Solutions to #1 Problem with Standby Generators William Kaewert Stored Energy Systems LLC (SENS) billk@sens-usa.com
Standby Generator Purpose Provide electricity when grid fails How valuable is your insurance policy if the genset fails?
Genset Failures Which percentage best represents the rate of genset failure rate due to electric starting systems? A. 33% B. 39% C. 80% D. 82%
The #1 Reason The number one reason standby generators fail to start is due to dead starting batteries. Over 80% of all starting failures are from this cause. Source: Cummins Power Generation pub. F-1536, 2004
No Magic Bullet Solution Root cause: low cost, old technology batteries There s no app for that Starting systems remain relatively crude Fixing this problem demands understanding
5 Differences Genset-Car Starting Which suffers a greater rate of failure: Typical genset starting system A. Car B. Genset BATTERY HEATER CHARGER
Typical Smaller Genset Battery charger Alternator Battery
Storage Battery Basics Battery characteristics Lead-acid, nickel cadmium How battery differs from other genset systems Temperature effect on battery
Electrochemical Couple + - + - + - Nickel cadmium (Ni-Cd) battery: 1.2 volt / cell Lead-acid battery: 2.0 volt / cell
Battery Performance Limitations Why can it only deliver < 10% of its theoretical performance? If this battery were perfect it could deliver [102 AH * 120], or 12,240 amps for 30 sec. Internal resistance Ion diffusion speed limit
Two Mainstream Battery Types Key difference between Lead-acid & Ni-Cd Function of electrolyte Lead-acid Ni-Cd Active material on plate and in electrolyte Electrodes: one oxidizer and one reducer.
Cold Temp. Performance Loss 110 Available Capacity at Various Temperatures 100 90 Available Capacity (%) 80 70 60 Capacity loss when cold 50-40 -30-20 -10 0 10 20 30 40 50 60 S/PBE (Ni-Cd) PP (Ni-Cd) Pb-acid Temperature ( C) What could we do to counteract cold temp capacity loss?
High Temperature Life Loss
Lead-acid Battery Flat plate Spiral wound plate Advantages & Disadvantages
Lead-acid battery Plate Corrosion Original size of the positive plate End of life size of the original positive plate
Nickel Cadmium Battery Pocket plate Fiber plate Advantages Disadvantages Sintered PBE
Battery Choice Arguments Lead-acid vs. Nickel Cadmium Lead-acid Buy what s standard and replace regularly Ni-Cd Buy the best available technology Argument: Low capital cost; unbeatable MTTR, easy to buy However Pre-emptive replacement is necessary to avoid start failure Arguments: Lower risk of application failure. Lowest total life-cycle cost over 20 years However replacement cells not always readily available
Charging Basics How does a battery get recharged? Is there a right and a wrong way to recharge? Specifying battery charger requirements is easy once we understand what the battery needs.
Constant Voltage Charging Boost and Float Charge Modes 1 Battery accepts charge current Source Reservoir Source Reservoir Voltage Charging NOT POSSIBLE Consumer (load) Voltage Charging Consumer (load) 2 Battery s internal resistance affects charging Ideal battery Internal resistance
Correct Charging Voltage DO adjust per battery mfgr s instructions DO NOT depend on rules of thumb DO NOT assume you know more than the battery mfgr DO NOT wing it Read the battery instructions! Set the charger to the battery maker s recommended charge voltage!
Battery Makers Say Proper and adequate 1 charging is the single most important factor in obtaining optimum life from a battery. 2 For maximum service life float charge using a wellregulated constant voltage source with thermal compensation for the charge voltage. 3 1 Installation and Operating Instructions for Absolyte IIP Batteries 2 SBS Operation and Maintenance Manual 3 Battery Application Handbook for Cyclon & Genesis Sealed-Lead Products
Correct Charging Voltage +1% Charger Voltage Regulation Float volts per cell 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2 Charge voltage per cell vs. at room temperature AGM Ideal float voltage* OVERCHARGE REGION: Early failure due to electrolyte dryout. Faster grid corrosion UNDERCHARGE REGION: failure due to sulfation -30 0 20 40 60 80 Temperature Degrees C * This value shown for illustration only. NOTE: The charger must regulate to within +1% or better of the target voltage.
It Changes With Temperature Battery Temperature Compensation Float volts per cell 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2 Charge voltage per cell vs. temperature AGM Ideal float voltage* UNDERCHARGE REGION: failure due to sulfation OVERCHARGE REGION: Early failure due to electrolyte dryout. Faster grid corrosion -30 0 20 40 60 80 Temperature Degrees C * This value shown for illustration only. NOTE: The charger must regulate to within +1% or better of the target voltage.
Sensing Battery Temperature Remote Temperature Compensation What does this situation depict? What is the problem? How can it be fixed?
Battery Maintenance Raise awareness Help you to diagnose problems Not teaching maintenance specifics Different format from other sections
Prevention & Inspection Safety Electrolyte Connections Visual Heat Records
Take Aways 1. Improper charging & maintenance are the #1 problem w/gensets 2. Temperature affects battery life and performance 3. Lead-acid batteries can fail suddenly after only a short time 4. Ni-cd batteries resist abuse and do not fail suddenly 5. All batteries need to be charged accurately 6. The right charging voltage is what the battery maker specifies 7. Battery charging must be temperature compensated 6. Regular battery maintenance is essential
Solutions to #1 Problem with Standby Generators William Kaewert Stored Energy Systems LLC (SENS) billk@sens-usa.com