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Old 09-05-2006, 10:48 AM   #15
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Originally Posted by Darrell Root
Lewster, does the same hold true for walmart deep cycle 6 volt wired in series ,just not as lng lasting. Also Walmart deep cycles are about 1/3 the cost of glass matt makeing the cost about the same , Darrell
Darrell,

I'm not sure about the ratings of the WM golf cart batteries, but in general, this type of battery is made with much heavier plates that translate to higher amp/hour capacities and more charge/discharge cycles. You still have to be religious about keeping the electrolyte at the proper level.
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Old 09-05-2006, 11:07 AM   #16
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Hmm, I'm building a generator shack. I couldn't stuff a lot, or even two of those 6 volt batteries in my trailer battery compartment, but I could stuff a lot of those batteries the shack (even 4 of them in a series/parallel combination). Then I could run some heavy gauge (3 or 6) wire from the shack buried underground to my trailer. My Honda 3000i generator is already setup to charge 12 volt batteries, which would be right next to the generator. What do you guys think?
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Old 09-05-2006, 11:13 AM   #17
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Great idea if you want to stay off-grid for a while. I have a golf cart in FL (no, I don't play golf) that the wife uses for running the dog around. It has a new set of 6 Lifelines in it ($$$$ ouch!) and it gets recharged about 1/2 the time we used to do with the older wet cells.
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Old 09-05-2006, 11:19 AM   #18
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A furnace runs at about 8 amps. A typical group 27 sized battery can provide about 50 amp hours before needing recharging or 100 amp hours to totally flat. That means you can run your furnace for a total of about 6 hours before it needs a recharge or 12 hours to totally flat. A two battery system will double these times.

Whether you are running 6v series or 12v parallel won't make much difference. Going group 31 size ups the time just a tad and a group 24 is a bit more limited and AGM's will take more abuse and charge faster but won't really make much difference as far as capacity - again, these are not really at issue in the overall scheme of things.

It is not hard to get 10 hours or more on a furnace over three nights. That's only a 30% duty cycle. And that doesn't consider other pulls on the battery like water pump, lights, alarms, and other stuff.

A good rule of thumb is to get enough battery to last you 2 nights and three days for the kind of camping you do. If you do cool weather camping in a trailer, this is likely to be 2 batteries (about 200 amp hour @ 12v). For cold weather camping you often have to have more than batteries and you'll need more propane capacity, too.

And, anticipating the numbers nerds - give it a break. I am talking a practical +/- 15% or more here. When it comes to keeping warm overnight, the difference (80 AH vs 110AH) between a group 24 vs group 31 is a second order issue. This kind of difference is well within the normal variability of overnight temp and user inside thermostat preferences. Yes bigger batteries provide additional reserve. Yes more rugged batteries (e.g. AGM) will take more abuse. The parallel vs serial 'debate' is fun - But there are practical limits, cost vs benefit concerns, and other factors that tend to need first consideration.

Three nights of furnace running is going to take a lot of battery no matter what way you cut it.
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Old 09-05-2006, 11:59 AM   #19
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Originally Posted by Leipper
...Three nights of furnace running is going to take a lot of battery no matter what way you cut it.
yep. seems to me, a catalytic heater is the way to go when boondocking. I'd only run a furnace on shore power.
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Old 09-05-2006, 12:53 PM   #20
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I wasn't talking about 3 straight nights without a charge. I was charging the battery using a the univolt and a generator for plenty of hours during the day. Seems to be it should power the furnace one night after being fully charged.
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Old 09-05-2006, 01:52 PM   #21
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.... Seems to be it should power the furnace one night after being fully charged.
yeah, seems it should...but it don't. I've heard it said from more than one person, that running the furnace over night = dead battery in the morning. Makes me wonder why they even made them to run on 12v. I guess you can run it for a couple of hours, or while driving down the road, etc. Or if you have more battery capacity than "standard".
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Old 09-05-2006, 02:24 PM   #22
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If the furnace draws 8 amps and I estimate it was running at 1/2 duty cycle max, and my current battery is rated for over 100 amp/hours, then I would expect it would only burn 5*10=50 amp/hours during a 10 hour night. When I first bought this battery it ran the furnace overnight and showed almost a full charge in the morning after a 40 degree night. Perhaps if I just buy the GPL-27T I'd be all set assuming it fits into the battery compartment.

