Standby battery bank discharge test 2

[BrkfldEE]

We have standby battery banks to provide DC power for our generating stations. Recently we started a monthly discharge test where we turn off the battery charger for five minutes to test the capacity/condition of the batteries. There has been some conflicting ideas on whether this is a good practice or not. Any insight?

 

[collies99]

Monthly is likely too frequent.

How old are your batteries ? What type ?
What was your previous discharge test frequency ? How deep of a discharge did you do in terms of % of its nominal terminal voltage ? How long before you got to the roll off voltage ?

 

[JG2828]

Take a look at the attached Megger Battery testing guide. It appears to give some pretty good information.


Capacity test (capacity test) should be done
▪ at the installation (acceptance test)
▪ Periodically. Intervals should not be greater than 25% of
the expected service life or two years, whichever is less.
▪ Where impedance values has changed significantly
between readings or physically changes has occurred
▪ annually when the battery shows signs of degradation or
has reached 85% of the expected service life. Degradation
is indicated when the battery capacity drops more than
10% from its capacity on the previous capacity test or is
below 90% of manufacturers rating.

 

[BrkfldEE]

We have multiple installations with varying ages from 1 year to 20 years. they are vented lead acid battery type. We had not been previuosly doing a discharge test.

 

[Zogzog]

A capacity test is much different than turning the charger off for 5 minutes, not sure what that tells you.

You may want to look at Impedence testing, using something like Maggers EBITE system. Works great for monitoring condition of your cells.

 

[genhead]

Turning the battery charger off will only tell you if there is already something seriously wrong with your battery, ie if the voltage collapses without the support of the battery charger.

 

[genhead]

Turning the battery charger off will only tell you if there is already something seriously wrong with your batteries, ie if the voltage collapses without the support of the battery charger.

 

[collies99]

It is amazing how things have changed. Impedance tester was not around 21 years or so ago. We have battery banks approaching 30 years old and with proper maintenance (mostly the addition of distilled water), yearly cell voltage and specific gravity measurement and data analysis if it requires equalization at that time have done OK for us. Capacity test every 3 years down to where voltage starts to roll off without going into deep discharge is how we do it, trending time to reach roll off voltage.

so far that procedure have not changed along with monthly visual inspection to ensure battery are either not being overcharged and floated properly and no visible sign of sulphation.

megger battery what ?

 

[sibeen]

Very well stated, collies99, and a star to boot.

I started in the UPS industry back in about '87. The only way to properly test a battery bank back then was to do a fairly deep discharge and monitor the voltage across each cell. Nearly 30 years later it still hasn't changed

Yes, an impedance test can certainly tell you that a battery has failed, or is about to, but it is still nowhere near the certainty that a discharge test will provide.