Alternator Not Charging Chassis Battery
1996 Lazy Daze on a Chevy P30 chassis. I have an alternator that is not charging. The simple answer might be that it is the alternator but these Chevies have an "exciter" circuit that determines wh...
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On my motorhome's dash I have a voltmeter monitoring the coach battery bank and another voltmeter monitoring whatever is feeding the always hot stock cigarette lighter receptacle on the dash - I assume that the dash receptacle directly tracks the engine battery voltage because it's always hot. I also have an ammeter on the dash monitoring current into and out-of the coach battery bank (two 115 amp hour 12V deep cycle AGMs).
Both voltmeters read within around 0.01 to 0.04 volts of each other all the time (if the automatic coach/engine battery interconnect solenoid is actuating fully and if it's contacts are in good condition). Both meters read well above 14 volts when the engine is started whether we start down the road or merely sit with the engine idling. Both meters show a gradual decline in voltage as the engine heats up, ending up averaging in the mid-13 volt range as we travel in moderate outside ambient temperatures. Both meters decline lower than the mid-13 volt range as we travel in high outside ambient temperatures. I've seen readings as low as 12.9X volts on both meters with a hot engine while traveling in scorching summer temperatures. I've seen the ammeter spike as high as 70 amps with 50% discharged coach batteries when the engine is idling. As the generator runs long enough, or the engine idles long enough, or we travel for 3-4 hours, the ammeter declines to show zero current flow - indicating that the coach batteries are fully charged.
Either the Ford alternator regulator or some Winnebago-installed device seems to be acting exactly as it should in caring for our coach batteries under all conditions. Again, there is no voltage difference to speak of (including isolation diode voltage drops) between the two voltmeter readings, so whenever the ignition key is on the coach batteries and engine battery seem to be all hooked together in direct parallel with each other.
For what it's worth for information, the link below shows the atlernator performance curves for three different size alternators as used in Ford vans back in 2005. Note that the alternator speeds (rpms) shown, are alternator shaft speeds ... not engine speeds. For our chassis, the alternator shaft is over-driven by a ratio of 2.72:1 times faster than engine rpm. Take some typical alternator shaft speed of say, 2000 rpm, and then compare the current output capability of the 120 amp (page 7), 140 amp (page 7), and 130 amp (page 6) Ford alternators. The difference in output current capabilities - at whatever the batteries will accept at whatever voltage the voltage regulator sets in any particular set of conditions - in my opinion is enough to make it a good practice to always install as large an RV alternator as will fit and one can afford:
https://www.fleet.ford.com/truckbbas/non-html/2005/vs_pdf/05elect.pdf
Both voltmeters read within around 0.01 to 0.04 volts of each other all the time (if the automatic coach/engine battery interconnect solenoid is actuating fully and if it's contacts are in good condition). Both meters read well above 14 volts when the engine is started whether we start down the road or merely sit with the engine idling. Both meters show a gradual decline in voltage as the engine heats up, ending up averaging in the mid-13 volt range as we travel in moderate outside ambient temperatures. Both meters decline lower than the mid-13 volt range as we travel in high outside ambient temperatures. I've seen readings as low as 12.9X volts on both meters with a hot engine while traveling in scorching summer temperatures. I've seen the ammeter spike as high as 70 amps with 50% discharged coach batteries when the engine is idling. As the generator runs long enough, or the engine idles long enough, or we travel for 3-4 hours, the ammeter declines to show zero current flow - indicating that the coach batteries are fully charged.
Either the Ford alternator regulator or some Winnebago-installed device seems to be acting exactly as it should in caring for our coach batteries under all conditions. Again, there is no voltage difference to speak of (including isolation diode voltage drops) between the two voltmeter readings, so whenever the ignition key is on the coach batteries and engine battery seem to be all hooked together in direct parallel with each other.
For what it's worth for information, the link below shows the atlernator performance curves for three different size alternators as used in Ford vans back in 2005. Note that the alternator speeds (rpms) shown, are alternator shaft speeds ... not engine speeds. For our chassis, the alternator shaft is over-driven by a ratio of 2.72:1 times faster than engine rpm. Take some typical alternator shaft speed of say, 2000 rpm, and then compare the current output capability of the 120 amp (page 7), 140 amp (page 7), and 130 amp (page 6) Ford alternators. The difference in output current capabilities - at whatever the batteries will accept at whatever voltage the voltage regulator sets in any particular set of conditions - in my opinion is enough to make it a good practice to always install as large an RV alternator as will fit and one can afford:
https://www.fleet.ford.com/truckbbas/non-html/2005/vs_pdf/05elect.pdf
