both
went back on the multi-stage SLA chargers and both were showing green
lights in under 30 minutes. Both batteries are 3 years old and were last
charged overnight 14 days ago directly after I last used them, so can
have lost very little charge since then.

Yeah, I know: its been GREAT summer weather over here!


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

VSLA? A123? Cycling chargers?? *I think this subject should have it's
own thread. *Unlike transponders, we almost all need them.

Powersonic 12Ah batt with a Battery Tender Junior charger, the 750mA
'wallwort' mini version version but still an auto 3-mode like bigger
ones. $40, very compact and works like a champ. I just put it on the
charger when it's thirsty.

-Paul

I've tried to put most useful info on this page along with offering trying
to offer only the best and most suitable types available
please see http://www.wingsandwheels.com/page25.htm
thanks
tim
Please visit the Wings & Wheels website at www.wingsandwheels.com


"Grider Pirate" wrote in message
...
VSLA? A123? Cycling chargers?? I think this subject should have it's
own thread. Unlike transponders, we almost all need them.

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On Aug 24, 7:03*am, Grider Pirate wrote:
VSLA? A123? Cycling chargers?? *I think this subject should have it's
own thread. *Unlike transponders, we almost all need them.


Some comments below, in general and picking up a few things in other
posts/threads and reposting some things I've said elsewhere recently.

Most "smart" chargers are really pretty dumb and have no way of
setting the bulk charge rate to match different size batteries. So you
purchase those chargers sized for the size battery you are charging. A
bulk charge amp rating in the range C/10 to C/5 is about right (where
C is the battery capacity in Ah.).

At the simplest level too low a bulk charge rate will take too long to
charge and too high a rate may not be good for the battery. But it is
actually more complex than that. Good VRLA battery chargers use a
constant current bulk charge mode, switch to "absorption
mode" (constant high voltage or a type of current limited high voltage
mode) and finally finish off with a lower float voltage. The trip
point between switching from bulk charge to absorption mode is usually
when the battery voltage crosses a voltage threshold, switching from
absorption to float mode is usually done when the current flowing into
the battery decreases below a certain value. Typical VRLA smart
chargers, use a value that is appropriate for the size battery they
are designed to charge. Any absorption mode current limits are also
matched to the size battery the charger is designed to charge. If you
charge a larger battery than intended the charger may never switch
into float mode and if you charge a smaller battery the charger may
switch into float mode way too early. Leave that battery on charge
overnight and it might be possible that you get less charge into the
battery than a properly designed charger (yes a "bigger" charger may
actually not charge as well as a properly sized "smaller" charger). So
it is really a good idea to aim for the C/10 to C/5 range, and even
better to read the manufacturer literature on what exact Ah capacity
the charger is designed to charge.

VRLA batteries have intrinsically low-self discharge rates. Quite
different to flooded lead-acid car batteries. So it is just not
necessary to leave them on chargers for long periods of time. e.g.
over winter VRLA batteries will do fine if you fully charge them and
then leave them in a cool place and recharge again before the new
season starts.

I tend to ignore as unproven or irrelevant marketing hype many of the
fancier claims or features that some charger manufacturers make. The
Detran Battery Minder brand makes a few of those claims but the
battery chargers themselves are very good. They are a good choice, as
are the Xentronix HPX series I personally use.

As mentioned in other threads fancy RC model DC-DC chargers can be
very handy for charging batteries where you don't have AC power. These
units typically do not have a float stage, not a problem when you are
doing a quick charge of your 7Ah VRLA battery at the model field but
some folks do want to use the same charger at home with a DC power
supply from the mains. In which case you don't want to leave the
battery on the charger for long periods of time.

The risk with overcharging, charging when too hot, or leaving on a non-
float charger for long times is that VRLA batteries have a very small
amount of electrolyte wetting the fiberglass mats between the plates
and this will evaporate that electrolyte from the batteries -- they
are not really "sealed" batteries, they have small neoprene valves
designed to hold a very slight overpressure.

RC model chargers often allow you to set the number of cells/nominal
pack voltage and the bulk charge current but as Eric Greenwell has
pointed out in another thread some commonly used ones may not get
charge voltage and transition points exactly where they should be.

I would be very cautious about using RC model chargers in club
situations etc. they have to many settings that people can mess up.
Besides RC model chargers another option is to look at DC-DC chargers
designed for charging wheelchair VRLA batteries. There are several out
there, but I have no experience with any of them.

Some people have commented on testing batteries not really being
worthwhile as batteries tend to die quickly. This may be true in some
cases, but likely what people are experiencing is the internal
resistance property of lead-acid batteries. As the battery discharges
the internal resistance increases significantly as the electrolyte
conductivity decreases. This gives lead-acid batteries a relative
rapid fall off in voltage under load as the battery depletes. Under
normal operation you don't see that sudden fall off, as the battery
ages you now see that sudden voltage-fall off behavior shift into
sight and the impression is a sudden failure of the battery. Regular
(typically annual, but cubs and FBOs may want to do this more
frequently) testing of batteries is a good idea. Make some simple
spreadsheet calculations and/or some measurements of your glider's
actual current load and then look up on the manufacturers discharge
curve for that battery how how long the battery should last a that
discharge rate. And pad with a good safety margin, allow 20% for
aging, and up to 50% for flying on cold wave days. Really cold/extreme
duration wave flights need more thought and possibly insulation,
heaters or different battery technology. If your 12 AH battery has a
7Ah actual capacity it is going to have a discharge curve close to a
new 7AH battery, which is related to what I said before about why the
batteries appear to fail quickly. Anyhow some modeling/measurements
and measuring the actual capacity of your battery should give you a
very good idea where you are in terms of battery health.

