# DOE Test Methodology for Battery Chargers

Issues with testing using lead acid batteries

## Marine and RV battery chargers differ from power t ool and small appliance chargers
DOE Testing assumes all variables are known

– battery chemistry, battery size. T his is not the case in Marine and RV applications.

• The battery charger manufacturer has no influence on the selection of batteries.

• The battery charger could be used to charge a single battery, single battery bank, multiple batteries or multiple battery banks

• The dominant batteries in these applications are Lead Acid  Lead Acid batteries are designed and rated for slower discharge rates than the test methodology in the standard (Less efficient at rapid discharge rates).  Few Lead Acid batteries are designed for full discharge, and those are typically less efficient at rapid discharge.  Charge and discharge rates have a profound impact on measurable capacity.  Final charge can be a slow process (Limited by diffusion of fluids in porous materials) which results in active charging while the test is supposed to be in a float/maintenance mode.

# Test Method should be modified to reduce errors introduced by Lead Acid Batteries

• Lead Acid batteries are sensitive to charge/discharge history

• Batteries “as received” will have received different care between manufacture, transport, storage and delivery. Seldom arrive fully charged.



### • Lead Acid batteries are designed and rated for slower rates of discharge than in the DOE test. Typical ratings are for discharge over 20 hours.

• Faster discharge leads to less predictable energy recovery

• Rapid discharge results in lower efficiency than targeted in real applications



### • Lead Acid batteries can have a very long, slow final charging period

• What is measured under DOE test protocol may include active charging as well as maintenance current. This distorts the maintenance data.

# Optional Battery Preconditioning

• Instead of making the standard condition “as received,” allow optional preconditioning to full charge under controlled conditions on site.

• Such preconditioning can include multiple cycles of charge and discharge, including use in prior tests of the Equipment Under Test or in other tests, up to the useful life of the battery.

• If reused for multiple tests, battery use should be discontinued if it shows signs of aging such as loss of capacity, higher impedance or higher maintenance current.

• Laboratories should set their own quality control to determine fitness of batteries.

# Optionally, allow longer discharge rates for lead acid batteries.

• Batteries are rated for discharge over 20 hour period

• Battery efficiency is degraded significantly at faster discharge rates

• Best practices in the marine industry recommend battery bank sizes for “house batteries” to able to handle loads for 24

- 48 hours with a discharge from about 85% SOC to 45% SOC. (only using 40% of battery capacity)

• 40% in 24 hours = average discharge rate of C/60 average

• 40% in 40 hours = average discharge rate of C/100

# Lower Discharge Rates are Superior

• More repeatable and accurate results

• Less energy can be extracted at high discharge rates

• How much less depends on an exponential function whose result is difficult to predict. ( Puekert’s equation describes phenomenon, but exponent is battery specific and hard to obtain or measure.)

• 5 hour discharge determines a significantly lower Ebatt figure than should be achieved in real applications.

# Charge and Discharge Curves Data from Home Power

– 1989 Typical curves for charge and discharge of Lead Acid Flooded Golf Car batteries used in off grid installations.

Notice 1. Charging at high rates requires elevated voltage. 2. Discharging at high rates causes considerable voltage drop. 3. Difference between charge curves and discharge curves is a loss in efficiency caused by the battery itself. 4. Nothing in charger design can alter the battery characteristics. 5. Choosing battery sizes to allow low relative rates of discharge can improve efficiency of the system.

# Discharge Efficiency

• Average Loss for flooded lead acid batteries with total discharge at C/5 is 7.35%*

• Average Loss for flooded lead acid batteries with total discharge at C/20 is 1.8%

• Average Loss for same flooded lead acid batteries with partial discharges at C/40 estimated to be 1%

- emulating application.

• Differences between C/20 and C/30 estimated to be less than 1% difference, reducing sensitivity to actual rate during test.

• Could simplify testing by eliminating repeated testing to hit a narrow time window.0 2 4 6 8 10 12 14 16

0 20 40 60 80 100 120% Loss During Discharge

State of Charge Battery Discharge Losses at Different Rates

C/100 C/20 C/10 C/5 C/3 C/5 Discharge has 7.4% Loss

Partial Discharge C/20 has 1.3% loss Partial Discharge C/100 has 0.8% loss

Based on data from Richard Perez in Home Power

- Aug. 1993

# Maintenance condition may not be obtained in 19

- 24th hours of charge cycle

• Unlike many other batteries, Lead Acid charging cycles can have a long, slow tail to final full charge

• Rates are limited by diffusion into porous material and equalization of acid density



### • If active charging current is still flowing, and not just the self discharge replacement current, we will overstate the maintenance mode power.

• We have observed the phenomenon in the lab, but do not have a complete study to characterize it.

• Simple test to extend the test until the current into the battery is stable and reaches an equilibrium.. That might be more like 48 hours.

# Extend test to determine Maintenance Mode

• Should be able to characterize phenomenon with a little dedicated lab work.

• Some data to be available by end of the month



### • Tentative solution:

• Extend test duration to point that maintenance mode power can be determined, probably 40

- 48 hours.

# Summary of Recommended Changes to DOE Test Methodology, options for Lead Acid Batteries

• Generally same instrumentation and test sequence.

• Allow Preconditioning at T ester and Charger Manufacturer’s option.

• Extend Discharge time to target to 20 to 24 hour window, at option.

• Extend duration of test charge cycle till charging amperage is stable

• Existing methodology is optional on these points if test batteries allow for adequate testing under existing standard.