Battery dischargers for capacity testing
Battery dischargers apply a controlled constant-current discharge to measure the real capacity of a stationary bank. It is the only test that proves how many minutes the battery will support a mains outage: float voltage and internal impedance are useful indicators, but they do not replace the capacity test.
What do they measure and how?
The unit switches in a regulated resistor bank and holds the discharge current constant while logging string voltage, cell voltages and elapsed time. The test ends at the specified end voltage (typically 1.75 V per lead-acid cell). Capacity is calculated against the rated regime (C5, C8 or C10) and judged against the IEEE 450 replacement criterion: replace below 80 %.
How to choose the right unit
- Discharge current and voltage: cover your banks’ test regimes (24–250 V DC are common).
- Portability: the BLU portable dischargers suit multi-site campaigns; AC resistance banks and containerised systems handle high power.
- Full cycles: the XD battery cycler automates discharge and recharge; the BLUD combines both duties.
- Per-cell logging: essential for finding the weak cells in a string.
Describe your bank at info@amperis.com and we will point you to the model.
Applications
- Acceptance and periodic tests of substation battery banks.
- Autonomy verification in power plants, telecom sites and data centres.
- Requalifying batteries after long storage.
Applicable standards
- IEEE 450: vented lead-acid batteries.
- IEEE 1188: VRLA batteries.
- IEEE 1106: nickel-cadmium batteries.
Frequently asked questions
How often should a capacity test be run?
IEEE 450 recommends an acceptance test, another within the first two years, then periodic intervals that shorten — down to yearly — once capacity approaches 85–80 %.
Does discharging harm the battery?
A controlled discharge to the standard end voltage is part of the bank’s design life. The real risk is the opposite: finding out during an outage that the bank had no capacity left.
Can I test without losing backup?
Yes: test redundant strings one at a time, use a temporary bank, or use equipment that can reconnect the battery instantly if an alarm occurs mid-test.
Resources and contact
Pair with battery testers for quarterly impedance checks. Quotations: info@amperis.com · +34 982 20 99 20.