Spring Cleaning and Battery Testing

One other thought for the automated "instant" testers - While this may
indicate the Ah capacity of the battery, is that an accurate
indication of the often asked question "But, how long will it last?"
Literally, does it tell me how many minutes do I have between full
charge and my minimum voltage threshold? There is certainly a
corrolation between Ah capacity and the duration of actual use, but is
there a formula?

Thanks once again, John DeRosa

On Mar 18, 8:01*am, ContestID67 wrote:
One other thought for the automated "instant" testers - While this may
indicate the Ah capacity of the battery, is that an accurate
indication of the often asked question "But, how long will it last?"
Literally, does it tell me how many minutes do I have between full
charge and my minimum voltage threshold? *There is certainly a
corrolation between Ah capacity and the duration of actual use, but is
there a formula?

Thanks once again, John DeRosa

Hi John,
I expect just about everyone that has a fancy set-up started with a
lamp, a voltmeter, and clock. It is a very accurate system at a very
low cost, I suspect more accurate than the "GOLD-PLUS Intelligent
Battery Tester". Just takes a lot longer.

Every battery has a certain Ah capacity at a given load. For example,
the 12120 battery is rated to deliver 1 amp for 14 hours (not all
batteries have such a lovely symmetry to their spec) and is rated to
deliver 24 amps for 12 minutes and 2.4 amps for 4 hours. Having a
discharge curve is useful. Looking at that curve I see the battery
will provide your load of .6 amps for about 17 hours. I have a
transponder, two varios one of which has an illuminated display, a
very bright LX Minimap, and still keep everything to .85 amp. So
according to that curve I'll get 10 or 12 hours from a new battery,
less as it gets cold or old. I plan to acquire a 12150 (15 Ah) and
also have a 2.4 Ah back-up I can switch to.

Is that what you were asking about as far as a formula? Really I
think you want to match the load (light bulb) to be as close to your
glider load as you can, or a little more. Then the length of your
test will be the same as the duration of your battery in flight. The
other consideration is that your battery will last much longer if you
don't discharge it all the to flat very often. In theory you could
take a 12120 and never fly it down past 12 volts and it would last
quite a few years.

Brian

On Mar 18, 8:52*am, brianDG303 wrote:
On Mar 18, 8:01*am, ContestID67 wrote:

One other thought for the automated "instant" testers - While this may
indicate the Ah capacity of the battery, is that an accurate
indication of the often asked question "But, how long will it last?"
Literally, does it tell me how many minutes do I have between full
charge and my minimum voltage threshold? *There is certainly a
corrolation between Ah capacity and the duration of actual use, but is
there a formula?

Thanks once again, John DeRosa

Hi John,
I expect just about everyone that has a fancy set-up started with a
lamp, a voltmeter, and clock. *It is a very accurate system at a very
low cost, I suspect more accurate than the "GOLD-PLUS Intelligent
Battery Tester". *Just takes a lot longer.

Every battery has a certain Ah capacity at a given load. *For example,
the 12120 battery is rated to deliver 1 amp for 14 hours (not all
batteries have such a lovely symmetry to their spec) and is rated to
deliver 24 amps for 12 minutes and 2.4 amps for 4 hours. *Having a
discharge curve is useful. *Looking at that curve I see the battery
will provide your load of .6 amps for about 17 hours. *I have a
transponder, two varios one of which has an illuminated display, a
very bright LX Minimap, and still keep everything to .85 amp. *So
according to that curve I'll get 10 or 12 hours from a new battery,
less as it gets cold or old. *I plan to acquire a 12150 (15 Ah) and
also have a 2.4 Ah back-up I can switch to.

Is that what you were asking about as far as a formula? *Really I
think you want to match the load (light bulb) to be as close to your
glider load as you can, or a little more. *Then the length of your
test will be the same as the duration of your battery in flight. *The
other consideration is that your battery will last much longer if you
don't discharge it all the to flat very often. *In theory you could
take a 12120 and never fly it down past 12 volts and it would last
quite a few years.

Brian

One thing to consider if using a lightbulb as a load is that the
resistance is current dependent. You will not get quite the same
discharge curve as you would using a fixed resistance load.

The variable resistance characteristic of lamps was made use of in
some battery charging circuits. A series lamp can be used to limit
current when the battery under charge is at low voltage but still
allow it to reach full charge voltage. Sure, this is late 70's
technology but it worked quite well before exotic computer controlled
chargers were available.

I still have my RST crew radio that used 2 car light bulbs in the
charging circuit. A relay split the 12v pack into 2 6v packs for
charging when plugged into the crew car.

Andy