Re: Battery life...how to test?

[Jim Kelly]

I guess a 12v automotive light bulb would be a readily available load?
Perhaps one of the electronic wizards here could suggest an
appropriate wattage for a meaningful, safe, fast test?

Also, is it valid to do a 'fast' test when a glider load is hopefully
closer to 10 to 20 hrs? Can we presume that if the battery can cope
with a 'fast' discharge then it should be able to handle a slow
discharge rate?

Cheers,

Jim Kelly.


"Dusty" > wrote in message
.com...
| Assuming your amp demand for your sailplane averages about 1 amp,
buy a 10
| to 15 ohm, 20 watt resistor. Safely hook up the resistor across the
battery
| (it will get hot), and measure periodically. When the voltage starts
| dropping fast (11 volts?), disconnect the resistor. Plot the voltage
versus
| time.
|
|
| "Kurt" > wrote in message
| om...
| > It seems that most ships are using a 12 volt 7 amp battery for
ships
| > power, radios, varios computers etc.. Is there a way to test the
| > battery to see when it should be replaced with a new one? I don't
| > know how old my ships battery is and I was hoping that someone had
a
| > "simple" way to test the battery at home (load test vs. time vs.
| > voltage?).
| >
| > Thanks
| >
| > Kurt
| >
|
|

[Eric Greenwell]

In article >,
says...
> I guess a 12v automotive light bulb would be a readily available load?
> Perhaps one of the electronic wizards here could suggest an
> appropriate wattage for a meaningful, safe, fast test?

The smallest dome light or similar from an auto store ought to be
close enough to a glider load that isn't running a transponder or a
PDA with a backlight. Measure the amp drain, see how long it takes to
drop down the lowest voltage you can use, then (time x amps)/(actual
glider amps) will give a good indication of your expected battery
life.

For maximum battery life, fully recharge after every flight, or at
least no later than about 50% depleted.

> Also, is it valid to do a 'fast' test when a glider load is hopefully
> closer to 10 to 20 hrs? Can we presume that if the battery can cope
> with a 'fast' discharge then it should be able to handle a slow
> discharge rate?

It's "valid", but it will understate the amp hours you can get at the
lower load. The data sheet for the battery will give you the capacity
at different rates, so you can adjust your measurement for the lower
rate in the glider.
--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

[Eric Greenwell]

In article >,
says...

> I think the best way is to buy a new battery if you are notsure about
> the condition of your old one. Cost about 30$ and gives a good
> feeling.
>
> I think i read somehere that the standard lead-acid-gel Battery can be
> charged about 600 times. So everyone can can calculate how many years
> the battery will be in best condition.

The number of charges varies greatly with how depleted it is when
recharged, so this number only applies to some batteries in use. For
example, the Powersonic data sheets shows about 220 recharges if the
battery is discharged 100% each time; about 1100 recharges for
discharges to 30%. This is to a 60% of original capacity life.

Also, age is a factor. Many pilots fly only 30 times a year, so even
220 recharges is 7 years, at which time the battery's capacity has
also diminished due to aging.

Your suggestion to change it if unsure is a good idea, especially if
it might be more than 5 years old.

--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)