Recharging batteries: genset vs. chassis alternator

[jillhop]

Please bear with me--I'm new to the RV world (purchased my first RV this past summer). 🙂

I am planning a trip to Wisconsin this coming April where I will be dry camping in a hotel parking lot for 7 nights. This trip is for a dog event, and I will have access to the hotel for showers, etc, but no electrical hookups. The weather averages for the time I will be there is for low in the upper 30's, high in the upper 50's, so I am concerned about recharging my single 85AH battery after using the furnace overnight.

I've been doing some experiments to try to learn what it takes to recharge my battery here in the driveway. After fully charging the battery (12.83V) from shore power, I ran the furnace from 4pm to 8am the next morning. This depleted the battery to about 50% (12.11V). After 24 hours with the battery disconnected (no charging or use) the reading rebounded to 12.25V (about 60%).

I then ran the generator several times, taking readings 24 hours after each "run":

2 hours generator increased battery to 12.35V (70%)

Another 4 1/2 hours brought it up to 12.54V (~85%)

Another 3 1/2 hours brought it up to 12.75V (100% on my chart, but still not back to the original 12.83V charge from shore power).

So, that was 10 hours of generator use to bring the battery back to full charge from one night of furnace use. This was on a colder night (low 20's) than I'm likely to need on my trip, but still...

I'm wondering if running the truck engine (Ford V10) would charge the battery more quickly? I have been doing some research on solar, but I wouldn't be comfortable installing myself, so that would be a pretty big expenditure for me. While I do dry camp regularly, except for this trip doing so for more than 2-3 nights in one spot (without a day of driving in between) isn't likely to happen.

My coach has pretty much original equipment, so just a basic 1998 converter. I know from what I've read that I could benefit from a better converter, and probably adding a second battery would be helpful. But, if I don't have charging capacity to charge the single battery I have, I'm not sure how helpful that would be.

So, does my 7 nights of dry camping sound workable with the equipment I have now? I'm interested in any and all suggestions!

[jillhop]

Just posting an update. After playing around with the battery/charging scenarios all winter (while buried in snow here in New England), I decided to go with the Fullriver AGM battery that pnichols suggested. Went and bought it yesterday, and I'm leaving on my big boondocking trip on Friday. I'm pretty confident that this will work for me. Thanks again for all the advice.

[jillhop]

Thanks, pnichols! It sounds one of these will work for me, especially if I can purchase one locally. Much appreciated!!

[pnichols]

Here's the detailed link to Fullriver's Group 27 AGM deep cycle battery (DC105-12). Notice on the right hand side about 2/3 of the way down that it's recommended float voltages are the same - 13.6 volts to 13.8 volts. Also, for what it's worth, I believe that these batteries are Made in America:

http://www.fullriverdcbattery.com/battery/DC105-12

[jillhop]

I looked at that one when you posted it the other day--thanks, pnichols. It looks like the Group 31 is a little longer than my current Group 27--I'll have to look at the compartment/battery rack and see if this will fit.

I really appreciate the rational about the technical charging specs matching with the (crappy) converter I have now. That is something that I would not have checked/noticed, and makes good sense. I see that they have a dealer/distributer near me, so I will likely pursue with them. It also looks like Fullriver has a Group 27 AGM battery with 105 AH, so if fitting a Group 31 would be a problem, would that battery also be compatible with my current converter?

Thanks!!!!!

[pnichols]

Here's the Fullriver AGM battery I recommended:

http://www.fullriverdcbattery.com/battery/DC115-12

Notice that it has 115 amp hours of capacity ... which is very good capacity for a Group 31 AGM battery. It also weighs in at about 72 lbs. and many folks think that means there's a lot of lead in the battery -> which they consider as indicating good construction. The recommended float voltage (the voltage to be kept on them while the RV is in storage and also OK to be kept on them all the time when camping with hookups) for this AGM battery is 13.6 to 13.8 volts, which is exactly the output range of the standard converter in many RVs. This battery can also be charged up using this same voltage from the same converter - it just takes longer than a charger with a higher boost-voltage range - but not as long as a regular wet cell battery would take because AGM batteries charge faster at all voltages due to their lower internal resistance.

This battery is not an inexpensive AGM battery - but it's not the most pricey, either.

[jillhop]

Sorry that I haven't responded--was away at a dog show all day.

Mex has pretty much convinced me that my first step will be to get an AGM battery. That's a little painful, since I just bought the battery I have (Group 27 deep cycle) in August. Maybe I can sell it on Craigslist ... Everyone's comments have been very helpful, and I now feel better about being able to keep a charge on my battery using the generator and chassis motor.

