Discharge Voltage

[jhoang]

I would like to write program to discharge batteries voltage (Vbat=3.2V), at first I input 100 ohm and step 5 second. Then I compare if voltage 2.6V<=V>=4V then End. If voltage still in the 3.2V range then I input current for 0.0005 Amp.I would like to calculate the Amp Hour , if Amp hour at 0.013 the program stop running. I am not sure the way I calculate the Amp Hour correct? Please Help. I would mlike to attachment my program for input. Thank you very much. John Hoang

[crossrulz]

I am not sure the way I calculate the Amp Hour correct?

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You could integrate the current and convert from A*sec to A*h

[jhoang]

I could not see the way you calculate the amp hour. Could you write again. Thank you

[johnsold]

When you load a battery with a fixed resistor, the current varies over time as the battery voltage drops. The capacity of a battery, expressed in ampere-hours, is a measure of the stored charge.  Charge, in coulombs, is the product of current (amperes) and time (seconds).  The mathematical process of integrating the (time varying) current over time will give the total charge.  This is what crossrulz is suggesting. If your dt (sampling period) is measured in seconds, you need to conver the result to hours to get battery capacity in ampere-hours.

Lynn

[MoReese]

That's going to depend on the AH rating of the battery you are using.  Take its rating and divide by the current draw.

Ex.  If you have a 7AH battery, you can draw 7AH / 20 hour test cycle = 0.375A over a 20 hour period before the battery is dicharged.  So, if our battery is drawing 0.5A, then 7AH / 0.5 = 14 hours.  This is how long I could expect this battery to last before discharge.  Word of note:  You should not drain your battery below the 50% mark unless you are doing some sort of distructive testing.

[SnowMule]

An amp-hour is a measurement of current over time, or charge.

A "perfect" battery that can provide exactly 1 amp of current for exactly one hour then dies has a capacity of one amp-hour. 

2 amps for half an hour is still 1 amp-hour.

If you're plotting current on a graph, the area under that curve is your charge capacity. 

[jhoang]

I am new in LabView, could you please to help me in this part. Thank you

[MoReese]

Simple integration from t1 to t2.  Use the integration tools under the Integration and Differentiation pallete.