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. Found
this at Harbor Freight:

http://www.harborfreight.com/cpi/cta...emnumber=96418

It's a 12 volt, 15 watt panel for cheap ($70).

I'm thinking that all he needs to do is wire it up to his battery to
trickle-charge it. I think I'd add a diode (IN200x) in series for
protection. So will this work?

Since they don't list the output voltage for the panel, except to say
"12 volts" in the description, I guess one could opt for this larger one:

http://www.harborfreight.com/cpi/cta...emnumber=40085
(20 watt panel, made for charging auto & RV batteries, $190)

which says it maintains a charging voltage of 17.5 volts, which seems a
little high: perhaps a string of 3 or 4 diodes in series would drop the
voltage just enough to bring it down to the recommended 13.6 volts or so.


--
Personally, I like Vista, but I probably won't use it. I like it
because it generates considerable business for me in consulting and
upgrades. As long as there is hardware and software out there that
doesn't work, I stay in business. Incidentally, my company motto is
"If this stuff worked, you wouldn't need me".

- lifted from sci.electronics.repair

Andy comments:

You'd be better off with the "battery maintainer" that sells for
6.95 and is
left connected to the battery. On sale, it is a few dollars less...

I've been using solar panels for many years, and if you don't aim
them,
they don't deliver the "promised" output. Plus clouds, rain, bird
doo....

I'm near Dallas and we average 5.5 hours of full sun per day.....
And get
full panel output ONLY if the panel is aimed at those particular
times.....

If you're going to pay $6 per watt, which is the going price for
panels,
make sure that you are familiar with all the ins and outs....

Still , $75 isn't so much to toss away while playing with a new
toy..... And people like me will buy your panel for pennies on the
dollar in
a few years after it decorates you garage wall until the wife makes
you sell it at a garage sale.......

Sorry.... but that's the way the cycle goes...

Andy in Eureka, Texas

On Thu, 26 Feb 2009 11:26:00 -0800, David Nebenzahl
wrote:

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. Found
this at Harbor Freight:

http://www.harborfreight.com/cpi/cta...emnumber=96418

It's a 12 volt, 15 watt panel for cheap ($70).

I'm thinking that all he needs to do is wire it up to his battery to
trickle-charge it. I think I'd add a diode (IN200x) in series for
protection. So will this work?

Since they don't list the output voltage for the panel, except to say
"12 volts" in the description, I guess one could opt for this larger one:

http://www.harborfreight.com/cpi/cta...emnumber=40085
(20 watt panel, made for charging auto & RV batteries, $190)


Without a charge controller, it will probably boil the battery. There
are items made to do what you want, a plain solar panel with no
regulation isn't one.

Chris Hill wrote in
:

On Thu, 26 Feb 2009 11:26:00 -0800, David Nebenzahl
wrote:

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. Found
this at Harbor Freight:

http://www.harborfreight.com/cpi/cta...emnumber=96418

It's a 12 volt, 15 watt panel for cheap ($70).

I'm thinking that all he needs to do is wire it up to his battery to
trickle-charge it. I think I'd add a diode (IN200x) in series for
protection. So will this work?

Since they don't list the output voltage for the panel, except to say
"12 volts" in the description, I guess one could opt for this larger one:

http://www.harborfreight.com/cpi/cta...emnumber=40085
(20 watt panel, made for charging auto & RV batteries, $190)


Without a charge controller, it will probably boil the battery. There
are items made to do what you want, a plain solar panel with no
regulation isn't one.


to -maintain- a charge,all you need is a few 100milliamps into the battery.
You won't boil it with that low a current.HF sells a small solar
panel,IIRC,1-1.5W. It plugs into a cig lighter socket.

--
Jim Yanik
jyanik
at
kua.net

Jim Yanik wrote in
:

Chris Hill wrote in
:

On Thu, 26 Feb 2009 11:26:00 -0800, David Nebenzahl
wrote:

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. Found this at Harbor Freight:

http://www.harborfreight.com/cpi/cta...emnumber=96418

It's a 12 volt, 15 watt panel for cheap ($70).

I'm thinking that all he needs to do is wire it up to his battery to
trickle-charge it. I think I'd add a diode (IN200x) in series for
protection. So will this work?

Since they don't list the output voltage for the panel, except to say
"12 volts" in the description, I guess one could opt for this larger
one:

http://www.harborfreight.com/cpi/cta...emnumber=40085
(20 watt panel, made for charging auto & RV batteries, $190)


Without a charge controller, it will probably boil the battery.
There are items made to do what you want, a plain solar panel with no
regulation isn't one.


to -maintain- a charge,all you need is a few 100milliamps into the
battery. You won't boil it with that low a current.HF sells a small
solar panel,IIRC,1-1.5W. It plugs into a cig lighter socket.


