7/28/2019 Battery Impedance

1/2

BATTERY IMPEDANCE TESTINGThe battery is the most important link in a Critical Power back up system.

WHY IS MONITORING BATTERY IMPEDANCE AN IMPORTANT PART OF PREVENTATIVE MAINTENANCE?

High impedance is another term for "high internal resistance"; this means with age or poor maintenance arechargeable battery develops a high internal resistance causing the battery to collapse with heavy current

demands.

Effects of impedance on battery load.

A battery with low impedance provides unrestricted current flow and delivers all available energy. A battery

with high impedance cannot deliver high energy bursts due to a restricted path and equipment may cut off

prematurely.

What can I do to maintain a reliable mains failure system?

Impedance testing is a safer, easier and more effective method of determining the battery condition without

the downtime and cost associated with load bank discharge tests. This involves passing a low frequency AC

current through the battery string. The resulting AC voltage produced across each cell is measured and simply

divided by the current to give the impedance of the cell. An individual cell can be immediately compared with

the average impedance results of the other cells to determine its condition. By comparing results over time,

the ageing of an entire battery can be plotted and replacement cost budgeted. By measuring across the cells

and adjacent interlinks any failing interconnections will also stand out during the test.

Advantages

Battery remains fully charged after the test

Battery life is not reduced by repeatedcycling

Individual weak or failing blocks are easily

identified

No load bank required reduces cost and

risk/downtime for connection

Safe injected AC current is low: batterieswill not fail catastrophically

OTHER MEANS OF TESTING WHICH MAY BE OFFERED BY ALTERNATIVE SUPPLIERS:Disadvantages of Battery Discharge Testing

Battery discharge testing can reveal if a battery string has failed and can be used to determine overall ageing

over time.

The disadvantages are this leaves the UPS system with a discharged battery:

The battery life expectancy will decrease with each discharge

The testing itself will accelerate the ageing process.

Also, to identify individual failing blocks, the voltage of each must be monitored during the

discharge test.

A serious task with 204 cells and a discharge time of only 10 minutes; and a serious safety hazardif a cell fails and ruptures under load.

2.0

3.0

4.0

5.0

6.0

7.0

1 4 7 10 13 16 19 22 25 28 31 34

ImpedanceResults

Cell Number

Plot of Impedance Results

MITCHELLWEST LTDElectrical & Mechanical Support for Mission Critical Systems

1

7/28/2019 Battery Impedance

2/2

Battery Impedance Maintenance offered by MitchellWestMitchellWest utilises testing equipment for battery impedance testing, this allows us to offer our customers

accurate information by utilising the most advanced technology. Our equipment helps determine the health oflead-acid cells up to 2000 AH by taking measurements of the most important battery parameters.

MitchellWest believes in the investment of the latest testing equipment to offer

our customers the most reliable and advanced methods of testing with

minimum down time and risks to their business.

Our Battery impedance testing equipment allows live

battery testing with no UPS down time which in turn

offers our customers less risk during battery testing

compared with load testing and other techniques.

Impedance testing results are calculated immediately by

the equipment allowing on site reviews to enable immediate decisions to be made

where required.

We are able to measure up to 2000 AH lead acid cells to test a wide range of

batteries. The equipment has the capacity to store 1 million cells in a string formation which means no stopping or

deleting of information is required to enable testing to continue.

Areas that lead to battery failure

Impedance testing and visual inspection can help determine such

faults and assist to maintain a secure back up supplyFLOODED LEAD ACID VRLA

POSITIVE GRID CORROSION POSITIVE GRID CORROSION

PORT SEAL LEAKING POST SEAL LEAKS

SHEDDING DRY OUT (LOSS OF COMPRESSION)

SULPHATION SULPHATION

HARD SHORTS HARD AND SOFT (DENDRITIC) SHORTS

SLIVERING THERMAL RUNAWAY

By conducting regular impedance testing of UPS batteries and visual inspections all of the above can be

determined, inspection of the UPS unit alone is not sufficient to maintain a reliable back support system,

carrying out regular battery impedance services will ensure reliable systems, by assisting in early warningsthat could have resulted in system failure during a mains outage.

By detecting the above defects early or as they start it is possible to eliminate some of these situations, by

lengthening the life of the battery system and being able to predict when battery replacement is required you

can make certain the system is as cost effective as possible by ensuring that the battery system is being

maintained in a healthy state.

MitchellWest engineers are trained to carry out all services required to maintain a reliable back up power

system and on every maintenance visit our engineers carry out battery impedance testing to ensure a secure

back up system as part of our service regime unlike most other service companies who charge this as an

additional service.

MITCHELLWEST LTDElectrical & Mechanical Support for Mission Critical Systems