**Contents:**

www.alcad.com

Battery Sizing

Scope

•

•

•

•

Battery selection criteria

Electrochemistry

Comparison of Lead Acid vs Nickel Cadmium

Battery Sizing – Understanding load profiles

Where and how you can save money

The Basics – Build a Load Profile

•

•

•

•

WHERE TO BEGIN

When will the battery discharge

LOADS TO CONSIDER

Continuous

Non-Continuous

Momentary

WHAT HAPPENS FIRST

Followed by?

For how long?

MARGINS

Design

Aging

Effects of temperature

Fluff

NORMAL OPERATION

AC Available

No Faults

2 amps for

indicating lights,

relays etc.

~

6 AMP

CHARGER

4.160KV

Switchgear

30 mA to float

charge battery

12 AMP TRIP

CURRENT

Basics

Charger goes to

current limit, puts

out 6 amps MAX.

~

6 AMP

CHARGER

4.160KV

Switchgear

0 mA to float

charge battery

Remaining 6

amps comes

from battery.

Load requirements exceed maximum charger output

12 AMP TRIP

CURRENT

ABNORMAL CONDITION

Charger Output Limited

Breaker Operating

1 amps max

coming from

charger.

4.160KV

Switchgear

~

6 AMP

CHARGER

0 mA going to

the battery

Remaining 11

amps comes

from battery.

Charger output is limited in some way.

12 AMP TRIP

CURRENT

ABNORMAL CONDITION

AC Failure

Charger Output @ Zero

No current

available from

charger

4.160KV

Switchgear

~

6 AMP

CHARGER

Full load comes

from battery.

Charger output is lost completely, due to rectifier or

AC failure.

12 AMP TRIP

CURRENT

Continuous Loads

• Loads that are energized for the duration

of the duty cycle

• Are normally supplied by the charger

• Can have a big effect on battery capacity

• Examples

Continuously operating motors / pumps

Relay coils

Indicating lights

Non-Continuous Loads

• Energized for only a portion of the duty

cycle

• Can be turned on or off automatically or

by operator action

• Special considerations:

If inception is known, but end is not, run to end of duty cycle

If end is known, and inception is not, consider the load from the

beginning of the duty cycle.

• Examples

Emergency lighting

Lube oil pumps

Communication

Momentary Loads

• Very short in duration, can be fraction of a

second

• Lead Acid - IEEE 485

Even though the load may last for only a few cycles, you must

treat it as lasting one full minute

• Nickel Cadmium - IEEE 1115

Even though the load may last for only a few cycles, you must

treat it as lasting one full second

• Examples

Switchgear operation

Engine starting

Field flashing

Dealing with Multiple

Momentary Loads

• Discrete Sequence Known

Load is maximum current at any instant

• Sequence Unknown

Load is sum of all loads in that period

Usually a greater demand on battery

Dealing with Multiple

Momentary Loads

IEEE States:

• If a discrete sequence can be established,

the load for the period shall be assumed to

be the maximum current at any instant

Example:

1 Trip - 3 breakers 45 amps

2 Trip - 5 breakers 75 amps

3 Trip - 4 breakers 60 amps

Duration

0.5 sec

1 sec

1 sec

Since we can determine the sequence, the load for the period

would be 75 amps for one minute (for lead acid)

Nicad can be broken into 3 distinct loads, or, 75A for 3 seconds

Dealing with Multiple

Momentary Loads

•

IEEE States:

If a discrete sequence cannot be established, the load for the period

shall be assumed to be the sum of all the loads occurring within that

period

Example:

Trip

Trip

Trip

- 3 breakers 45 amps

- 5 breakers 75 amps

- 4 breakers 60 amps

Duration

0.5 sec

1 sec

1 sec

Since we cannot determine the sequence, you must treat

the load as occurring all at once

180A for 1 minute - Lead

180A for 1 second - Ni-Cd

The Duty Cycle

M o m e n ta r y lo a d

1 m in - L e a d A c id

1 s e c - N ic k e l C a d m iu m

N o n C o n tin u o u s L o a d

C o n t in u o u s L o a d

Sizing Margins or

Making Batteries Bigger

• Aging Factor

25% Recommended

•

•

•

•

Applicable to:

All types of flooded lead acid

VRLA

Nickel Cadmium

• Exception is Plante`

Sizing Margins or

Making Batteries Bigger

• Low Temperature Correction

For operation below rated temperature

• High Temperature

Improves performance slightly

Not normally used in sizing calc’s.