You must mean this one:
http://www.harborfreight.com/cpi/cta...emnumber=44768

If solar is not a groundrule a couple more possibilities:

http://www.harborfreight.com/cpi/cta...emnumber=42292

This one looks interesting since it's mounted under the hood and you
just plug it in to an extenion cord.

http://www.harborfreight.com/cpi/cta...emnumber=99857


Of course, I have no idea if any are worth anything or if they will
trash the battery.

David Nebenzahl wrote:

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. Found
this at Harbor Freight:

http://www.harborfreight.com/cpi/cta...emnumber=96418

It's a 12 volt, 15 watt panel for cheap ($70).

I'm thinking that all he needs to do is wire it up to his battery to
trickle-charge it. I think I'd add a diode (IN200x) in series for
protection. So will this work?

Since they don't list the output voltage for the panel, except to say
"12 volts" in the description, I guess one could opt for this larger one:

http://www.harborfreight.com/cpi/cta...emnumber=40085
(20 watt panel, made for charging auto & RV batteries, $190)

which says it maintains a charging voltage of 17.5 volts, which seems a
little high: perhaps a string of 3 or 4 diodes in series would drop the
voltage just enough to bring it down to the recommended 13.6 volts or so.


The 45W three panel package that Harbor Freight sells for ~$200 is the
best value $/W and the panels are decent. You have to replace the junk
charge controller they provide with a decent unit though.

On 2/26/2009 1:13 PM Pete C. spake thus:

David Nebenzahl wrote:

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. Found
this at Harbor Freight:

http://www.harborfreight.com/cpi/cta...emnumber=96418

It's a 12 volt, 15 watt panel for cheap ($70).

The 45W three panel package that Harbor Freight sells for ~$200 is the
best value $/W and the panels are decent. You have to replace the junk
charge controller they provide with a decent unit though.

Any suggestions? I'm not familiar with these units (charge controllers),
could use a little guidance here.


--
Personally, I like Vista, but I probably won't use it. I like it
because it generates considerable business for me in consulting and
upgrades. As long as there is hardware and software out there that
doesn't work, I stay in business. Incidentally, my company motto is
"If this stuff worked, you wouldn't need me".

- lifted from sci.electronics.repair

On Thu, 26 Feb 2009 15:43:15 -0800, David Nebenzahl
wrote:

On 2/26/2009 1:13 PM Pete C. spake thus:

David Nebenzahl wrote:

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. Found
this at Harbor Freight:

http://www.harborfreight.com/cpi/cta...emnumber=96418

It's a 12 volt, 15 watt panel for cheap ($70).

The 45W three panel package that Harbor Freight sells for ~$200 is the
best value $/W and the panels are decent. You have to replace the junk
charge controller they provide with a decent unit though.

Any suggestions? I'm not familiar with these units (charge controllers),
could use a little guidance here.

Sunsei makes some relatively inexpensive ones that are pretty good.
Under $100.

David Nebenzahl wrote:

On 2/26/2009 1:13 PM Pete C. spake thus:

David Nebenzahl wrote:

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. Found
this at Harbor Freight:

http://www.harborfreight.com/cpi/cta...emnumber=96418

It's a 12 volt, 15 watt panel for cheap ($70).

The 45W three panel package that Harbor Freight sells for ~$200 is the
best value $/W and the panels are decent. You have to replace the junk
charge controller they provide with a decent unit though.

Any suggestions? I'm not familiar with these units (charge controllers),
could use a little guidance here.

45W = 3.75A or so so you don't need a big one.

http://shop4.frys.com/product/498009...H:MAIN_RSLT_PG

Sunforce 60012 7 amp Charge Controller

Solar:
FRYS.com #: 4980091

or

http://shop4.frys.com/product/563300...H:MAIN_RSLT_PG

ICP CC-10000 10Amp Battery Charge Controller

ICP:
FRYS.com #: 5633001

Would do the job. I got the later one, I think it's a bit nicer. Either
one gives some headroom to add a few more panels.

Fancier MPPT controllers will give the best efficiency, but the extra
cost probably isn't worthwhile for a tiny array.

The HF kit also comes with a couple decent little 12V CFL lights which
can be handy and a basic rack for the panels.

http://www.harborfreight.com/cpi/cta...emnumber=90599

The HF stores usually stock the panel kit, and if you sign up for the
flyers and emails you can often get a 20% off coupon for the stores.

