Help!

I have carefully measured my current draw in my glider at .8 amp. l would
like to know if there is any reasonable explanation for why a 9 amp hour
battery goes from 13 volts open circuit fully charged to 11.6 volts in 4
hours.

MC

Mike McCarron wrote:
> Help!
>
> I have carefully measured my current draw in my glider at .8 amp. l would
> like to know if there is any reasonable explanation for why a 9 amp hour
> battery goes from 13 volts open circuit fully charged to 11.6 volts in 4
> hours.

Short answer: 9AH is the nominal capacity, the actual capacity
depends on temperature, discharge rate and battery age..

Long answer: have a look at the graphs in, for example,
<http://www.standbattery.com/linkfiles/Technology%20Manual.pdf>

At 23:10 23 September 2012, Tom Gardner wrote:
>Mike McCarron wrote:
>> Help!
>>
>> I have carefully measured my current draw in my glider at .8 amp. l
>would
>> like to know if there is any reasonable explanation for why a 9 amp
hour
>> battery goes from 13 volts open circuit fully charged to 11.6 volts in
4
>> hours.
>
>Short answer: 9AH is the nominal capacity, the actual capacity
>depends on temperature, discharge rate and battery age..
>
>Long answer: have a look at the graphs in, for example,
>
>
>

Could not find the graphs. Brand new battery and very reliable battery
charger.

At 23:10 23 September 2012, Tom Gardner wrote:
>Mike McCarron wrote:
>> Help!
>>
>> I have carefully measured my current draw in my glider at .8 amp. l
>would
>> like to know if there is any reasonable explanation for why a 9 amp
hour
>> battery goes from 13 volts open circuit fully charged to 11.6 volts in
4
>> hours.
>
>Short answer: 9AH is the nominal capacity, the actual capacity
>depends on temperature, discharge rate and battery age..
>
>Long answer: have a look at the graphs in, for example,
>
>
>

Could not find the graphs. Brand new battery and very reliable battery
charger.

Also, 0.8 amps is about double the load the battery is rated for. The capacity of your 9 A.h battery should be about 10 hours at 25 degrees C. Your battery sounds cold or tired or both!

Plus, do you ever use your radio?

Mike

On 9/23/2012 4:32 PM, Mike McCarron wrote:
> At 23:10 23 September 2012, Tom Gardner wrote:
>> Mike McCarron wrote:
>>> Help!
>>>
>>> I have carefully measured my current draw in my glider at .8 amp. l
>> would
>>> like to know if there is any reasonable explanation for why a 9 amp
> hour
>>> battery goes from 13 volts open circuit fully charged to 11.6 volts in
> 4
>>> hours.
>>
>> Short answer: 9AH is the nominal capacity, the actual capacity
>> depends on temperature, discharge rate and battery age..
>>
>
> Could not find the graphs. Brand new battery and very reliable battery
> charger.

Fully charge the battery, then do a discharge test at about 0.8 amps.
Even a new battery can be defective, so I always do a discharge test on
new batteries before using them in the glider.

It could also be the charger. Have you tested it's charging ability
recently?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

At 23:34 23 September 2012, Mike the Strike wrote:
>Also, 0.8 amps is about double the load the battery is rated for. The
>capacity of your 9 A.h battery should be about 10 hours at 25 degrees C.
>Your battery sounds cold or tired or both!
>
>Plus, do you ever use your radio?
>
>Mike
>
>
Where does it say that I should only draw 400 ma? The battery is brand new
and fully charged. Open circuit wasr 12.0 to start.

What is the problem?

Mike

At 00:07 24 September 2012, Mike McCarron wrote:
>At 23:34 23 September 2012, Mike the Strike wrote:
>>Also, 0.8 amps is about double the load the battery is rated for. The
>>capacity of your 9 A.h battery should be about 10 hours at 25 degrees C.

>>Your battery sounds cold or tired or both!
>>
>>Plus, do you ever use your radio?
>>
>>Mike
>>
>>
>Where does it say that I should only draw 400 ma? The battery is brand
new
>and fully charged. Open circuit wasr 12.0 to start.
>
>What is the problem?
>
>Mike
>
>
>
As a correction to the above I meant to say the open circuit voltage was 13
volts when I started everything up. I do use the radio as little as
possible.

On 9/23/2012 5:07 PM, Mike McCarron wrote:
> At 23:34 23 September 2012, Mike the Strike wrote:
>> Also, 0.8 amps is about double the load the battery is rated for. The
>> capacity of your 9 A.h battery should be about 10 hours at 25 degrees C.
>> Your battery sounds cold or tired or both!
>>
>> Plus, do you ever use your radio?
>>
>> Mike
>>
>>
> Where does it say that I should only draw 400 ma? The battery is brand new
> and fully charged. Open circuit wasr 12.0 to start.

