Kohler 20--2800 kW manual Electrical Requirements, Batteries

Section 7 Electrical Requirements

Before installing the generator set, provide for electrical connections through conduit to the transfer switch and other accessories for the generator set. Carefully install the selected generator set accessories. Route wiring to the generator set through flexible connections. Comply with all applicable codes when installing a wiring system.

AC circuit protection. All AC circuits must include circuit breaker or fuse protection. Select a circuit breaker for up to 125% of the rated generator set output current. The circuit breaker must open all ungrounded connectors. The circuit breaker or fuse must be mounted within 7.6 m (25 feet) of the alternator output terminals.

7.1 Batteries

Batteries should be located in a clean, dry area. Position them so that the caps are readily accessible for checking the electrolyte level. Keep batteries out of areas subject to high temperatures. Locate them close to the set to keep cables short and thus insure maximum output. Several types of battery racks are used throughout the product line—be sure to refer to the submittal drawings for your unit. Figure 7-1 shows a typical battery system.

Starting batteries are usually lead-acid type sized according to the engine manufacturer’s recommendation for a particular ambient temperature and required cranking time. Recommended cranking periods are specified in NFPA 110. It allows a single 45-second cranking cycle for generator sets below

20kW. For larger models, three 15-second crank cycles separated by 15-second rests are required. The battery industry rating standard most commonly used to specify batteries is the cold-cranking ampere rating. Refer to the unit’s specification sheet for battery cold-cranking ampere rating.

Nickel cadmium batteries are sometimes used for standby generator sets because of their long life (20 years). This is offset by their high initial cost, larger space requirements, and special charging requirements. Conventional lead-acid batteries have proven satisfactory for the majority of generator set applications.

Batteries are charged by engine-driven, battery charging alternators whenever the generator set operates. These systems are normally capable of charge rates of 30 amperes or more and can restore the charge used in a normal cranking cycle within a short

period of operation. When the engine is not operating, a very low charge rate from an AC-powered battery charger is sufficient to maintain the batteries fully charged. These chargers may be automatic or manual with a high charge rate of 2 amperes and a trickle charge rate up to 300 milliamperes. They can be separate, self-contained units or built into the automatic transfer switch. Due to the low maximum charge rate, they are not well suited to restoring fully discharged batteries. Automatic float chargers with high charge rates of 10 amperes or more are available if full recovery capability independent of the engine-driven charging system is required.

The most common reason for the failure of an emergency generator set to start when needed is starting battery failure. Two common causes of battery failure are: a manual charge rate set too low to maintain the battery, or a manual chase rate set too high, which results in loss of battery electrolyte. For this reason, automatic float chargers, which vary the charge rate in response to battery condition, are strongly recommended over manual types.

For large engines using two starters, either one bank of batteries and chargers for both starters, or separate battery systems may be used. The latter system is preferable since it reduces the chance of one component’s failure making the entire system inoperative.

Battery cables. A UL-2200 listed generator set requires battery cables with positive (+) lead boots. Factory-supplied and optional battery cables include positive (+) lead boots. When battery cables are not factory-supplied, source battery cables with positive (+) lead boots for UL-2200 compliance.

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	TP-5700-7
1.	Battery cables
2.	Battery secured in mounting rack
3.	End view
4.	Generator set skid

Figure 7-1 Typical Battery System, Side View

TP-5700 7/93 Section 7 Electrical Requirements 35