Design margin for maximum life

Sizing Margins or

Making Batteries Bigger

• Design Margin

Normally considered for future equipment or load growth

Allows for operation at lower than expected temperature

Can cover for less than adequate maintenance

• Almost every sizing has one!

Sizing Margins or

Making Batteries Bigger

• If the calculation requires a 220 Ah

battery, and the next cell size up is 250 Ah

-• The 30 Ah difference is a 13% margin,

“designed” in

• An additional margin of 10% might not be

required

Knowledge is not

only Power

It’s Money

• Develop load profile using worst case

• Try to determine sequences

Not knowing requires conservatism

Conservatism can increase required capacity

Increased capacity - More $

• Closely review various sizing factors

Low temperature increases battery size

Aging factors are good ideas - ensure long reliable life

Evaluate design margins, especially after sizing a battery

Have we lost anyone

So far we’ve covered...

• Various discharge scenarios

Pick the worst case

• Various load types

Continuous

Non-Continuous

Momentary

• Sizing margins / factors

Temperature correction

Aging factor

Design margins

Sizing - What’s needed

• Load profile

Include all prudent margins

• Voltage

Maximum

Minimum

• Manufacturers data

Yes, you do need us

• Capacity rating - Kt factors

Amps per positive plate - Rt factors

• Battery type

Flooded lead acid

Nickel cadmium

VRLA

The load profile

15 BREAKERS

TRIP

- 10A, 5 CYCLES

Sim./Brkr

CLOSE

- 7A, 5 CYCLES

Seq./Brkr

SP. CHG - 4A, 6 SECONDS

TWO OPERATIONS,

Beginning and end of 8 hr duty cycle

2A CONTINUOUS LOAD

EMERGENCY LIGHTING LOAD

1200 Watts - 90 minutes

Starts at outage

Seq./Brkr

The load profile

Trip 15 Breaker

1 min. - Lead Acid

1 sec. - Ni-Cd

150 A

Trip Breakers at

End Of Cycle

Close & Spring

Charge Loads

Trip Load

1 min. - Lead Acid

92 sec. - Ni-Cd

?

7A

10A

Lighting Load

2A

Continuous - 8 HR

90 minutes

Load profile defined

•

Nickel Cadmium

162A

19A

12A

2A

152A

1 second

92 seconds

88.45 minutes

390 minutes

1 second

•

Lead Acid

162A

19A

12A

2A

152A

1 minute

1 minutes

88 minutes

389 minutes

1 minute

Voltage window

• Maximum and Minimum values

Determined by DC powered equipment

• Allow widest possible range

Uses maximum number of cells

• More cells = lower end of discharge

voltage

• More efficient capacity utilization

• Least expensive battery

Impact of voltage window

• IEEE 485 Example:

140V - 105V window

60 cells, to 1.75 VPC

- 1,010.4 Ah req'd

• Wider voltage window

62 cells, to 1.69 VPC

- 944 Ah req'd

3% increase cell qty, 7% capacity reduction

• Narrower voltage window

58 cells, to 1.81 VPC - 1,186 Ah req'd

3% decrease cell qty, 17% increase in capacity

• 100Ah High rate ni-cd cell

One minute rate To 1.14 VPC

One minute to 1.05 VPC

243 amps

406 amps

No. of cells calculation

Max. Volts - Determines number of cells that can be adequately

charged.

