The COST of Battery Maintenance
Can you afford to be without it?
1
Why Batteries are Needed ?
§  Electric generating stations and substations for protection and
control of switches/breakers and relays
§  Telephone companies to support phone service
§  Back up of critical power dependant equipment (life support
systems, business information systems, data centres)
§  Industrial applications for protection and control
§  Industrial process control
Failure is not an Option
2
Battery Types
n  Primary Cells – These
are non-rechargeable
batteries. These include
the standard Alkaline
battery and Lithium
batteries.
n  Secondary Cells –
These are the rechargeable batteries.
These include lead acid
batteries, NiCD as well
as Lithium Ion.
3
Secondary Batteries
n  Cyclic Batteries – These are
batteries that are used on a
regular basis. The most
common of these is automotive batteries or portable
battery operated devices.
n  Standby Batteries – These
are batteries that remain
charged but are not used
unless needed.
•  Sub-stations (Relays)
•  Telecom (Communication)
•  Data Centers (UPS)
4
Basic Types
n  Lead-acid
•  Flooded
•  Sealed
n  Nickel-cadmium
•  Flooded
•  Sealed
n  Other chemistries
•  Li Ion
•  NiMH
5
Common Failure Modes
6
Positive Grid Corrosion
n  Normal failure mode in
flooded lead-acid and VRLA
batteries
n  Lead alloy turns to lead
oxide.
n  Plates grow
n  Designed into batteries
n  Acceleration due to:
•  Overcharging
•  Excessive cycling
•  Excessive temperature
n  Increase in internal
impedance
7
Sediment (Shedding)
n  Sloughing off of active material from plates into white lead
sulfate.
n  Small amount is normal
n  Can cause plate shorts
n  Due to overcharging and excessive cycling.
n  sulfation slough off - undercharging
n  Seen in flooded batteries, most common in UPS systems.
8
Plate Sulfation
Active plate material turns to lead sulfate.
Lead Sulfate = Inactive material
Occurs in both Flooded and VRLA batteries
Natural process during discharge.
Recharging reverses the process.
Undercharging causes sulfate crystals to form on the plate
surfaces.
n  Not enough current flowing to keep the battery fully charged.
n
n
n
n
n
n
9
Plate Sulfation
n  Sulfate crystals that harden
over a long period of time.
n  These will not go back in
solution when proper voltage
is applied.
n  Decreases total active
material/capacity
n  Result in a permanent loss
of capacity.
n  Increase in internal
impedance
10
Shorts
n  Shorts can occur in both Flooded and VRLA cells.
n  Hard sorts are typically caused by paste lumps pushing
through the matte and shorting out to the adjacent (opposite
polarity) plate.
n  Soft shorts, on the other hand, are caused by deep
discharges.
n  When the specific gravity of the acid gets too low, the lead will
dissolve into it. Since the liquid (and the dissolved lead) are
immobilized by the glass matte, when the battery is
recharged, the lead comes out of solution forming dendrites
inside the matte.
n  In some cases, the lead dendrites short through the matte to
the other plate.
11
Dry-Out (Loss of Compression)
n  VRLA batteries only
n  Dry-out is a phenomenon that occurs due to
excessive heat, over charging can cause elevated
internal temperatures as well as high ambient
(room) temperatures.
n  At elevated internal temperatures, the sealed cells
will vent through the PRV.
n  When sufficient electrolyte is vented, the glass
matte no longer is in contact with the plates, thus
increasing the internal impedance and reducing
battery capacity.
12
Thermal Run-away
n  Thermal run-away is when a battery internal components
melt-down in a self-sustaining reaction.
n  Failure mode VRLA batteries
n  Can end in complete and catastrophic failure
n  Primarily due to oxygen recombination cycle
n  Thermal run-away is relatively easy to avoid, simply by using
temperature-compensated chargers and properly ventilating
the battery room/cabinet.
n  Temperature-compensated chargers reduce the charge
current as the temperature increases.