There will be 20-30 RV's parked at the hotel for this event, at the far end of the parking lot from the rooms/ballroom where our event is held, so I don't think that it will be feasible to tap into hotel power. Running the generator for several hours a day won't be a problem--I expect all us RV'ers will be doing the same thing. I'm not comfortable sleeping with the generator running, so that's not an option.

My last overnight trip this fall involved spending the night on top of a mountain in upstate NY in a farmer's field. It snowed overnight, and there were 30mph winds (gusts to 50). I was fine running the furnace all night. My coach is pretty small, no slides, and I have pieces of that quilted foil insulation cut to cover all the windows that I put up once the sun goes down. The furnace did NOT have to run all the time to keep the coach nice and warm. I'm mostly worried about the cumulative effect of using the battery heavily without full recharging for 7 nights in a row, but you guys have convinced me that I will be OK (especially if I get a better battery).

I know that I should avoid Optima AGM batteries, and pnichols recommended a Fullriver battery as a good one. Any other suggestions on what to get or avoid?

Thanks again for all the great info!!

Jill

[DrewE]

pnichols wrote:

Mex wrote:
Ever see a voltage adjustment rheostat mounted on the dash?

Nope ... don't want to have one on my dash, either. I'd get into an accident because I'd be looking down to turn it all the time ... worst than texting for me. 😉

I have one on my motorhome. It only adjusts the voltage for the dashboard lights, but still....
:B

[pnichols]

Mex wrote:
Ever see a voltage adjustment rheostat mounted on the dash?

Nope ... don't want to have one on my dash, either. I'd get into an accident because I'd be looking down to turn it all the time ... worse than texting for me. 😉

I'm glad that Ford is somehow doing this for me now ... I wonder if they're using a computer controlled servo motor to turn a rheostat next to the alternator on my RV? :B

However, my buddy in high school once had a car where ya push/pull a doorknob on the end of a shaft sticking out of the dash to shift it's auto tranny.

[MEXICOWANDERER]

That's a good alternator and since Ford has resisted hiring escapees from an insane asylum from incorporating the voltage regulator into the ECU It makes for a great charging platform. My old Chevy tow vehicle had a 280 amp Leece-Neville charging trailer batteries. Ever see a voltage adjustment rheostat mounted on the dash?

[pnichols]

Over-nighting in hotel/motel/church parking lots and tent campsites are exactly the special situations where I would idle our V10 engine to partially charge the coach batteries. The idling V10 engine is far quieter than any generator ... almost as quiet as solar (;)) ... and we can do it when the sun isn't shining.

[MrWizard]

They guests won't even notice it unless they are outside
Coming and going is the only time they will hear it

[IDman]

If you will be in a hotel parking lot, I doubt if the hotel mgmt. and guests will be happy listening to your generator run!

[MEXICOWANDERER]

Here's a little post script. The new to me WFCO is a 55 ampere unit, right?

Voltage limited to 13.6 - 13.71 depending on what mood it's in...

Well it managed a 51 amperes charge rate into my group 31 AGM.

The OP's MAGNATEK is ALREADY set up to deliver 13.6 volts.

Purchasing a Looney Tunes smart charger to push 35 amperes into a flooded group 24 battery is a waste of money. It's going to be cold there. What do I have to do to get this point across?

An hour charging before bedtime and a group 31 AGM will provide capacity to live a normal lifestyle all night without recharging and without worry. The 31 can provide 80+ amp hours of capacity then accept a charge rate TWICE THAT of a flooded 24. Using his EXISTING charging devices.

[MEXICOWANDERER]

Voltage limited to CONSTANT 15.0 that group 24 will start out at around 35 amps charge rate then decrease rapidly from there. Expect to regain around 22-30 amp hours in an hour's charge time at an instant charging level of 15.0 volts. Know of any portable chargers that can start out and maintain 15.0 volts on a group 24 battery? If you do please let me know which one so I can buy one too. The OP is going to end up with the lifestyle of a Neaderthal trying to conserve precuis amp hours. IMHO this is silly. Even WITH the Magnatek an AGM will get more amp hours stuffed in it using the generator rather than the alternator. It is HIGHLY suggested that some time spent gaining hands-on experience versus theory be conducted. You might be surprised at what you'll discover...

[Greydennyhawk]

Our bass club rents rooms often from motel/hotels that do not have outside access to 15/20 amp plugs. We have never had problems running 100 ft outdoor cords from first floor ( or second floor ) rooms, to charge our boat batteries. Inquire with the management about a feasible parking spot where you could run the cord to power your furnace, lights etc. sometimes they charge us $5.00 or so more, but it's worth the hassle. Some decent managers actually place cones in areas to designate our parking areas!
Dogs rule!