Equalize value is normally used as determining cell voltage

Ex

140V max

2.33VPC

or

140V max

1.46VPC

= 60 cells (lead acid)

= 96 cells (nickel cadmium)

End of discharge calculation

Min. Voltage - Lowest value system designed to operate at

Min. Volts

# of cells = End of discharge voltage / cell

Ex. 105 VDC

60 cells

= 1.75 VPC Lead Acid

Ex. 105 VDC

96 cells

= 1.09 VPC Nickel Cadmium

Sizing factors

• Kt factors

Based on performance per rated ampere hour

Kt factor = Rated ampere hours

Amps available for time t

• Rt factors

Based on performance per positive plate

Used primarily with lead acid cells

Rt factor = Amps available for time t per positive plate

Capacity rating factors

• Kt factors

Determined from tabular data

• Examples

160 Ah rated cell

8 hr discharge rate - 20 amperes

Kt = 160 Ah / 20 amps

8 Hr rate Kt = 8

• One minute discharge rate - 320 amperes

Kt =

160 Ah / 320 amps

One minute Kt = 0.5

• Kt factors are multipliers in IEEE

worksheets

Capacity rating factors

• Rt Factors

Found in plate performance curves

Not all manufacturers publish them

When not available, use Kt

• Rt factors are divisors in IEEE worksheets

Did you know this?

• Most lead acid model numbers indicate

number of plates per cell

3CC7 = Seven plates per cell

4JC11= Eleven plates per cell

• One more negative plate than positive

Seven plates = 4 Neg - 3 Pos

Eleven plates = 6 Neg - 5 Pos

• 50Ah / positive plate

150Ah cell from above example (3 pos x 50Ah)

250Ah cell for eleven plate cell (5 pos. x 50Ah)

• Positive plates are same for the range

More things you should know

• Ampere hour nomenclatures

Most nickel cadmium

Some VRLA

• Pos. plates are not identical thru range

• Wider or taller plate = higher capacity

• More plates per cell = higher capacity

Real life

• Create a duty cycle

• Periods

Amps__________ Duration_________

Amps__________ Duration_________

Amps__________ Duration_________

• Voltage window

Max__________

MIn__________

• Calculated No. of cells

Lead acid___

Nickel cadmium___

• Environment

High Temp_____

Lowest Temp_______

• Aging factor _______ (not for Plante')

• Design margins

_______

Summing up

•

Battery Sizing is a science

•

Building the load profile is an

art

Electro-chemistries vary

greatly

•

•

You have more control over

your battery selection than you

think

www.alcad.com

Thank you for

your attention

Alcad: presentation title

37

Battery Sizing

Scope

•

•

•

•

Battery selection criteria

Electrochemistry

Comparison of Lead Acid vs Nickel Cadmium

Battery Sizing – Understanding load profiles

Where and how you can save money

The Basics – Build a Load Profile

•

•

•

•

WHERE TO BEGIN

When will the battery discharge

LOADS TO CONSIDER

Continuous

Non-Continuous

Momentary

WHAT HAPPENS FIRST

Followed by?

For how long?

MARGINS

Design

Aging

Effects of temperature

Fluff

NORMAL OPERATION

AC Available

No Faults

2 amps for

indicating lights,

relays etc.

~

6 AMP

CHARGER

4.160KV

Switchgear

30 mA to float

charge battery

12 AMP TRIP

CURRENT

Basics

Charger goes to

current limit, puts

out 6 amps MAX.

~

6 AMP

CHARGER

4.160KV

Switchgear

0 mA to float

charge battery

Remaining 6

amps comes

from battery.

Load requirements exceed maximum charger output

12 AMP TRIP

CURRENT

ABNORMAL CONDITION

Charger Output Limited

Breaker Operating

1 amps max

coming from

charger.

4.160KV

Switchgear

~

6 AMP

CHARGER

0 mA going to

the battery

Remaining 11

amps comes

from battery.

Charger output is limited in some way.

12 AMP TRIP

CURRENT

ABNORMAL CONDITION

AC Failure

Charger Output @ Zero

No current

available from

charger

4.160KV

Switchgear

~

6 AMP

CHARGER

Full load comes

from battery.

Charger output is lost completely, due to rectifier or

AC failure.

12 AMP TRIP

CURRENT

Continuous Loads

• Loads that are energized for the duration

of the duty cycle

• Are normally supplied by the charger

• Can have a big effect on battery capacity

• Examples

Continuously operating motors / pumps

Relay coils

Indicating lights

Non-Continuous Loads

• Energized for only a portion of the duty

cycle

• Can be turned on or off automatically or

by operator action

• Special considerations:

If inception is known, but end is not, run to end of duty cycle

If end is known, and inception is not, consider the load from the

beginning of the duty cycle.

