[p]After spending several days camped in Acadia National Park and noticing all of the generators that were either misused or used unnecessarily, I thought I would write this and make it something of a tutorial. FWIW I have spend more than 20 years as a boat owner, three of which were living aboard full time. That experience makes me fairly cognizant of DC usage on a boat and by extension, an RV.[/p][p]
[/p][p]At the Acadia National Park, every morning at 8:00 (the official usage hour). 4-6 generators start up around me. That makes one out of every three RVs a daily generator user. They run for an hour or two and then shut down. They usually start up again by 5:00 or so and are obligated to shut down again by 7:00 PM.[/p][p]
[/p][p]When I walked around the campgrounds, one in three generators in usage were the Honda 1000 or 2000EU. The others were built in LPG units. Of the Hondas almost universally they were connected to the RV's batteries by the 12V outlet on the Honda. This is crazy.[/p][p]
[/p][p]That outlet is good for at best 10 amps at a nominal 12V or about 120 watts. That means the Honda 1000 is using 1/8 of its power capability and the 2000 is using 1/16. The right way to use that type of generator is to plug in the RV's 30 amp shore power cord so it can power the built in converter. Most converters are rated at 30 to 40 amps DC which means it will charge 3-4 times faster than the 12V outlet on the Honda. And that DC charging capacity should not tax the AC output capability of the Honda. 40 amps DC probably means about 6 amps AC (converters are notoriously inefficient) which is within the capability of the little Honda 1000. I won't go into the merits of RV converters. I suspect that they are not nearly as sophisticated as a marine three step battery charger. But neither is the 12V output on the Honda either.[/p][p]
[/p][p]But why are they charging batteries anyway? We stayed at one campsite for three days. When we arrived the single 70 amphour Group 24 battery on my 16TBS was full and by the time we left it was a little over half full. That means I used about 10 amphours each day. Now I don't have the Dometic frame heater on the model of refrigerator on my RV and if you do (it is the one with a separate freezer door) then your usage will double.[/p][p]
[/p][p]Unless I were camping for more than one week in a single site, then I wouldn't worry about charging. Yes over a full week I would probably run the battery down completely and that isn't good for them. But to do so once a year will result in a tolerable lost life- maybe you will get 100 charge/discharge cycles rather than 200+. Lead acid batteries will hold up best if not discharged below 50%.[/p][p]
[/p][p]So how do you recharge if you move around every few days. The TV's 7 pin connector has a terminal that is connected to your RV's battery. It will supply about 10 amps to the battery while the TV's engine is running. If I drive a couple of hours to my next camping site, my batteries should be topped off when I arrive if I have pulled them down 20 AH after two days of camping. Tomorrow we head home and it is 7-8 hours away. The battery should be fully charged by then.[/p][p]
[/p][p]How about solar panels? Well I have RV camped about a 100 days over the last 15 years and only twice did I end up in a campsite with sun. I like woods and shade and that doesn't work for solar panels.[/p][p]
[/p][p]There is something else you can do in a pinch to recharge your RV's battery. Make up a pig tail connector with a male 7 pin connector on one end and alligator clips on the other. Then you can remove the battery when you drive to hiking or site seeing spots and leave it in the trunk connected to the TV's power connector. This is a little tricky- if by chance you short the alligator clips you will blow the fuse on your TV, so it isn't for the faint or heart. Probably would be better with ring terminals so you could positively connect them. I have never done this, but I am certain it will work- if you drive long enough to your site seeing destination your battery will get recharged.[/p][p]
[/p][p]And that reminds me. Some TV's (Ford pickup trucks from the 2000 era for one) do not have the fuse installed from the factory to power the pin. You have to add one, usually a 30 amp, for the TV to supply power.[/p][p]
[/p][p]So what if you camp for more than 7 days at a time or you have the frame heater on your fridge. A second battery is a good investment. My 16TBS came with a frame for a battery box just big enough for a single Group 24 of about 70 AH capacity. But if I wanted to (and I don't because I never camp for enough consecutive days to matter) I would put two cross bars of aluminum angle across the tongue where the old single battery went and bolt it down to the outside tongue members. Make it wide enough to hold a dual battery box. The best bang for your buck is to use two 6V golf cart batteries wired in series to make 12V. This will give you 220 AHs, about triple the capacity of the single Group 24. With such a rig I could camp for 10 days consecutively and stay within the 50% mark or a full week if I were willing to go down to 30%.[/p][p]
[/p][p]What about lithium batteries you say. Well I have read a couple of articles about do it yourself LiFeO batteries (on boats) and it isn't for the faint of heart and it isn't cheap. There are commercial packagers who sell a full Li package of batteries, charger and electronic controls to keep it all together- Gensun for one, but it costs $2,000 for 100 amphours of capacity. Stick with golf cart batteries at 1/20 the price.[/p][p]
[/p][p]So there you have it. RV's are inherently easier to power with 12V without doing any recharging because the fridge is LPG powered unlike boats which use 12V DC. Live aboard cruising boats use 50-150 amphours each day and often have 500 amphours of battery capacity and 200-400 watts of solar to keep them charged. RVs don't need this. And they don't need to run their generator for 4 hours each day either.[/p][p]
[/p][p]David[/p][p]
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[quote source="/post/2813/thread" timestamp="1408563827" author="@david"][p]
[/p][p]Now I don't have the Dometic frame heater on the model of refrigerator on my RV and if you do (it is the one with a separate freezer door) then your usage will double.[/p][p]
[/p][p]David[/p][p]
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[/p][/quote][font size="3"]Not if you implement the TinkeringTechie/CharlieM heater disable mod :) Other than that, and excellent writeup. Noise avoiding neighbors will thank you.