800 ma isn't too much to take from the battery. It will reduce the
capacity about 10% from the 400 ma, ~20 hour rate used to measure the
rated capacity.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

The 9A.h batteries I use would have a rated capacity of about 8A.h at a current of 0.8A - that's about ten hours' worth. Dropping the temperature to freezing will drop that to about 7 to 8 hours - still more than you're getting.

Also remember that the current drawn by some devices may increase as the voltage drops. I'd suggest checking your current draw at a range of battery voltages.

If your charger's ok, it sounds like your battery isn't.

Mike

Actually it is not 10 hours worth....its about 4 hours worth.

The "rated" 9 AH is rated at .05C or 450 ma.

If you run at 800 ma, that's about .1C.....so you don't get half the time,
you get way less than half...........

Also they rate the batteries as "dead" at 10.5 volts, but for glider
equipment, once you get down to 11.5 or so, stuff doesn't work well.

Actually anything under 12 volts means time to recharge.....below 10.5
volts and battery damage can occur.

For an 800 ma draw, the proper battery would be 16 AH.....this in theory
would last 20 hours, and leave you at 10.5 volts.....probably 10 hours to
stay above 11.5...

Cookie





At 03:30 24 September 2012, Mike the Strike wrote:
>The 9A.h batteries I use would have a rated capacity of about 8A.h at a
>current of 0.8A - that's about ten hours' worth. Dropping the
temperature
>to freezing will drop that to about 7 to 8 hours - still more than you're
>getting.
>
>Also remember that the current drawn by some devices may increase as the
>voltage drops. I'd suggest checking your current draw at a range of
>battery voltages.
>
>If your charger's ok, it sounds like your battery isn't.
>
>Mike
>

Actually it is not 10 hours worth....its about 4 hours worth.

The "rated" 9 AH is rated at .05C or 450 ma.

If you run at 800 ma, that's about .1C.....so you don't get half the time,
you get way less than half...........

Also they rate the batteries as "dead" at 10.5 volts, but for glider
equipment, once you get down to 11.5 or so, stuff doesn't work well.

Actually anything under 12 volts means time to recharge.....below 10.5
volts and battery damage can occur.

For an 800 ma draw, the proper battery would be 16 AH.....this in theory
would last 20 hours, and leave you at 10.5 volts.....probably 10 hours to
stay above 11.5...

Cookie





At 03:30 24 September 2012, Mike the Strike wrote:
>The 9A.h batteries I use would have a rated capacity of about 8A.h at a
>current of 0.8A - that's about ten hours' worth. Dropping the
temperature
>to freezing will drop that to about 7 to 8 hours - still more than you're
>getting.
>
>Also remember that the current drawn by some devices may increase as the
>voltage drops. I'd suggest checking your current draw at a range of
>battery voltages.
>
>If your charger's ok, it sounds like your battery isn't.
>
>Mike
>

Actually it is not 10 hours worth....its about 4 hours worth.

The "rated" 9 AH is rated at .05C or 450 ma.

If you run at 800 ma, that's about .1C.....so you don't get half the time,
you get way less than half...........

Also they rate the batteries as "dead" at 10.5 volts, but for glider
equipment, once you get down to 11.5 or so, stuff doesn't work well.

Actually anything under 12 volts means time to recharge.....below 10.5
volts and battery damage can occur.

For an 800 ma draw, the proper battery would be 16 AH.....this in theory
would last 20 hours, and leave you at 10.5 volts.....probably 10 hours to
stay above 11.5...

Cookie





At 03:30 24 September 2012, Mike the Strike wrote:
>The 9A.h batteries I use would have a rated capacity of about 8A.h at a
>current of 0.8A - that's about ten hours' worth. Dropping the
temperature
>to freezing will drop that to about 7 to 8 hours - still more than you're
>getting.
>
>Also remember that the current drawn by some devices may increase as the
>voltage drops. I'd suggest checking your current draw at a range of
>battery voltages.
>
>If your charger's ok, it sounds like your battery isn't.
>
>Mike
>

On 9/24/2012 8:39 AM, Bob Cook wrote:
> Actually it is not 10 hours worth....its about 4 hours worth.
>
> The "rated" 9 AH is rated at .05C or 450 ma.
>
> If you run at 800 ma, that's about .1C.....so you don't get half the time,
> you get way less than half...........
>
> Also they rate the batteries as "dead" at 10.5 volts, but for glider
> equipment, once you get down to 11.5 or so, stuff doesn't work well.
>
> Actually anything under 12 volts means time to recharge.....below 10.5
> volts and battery damage can occur.
>
> For an 800 ma draw, the proper battery would be 16 AH.....this in theory
> would last 20 hours, and leave you at 10.5 volts.....probably 10 hours to
> stay above 11.5...

