outwestbound
Member
I agree. I don't know anyone who uses a generator for the last 10% on any regular basis. I had a bad controller and no solar for about 4 months, so I hear what you're saying. It takes a crazy amount of generator fuel to get them full going all the way through absorption. Clearly, generators are most efficient at the bulk stage, as folks have said. When I didn't have my solar, I was doing what you say you're doing; rolling though campgrounds at least every 4-5 days just to top them off. I get down as much as 200AH regularly on an 800AH bank. My system is designed for a max DOD of about 25-30% of bank capacity because I full time and am in it for the long haul. I agree that battery monitors are essential for 1 battery or many. The beauty of solar for me, as a full time traveler, is that, depending on the weather, I can usually not run the generator (I only carry a Honda 2000) at all, or if necessary, just an hour or so in the am, then let solar bring the batts up to 100%, even while on the road.I neglected to indicate that my "strategy" is only used when shore power is not available, which is less than 50% of the time and never for more than 4-5 days at a time. Otherwise, traveling or shore power gets me to 100%.
Voltage alone is not nearly good enough to know the state-of-charge (SOC) of the batteries for the reason you mentioned (batteries at rest) plus SOC is very sensitive to voltage and to temperature. I have learned that a good battery monitor is essential for anyone who camps without shore power for more than a day. It also confirms my point that amps-in drops off rapidly as the SOC increases. Without a battery monitor, you really have no way of knowing the charging amps. IMO it's not worth running the generator once the SOC reaches about 80%. Plus 80% SOC easily gets me another day until the SOC reaches 50% again.
Anyone who does an energy balance on charging via generator (fuel consumption vs energy to the batteries) will find it very inefficient, but sometimes that's the only option.
I don't have (or want) solar, but that's another story.
P.S.My 2 Lifeline GPL-4CT batteries are more like $400 each, but have significant advantages over most other "deep discharge" batteries used in RVs.
I'm looking at a 23' class C for a year long trip to South America and will likely only have a 200AH bank due to space. I'm going to set it up with a large alternator for charging while driving, or if parked. I don't know if I can retrofit the technology, but I want to get the auto start feature that starts the engine/ alternator, if the battery bank (not engine starting battery) hits a certain low set point, during the night, then kills the vehicle engine once a certain time expires. The original OP would be well served by this strategy, if it can be fitted to existing vehicles. Hymer has this on their new vans (via Roadtreck acquisition) and maybe Winnegago puts this into their vans. This allows these manufacturers to delete the generator so save weight and space. I would carry my Honda 2000, in place of an existing Onan 3.6Kw from the Class C I'm looking at. I'll remove the AC for this trip, cuz there isn't shore power down there much, so the Onan isn't needed, and that weight is better applied to cargo.
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