Skip to the main content.

Genset Starting Education Module #1

Introduction to Genset Electrical  Starting System Problems

William F Kaewert | SENS – Stored Energy Systems LLC 

Standby generators save lives and reduce financial losses 

The foundation technology of modern life is electric power. Indispensable to every infrastructure,  electricity enables fuel refining and transportation, communications, fresh and waste water treatment,  the financial system, manufacturing, health care, food production and more. 

Emergency and standby generators (gensets) exist to power these essential functions when the bulk  power grid fails. Gensets are frequently mandated by law1 to insure life safety applications such as health  care, or are specified by facility owners to avoid large financial losses. For example, the average cost of  data center downtime across multiple industries is $5,600 per minute and up to $1 million for a single  power outage at data centers delivering IT and networking services.

Introduction to, and problems with, genset electric start systems

Although the components of genset electric starting systems are just as vital to the function of a genset  as major systems elements such as engine, alternator and fuel system, they are considerably lower in  cost and tend to receive commensurately less attention from specifiers and end users. Batteries and  battery chargers, the key components of electric starting systems, are some of the last systems that many  OEMs consider covering under their factory warranty programs. The net result is that the quality and  reliability performance of electric starting systems continues to lag that of many other genset systems. 

Insufficient starting energy is the leading cause of genset failure 

Most of us have positive experience employing batteries to start engines. We do it every day when we  start our cars. Like the family car, most gensets depend on an electric storage battery to start the prime  mover.3 Unlike the family car, however, failure of a genset to start can mean loss of life or significant  financial losses. Failed starting batteries are the primary cause of genset failure. According to Cummins,  “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.”4 According to Caterpillar, “The greatest cause of inoperable standby  generator sets is lack of maintenance - usually discharged or dry batteries.”5 These powerful statements  suggest that making minor investment in one of the lowest cost genset systems has the potential to  deliver enormous gains in genset dependability.  

Why is genset starting less reliable than the family car? 

The above statements by genset makers seem at odds with our own almost always successful personal  experience starting our cars. Some probable causes for this dissonance are that: 

  1. Including National Electric Code Article 517 – Health Care Facilities, Life Safety Code - NFPA 101, and Standard for  Health Care Facilities – NFPA 99. 
  2. "Understanding the Cost of Data Center Downtime: An Analysis of the Financial Impact of Infrastructure  Vulnerability", Ponemon Institute, May 2011. 
  3. Gensets in specialty applications such as nuclear power plants are started by other means such as compressed air. 
  4. Cummins Power Generation publication F-1536, 2004. 
  5. Caterpillar genset installation/operation manual.
  • Gensets are used very differently from the family car and impose stresses on components  designed for cars beyond those which the component designer intended. For example, the “use  model” of car batteries is to charge them only intermittently versus 24/7 as is required of a  genset battery. 24/7 charging isn’t inherently bad, but the consequence of incorrect charging  settings is magnified many times for the genset battery because of the much greater time on  charge. This problem is accentuated when AGM/VRLA6 type lead-acid starting batteries are used  because there is no means to replenish electrolyte if they are overcharged. 
  • Car drivers often avoid failure to start by detecting and pre-emptively replacing weak batteries.  It is easy to sense deteriorating crank performance in a car driven frequently just by listening  during engine start. The “use model” of genset batteries, in contrast, is more severe. Gensets  operate infrequently, must start unattended, and offer either only crude sensors or no sensor at  all to detect deteriorating crank performance.  
  • Gensets are made in much lower volume than cars, and most do not enjoy the extensive system  testing under extreme conditions typical of most vehicle design verification tests. This is  particularly true with non-factory built gensets. The key to addressing this problem is giving adequate consideration to matching attributes of starting system components to the genset’s  environment, use condition and maintenance regime. These will all be discussed below. 

Genset batteries are used very differently from car batteries 

The battery of an average vehicle is charged by an engine-driven alternator about 500 hours per year.7 In  contrast, the battery on a genset is typically charged 8,760 hours/year8, or almost 18 times more  charging hours than your car. The effect of imprecise charging to genset batteries is thus about 18 times  more harmful than to your car battery. In an ideal world the battery would be less susceptible to charging  errors but, as will soon be discussed, the lead-acid battery is extremely sensitive. 

In addition to the amplified problem of charging accuracy, many gensets are equipped with additional  systems such as battery heaters, redundant batteries, battery charger alarm systems and other  equipment designed to improve starting system reliability. The addition of each additional system can  complicate the overall starting system in non-obvious ways so unless these subsystems are properly  specified and installed, addition can in some cases introduce new genset reliability problems. 

These SENS genset starting education modules provide additional data and solutions to engine starting  issues: 

  • Module #2 – Engine Start Battery Performance Characteristics is a brief primer discussing application issues related to applying batteries to start engines, including high rate discharge considerations, minimum allowable voltage, effects of cold temperature on battery performance  and battery life versus temperature. 
  • Module #3 – Solutions to Leading Causes of Battery Failure in Gensets explains why the leading  causes of battery failure are improper charging and lack of maintenance, and provides solutions to the problem.  
  • Module #4 – Genset Start Battery Strengths, Weaknesses and Use Strategies compares the  different characteristics and use strategies of two mainstream engine start battery technologies:  lead-acid and nickel-cadmium. 

AGM (Absorbed Glass Mat)/ VRLA (Valve Regulated Lead-Acid) water usage is about 1% the water usage of a  typical flooded type SLI (starting, lighting and ignition) battery but only when properly charged. 7 Assuming 15,000 miles traveled at an average speed of 30 mph.  

National Electric Code (NEC) Article 700 mandates the use of an automatic battery charger independent of the  generator’s charging alternator. This means around the clock, 365 days/year charging.

  • Module #5 – How to Specify a Genset Battery Charger identifies and explains battery charger  characteristics that are critical to success in genset applications. 
  • Module #6 – Battery Charging Basics briefly discusses how batteries get charged, why different  charging voltages of float and boost are necessary, and the pros and cons of different methods of  float/boost mode control. 

Summary of key points

  1. Gensets are essential to nonstop operation of mission-critical processes, and cost of genset  failure can be extremely high.  
  2. Problems with starting batteries are the #1 cause of failure in gensets. 
  3. Automotive batteries that are used in genset applications tend to perform less reliably than in  vehicles because genset batteries are used very differently from car batteries. 
  4. Although genset electric starting systems components are just as vital to the function of a genset  as major systems, they are considerably lower in cost and therefore receive considerably less  attention from specifiers and end users. 
  5. Minor investment in one of the lowest cost genset systems has the potential to deliver huge  gains in genset dependability.  
  6. Improving genset starting system reliability therefore represents a very large potential return on  investment.