Basic battery charging question

Eric:

My glider uses three 12V 7 amp/hr batteries. At least two, and usually
all three, have to be recharged after every flight. (One of the three
operates the transponder alone.) I often don't have the time to charge
each battery one at a time between flights on consecutive days. (And at
contests I will have 6, if not 9, batteries!) I wanted to find out if I
can charge them three at a time before I invested in two more chargers.

-ted/2NO

I would only charge SLA batteries in parallel if they were also
discharged in parallel. Otherwise you run the risk of substantial
currents flowing from the battery with a higher to charge to the other.
You could use 3 lamp timers so you didn't have to attend the things.

Tom Seim
2D DG-400

wrote:

I would only charge SLA batteries in parallel if they were also
discharged in parallel. Otherwise you run the risk of substantial
currents flowing from the battery with a higher to charge to the other.
You could use 3 lamp timers so you didn't have to attend the things.

Prudence suggests following Tom's advice to use a charger for each
battery. If you use chargers that switch to float voltage automatically,
you won't need the timers. Besides being faster chargers that will make
your batteries last longer, they are simpler to use: connect and forget.

A clever person could use a single charger with 3 diodes in the output,
so the charge would be delivered to the lowest battery first. If the
charger sufficient amp output to replace all the combined amphours
needed by the three batteries in a day, and the charger was adjusted to
compensate for the diode voltage drop, that might also be satisfactory.
With as many batteries as you have, I still think buying two more
chargers would be the way to go!

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Ack! Thanks everyone. Very informative.

Now if I can figure out why my water pump slows from 2 gallons a minute
on startup to a quarter gallon a minute a short time later ...

~ted/2NO

Eric Greenwell wrote:
wrote:

Can I charge 2 or more batteries simultaneously, connected in parallel?

(Assuming all batteries are the same type and approximately the same
age.)


What situation prompted you to ask this question? A better answer can be
provided with that knowlege.


I know that this is an old thread but I thought that I would pose this
question. First some history: the longest lasting glider battery that I
ever had was 6 years and I only replaced it because I believed that it
HAD to quit any minute due to its age. It was a 14 volt SLA that I built
from two 2.0 volt 4AH batteries in parallel and one 7AH battery in
series with the pair. The charger was a 12 volt gel cell charger. I
never charged for a period longer than overnight. Now the question...is
it possible that undercharging e.g. charging a 14 volt battery with a 12
volt charger is responsible for the longevity of the battery? BTW, I
built another, same way, 4 years ago and it is doing fine.

Paul

P. Corbett wrote:
Eric Greenwell wrote:
wrote:

Can I charge 2 or more batteries simultaneously, connected in parallel?

(Assuming all batteries are the same type and approximately the same
age.)


What situation prompted you to ask this question? A better answer can
be provided with that knowlege.


I know that this is an old thread but I thought that I would pose this
question. First some history: the longest lasting glider battery that I
ever had was 6 years and I only replaced it because I believed that it
HAD to quit any minute due to its age. It was a 14 volt SLA that I built
from two 2.0 volt 4AH batteries in parallel and one 7AH battery in
series with the pair. The charger was a 12 volt gel cell charger. I
never charged for a period longer than overnight. Now the question...is
it possible that undercharging e.g. charging a 14 volt battery with a 12
volt charger is responsible for the longevity of the battery? BTW, I
built another, same way, 4 years ago and it is doing fine.

Generally, undercharging lead acid batteries leads to shorter life, not
longer. Six years is not uncommon for a SLA battery, though it's
capacity will be diminished. If it's reduced capacity was still adequate
for your flights, you wouldn't know how good it was unless you tested it
for it's actual capacity.

Now, I have to ask: why are you using a 14 volt battery? If it's for
your radio, what radio do you have? You may not need 14 volts at all.

--
Change "netto" to "net" to email me directly

Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"

Eric Greenwell wrote:
P. Corbett wrote:

Eric Greenwell wrote:

wrote:

Can I charge 2 or more batteries simultaneously, connected in parallel?

(Assuming all batteries are the same type and approximately the same
age.)



What situation prompted you to ask this question? A better answer can
be provided with that knowlege.


I know that this is an old thread but I thought that I would pose this
question. First some history: the longest lasting glider battery that
I ever had was 6 years and I only replaced it because I believed that
it HAD to quit any minute due to its age. It was a 14 volt SLA that I
built from two 2.0 volt 4AH batteries in parallel and one 7AH battery
in series with the pair. The charger was a 12 volt gel cell charger. I
never charged for a period longer than overnight. Now the
question...is it possible that undercharging e.g. charging a 14 volt
battery with a 12 volt charger is responsible for the longevity of the
battery? BTW, I built another, same way, 4 years ago and it is doing
fine.


Generally, undercharging lead acid batteries leads to shorter life, not
longer. Six years is not uncommon for a SLA battery, though it's
capacity will be diminished. If it's reduced capacity was still adequate
for your flights, you wouldn't know how good it was unless you tested it
for it's actual capacity.

Now, I have to ask: why are you using a 14 volt battery? If it's for
your radio, what radio do you have? You may not need 14 volts at all.

Eric

I have a Terra 720 and the manual states that the radio wants 13.75 VDC.
Ironically, I don't talk on the radio much because the many
conversations going on are distracting to me so I leave it off most of
the time. On a typical flight, it sees a 25% duty cycle. But if I need
it, I want it to work well, thus the 14 VDC. Overkill? What do you think?

Paul

These battery threads are almost as entertaining as the PW 6/2-33
threads. How about addressing the "memory" issue? Myth or reality?
Thank god the season is upon us here in the NE USA. I'm looking forward
to trying out my newly purchased gizmos (PDA GPS etc). I just hope the
batteries work.

Mike

P. Corbett wrote:
Eric Greenwell wrote:

Now, I have to ask: why are you using a 14 volt battery? If it's for
your radio, what radio do you have? You may not need 14 volts at all.

Eric

I have a Terra 720 and the manual states that the radio wants 13.75 VDC.
Ironically, I don't talk on the radio much because the many
conversations going on are distracting to me so I leave it off most of
the time. On a typical flight, it sees a 25% duty cycle. But if I need
it, I want it to work well, thus the 14 VDC. Overkill? What do you think?

Paul

That radio is old enough that 14 volts might be a reasonable strategy.
The TPX 720 handheld I'm familiar with works well on 12 volts, but I
don't know if that would apply to the panel mount 720.

Maybe some pilots out there have experience with a 720 on 12 volts and
can tell us how well it worked.

--
Change "netto" to "net" to email me directly

Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"