• Examples

Emergency lighting

Lube oil pumps

Communication

Momentary Loads

• Very short in duration, can be fraction of a

second

• Lead Acid - IEEE 485

Even though the load may last for only a few cycles, you must

treat it as lasting one full minute

• Nickel Cadmium - IEEE 1115

Even though the load may last for only a few cycles, you must

treat it as lasting one full second

• Examples

Switchgear operation

Engine starting

Field flashing

Dealing with Multiple

Momentary Loads

• Discrete Sequence Known

Load is maximum current at any instant

• Sequence Unknown

Load is sum of all loads in that period

Usually a greater demand on battery

Dealing with Multiple

Momentary Loads

IEEE States:

• If a discrete sequence can be established,

the load for the period shall be assumed to

be the maximum current at any instant

Example:

1 Trip - 3 breakers 45 amps

2 Trip - 5 breakers 75 amps

3 Trip - 4 breakers 60 amps

Duration

0.5 sec

1 sec

1 sec

Since we can determine the sequence, the load for the period

would be 75 amps for one minute (for lead acid)

Nicad can be broken into 3 distinct loads, or, 75A for 3 seconds

Dealing with Multiple

Momentary Loads

•

IEEE States:

If a discrete sequence cannot be established, the load for the period

shall be assumed to be the sum of all the loads occurring within that

period

Example:

Trip

Trip

Trip

- 3 breakers 45 amps

- 5 breakers 75 amps

- 4 breakers 60 amps

Duration

0.5 sec

1 sec

1 sec

Since we cannot determine the sequence, you must treat

the load as occurring all at once

180A for 1 minute - Lead

180A for 1 second - Ni-Cd

The Duty Cycle

M o m e n ta r y lo a d

1 m in - L e a d A c id

1 s e c - N ic k e l C a d m iu m

N o n C o n tin u o u s L o a d

C o n t in u o u s L o a d

Sizing Margins or

Making Batteries Bigger

• Aging Factor

25% Recommended

•

•

•

•

Applicable to:

All types of flooded lead acid

VRLA

Nickel Cadmium

• Exception is Plante`

Sizing Margins or

Making Batteries Bigger

• Low Temperature Correction

For operation below rated temperature

• High Temperature

Improves performance slightly

Not normally used in sizing calc’s.

Design margin for maximum life

Sizing Margins or

Making Batteries Bigger

• Design Margin

Normally considered for future equipment or load growth

Allows for operation at lower than expected temperature

Can cover for less than adequate maintenance

• Almost every sizing has one!

Sizing Margins or

Making Batteries Bigger

• If the calculation requires a 220 Ah

battery, and the next cell size up is 250 Ah

-• The 30 Ah difference is a 13% margin,

“designed” in

• An additional margin of 10% might not be

required

Knowledge is not

only Power

It’s Money

• Develop load profile using worst case

• Try to determine sequences

Not knowing requires conservatism

Conservatism can increase required capacity

Increased capacity - More $

• Closely review various sizing factors

Low temperature increases battery size

Aging factors are good ideas - ensure long reliable life

Evaluate design margins, especially after sizing a battery

Have we lost anyone

So far we’ve covered...

• Various discharge scenarios

Pick the worst case

• Various load types

Continuous

Non-Continuous

Momentary

• Sizing margins / factors

Temperature correction

Aging factor

Design margins

Sizing - What’s needed

• Load profile

Include all prudent margins

• Voltage

Maximum

Minimum

• Manufacturers data

Yes, you do need us

• Capacity rating - Kt factors

Amps per positive plate - Rt factors

• Battery type

Flooded lead acid

Nickel cadmium

VRLA

The load profile

15 BREAKERS

TRIP

- 10A, 5 CYCLES

Sim./Brkr

CLOSE

- 7A, 5 CYCLES

Seq./Brkr

SP. CHG - 4A, 6 SECONDS

TWO OPERATIONS,

Beginning and end of 8 hr duty cycle

2A CONTINUOUS LOAD

EMERGENCY LIGHTING LOAD

1200 Watts - 90 minutes

Starts at outage

Seq./Brkr

The load profile

Trip 15 Breaker

1 min. - Lead Acid

1 sec. - Ni-Cd

150 A

Trip Breakers at

End Of Cycle

Close & Spring

Charge Loads

Trip Load

1 min. - Lead Acid

92 sec. - Ni-Cd

?