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Without getting into to many "what if" scenarios I think this is a good point. I like the fact that you are trying to stay away from using the generator to charge the battery but I think you are making some assumptions when you are saying people shouldn't need to charge their batteries as often as you observed.
I run at least one if not 2 12v fans at night when I'm out and between 1 to 2 lights when needed. I think I recall the fan and lights draw 2.6 amps if I'm running both fans and lights at the same time. I don't recall the specific draw for just a single fan but if they run just 8 hours a night that can add up. To make the math easy lets say its 1.5 amps for the two fans over 8 hours. Thats 12 amps hours in just one night and if we are not wanting to draw a 70 amp hour battery below 50%, 12 amp hours is a third of the usable power right there. Lets add a couple of hours of light used at the end of the day so now we are up to 14 or 15 amp hours used in a single night. This is purely based on numbers I was able to pull up for the fan so I cant say definitively one way or the other on how accurate this is.
In that situation I could see myself wanting to recharge my battery each day and a generator would be the quickest option to do so. Now to your point about the gensets being hooked directly to the battery via the 12v connection. I'd be curious to see what the number come out to be when compared. On the surface it seems inefficient to take a generator that produces 12v that then runs to an inverter to give 120V AC, to then run to your shore line power unit, which then steps the AC back down to 12v DC.
The Honda EU2000 is rated at 13A for the 120v circuit which I don't know if I believe would be all that more effective after all the efficiency lost to the different systems. I'm just thinking about this quickly so perhaps I'm overlooking something but I'm not seeing the gains in using the shore line plus a converter to charge the battery over a direct DC connection.
Sean:
You are correct that different folks have different strokes to reverse an old saying. Some could use many more amp hours than we do, such as for your fans. For these campers a bigger battery bank is a cheaper and better solution than buying and running a generator once or twice a day.
So figure out how much you really use by checking your battery's specific gravity after a few days of use and charge accordingly and install a bigger battery bank if necessary. Very few campers do this. They just crank up the generator twice a day and often it is just making noise because the batteries are near full.
With a 220 amp hour battery bank, you should be able to go ten days without charging if you use 20 amp hours each day. So do you really need to run your generator every day? Or if you only have 70 amp hours like I do, do you need to run your generator for a weekend camping trip even if you draw 20 amp hours daily?
That was the main point of my posting- most generators just make noise and do little charging because the batteries are probably already charged enough. And even if they are needed the 12 V plug is a slow way to recharge.
To your other point about the efficiency of charging with the Honda's 12V output or with the converter. By efficiency I suspect that you mean how long it takes to put x amphours back into the battery, rather than the efficiency of burning gasoline to make power to run a generator to make 120V which then has to be converted to 12V in an RV's converter. A short answer to the latter is that running a Honday EU 2000 to make 10 amps at 12V at the charging plug is very inefficient. More load is almost always better for the efficiency of an engine.
I don't really know the exact answer to the former measure of efficiency- charging time, but I have a strong suspicion. I believe that the Honda's 12V output is a simple voltage regulated output that is regulated to about 13.5 V like your TV's alternator. The converter may or may not be better. Converter manufacturers never talk about three stage charging algorithms (bulk, acceptance and float) like marine charger manufacturer's do, so it impossible to know how effectively they charge. If an RV's converter were designed like a marine three stage charger, then it would be dramatically more efficient than a simple voltage regulated 10 amp output such as the Honda's.
To charge lead acid batteries fast you need to get the voltage up to 14.5 V or so at the latter stages of charging which is what marine chargers do. I have measured the voltage of my RV's converter and it never seems to reach that level.
But in any case 40 amp capability from the converter is better than 10 amps from the Honda's 12V connector even if the charging algorithms are the same. So please, use your shore power connector and charge your batteries with the converter. That should significantly reduce generator running time.
David