Half Power Mode – Selected by shorting the Alternator NTC temperature sensor wires. Half-power mode may also be selected when engine RPMs fall below the threshold set via <Trigger Half-power RPMS> in the $SCT: commend below, or via the Feature-In (See $SCO: command below). In operation, De-rating values are applied to BOTH the Alt Amp Cap as well as the internal maximum field PWM drive. In this way, a smaller alternator is protected, even if the amp shunt is not connected. If a given Alt Derate values is set = 0.0 (0%), this will cause the alternator to be shut down and the regulator to enter a ready-idle state. Such a condition can be useful if deploying a DC-DC converter (See $CDD command on 60) by always powering the regulator and using half-power to select between when the engine is running or turned off, but in all cases allowing the DC-DC converter to be managed. When released from read-idle mode, the alternator will change to pre-ramp mode and do its normal startup process.
Note: When setting the ‘Alt Derate(x)’ values, make sure the ‘Normal’ derate value is as large or larger than any of the other two, else an internal error/hard fault may occur.
PBF: < INTEGER (-1 10)> Pull-back factor for reducing Field Drive at lower RPMs. If the WS500 Alternator Regulator is able to determine RPMs (via the Stator wire), the Alternator Field Drive will be reduced when the regulator detects the engine is at Idle. At idle the max PWM will be capped at around 1/4 of full field, which should result in some current bring produced. As RPMs are increased, this ‘Field Drive Capping’ will slowly be removed. PBF determines how quickly this pull-back is scaled off.
Set = 0 (DEFAULT) to disable this feature.
Set = -1 to cause Field Drive to be reduced to a maximum of 70% drive in the case where the WS500 Alternator Regulator is no longer able to measure RPMs via the Stator-in signal. This might be for example where an engine is operating at extremely low RPMs, below the cut-in point for the alternator. Or where the engine is no longer running. The 70% limit will only be enabled if at one time during operation the regulator was able to measure RPMs successfully.
If PBF is used, for many engine / alternator combinations a value of 1 will result in good operations. However, if you have installed a large alternator on a rather modest sized engine, you might notice the engine struggles when trying to increase RPMs from idle. In that case, increase the PBF value. A factor of 8x or so might be needed in the case of a small sail-boat engine with a large 150A or greater alternator (consider also using the Alt Amp Cap and/or System Watts Cap capabilities as well to restrict maximum engine loading at higher RPMs). If the engine has a large capacity relative to the alternator size, consider reducing the PBF to 1. Doing so will allow a greater production of amps while at idle, while at the same time preventing the alternator from being driven at Full Field during low RPMs (and hence low cooling) Finally, if your system matches an engine with great capability, and the alternator has good cooling / heat management – you can set the PBF factor = 0 to disable any capping of field drive while the engine is at idle. This will allow for maximum alternator output at idle, however if the regulator is enabled but the engine is not
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