7A

10A

Lighting Load

2A

Continuous - 8 HR

90 minutes

Load profile defined

•

Nickel Cadmium

162A

19A

12A

2A

152A

1 second

92 seconds

88.45 minutes

390 minutes

1 second

•

Lead Acid

162A

19A

12A

2A

152A

1 minute

1 minutes

88 minutes

389 minutes

1 minute

Voltage window

• Maximum and Minimum values

Determined by DC powered equipment

• Allow widest possible range

Uses maximum number of cells

• More cells = lower end of discharge

voltage

• More efficient capacity utilization

• Least expensive battery

Impact of voltage window

• IEEE 485 Example:

140V - 105V window

60 cells, to 1.75 VPC

- 1,010.4 Ah req'd

• Wider voltage window

62 cells, to 1.69 VPC

- 944 Ah req'd

3% increase cell qty, 7% capacity reduction

• Narrower voltage window

58 cells, to 1.81 VPC - 1,186 Ah req'd

3% decrease cell qty, 17% increase in capacity

• 100Ah High rate ni-cd cell

One minute rate To 1.14 VPC

One minute to 1.05 VPC

243 amps

406 amps

No. of cells calculation

Max. Volts - Determines number of cells that can be adequately

charged.

Equalize value is normally used as determining cell voltage

Ex

140V max

2.33VPC

or

140V max

1.46VPC

= 60 cells (lead acid)

= 96 cells (nickel cadmium)

End of discharge calculation

Min. Voltage - Lowest value system designed to operate at

Min. Volts

# of cells = End of discharge voltage / cell

Ex. 105 VDC

60 cells

= 1.75 VPC Lead Acid

Ex. 105 VDC

96 cells

= 1.09 VPC Nickel Cadmium

Sizing factors

• Kt factors

Based on performance per rated ampere hour

Kt factor = Rated ampere hours

Amps available for time t

• Rt factors

Based on performance per positive plate

Used primarily with lead acid cells

Rt factor = Amps available for time t per positive plate

Capacity rating factors

• Kt factors

Determined from tabular data

• Examples

160 Ah rated cell

8 hr discharge rate - 20 amperes

Kt = 160 Ah / 20 amps

8 Hr rate Kt = 8

• One minute discharge rate - 320 amperes

Kt =

160 Ah / 320 amps

One minute Kt = 0.5

• Kt factors are multipliers in IEEE

worksheets

Capacity rating factors

• Rt Factors

Found in plate performance curves

Not all manufacturers publish them

When not available, use Kt

• Rt factors are divisors in IEEE worksheets

Did you know this?

• Most lead acid model numbers indicate

number of plates per cell

3CC7 = Seven plates per cell

4JC11= Eleven plates per cell

• One more negative plate than positive

Seven plates = 4 Neg - 3 Pos

Eleven plates = 6 Neg - 5 Pos

• 50Ah / positive plate

150Ah cell from above example (3 pos x 50Ah)

250Ah cell for eleven plate cell (5 pos. x 50Ah)

• Positive plates are same for the range

More things you should know

• Ampere hour nomenclatures

Most nickel cadmium

Some VRLA

• Pos. plates are not identical thru range

• Wider or taller plate = higher capacity

• More plates per cell = higher capacity

Real life

• Create a duty cycle

• Periods

Amps__________ Duration_________

Amps__________ Duration_________

Amps__________ Duration_________

• Voltage window

Max__________

MIn__________

• Calculated No. of cells

Lead acid___

Nickel cadmium___

• Environment

High Temp_____

Lowest Temp_______

• Aging factor _______ (not for Plante')

• Design margins

_______

Summing up

•

Battery Sizing is a science

•

Building the load profile is an

art

Electro-chemistries vary

greatly

•

•

You have more control over

your battery selection than you

think

www.alcad.com

Thank you for

your attention

Alcad: presentation title

37