Battery Discharge Calculations

[orcuns91]

Hi guys,
I would like to ask a theoretical question about batteries.
If a battery with a capacity of 100 Amp-hour is discharged with an average of 0.5A PER MINUTE, in how many hours does the battery discharge at full capacity?

 

[Easy peasy]

0.5 A / per minute, is the same as 0.5 A continuous ..... or just 0.5 A

200 hrs is the answer - but it is dependent on temperature - and assumes the fully charged battery has that capacity

also if you discharge with a resistor - as the Vbatt drops the current will drop over time

for a constant power load the current will go up over the 200 hrs

only a true constant current load will give you 200 hrs ... ( approx )

 

[KlausST]

Hi,

Are you sure you mean "0.5A per minute"?
So after:
1 minute is 0.5A
2 minute is 1.0A
3 minute is 1.5A
.. and so on

Then the "1 minute" has to be formed as "1/60 h" ( to meet the "h" in "Ah" of the battery)
So it is a rate of 30A/h.
Now you have a complete formula using integral calculation.
0.5 × 30A/h × t^2 = 100Ah
t^2 = 100Ah / ( 0.5 × 30A/h) = 100Ah / 15A/h = 6.6666^2 h
t is about 2.58h.
.
Klaus

 

[Audioguru]

The battery voltage drops as it is discharged. Some batteries are rated for a "deep discharge" but if your load does not work at the very low deep discharge voltage then the Ah rating is higher than you can use.

With an Energizer 9V alkaline battery at a fairly low load current, its Ah rating is when its voltage has dropped to almost half. A graph shows it dropping to 8V in 1/5th its 0.6Ah rating.
So you must find out the lowest voltage that your load still works at and find out the Ah graph showing that current and that voltage.

 

[c_mitra]

I would like to ask a theoretical question about batteries.
If a battery with a capacity of 100 Amp-hour is discharged with an average of 0.5A PER MINUTE, in how many hours does the battery discharge at full capacity?

Your question is badly asked.

Battery capacities are commonly rated in AH (amps x hours). So a battery rated at 100 AH can supply 100 amps for 1 hour or 1 amp for 100 hours. For that matter it can supply 0.5A for 200 hours. All these give the same amp x hour product (100 AH).

In reality, batteries are not 100% efficient. the capacity, i.e., the AH number slowly decreases with time AND number of charge discharge cycles.

Also, a battery of 100AH capacity cannot give 100A for 1H but can give 5A for 20H. Why? High current means higher inefficiency.

Also, batteries suffer from leakage. Its capacity decreases even if does not supply any current.