Quality of Charge

[Anonymous user]

I'm putting together a protocol to assess quality of batteries charge on many of the units at my facility.  Does anyone have an idea of how to test the duration of charge remaining on a battery?  If there is equipment that gives me percentage, that is relative and possibly provides false positives for our needs.  The batteries are for BE350G units.  I must add, what is the Part Number of the stock batteries?  Part number is provided for replacement ones, but I'm just putting together testing regimen for stock ones.

Any thoughts?

[Brad_C · Accepted solution]

Most SLA batteries are rated at a C/20 rate (full discharge over 20 hours).

For capacity testing, up to a 33AH battery I use one of these : Imax B8+

To re-charge properly prior to and after a capacity test I use the Imax and then soak at float voltage with a regulated bench power supply for the best part of a day.

For example, I'm currently testing a Yuasa NP7-12. Set the Imax up for Lead Acid, Discharge current of 0.3A and 6S (12V - 6 cells in series) battery. The unit will sit there and pull 300mA from the battery until it drops below the threshold voltage (9V by default). That's a bit low, but it gives a relatively accurate measure of the batteries remaining capacity.

I recently tested a set of CSB GP1272 batteries from a SU1400RMI2U. They were 4 years old and the UPS was failing self-test. Three of the batteries measured at about 3.5Ah and one had a collapsed cell under load. So they dropped from 7.2Ah to 3.5Ah in 4 odd years.

Bear in mind a proper discharge test will take up to 20 hours, and a proper charge should probably last for 24 hours (based on a multi-stage charge and the manufacturers data sheet).

The Imax charger is not what you'd call a quality item, nor is it particularly accurate but I happened to have a couple lying around from RC hobby stuff and they turnout to be accurate *enough* to cycle test SLA batteries up to about 33Ah. I did use the B8 to test some Vision 55Ah batteries, but that took well in excess of 24 hours and the discharge rate was less than C/20 (the discharger is limited to about 20W).

The other required test is a test under heavy load. I've had batteries pass C/20 capacity tests and still collapse under heavy load. The UPS self-test is sufficient for that.

As for estimating battery capacity *without* performing a full cycle test, it's a wild guess at best. The SmartUPS series does a credible job with its battery constant calibration, but that only works with routine self tests, a decent load and lots of time.