Battery Charging Question
I have been running my Cummins/Onan 4000 generator to charge the batteries on my coach a couple of hours a day when boondocking; is there any advantage to using the motor on my motorhome to do the sam...
Forum Discussion
Some of the above discussion is the opposite of how we have been camping with our Class C motorhome now for about 9 years.
I just traded in a set of two 12 volt 100 amp hour Group 29 AGM deep cycle batteries that were around 8 1/2 years old and still had life left in them. I replaced them a couple of weeks ago with a couple of 12 volt 115 amp hour Group 31 AGM deep cycle batteries.
My coach batteries see weeks and weeks on the stock single stage converter at home for storage maintenance (the specified float voltage for the batteries is 13.6 - 13.8 volts). When camping, the batteries are charged for a few hours by the converter powered by the Onan or a small portable generator we carry along. Sometimes we idle the V10 first for up to an hour to hit the batteries with 14.XX volts and dump 25-35 amp hours into them before shutting down the V10 - and then finish bringing the batteries up to around 90% state of charge with the converter powered by the Onan or portable generator. We can do this several times on a long dry camping trip without battery damage because between dry campsites we may drive for several hours, during which the alternator will completely charge the batteries. I monitor all this with a coach battery voltmeter and ammeter mounted right on the cab dash. Amps going into the coach batteries from the alternator tapers to zero after around 4-5 hours of driving.
Our 130 amp alternator can deliver 60-70 amps with the V10 at idle, per the alternator's performance curve as published by Ford ... so it can deliver 30-35 amps into the coach batteries easily during about 1 hour of idling before I switch over to Onan or portable generator charging via the 13.6 volt stock converter. Nowhere on the 130 amp alternator's performance curve or footnotes does it say anything about the alternator not being rated for continuous use. Ford V10 powered vehicles sometimes idle the engine for long periods at incidence sites. Folks with scan gauges in these forums have reported the V10 as consuming about 0.7 gallons per hour when idling. It costs a little more, but I use only Mobil 1 EP (Extended Performance) synthetic oil in the V10.
Per the 4000 watt Onan specifications, I estimate it consumes only about 1 gallon of gasoline per 2 1/2 hours of runtime when powering the coach's air conditioner - so it consumes even less fuel when merely charging the coach batteries through the converter. Even though the Onan runs at a constant RPM, it's rate of fuel consumption depends primarily on the load on it, so this has to be taken into account when viewing it's fuel consumption rate as shown in it's specification - which is at a specific load. An RV converter charging coach batteries at 30-40 amps at 13.6 volts is only around a 1/5 load on a 4000 watt Onan. Using a multi-stage charger - which puts 14.XX volts on the batteries during boost stage charging - loads the Onan only slightly more. I use Mobil 1 EP synthetic oil in the Onan. When using the portable generator to power the converter for battery charging it consumes about 1/2 gallon of gasoline every 5 hours. The oil in it is Mobil 1 synthetic also.
The above procedures work fine for our style of a few days here, and few days there, of drycamping. It works under any condtions - no solar panels or sun required - shade or clouds is just fine. However, for extended drycamping days or weeks on end out in the sun - solar should be added into the mix ... although even then I would also make sure the RV had good generator powered battery charging capability on board because I no longer expect Mother Nature to act as she used to.
I just traded in a set of two 12 volt 100 amp hour Group 29 AGM deep cycle batteries that were around 8 1/2 years old and still had life left in them. I replaced them a couple of weeks ago with a couple of 12 volt 115 amp hour Group 31 AGM deep cycle batteries.
My coach batteries see weeks and weeks on the stock single stage converter at home for storage maintenance (the specified float voltage for the batteries is 13.6 - 13.8 volts). When camping, the batteries are charged for a few hours by the converter powered by the Onan or a small portable generator we carry along. Sometimes we idle the V10 first for up to an hour to hit the batteries with 14.XX volts and dump 25-35 amp hours into them before shutting down the V10 - and then finish bringing the batteries up to around 90% state of charge with the converter powered by the Onan or portable generator. We can do this several times on a long dry camping trip without battery damage because between dry campsites we may drive for several hours, during which the alternator will completely charge the batteries. I monitor all this with a coach battery voltmeter and ammeter mounted right on the cab dash. Amps going into the coach batteries from the alternator tapers to zero after around 4-5 hours of driving.
Our 130 amp alternator can deliver 60-70 amps with the V10 at idle, per the alternator's performance curve as published by Ford ... so it can deliver 30-35 amps into the coach batteries easily during about 1 hour of idling before I switch over to Onan or portable generator charging via the 13.6 volt stock converter. Nowhere on the 130 amp alternator's performance curve or footnotes does it say anything about the alternator not being rated for continuous use. Ford V10 powered vehicles sometimes idle the engine for long periods at incidence sites. Folks with scan gauges in these forums have reported the V10 as consuming about 0.7 gallons per hour when idling. It costs a little more, but I use only Mobil 1 EP (Extended Performance) synthetic oil in the V10.
Per the 4000 watt Onan specifications, I estimate it consumes only about 1 gallon of gasoline per 2 1/2 hours of runtime when powering the coach's air conditioner - so it consumes even less fuel when merely charging the coach batteries through the converter. Even though the Onan runs at a constant RPM, it's rate of fuel consumption depends primarily on the load on it, so this has to be taken into account when viewing it's fuel consumption rate as shown in it's specification - which is at a specific load. An RV converter charging coach batteries at 30-40 amps at 13.6 volts is only around a 1/5 load on a 4000 watt Onan. Using a multi-stage charger - which puts 14.XX volts on the batteries during boost stage charging - loads the Onan only slightly more. I use Mobil 1 EP synthetic oil in the Onan. When using the portable generator to power the converter for battery charging it consumes about 1/2 gallon of gasoline every 5 hours. The oil in it is Mobil 1 synthetic also.
The above procedures work fine for our style of a few days here, and few days there, of drycamping. It works under any condtions - no solar panels or sun required - shade or clouds is just fine. However, for extended drycamping days or weeks on end out in the sun - solar should be added into the mix ... although even then I would also make sure the RV had good generator powered battery charging capability on board because I no longer expect Mother Nature to act as she used to.
