LOW IDLE ENGINE SPEEDS AFFECTING ALTERNATOR CHARGING PERFORMANCE Caterpillar

LOW IDLE ENGINE SPEEDS AFFECTING ALTERNATOR CHARGING PERFORMANCE

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LOW IDLE ENGINE SPEEDS AFFECTING ALTERNATOR CHARGING PERFORMANCE

CONFIDENTIAL TIBU3790-00

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TECHNICAL INFORMATION BULLETIN	February 12, 2003
PRODUCT FAMILY(S)	SALES MODEL (2KS)
	Component Code(s) 1205 1405 1425

SUBJECT: Low idle engine speeds affecting alternator charging performance

PROBLEM:

Alternator speeds may be to low too charge the batteries of the vehicle when the engine low idle is set to 600 rpm.

SOLUTION:

When investigation the charging performance of an alternator consider the engine idle speed during operation. Programming the engine low idle speed on EUI engines is very flexible, and this may cause the alternator to be rotating below its normal operating range. The operating range for the Caterpillar 9X-7803 alternator is 2300 rpm to 8000 rpm. To obtain a desirable low idle speed for the alternator the engine idle should be set to 700 rom. If there is a change in the crankshaft pulley diameter, a change should also be made to the alternator to keep the alternator within its desired operating range. The following chart is a selection of alternator pulley arrangements, and crankshaft pulleys to obtain the desired alternator rotation speed.

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Alternator and crankshaft pulley arrangements
Alternator Pulley	Crankshaft Pulley	Alternator drive ratio
117-0177 68.5mm (2.69in) diameter with 8 groove for K rib belt.	116-5444 228.5mm (9in) diameter with 8 groove for K rib belt.	3.34 x engine speed
123-0789 57mm (2.24in) diameter with 8 groove for K rib belt.	117-2795 190.5 mm (7.5in) diameter with 8 groove for K rib belt.	3.34 x engine speed
138-2516 82mm (3.23in) diameter with 8 groove for K rib belt.	116-5444 228.5mm (9in) diameter with 8 groove for K rib belt.	2.8 x engine speed

The Caterpillar 9X-7803 alternator output at 2300 rpm will be 1/3 of rated output, and if the vehicle?s electrical power requirements are above this, battery life will be limited.

In some instances the alternator is driven from the fan pulley rather than the engine crankshaft pulley, in these cases the fan speed ratio to crankshaft is needed to calculated the alternator?s speed.

COPYRIGHT 2003 CATERPILLAR
ALL RIGHTS RESERVED

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