Posted by Mike Hill on August 10, 2003, 11:49 am
I presently use my radio on campsites using a 12v 4ah sealed lead
acid cell. Bearing in mind I'm in the UK, is it feasible to use SP to
charge this cell during the day, for it to be used in the evening ? If
so, please answer the following :
I can get five 12v 5w panels fairly cheap, would these be suitable ?
How many of these should I use ?
Do I need a controller, as I don't mind checking the voltage regularly
? Does it damage the panel if I connect it directly to the battery ?
Sorry if these are basic questions, but I have no idea ;-)
Any help much appeciated, Mike.
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Posted by Joe Fischer on August 10, 2003, 1:16 pm
: I presently use my radio on campsites using a 12v 4ah sealed lead
: acid cell. Bearing in mind I'm in the UK, is it feasible to use SP to
: charge this cell during the day, for it to be used in the evening ? If
: so, please answer the following :
: I can get five 12v 5w panels fairly cheap, would these be suitable ?
: How many of these should I use ?
To charge the battery in four hours would
require one amp of panels at 12 volts.
Maybe one 5w panel would be 5/12ths of an amp,
so five panels would charge the battery in a little
more than 2 hours.
: Do I need a controller, as I don't mind checking the voltage regularly
Maybe not if not connected to the panels more
than 2 hours (provided it was fully discharged), and
provided the battery type allows a 2amp charge rate.
Find the information on maximum charging rate,
some sealed batteriescan be damaged if charged at too
high a rate. I bought a NAPA orbital car battery,
and it is not supposed to be charged at greater than
4amps, which I didn't know when I bought it.
Supposedly the voltage regulator is supposed
to be set at close to 14 volts to prevent a too-high
charging rate, but I have a 100amp alternator and
I think the voltage is more than 15 volts, so I am
waiting to see how long the battery lasts (it is
2 years old now).
: ? Does it damage the panel if I connect it directly to the battery ?
Probably not provided it is not left charging
too long, the problem is knowing how much the battery
is discharged before starting the charge.
Unless it is a deep cycle battery or certain
other types of battery (like nickel-cadmium), it
will not take many full discharges.
And if it is at half charge, then 5 panels
might charge it fully in one hour or so.
Somebody please check the numbers. :-)
Posted by Scott Willing on August 12, 2003, 12:35 am
Leaping in to check your numbers as requested.
...true, assuming the battery was flat empty, and it won't live long
if it's run flat very often.
Or an hour (ignoring inefficiencies and losses), if it was only
discharged to a maximum of 50% as it should be...
An extremely good point. I happen to have a couple of 4AHr 6V gell
batteries (luckily enough, the exact equivalent of a 4AHr 12V battery)
and the specs printed right on the batteries indicate a maximum
initial current of 1.6A.
That would imply that 4 of those panels would produce around the
maximum, assuming ideal conditions aimed directly at the sun, yadda
yadda... but in real life the 5 panels would probably be fine since
you're almost never going to see the full spec output from them
Actually there shouldn't be any damage to the panels regardless, given
that they can operate happily into a dead short. Indeed you can
connect a nominal 12V panel to a 6V battery, or even to a 2V gell cell
or a 1.25V nicad cell as long as the panel current isn't too high and
you don't allow the battery / cell to get overcharged.
However, note that in the absence of a controller, at the very least
there should be a diode introduced into this situation to prevent the
battery from discharging into the panels when the sun goes away, which
it will at some point, if only due to a passing cloud. A Schottky
(that spelling doesn't look right) could be chosen for minimal volt
drop / power loss, but with the five panels a garden-variety silicon
diode would be fine.
A-ha, this is where I came in. :-)
Done, I think. Good post Joe.
Posted by Mike Hill on August 12, 2003, 4:02 pm
On Mon, 11 Aug 2003 19:35:41 -0500, Scott Willing
I have ordered a controller, as you imply that would be the safest
bet. I'll do a bit of experimenting at home first. Will start with one
panel then work my way up, making sure the battery isn't being charged
It's geting a bit addictive this solar lark. I'm now looking at a
wind generator too, might be a good back-up, especially in the UK ;-)
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Posted by Andy Ball on August 13, 2003, 12:50 am
MH> I have ordered a controller, as you imply that would
> be the safest bet. I'll do a bit of experimenting at
> home first. Will start with one panel then work my way
> up, making sure the battery isn't being charged too
I was looking at some PV panels at a hamfest on Sunday: US$
35 for claimed 13.8V 5W, which I think would be an
appropriate place for me to start.
My sole radio at present is a Radio Shack HTX-200 2m HT, and
according to the manual it draws 600mA at 3V DC for about
200mW out, or 900mA at 9V DC for closer to 2W. I may look
for a 10W or 15W panel, which would give me some scope for
Maplin used to carry some solar panels, as well as 12V DC
fluorescent strip-lights and other potentially useful
things. They may still stock them.
- Andy, KB9YLW