Consulting-Specifying Engineer - November 2007 - (Page S9)

on-peakperformance Charger A Charger B + + - Do Not Use a Diode Splitter with an Alternator - Best Battery Selector Battery A + + Battery B - To Starters Alternator Diode Splitter Figure 5 - If an alternator is required to be connected into the system, the alternator should be connected directly to the battery it is charging, not connected through a diode. to the battery it is charging, not connected through a diode. If two alternators are used, Alternator A should be connected directly to Battery A, and Alternator B connected to directly to Battery B, with no diodes or cross connections used. Specifier considerations A BBS with sufficiently large diodes can provide significant value-added functions in an engine starting system, coupling good batteries and isolating a failed battery. Because there are no ideal diodes, there is always a power penalty in using a BBS. For engine starting systems that use a BBS: ■ A BBS rated for worst-case starting conditions must be chosen. ■ The installer must minimize voltage drops in cabling and wire terminations. ■ The battery capacity must be increased to deliver specified performance to EGSA standard or manufacturer-specified end voltage (whichever is higher) plus worst-case voltage drop across the BBS and additional voltage drop in extra starter circuit cabling. >>A BBS with sufficiently large diodes can provide significant value-added functions in an engine starting system, coupling good batteries, and isolating a failed battery. The specification should be for worst-case BBS voltage drop to be less than 1.15 volts total, with worst-case starting current flowing through only one diode. ■ The specification should be for 100% final test of BBS units, to include operation at full rated current. BBS for gensets up to 1 MW should be tested at 1,000 amps and BBS for larger gensets at 2,000 amps. ■ The alternators must be connected to assure system integrity and correct battery recharge. An alternator diode splitter should not be used. A BBS with sufficiently large diodes can provide significant value-added functions in an engine starting system—but designers must spec the system right. ■ november2007 9

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - November 2007

Consulting-Specifying Engineer Contents Editor's Viewpoint Letters In The News M/E Roundtable Emergency Power for Healthcare 2007 Products of the Year Industrial-strength Lighting Hazardous HVAC Codes and Standards Management Report Jobs/Classifieds Specifier's Notebook On-Peak Performance Contents Best Battery Selector in Engine Starting Applications NEC 708: Practical Impact on Backup Power Systems Protecting Power: Specifying Outdoor Generator Enclosures Investing in Backup Power Systems Coes, Consultants, Manufacturers, and Standby Power Systems

Consulting-Specifying Engineer - November 2007

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