# Battery Charger Efficiency

Issues with Marine and Recreational Vehicle Battery Chargers

## Marine and RV battery chargers differ from power
t ool and small appliance chargers

CEC 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.Cordless Drill Battery Toothbrush Battery Marine Battery 

# Consumer Electronics vs. Marine Batteries

Cell Phone Battery

# Marine Battery Banks don’t look like power tools!

# Marine and RV Chargers D iffer from Automotive Chargers

• The core strategy in the CEC standard is to shut down the charger when “charge is complete,” but this conflicts with what is needed for “whole

- house” loads (Refrigerators, CO/fire alarm systems, bilge pumps).

• Chargers function as converters/power supplies for active loads

 Power is supplied directly to DC loads when AC power is available
 “Float Mode” is continued in order support the loads, which is more efficient than discharging and recharging the batteries.
 Keeping batteries fully charged and providing power supply to bilge pump and alarm systems is a safety concern in marine applications

# Typical Loads also served during charging

# Testing to CEC is possible, but deceptive

• Batteries must be carefully chosen to tolerate rapid discharge effectively.

 Don’t generally represent what is used in the field

• Battery sizes may be limited to what generates best test results

 Need small enough battery banks to avoid slow tail of charge curve in last four hours of 24 hours
 Need to use large enough battery banks so that the charge rate is in the efficient part of charge curves
 These battery sizes may promote less overall charging efficiency in actual use.

• Chargers are permitted to be modified to have a distinct test mode, but are automatically superseded in use when loads are present.

# Lead Acid Batteries are Poor Test Instruments Tests are difficult and non

- repeatable

• Battery characteristics are not stationary. Initial cycling of new batteries may improve performance, and additional cycling may degrade it.

• Batteries may have more or less amp

- hour capacity than their stated nominal capacity at the time of test.

• Capacity at the 5 hour discharge rate is not readily predicted from the rating at 20 (C20) hour discharge rate used in the industry.

• The rate of discharge that results in matching the discharge time window may take several repetitions to find.