Hi Cookie - I agree it's a good rule of thumb to use batteries at the 20
hour rate, and I encourage pilots use it; however, it doesn't seem to be
the problem. Using a bigger battery is desirable in general, but may be
awkward to do in practice.

SLA data sheets show a 10% reduction in AH capacity at the 0.1C rate,
and if you restrict the voltage drop to 11.5 volts, you lose another
10%. That lowers his 9 AH to 7.2 AH, allowing a nominal 9 hour run time
at 800 ma. Since he is getting only 4 hours, something is dramatically
wrong. A full charge, then a discharge test at 800 ma can rule out
charger/battery problems, and it's easy, so that is where I would start.

Also, unless you have old "stuff", 11.5 volts is plenty of voltage to
run things, and he didn't mention any problems.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

On Monday, September 24, 2012 11:45:03 AM UTC-4, Cookie wrote:
> Actually it is not 10 hours worth....its about 4 hours worth.
>
>
>
> The "rated" 9 AH is rated at .05C or 450 ma.
>
>
>
> If you run at 800 ma, that's about .1C.....so you don't get half the time,
>
> you get way less than half...........
>
>
>
> Also they rate the batteries as "dead" at 10.5 volts, but for glider
>
> equipment, once you get down to 11.5 or so, stuff doesn't work well.
>
>
>
> Actually anything under 12 volts means time to recharge.....below 10.5
>
> volts and battery damage can occur.
>
>
>
> For an 800 ma draw, the proper battery would be 16 AH.....this in theory
>
> would last 20 hours, and leave you at 10.5 volts.....probably 10 hours to
>
> stay above 11.5...
>
>
>
> Cookie
>
>
>
>
>
>
>
>
>
>
>
> At 03:30 24 September 2012, Mike the Strike wrote:
>
> >The 9A.h batteries I use would have a rated capacity of about 8A.h at a
>
> >current of 0.8A - that's about ten hours' worth. Dropping the
>
> temperature
>
> >to freezing will drop that to about 7 to 8 hours - still more than you're
>
> >getting.
>
> >
>
> >Also remember that the current drawn by some devices may increase as the
>
> >voltage drops. I'd suggest checking your current draw at a range of
>
> >battery voltages.
>
> >
>
> >If your charger's ok, it sounds like your battery isn't.
>
> >
>
> >Mike
>
> >

Cookie nailed it. Also, that is all for a new battery. The numbers all go sour as the battery gets old and abused. Deep discharge is the worst offender over time. Keep 'em charged boys! (Yes even in off-seasons).

-Jim

If I am reading the data sheet correctly, I see a lot more than a 10%
reduction in AH at the .1C rate...more like 50%

Cookie






At 17:41 24 September 2012, Eric Greenwell wrote:
>On 9/24/2012 8:39 AM, Bob Cook wrote:
>> Actually it is not 10 hours worth....its about 4 hours worth.
>>
>> The "rated" 9 AH is rated at .05C or 450 ma.
>>
>> If you run at 800 ma, that's about .1C.....so you don't get half the
>time,
>> you get way less than half...........
>>
>> Also they rate the batteries as "dead" at 10.5 volts, but for glider
>> equipment, once you get down to 11.5 or so, stuff doesn't work well.
>>
>> Actually anything under 12 volts means time to recharge.....below 10.5
>> volts and battery damage can occur.
>>
>> For an 800 ma draw, the proper battery would be 16 AH.....this in
theory
>> would last 20 hours, and leave you at 10.5 volts.....probably 10 hours
>to
>> stay above 11.5...
>
>Hi Cookie - I agree it's a good rule of thumb to use batteries at the 20
>hour rate, and I encourage pilots use it; however, it doesn't seem to be
>the problem. Using a bigger battery is desirable in general, but may be
>awkward to do in practice.
>
>SLA data sheets show a 10% reduction in AH capacity at the 0.1C rate,
>and if you restrict the voltage drop to 11.5 volts, you lose another
>10%. That lowers his 9 AH to 7.2 AH, allowing a nominal 9 hour run time
>at 800 ma. Since he is getting only 4 hours, something is dramatically
>wrong. A full charge, then a discharge test at 800 ma can rule out
>charger/battery problems, and it's easy, so that is where I would start.
>
>Also, unless you have old "stuff", 11.5 volts is plenty of voltage to
>run things, and he didn't mention any problems.
>
>--
>Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
>email me)
>

just rechecked the powersonic manual....