13
Thermal Run-away
n  Flooded cell allows gas to
escape
n  VRLA recombines oxygen
and forms water
n  Reaction produces heat
n  Due to:
•
•
•
•
Overcharging
High ambient
Low air flow
High float voltage
n  Heating is a function of the
square of the current
14
Separator Deterioration
n  Separator Deterioration
n  Effects Ni-Cd cells
n  This will occur in all NiCd batteries as they
age.
n  The separator breaks
down allowing the
plates (electrodes) to
touch and short out the
battery.
15
Carbonation
n  Carbonation occurs as part of the aging process in NiCD cells.
n  The potassium hydroxide (KOH) electrolyte enters into
chemical combination with atmospheric carbon dioxide (CO2)
and forms potassium carbonate (K2CO3).
n  This removes the KOH ions from the electrolyte and makes
the cell less able to conduct electricity.
n  The decrease in electrolyte conductivity makes the cell reach
a lower voltage much more quickly under discharge.
n  As such, electrolyte carbonation appears to the cell's user as
diminished capacity.
n  This can be reversed by exchanging the electrolyte.
16
Loose Connections
n  Frequent Problem all battery types
n  Easily found with resistance measurement
n  High resistance = elevated temperature = higher resistance
n  When serving load high temperatures can melt lead posts
Watts Lost = (Current)2 (Resistance)
17
Why maintain batteries?
Several things can happen when batteries are
left un-monitored:
•  Battery terminals can become corroded
•  Ventilation systems can fail
•  Battery housing can build up pressure and crack
•  Batteries will not deliver when needed
18
Bad things can happen when Batteries do not
function properly
20MW Generator Damage after DC System
Failure – Machine lost DC Oil Pumps and
Breaker Failed to trip. Unit motorized for 45
minutes. Shaft sheared in 3 places. Repairs
exceeded $3M and 6 months downtime.
19
Battery Explosion
§  Internal generated sparks and
extreme temperature rise
caused by high-resistance
internal parts, can lead to
dangerous cell explosion.
§  Damage: Battery explosion
damaged Battery Room and
caused hazardous battery
fumes to infiltrate the adjacent
Switchgear room causing
further damage.
20
Battery Explosion Results can be Catastrophic
This Battery room lost
ventilation and the
Hydrogen Monitors
were in Alarm Mode
for 3 days prior to the
explosion, but nobody
paid attention to them.
The resulting explosion
caused a 400 sq ft hole
in the roof.
21
Well Maintained & Clean Battery Installation
22
Poorly Maintained &
Corroded Battery Terminal
23
Battery Maintenance
24
Intro
n  No single test tells the whole story
n  Determine condition
n  Where condition is headed
n  How fast
n  Don’t find out during an outage that your battery
failed
n  Gather as much test data as possible
25
Test Methods
n  Visual Inspection
n  Float Voltage
n  Float Current
n  Ripple Current
n  Specific Gravity
n  Temperature
n  Discharge Testing
n  Ohmic Testing
n  Strap Resistance
26
Visual Inspection
n
n
n
n
n
n
n
Check entire system
Battery Electrolyte Level (Flooded Batteries)
Ventilation system, floor & room clean
Battery support system
Check batteries for cracks, leaks and deformation
Strap corrosion
Record information
•  Visual inspection will locate such things as cracks, leaks
and corrosion can be found before they become
catastrophic failures. However, visual inspection tells us
nothing about the strings State of Charge (SOC), capacity
or State of Health (SOH).
27
Float Voltage
n  Measure across each cell
n  Measure at posts
n  During float conditions
n  Not during discharge or
recharge
n  Compare float voltage to
manufacturers
recommendation
28
Float Voltage
n  Applied voltage to cell from charger
n  Different voltages for different chemistries
n  Low float voltage > not fully charging
•  Can’t supply full capacity
•  Plate Sulfation
n  High float voltage > Over charging
•  cooks the battery
•  higher temperature
•  Grid corrosion
•  Thermal runaway
•  Dry-out
■  Float Voltage will tells us if something is wrong but it will not
tells us anything about SOC, Capacity or SOH.
