Usage:
245 Excavators With OMS, All Caterpillar Machines With EMS
This article provides a comparison between the process required to activate the LOW VOLTAGE indicator on the Operating Monitoring System (OMS) and the process required to activate the ALTERNATOR indicator on the Electronic Monitoring System (EMS).
The ALTERNATOR indicator on the EMS is activated if the voltage, which is sampled from the alternator R terminal, is either low (approximately 10.0 volts), or the ripple is too great (open rectifier). If either of these threshold values are exceeded, the ALTERNATOR indicator light will flash. This can indicate that the 24 volt charging system is defective or out of specification.
The LOW VOLTAGE indicator on the OMS functions in a different manner. Instead of sampling the alternator R terminal voltage, the electrical system voltage is sampled. The electrical system voltage can be verified with a VOM. With the engine running, the VOM will indicate 27.5 ± 1 volts for a fully charged system. If the system voltage drops below approximately 22.5 ± .25 volts, the LOW VOLTAGE indicator light will flash. In addition, this system monitors a 5 amp fuse contained within the WARNING LAMP circuitry. See the schematic. If the fuse is open, this will also cause the LOW VOLTAGE indicator light to flash. If this occurs, the WARNING LAMP, which should flash when a Level II or Level III warning occurs, will be unable to do so.
However, there is a quick way to determine which situation caused the LOW VOLTAGE indicator light to flash. When the LOW VOLTAGE indicator light is flashing, shut the machine OFF, but leave the disconnect switch turned ON. If the WARNING LAMP is flashing then, the problem is within the 24 volt charging system. If the WARNING LAMP does not flash then, the problem is contained in the WARNING LAMP circuitry, which includes the 5A fuse.
Schematic of WARNING LIGHT circuit.