Unfortunately a common wrongly done test for battery charge state is
to just take a battery off charge and measure its open circuit
voltage. This often tells you nothing that useful about the battery
state of charge. What you are measuring is an effect called surface
charge and the actual voltage of the battery may be significantly
lower. Measured properly the open circuit voltage is a good estimate
the state of charge (that voltage is fundamentally connected to the
chemical process giving the battery power) you need to "burn off" the
surface charge. For typical batteries we use connect a car or truck
tail light bulb across the battery for several minutes then leave the
battery sit for 10 minutes or so to let the voltage relax to a steady
state and then measure that open circuit voltage. Then look up on a
table or chart whan state of charge that voltage implies. There is a
chart in my presentation at http://www.darryl-ramm.com/glider-batteries
or see the state of charge table at http://www.batteryfaq.org (which
shows temperature effects). Batteries that have been off charge for
days will naturally have lost their surface charge.

Measuring that open circuit voltage tells you about the state of
charge, it does not tell you about the battery capacity. A big 120Ah
VRLA battery for a large UPS system and a 7Ah VRLA battery in your
glider have pretty much the same open circuit voltages when fully
charged. To determine the battery capacity you really need to fully
charge the battery and then do a discharge test. You can do this by
hand with a resistor/light bulb etc. and just measuring the voltage
over time or usually much easier to use an automatic tester.

A good battery tester like the CBA II from West Mountain radio can
monitor charge cycles as well as discharge test the battery. These are
ideal for club/FBO purchase. For more technical folks monitoring the
charge process along with a separate ammeter in the circuit lets you
confirm things like the charger correctly goes into float mode, that
the other charge rates look about right.

BTW my interest in trying to evangelize battery knowledge in the
gliding community was largely driven by lots confusion about battery
capacity and proper handling related to powering transponders in
gliders. I saw both sides of this issue, some people overestimating
problems from adding a transponder with ~0.5 amp load (now 0.3 amp
with a Trig TR21) and those with real battery capacty issues with lots
of avionics/toys and kind of stuck as to what they should/could do
about it. One current issue where I see gliders with power problems
seems to be ClearNav and similar installations. At around 0.7 amp at
full brightness owners installing a ClearNav or similar products
probably need to think about their gliders power budget and battery
capacity. Even large PDAs can consume up to 0.5 amp and they often
seem to be installed with even less though about power consumption.


Darryl

On Tue, 24 Aug 2010 16:49:51 -0700, Darryl Ramm wrote:

On Aug 24, 7:03Â*am, Grider Pirate wrote:
VSLA? A123? Cycling chargers?? Â*I think this subject should have it's
own thread. Â*Unlike transponders, we almost all need them.


Some comments below, in general and picking up a few things in other
posts/threads and reposting some things I've said elsewhere recently.

An excellent summary, especially of the low-tech ways of testing SLAs.

I would, however, take issue over there being many RC chargers without a
float mode. I've not yet seen a multi-chemistry charger that didn't have
some sort of float mode for all chemistries: its essential for Li-poly
and for high-rate charging of NiCd/NiMH and anyway these charger/cyclers
are all microprocessor based, so leaving it off is inexcusably cheap
design. Did you mean that some just omit peak detection for lead-acid
batteries?

The only place I've been happy to use untimed chargers is with low
capacity NiCds. My favoured approach there is to use a "1% charge rate",
i.e. charge at 0.01C, and leave the battery permanently on charge unless
I'm flying the model its installed in. NiCds are frequently used as low-
maintenance emergency batteries and these are invariably left on charge
at the 1% rate for years at a time so they like this treatment. Its
really convenient: put the model box back on its rack after a contest or
trimming session, open the lid, connect the charger and forget about it
until next time you go flying.


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

On Aug 24, 6:07*pm, Martin Gregorie
wrote:
On Tue, 24 Aug 2010 16:49:51 -0700, Darryl Ramm wrote:
On Aug 24, 7:03*am, Grider Pirate wrote:
VSLA? A123? Cycling chargers?? *I think this subject should have it's
own thread. *Unlike transponders, we almost all need them.

Some comments below, in general and picking up a few things in other
posts/threads and reposting some things I've said elsewhere recently.

An excellent summary, especially of the low-tech ways of testing SLAs.

I would, however, take issue over there being many RC chargers without a
float mode. I've not yet seen a multi-chemistry charger that didn't have
some sort of float mode for all chemistries: its essential for Li-poly
and for high-rate charging of NiCd/NiMH and anyway these charger/cyclers
are all microprocessor based, so leaving it off is inexcusably cheap
design. Did you mean that some just omit peak detection for lead-acid
batteries?

Its not "omitting" peak-detection, peak detection does not work with
lead-acid batteries and so is irrelevant. Lead acid chargers will at
least use a constant current bulk mode, then hopefully a constant
voltage (or current limited constant voltage) absorption mode and then
maybe a float mode. Working out what many of these RC chargers do from
their marketing datasheets or manuals can be a challenge hard.

Not seen any that don't have float mode? You may want to double check
the one you use. I believe (based on measurements from Eric Greenwell)
the Multiplex LN5014 for example does not float a VRLA battery and it
looks like you may be using the same OEM charger under a RipMax brand
right? To float a VRLA battery the charger should be stepping down to
13.5 to 13.8V from a 14.4 to 14.7V voltage during absorbtion stage.
And the Multiplex charger only every pulls up to 14.0 volts which is a
bit low as Eric has noted. The charger simply ends charge when the
charge current falls to 10% of the bulk charge rate you set. I does
not enter float mode. (all based on separate conversations with Eric).
For most/occasional use this won't matter, but you do leave some
capacity on the table.

Can you me some examples of widely available RC chargers that have a
float mode for VRLA batteries - and a link to a source that shows they
have that.

[snip]

Thanks

Darryl

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