On Sun, 13 Mar 2005 23:18:41 -0800, the inscrutable Fly-by-Night CC
Batteries wear out. Chances are very high that they all need
replacement. Check the solar electric stores for tips.
Ain't gonna cut it. Take a hydrometer to check the individual cells
after charging. That might show you a bad cell, ruling out a battery
Carefully. (Sorry, couldn't resist.)
You'll need to charge the batteries with the generator then test them
with a load tester, Owie. Got a friend at a gas station (or slight
chance: rental yard) where you can borrow one? If the batteries are
more than 4 years old, don't worry about going to all that trouble
Just have them replace them. When I was researching solar a few years
ago (just after moving up here; off-grid folks go through batteries
like terlit papah), I read up a bit on batteries. Newer styles last
anywhere from 4 to 10 years, max, depending upon the percentage of
discharge each time. The higher the discharge rate and lower the
discharge level before recharging, the quicker they die. I'm betting
that those batteries are worn out in that environment.
David's William Darden link has good info. Here are more:
http://www.homepower.com/ magazine articles, check your lib
(Wow, half my bookmarks are dead already!)
Marine/solar deep-cycle @ $100-200 a pop.
House them in a warmer environment, like a basement. Keep them
charged even when the owners are not there. (solar trickle)
Thanks are unnecessary. Send mass quantities of cash instead. ;)
First off, for this kind of use, you don't want "auto-style
batteries", you want deep-cycle batteries. You will find these in a
store that sells to the marine or RV markets.
A regular car battery is designed to produce large bursts of current
to crank the starter motor, and then immediately get recharged and be
kept topped off. This kind of battery has many thin plates to give
lots of surface area, so it can generate the high current burst. The
problem is that if you repeatedly run it all the way down then charge
it back up (like you're doing), you will quickly ruin the plates.
A "deep cycle" battery looks similar on the outside, but inside has a
fewer number of thicker plates. It cannot produce the same
high-current surge a car starting battery can, but it is designed to
handle many cycles of being deeply discharged and then recharged. If
your friend really is using regular car batteries, that could be part
of the problem.
If it's not holding a charge, it's faulty :-). Somebody else
suggested a hygrometer, which will measure charge level indirectly by
measuring the density of the electrolyte (water-acid mixture) in the
If the 4 batteries are in series, I'd go armed with 4 voltmeters (you
can get them plenty cheap at Radio Shack). Hook one up to each
battery, charge up the whole bank to full charge, and watch the
voltages as you use power. If one is dropping significantly faster
than the others, that's your problem. You could just use a single
meeter, but 4 is simplier (and increases the geek factor).
Deep cycle (see above).
Make sure the battery is fully charged and kept topped off. A dead
battery will freeze, which will probably destroy it. Make sure the
outside of the battery is clean; crud accumulating on the outside of
the case can form a conductive path between the terminals leading to
discharge. A battery will self-discharge slowly anyway, hence the
need to keep it topped off. Sounds like a good application for some
solar cells; they won't provide enough power to run the whole place,
but will do fine to keep things topped off over the winter with no
If it were me, I'd take the batteries home, charge them each up on the
AC charger, and bring them to Autozone. They have equipment for
checking batteries that beats a simple home battery tester.
You can test a battery's remaining capacity by charging it with an AC
charger and them hooking it up to a light bulb (like an old
headlight). If you know the watts of the light, you can calculate the
watt-hours the battery is capable of storing.
Batteries should always be tested separately.
Replace these batteries with deep cycle batteries, not regular car
Could ramble on for hours about "house banks" of batteries, it is a
major topic of discussion among cruising sailors, but will try to be brief.
Chances are pretty good the existing automotive batteries are at end of
life and need replacement.
A hydrometer is needed to do basic battery health investigation.
Use T-105, 6V, golf cart batteries as replacements, basically a 200 AH
unit designed specifically for this purpose, wired in series and
parallel as req'd.
When it comes to batteries in a house bank, they are like clamps to a
wood worker, you can't have too many.
In this application, I'd probably use at least 8, T-105 units.
SFWIW, I will be putting 16 of them on my boat to provide a 12 VDC house
Your description of the system is confusing.
1) Is the cabin electrical system being operated at 120 VAC, being fed
by the batteries and an inverter?
2) Are the batteries being charged at 12 VDC from the Honda generator?
BTW, to extend the life of the batteries, recharge more frequently.
Maximum discharge of a bank is 50%, but if you do that, you sacrifice life.
