Author Topic: When Discharge Testing a Battery, how do you set your cut off voltage?  (Read 90 times)

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Offline ThermallyFrigid

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  • Country: us
Hello,

Let's say you are testing a 12v 100Ah SLA battery.

So let's say at the moment it reaches that full SOC you connect it to a dummy load discharge capacity tester. In my case I use a DL24P, 180 watt device.

What do you set the Cut-off voltage to? If you set it to 10.8 (or whatever the data sheet specifies), you will never reach that discharge voltage because voltage at the testing device is lower than at the battery terminals.
At least not on this discharge tester. Does your discharge tester go by battery terminal voltage or internal to tester voltage drop voltage?

You have your actual battery voltage at the battery terminals, and then you have your loaded voltage internally at the discharge device which will be significantly lower due to voltage drop and resistance Even if you use 0 gauge cables you will still have voltage drop.

So for example, if you set your cut off voltage on the tester at 10.8v.....you will actually stop the test at a battery terminal voltage of 11.2v

So do you set the cut off voltage at the batteries specified cut off voltage and know that the battery will never actually reach that voltage because the discharge device will react to the loaded internal voltage and not the actual cell voltage....resulting in the appearance of reduced capacity.....

Or do you set the cut off voltage so that the voltage at the battery terminals reaches the data sheet minimum discharge voltage?

Thanks
« Last Edit: May 06, 2021, 01:52:17 pm by ThermallyFrigid »
 

Offline SuzyC

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  • Posts: 602
Set the cut off voltage so that the voltage at the battery terminals reaches the data sheet minimum discharge voltage.

The data sheet is likely been written after careful testing to specify an end of discharge point, always the best authority.
 


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