at .1c a 12 volt battery will drop below 12 volts in about 5 hours...below
11.5 in about 6.........10.5 almost 10 hours

Cookie




At 17:41 24 September 2012, Eric Greenwell wrote:
>On 9/24/2012 8:39 AM, Bob Cook wrote:
>> Actually it is not 10 hours worth....its about 4 hours worth.
>>
>> The "rated" 9 AH is rated at .05C or 450 ma.
>>
>> If you run at 800 ma, that's about .1C.....so you don't get half the
>time,
>> you get way less than half...........
>>
>> Also they rate the batteries as "dead" at 10.5 volts, but for glider
>> equipment, once you get down to 11.5 or so, stuff doesn't work well.
>>
>> Actually anything under 12 volts means time to recharge.....below 10.5
>> volts and battery damage can occur.
>>
>> For an 800 ma draw, the proper battery would be 16 AH.....this in
theory
>> would last 20 hours, and leave you at 10.5 volts.....probably 10 hours
>to
>> stay above 11.5...
>
>Hi Cookie - I agree it's a good rule of thumb to use batteries at the 20
>hour rate, and I encourage pilots use it; however, it doesn't seem to be
>the problem. Using a bigger battery is desirable in general, but may be
>awkward to do in practice.
>
>SLA data sheets show a 10% reduction in AH capacity at the 0.1C rate,
>and if you restrict the voltage drop to 11.5 volts, you lose another
>10%. That lowers his 9 AH to 7.2 AH, allowing a nominal 9 hour run time
>at 800 ma. Since he is getting only 4 hours, something is dramatically
>wrong. A full charge, then a discharge test at 800 ma can rule out
>charger/battery problems, and it's easy, so that is where I would start.
>
>Also, unless you have old "stuff", 11.5 volts is plenty of voltage to
>run things, and he didn't mention any problems.
>
>--
>Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
>email me)
>

On Sep 24, 6:45*pm, Bob Cook > wrote:
> If I am reading the data sheet correctly, I see a lot more than a 10%
> reduction in AH at the .1C rate...more like 50%

Ctrl-C/Ctrl-V:

Nominal Capacity
20-hr. (450mA to 10.50
volts) .................................................. ..... 9.00
AH
10-hr. (810mA to 10.50
volts) .................................................. ....... 8.10
AH

B.

http://www.power-sonic.com/images/powersonic/technical/1277751263_20100627-TechManual-Lo.pdf

See page 8.....

Chart for certain temp. and new battery...Colder or older will net worse
time.

You really want to stay in the "over 12 volt" range of this chart.

Again... 9 AH rated battery is kind of borderline for glider flying at 800
Ma draw....

Solution = larger battery or second battery.

Cookie






At 01:50 25 September 2012, Bart wrote:
>On Sep 24, 6:45=A0pm, Bob Cook wrote:
>> If I am reading the data sheet correctly, I see a lot more than a 10%
>> reduction in AH at the .1C rate...more like 50%
>
>Ctrl-C/Ctrl-V:
>
>Nominal Capacity
> 20-hr. (450mA to 10.50
>volts) .................................................. ..... 9.00
>AH
> 10-hr. (810mA to 10.50
>volts) .................................................. ....... 8.10
>AH
>
>B.
>

On Sep 25, 4:15*am, Bob Cook > wrote:
> >On Sep 24, 6:45=A0pm, Bob Cook *wrote:
> >> If I am reading the data sheet correctly, I see a lot more than a 10%
> >> reduction in AH at the .1C rate...more like 50%
> >Ctrl-C/Ctrl-V:
> >Nominal Capacity
> > 20-hr. (450mA to 10.50
> >volts) *................................................. ...... 9.00
> >AH
> > 10-hr. (810mA to 10.50
> >volts) *................................................. ........ 8.10
> >AH
> http://www.power-sonic.com/images/powersonic/technical/1277751263_201...
>
> See page 8.....
>
> Chart for certain temp. and new battery...Colder or older will net worse
> time.

Yeah, I still see about 10% reduction in capacity at 0.1C. Where you
see the 50% reduction, I have no idea. Unless you thought "reduction
in discharge time" but wrote "reduction in AH."

Bart