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Old 09-05-2006, 10:49 PM   #23
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Wacnstac,
100 amp hours is rated energy output probably at the 20 hour rate which also defined terminal that voltage will fall to about 9 volts after this 5 amp load for 20 hours (if I remember ABA specs correctly) assuming starting with a new fully charged battery. To obtain maximum battery life most makes say not to discharge below 50% capacity. The 20 hour rating does not mean you can pull 10 amps for 10 hours; maybe you could pull 10 amps for six to eight hours or so before reaching 9 volts . Another issue is ratings are based on automotive standards for starting duty batteries, not for true deep cycle discharge batteries. Consult your battery manufacturer's web site for more in depth data. One of the better resources is at the lifeline (Concorde) site: http://www.lifelinebatteries.com/rv.php
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Old 09-05-2006, 11:48 PM   #24
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i've boondocked for years using the furnace.

mild falls or spring nights and dead of winter.

even in spring/fall the central heating is so much more effective than a cat or heatpump...

my batteries are nearly full just from solar on all but the over cast/rainy days...

in colder temps when the furnace runs most of the day...

a catalytic heater helps...and will reduce the amps drawn by central heating...

but used in solo cats are useless on colder days...

lines, tanks, cabinets, furniture and the aluminum structural materials will get cold and stay cold... and a cat heater MUST have a fresh air source into the trailer....i've experience catalytic hypoxia....and got outside just in time...

agm are more expensive...but
-they can be discharded to a deeper level.
-they can take the 'battery abuse' most campers deny inflicting...
-they can be recharged quicker...taking a higher charge without losing water or spilling electrolyte...
-they function a little better than the others when the battery gets cold.
-3 times the duty cycles...and practially no maintenence...
-and extras can be rotated or connected INSIDE the trailer without the issue of venting gases or spilling acid.

in wacnstac situation...the meter is likely WAY off...
one day, checking cell specific gravity and comparing to the meter...
would be a calibration lesson...and a surprise about what 'full' means in reality.
also what univolt/charger model is in use? charge rates and all that...

even with a good charger 3-4 hours will only get batteries back to 80-85%..
could take up to 10 hours or more for the last 10-15% fill.

so thats another issue. with the agm batts...they could be connected directly to the generator and charged quicker...IF the gen out put has been measured...

as for the generator shack....i might try heating water in the shack too on lp or generator electic...hot water could warm the building which would help the batteries....and a insluated pipe feed the trailer hot water from a bigger tank...

i sure want to see the pictures of this setup...

is there plans for a a still too?
for medicinal purposes or to make fuel?

cheers
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Old 09-06-2006, 01:46 AM   #25
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Quote:
Originally Posted by Leipper
Whether you are running 6v series or 12v parallel won't make much difference. Going group 31 size ups the time just a tad and a group 24 is a bit more limited and AGM's will take more abuse and charge faster but won't really make much difference as far as capacity - again, these are not really at issue in the overall scheme of things.

Leipper, excellent post. I thought that one advantage of running batteries in series vs. parallel is that if you have one bad cell on a battery running in parallel (and you have 2 12 volts) it would drag both batteries down?

Also, . given the choice…. if cost and space are not an issue…. Would not two 6 volt golf cart batteries or AGM's in series be a better choice in terms of capacity and service life?

Thanks

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Old 09-06-2006, 09:05 AM   #26
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The series vs parallel argument is one of those religious ones whose basis seems to be in the really really fine points. For a small bank, like in travel trailers with 2 to 4 batteries, the real issue is what you can get that will fit in the space available.

Dramatic failure mode considerations devolve into the low odds hypothetical. Good for debate but not so constructive for making decisions. If you have a cell failure in your RV bank, you need new batteries, that's all.

Capacity comparisons runs afoul of Peukert - the lower current from each battery in parallel is more important than any 6v cell size for equivalent batteries. (that's been touched on above, too) - see Parallel or Serial for your Battery Bank?

AGM batteries are another consideration entirely. As 2air' noted, they have lower internal resistance and are much more tolerant of abuse. They also don't require ventilated compartments (but some say you need one anyway) so they can be stashed in out of the way places. But they are expensive. (and most don't like equalization charges, which is the only significant difference to worry about from standard wet cell charging)

An RV off grid is extremely energy constrained. It is also very innefficient in terms of heating and cooling. That means significant life-style adjustments are often needed. For most of us, though, I think that is one of the attractions of the avocation.
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Old 09-06-2006, 09:18 AM   #27
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Quote:
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my batteries are nearly full just from solar on all but the over cast/rainy days...
well, the solar array isn't "standard". I suppose the catalytic isn't, either, but its cheaper by a factor of at least 10 to install. I just meant that the manufacturers install "a" battery, and "a" furnace, among other things, but the systems provided are not always optimal for every possible configuration. some customizing may be needed.
Quote:
Originally Posted by 2airishuman
..but used in solo cats are useless on colder days...
again, "your mileage may vary"...that must be the "dead of winter" scenario. From my own experience in my smaller trailer...on a 35 degree night, the cat kept the trailer at 75. Too hot. on its lowest setting. Low as I could get it and keep it running. AND the vent was open. Maybe on a "long, long trailer", you'd need 2 of them. That would burn twice as much electricity, though.
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Old 09-08-2006, 09:36 AM   #28
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Does anybody know where I can buy a GPL-27T retail? Seems like it would be a lot more efficient than having one shipped to my house.
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