Good resources here as well: http://www.homepower.com/sample/

Look through the sample issue where you will find plenty of vendors. The
electronic edition subscription (download pdf) is a decent value.

wrote:

On Thu, 26 Feb 2009 17:55:56 -0600, "Pete C."
wrote:


David Nebenzahl wrote:

On 2/26/2009 1:13 PM Pete C. spake thus:

David Nebenzahl wrote:

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. Found
this at Harbor Freight:

http://www.harborfreight.com/cpi/cta...emnumber=96418

It's a 12 volt, 15 watt panel for cheap ($70).

The 45W three panel package that Harbor Freight sells for ~$200 is the
best value $/W and the panels are decent. You have to replace the junk
charge controller they provide with a decent unit though.

Any suggestions? I'm not familiar with these units (charge controllers),
could use a little guidance here.

45W = 3.75A or so so you don't need a big one.

How do you come up with this Amp figure?

P/V=I

45W/12V=3.75A

It won't be exactly that since the voltage won't be exactly 12V, it
could be more like 3.21A @ 14V. It's also unlikely that it will get
quite up to the 45W rating unless you have a MPPT charge controller on
it.

I was looking at the 5 watt model that Harbor Freight has for $37
http://www.harborfreight.com/cpi/cta...emnumber=41144
which is made to clip right to the car battery. I was trying to
determine what the Amp output would be?

~0.4A or so.

And what kind of amperage does a standard car battery actually put
out?

Entirely variable. You usually don't find a proper Ah rating on a car
battery either, just a "group" and a "CCA" rating.

My truck battery is rated at 525 Amps, but I know thats the
rated starting amps, which I know is way overrated peak power.

Not over rated, it is probably "CCA" or Cold Cranking Amps, a rating of
the amperage the battery can supply for a short time in cold conditions.
It doesn't really translate into an total capacity figure like Ampere
Hours.


So, lets use the figure that you used above for a 45W solar panel
putting out 3.75 A. If I can charge my drained car battery in two
hours with a 10A plug in charger, will this solar charger charge the
same battery in 5.4 hours? 10A divided by 3.75 is 2.7 (approx), times
2 hours equals 5.4. (of course under full sunlight and proper aiming).

Roughly. Battery charging is a complex thing and as you may have noticed
with a battery charger that has an amp meter on it, charging isn't
constant current and the battery will only draw 10A at the start and
then slowly drop off over time as the battery charges.


With this in mind (if it's accurate), that 5 watt solar panel would
take 9 times as much time, or about 49 hours.

Of course I know these are not really intended to charge a drained
battery, but to add power and keep them at full charge.

Exactly. They are intended mainly to compensate for the battery's self
discharge and small loads like engine computers and radio memory.


Speaking about charging batteries. I recently had a really dead
battery (left the dome light on all night in real cold weather). I
needed to get the car started ASAP. I hooked TWO battery chargers up
at the same time.(a 10A and a 6A). It worked and charged pretty fast.

LM

On 2/26/2009 11:41 AM spake thus:

On Thu, 26 Feb 2009 11:26:00 -0800, David Nebenzahl
wrote:

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. Found
this at Harbor Freight:

http://www.harborfreight.com/cpi/cta...emnumber=96418

It's a 12 volt, 15 watt panel for cheap ($70).

I'm thinking that all he needs to do is wire it up to his battery to
trickle-charge it. I think I'd add a diode (IN200x) in series for
protection. So will this work?

Since they don't list the output voltage for the panel, except to say
"12 volts" in the description, I guess one could opt for this larger one:

http://www.harborfreight.com/cpi/cta...emnumber=40085
(20 watt panel, made for charging auto & RV batteries, $190)

which says it maintains a charging voltage of 17.5 volts, which seems a
little high: perhaps a string of 3 or 4 diodes in series would drop the
voltage just enough to bring it down to the recommended 13.6 volts or so.

A little more information is needed. How many amphours per day will he
need? What type of battery? Is it flooded, gel or AGM? What size is
the battery?

Not sure of current draw. Standard-size automotive battery; I already
stated that.

Solar panels rarely put out more than half the "rated"
wattage.However, most have output voltage around 18 volts, and a
charge controller is used to prevent overcharging. AGM's and
especially GEL batteries will have dramatically shortened lives if
charged at too high a voltage. For an AGM it's 14.7 volts max.

Passive voltage control won't work for this application. If you limit
the maximum voltage enough to prevent overcharging or overvoltage, you
will have no charging at all under average daylight conditions.

So how about an active regulator (say, a 78xx) that would limit the
voltage to the rated max for a lead-acid battery?


--
Personally, I like Vista, but I probably won't use it. I like it
because it generates considerable business for me in consulting and
upgrades. As long as there is hardware and software out there that
doesn't work, I stay in business. Incidentally, my company motto is
"If this stuff worked, you wouldn't need me".

- lifted from sci.electronics.repair