29
Float Current
n  Kirchhoff current law
n  Measure anywhere in the
string
n  Usually low value
n  Measure during float
conditions
n  Not during discharge or
recharge
n  Increase in float current
precursor to Thermal Runaway VRLA
30
Float Current
n  Current through each cell
•  Interaction between float voltage and internal resistance
n  Supplied by charger
n  Electrochemical process reversed
•  Lead sulfate on plates converted to sulfuric acid and active
material
n  High float current precursor to thermal runaway
•  Short circuits
•  Ground faults
•  High float voltages
■  Float Current will tells us if something is wrong but it will not tells
us anything about SOC, Capacity or SOH.
31
Ripple Current
n
n
n
n
By-product of charging system
Design, quality and age dictate
Internal heating of battery and overcharging
No more than 5A for every 100Ah
32
Specific Gravity
n  Ratio of density of liquid with
respect to density of water
n  How much sulfate is in
electrolyte – lead acid
n  Gives SOC but not Capacity
or SOH.
n  Density is temperature
dependent
•  So Specific Gravity is also
Density =
Mass
Volume
33
Temperature
n  High temp = short life
n  Low temp = low capacity possible damage
n  10 °C rise = ½ life
120
30
110
25
100
20
90
15
80
10
70
Battery Life (yrs.)
Capacity (%)
Temperature Effects
5
60
50
0
47
62
77
92
107
Temperature (F)
% Capacity
Life (yrs.)
34
Discharge Testing
n  Single absolute test
n  Complexity & cost
n  Acceptance Test
•  Beginning of life based on design capacity
n  Performance Test
•  After two or three years when new then every five years
•  Based on design capacity also
n  Service Test
•  As needed to determine if battery will support existing load
n  Discharge Testing is the only test that will determine the capacity of the string, but not
necessarily the SOH.
Volts per Cell
Partial Load Test
2.3
2.1
1.9
1.7
1.5
0
5
10
15
30
45
60
75
90 105 120 135 150 165 180 195 210 225 240
Time (min)
Passes
Better
Failure
35
Ohmic Test
n  Impedance, Conductance &
Resistance
n  IEEE uses term ohmic
n  DC based on V=IR : AC based on
V=IZ
n  As a battery ages it may corrode,
sulfate, dry-out or suffer a host of
other effects based on
maintenance, chemistry and usage.
All of these effects cause a
chemical change in the battery;
which in turn causes a change in
the batteries internal impedance /
resistance.
n  Ohmic testing measures the SOH.
36
Inter-Cell Resistance
n  If the torque not sufficient
this will cause a higher
resistance causing a voltage
drop that causes heat.
n  Measure across strap
•  Not on Strap
•  On Post
37
Inter-Cell Resistance
n  Must include all resistance
between posts
n  Multiple straps – Multiple
measurements
n  Low resistance ohm meter or
device designed for batteries
38
Ohmic Testing
39
Ohmic Testing
n  Ohmic battery testing is a
method of testing batteries that
compliments discharge testing.
Discharge testing is an absolute
way of measuring battery
capacity. Ohmic testing is a
relative measurement used to
supplement discharge testing,
Discharge testing is expensive,
time consuming and can reduce
the overall total life of the battery
string.
40
Ohmic Testing
Ohmic testing; which
includes resistive testing,
impedance testing and
conductance testing is a
relative test. It compares an
ohmic measurement to a
previous ohmic
measurement as well as the
average ohmic
measurement of the string.
When performing ohmic
measurement a baseline
should be established.