Yeah, I meant to mention golf cart batteries.
But paralleling is bad, as mentioned, because of dragging each other down.
Series is better also because the higher voltage means less current is
needed to the appliances and to an inverter. Less current means less
voltage drop and smaller connectors and wire.
I'd bet that a good inverter on 48, 72, or 96 volts input and 120VAC output
will give superior performance, long term, UNLESS it is way oversize. At
near full load, they can be in the 90% efficiency range. Ideally, one could
use multiple inverters, so that each runs something that puts it at near
Obviously there are lots of tradeoffs, but the 12V appliances/electronics
are great. Having multiple 12V batteries that can be switched in as needed
would be a good way too handle the TV load.
Then again, there's a lot to be said for peace and quiet! Buy some books!
More efficiency talk:
For something that isn't on long, like a blender or microwave, efficiency
isn't all that big a deal, so an inverter for that stuff is fine. The same
inverter will carry small tools, like drills and sanders.
For radio, a car radio and some good speakers is a fine choice.
For TV, if it has to be big, then an inverter just big enough to carry it
will be best.
2KW is a big generator. You should be taking a few hours for a full charge.
Say you run 50V at 15A, that's only 750W. There are some small water
heaters at about 1-1.5KW, so you could heat enough water for a shower or two
at the same time. Larger generators are gas hogs, especially when not
I'm not disagreeing with all of this, as my limited real-world experience
is several decades old.
I'm curious, however, about why one would consider an electric water
heater, off-grid? It seems that burning a fossil fuel to make electricity
to make resistance heat for water HAS to be less efficient than applying
that burning fossil fuel directly to the water tank. Or so I would think.
In a vacation home, one could consider a wood fired water heater, no?
who loves these electrical, educational threads, generally from a distance.
Yep, I was just letting that thought run. A propane water heater is fine,
if it's not too hard to carry the tanks in, ot if they are delivered. I'd
love a wood water heater, if there's good wood available, but most of the
ones I've seen take only tiny wood.
A 2KW generator is not a very big generator at all. One of my Honda's is a
It is small, quiet and efficient.
My other one is 5500W, water cooled, quiet and will run my entire house with
kids for 10 hours on 3 gals of fuel.
The OP said the cabin had most appliances on propane so I don't think an
electric water heater is much of an option.
The batteries power an inverter to provide AC to the lights and TV/VCR.
The batteries are old - +2 years.
Small Honda generator 2000 watts or less.
The use of an inverter to provide AC is a poor use of battery resources.
Suggest the owner get a new, larger generator. The new generators are more
efficient and significantly quieter.
Replace the lamps in the cabin with RV style fluorescent 12V lamps.
Replace the TV/VCR with 12V style as well.
Replace the batteries with RV/Boat batteries (deep cycle).
Keep from freezing. / Disconnect all cables when not in use for long
Most important - Keep then clean and dry!
Many of the other suggestions for testing are good. Forget the hydrometer
however, a load test is the best method. If they are a newer, car type
batteries you won't be able to access the individual cells anyway
Very interesting thread
Does anyone have links as to what and where to buy 12v appliances?
I am new to the world of camping and will be setting up a cabin off
grid later this year.
Any suggestions are appreciated.
One of the things you have to watch out for in a set up like the one
your friend is using is if the batteries are deep discharged you stand a
chance of "cell reversal". With lead-acid batteries no cell should be
allowed to discharge below 1.75 volts. See:
Wow, 40 messages and even some divergance to plasma torches... Did I
mention that you guys are not only worldly and wise but WORDY?
Thank you all for the hydrometer suggestion. Given the "maintenance
free" batteries of the last decade or more, I'd pretty much forgotten
about hydrometer testing.
I've passed along the replies that I thought the cabin owner could use.
I'm going to recommend that I bring back the batteries after our stay
and he can then have them load tested - and likely replaced. I'll also
recommend that he replace the 4 with 6 or 8 deep-cycle batts. Plus hook
up some sort of solar trickle charger for the periods between visits.
(Not sure how effective they may be as the cabin is well surrounded by
tall trees - plus the often cloudy/rainy October to April up here.)
Thanks again - I knew I'd get good feedback from you old farts. Age wise
over youthful beauty, no?
Well, you know the saying about "If you can't dazzle them with brilliance,
then baffle them with . . . ". You get both ends of the spectrum here, Owen.
Sorry about the "troll" remark, but it sounded *almost* like one.
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