On Fri, 27 Feb 2009 16:38:15 -0800, David Nebenzahl
wrote:
On 2/27/2009 12:27 PM Pete C. spake thus:
David Nebenzahl wrote:
On 2/26/2009 11:26 AM David Nebenzahl spake thus:
Told a guy I'd do some research for him into a small simple solar system
for use in maintaining the charge on a 12 volt automotive battery.
Update: I'm going to recommend this small charger from Harbor Freight to
the guy:
http://www.harborfreight.com/cpi/cta...emnumber=41144
It's a 5-watt[1] panel for $37. Should be good for starters to see how
he likes the idea, and to figure out how to mount it, etc. (The vehicle
is a truck with a camper shell.)
You should really get a meter on the battery in question and find out
what the standby load on it is. Then you can get a better idea of what
sized panel would be needed to keep up with it.
I can tell you that he wants to be able to run a small portable TV, a
radio (not at the same time) and maybe a small light or two (this is at
night). I have no way of actually measuring the actual power draw, as he
doesn't have this stuff at this time. As I said, close enough is close
enough. Plus, $$$ is limited.
I can tell you the outcome of your experiment, but I already know you
only want someone to agree with your suppositions.
For openers, a 10 watt lamp draws about 1 amp at 12 volts. That's a
very small lamp, like the dome light in your car. A small TV is going
to draw 5+ amps at 12 volts. So with a small TV and two very dim
lights, you will be USING about 7 amps an hour. The TV may draw twice
my estimate, but lets call it 5 amps.
A DEEP CYCLE battery can be drawn down to 50% and then recharged many
times. A Group 24 Deep Cycle battery is about the size of a large car
battery and is rated at around 75-80 amp hours. You can only use half
that capacity at MOST. So 40 amp hours. Divide 40 by 7 and you know
how long you can run the tv and lights before you need long and
substantial charging. Remember, this is a DEEP CYCLE battery designed
to do this. A "car battery" will be ruined very quickly by the same
type of usage.
Charging is not a simple matter of replacing exactly what you used. It
will take more amp hours of charging than you used.
A "car battery" isn't going to cut it at all. Neither will a trickle
charger. You need a minimum of a 100 watt solar panel with a good
controller, and probably 2, group 27 (100 amp hour each) DEEP CYCLE
batteries to come anywhere close to doing what you propose. The far
more expensive AGM deep cycle batteries take a charge much easier and
faster, and will last even longer than a deep cycle flooded battery,
but the up front cost will probably stop you cold. A decent flooded
Group 27 deep cycle battery is about $100. An AGM that size will be
between $200 and $400. You need two of whatever you select.