Ascending Impedance with Corresponding End Voltage
2.5
Impedance (mOhms) & End Voltage
n
2.25
2
1.75
1.5
1.25
1
0.75
0.5
0.25
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Imp
0.27
0.27
0.27
0.56
0.61
0.63
0.65
0.68
0.71
0.72
0.74
0.75
0.79
0.8
0.82
0.84
0.89
0.9
0.91
0.94
0.96
1.17
1.19
2.1
End V
2.03
2.04
2.03
1.98
1.97
1.94
1.9
1.91
1.88
1.89
1.9
1.89
1.89
1.84
1.82
1.84
1.81
1.84
1.8
1.73
1.82
1.74
1.33
0.1
Cell #
11
15
16
3
18
22
13
24
10
14
23
20
5
9
6
4
21
8
1
12
2
17
7
19
41
Type of Ohmic Testing
n  Resistance – Measures only the resistive value of a
battery, The battery also has capacitive and
inductive values as well.
n  Conductance – (Actually Admittance) This is the
reciprocal of impedance.
n  Impedance Testing – Measures the resistive,
capacitive and inductive qualities of the battery.
n  NOTE: Ohmic testing is a relative test NOT an
absolute test. We do not test against an absolute
value. We test and compare that data to a previous
test result.
n  Repeatability is KEY.
42
Impedance Test
n  Impedance testing has a distinct advantage over resistive type testing. When
we look at a schematic representation of a battery there are more than just
resistive components to that battery. There are also capacitive and inductive
characteristics.
n
This means that impedance testing will be able to detect certain
problems that resistive measurements can miss; these include negative lug
rot as well as negative plate corrosion. These failures will show themselves as
changes in inductance and capacitance, not in resistance. In addition many
chemical changes in a battery will be seen as impedance changes before
they are seen as resistive changes.
43
Impedance Test
n  Provides SOH rather than just SOC
n  As the battery ages and sulfates the impedance of the battery
will increase as the capacitance decreases.
Ascending Impedance with Corresponding End Voltage
Impedance (mOhms) & End Voltage
2.5
2.25
2
1.75
1.5
1.25
1
0.75
0.5
0.25
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Imp
0.27
0.27
0.27
0.56
0.61
0.63
0.65
0.68
0.71
0.72
0.74
0.75
0.79
0.8
0.82
0.84
0.89
0.9
0.91
0.94
0.96
1.17
1.19
2.1
End V
2.03
2.04
2.03
1.98
1.97
1.94
1.9
1.91
1.88
1.89
1.9
1.89
1.89
1.84
1.82
1.84
1.81
1.84
1.8
1.73
1.82
1.74
1.33
0.1
Cell #
11
15
16
3
18
22
13
24
10
14
23
20
5
9
6
4
21
8
1
12
2
17
7
19
44
Discharge Testing
n  Discharge Testing is a direct measurement of a
battery strings capacity.
n  It is a long test that requires the string to be taken
off line most times.
n  Why perform discharge testing?
n  IEEE requires it and it is the only true measurement
of capacity.
n  Temperature must be taken into account during
testing.
45
Discharge Testing
n  Calculating a Batteries Capacity from a Discharge Test
n  Use the equation below to determine the battery or cell/unit capacity
for a discharge test that runs 1 h or longer.
•
•
•
•
C
tA
tS
KT
Is the % capacity at 25 ºC
is the actual time of the discharge test.
is the calculated time of the discharge test.
is a correction factor for the cell temperature.
46
Discharge Testing
n  This table is based on flooded lead acid batteries with a
nominal 1.215 specific gravity. For cells with other specific
gravities or chemistries refer to the manufacturer.
47
Conclusions
n  Regular Battery Maintenance is essential for the
safe and reliable operation of a DC System
n  Maintenance needs to include Load Testing and
Impedance Testing.
n  Online Load Testing is an option for determining
battery capacity when offline is not practical.
n  Impedance Testing is used to compliment
discharge testing and is the only way to determine
battery state of health.
48
Thank you
49