Battery Power

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