I purchased a small flexible solar panel from Silicon Solar Inc. Their web
site advises that the panel is "perfectly suited as a 12V battery charging
solar solution." Just what I need for trickling the 12 volt starting battery
for my dinghy. The solar panel produces 7.2v 100 mA.



A friend, who is an engineer, informed me that I am wasting my time. He says
I need 12Volts from the solar panel to charge a 12 volt battery. Thus the
7.2V will not do it.



Who's right, the manufacturer or my friend?

John wrote:
I purchased a small flexible solar panel from Silicon Solar Inc.
Their web site advises that the panel is "perfectly suited as a 12V
battery charging solar solution." Just what I need for trickling the
12 volt starting battery for my dinghy. The solar panel produces 7.2v
100 mA.



A friend, who is an engineer, informed me that I am wasting my time.
He says I need 12Volts from the solar panel to charge a 12 volt
battery. Thus the
7.2V will not do it.



Who's right, the manufacturer or my friend?

Must be the pocket version. You need something around 3 foot by 5 foot,
shoving out 13 volts min.@ 1AH.

Dennis

In article , "Dennis Pogson" wrote:
John wrote:
I purchased a small flexible solar panel from Silicon Solar Inc.
Their web site advises that the panel is "perfectly suited as a 12V
battery charging solar solution." Just what I need for trickling the
12 volt starting battery for my dinghy. The solar panel produces 7.2v
100 mA.



A friend, who is an engineer, informed me that I am wasting my time.
He says I need 12Volts from the solar panel to charge a 12 volt
battery. Thus the
7.2V will not do it.



Who's right, the manufacturer or my friend?

Must be the pocket version. You need something around 3 foot by 5 foot,
shoving out 13 volts min.@ 1AH.

Dennis

1 amp is certainly not trickel charging. That may even boil the battery too
much. A Harbor Freight 120 ma. 3 inch by 12 inch panel would work, but is this
salt water ??

greg

A friend, who is an engineer, informed me that I am wasting my time. He
says
I need 12Volts from the solar panel to charge a 12 volt battery. Thus the
7.2V will not do it.



Who's right, the manufacturer or my friend?


Neither. You need over 13 volts at a minimum to charge a 12 volt battery.
100
milliamps isn't going to do squat, either. Also be aware that solar panels
are
rated under ideal conditions, and you will likely NEVER see anything close
to
the rated output. The panel you describe will actually DRAIN the battery.


All of the small trickle charger solar panels (from decent companys) have a
blocking diode that won't allow the panel to drain the battery. Even a
quality 14V panel will drain a battery at night without a blocking diode.
A 7.2V panel is made to charge a 6V battery, not a 12V battery.

Try a couple tests...
Voc (Open circuit voltage) Test the terminals in FULL Sun. Should be
about 15-18 volts
Vbatt Test the voltage of your battery after it has been charged.
12.4-12.8 V ???
watch the voltage as you connect the solar cell. It should go up a few
10ths of a volt and eventually hit 13-13.5 volts for a small trickle
Do you have a DC ammeter? Do you know how to connect the leads? (it is
usually different than for measuring voltage)
Connect the ammeter in series with the batt and the panel. you should see
some current flow in full sun. Cover the panel. Did it stop? did it go
in reverse? (if it went in reverse... return the panel... no blocking
diode)

I have a small panel (10x14") that I use to keep my underwater scooter
battery fresh. it is the size of a motorcycle battery and although the
panel will NOT charge it, it does keep it healthy in my dock box. it
would not make a dent in my starting batteries. They are too large and
would need a much larger panel to overcome the internal resistance and the
occaisonal bilge pump load.

In article , wrote:
On Mon, 21 Apr 2008 12:58:24 GMT, (GregS)
wrote:

In article , "Dennis Pogson"
wrote:
John wrote:
I purchased a small flexible solar panel from Silicon Solar Inc.
Their web site advises that the panel is "perfectly suited as a 12V
battery charging solar solution." Just what I need for trickling the
12 volt starting battery for my dinghy. The solar panel produces 7.2v
100 mA.



A friend, who is an engineer, informed me that I am wasting my time.
He says I need 12Volts from the solar panel to charge a 12 volt
battery. Thus the
7.2V will not do it.



Who's right, the manufacturer or my friend?

Must be the pocket version. You need something around 3 foot by 5 foot,
shoving out 13 volts min.@ 1AH.

Dennis

1 amp is certainly not trickel charging. That may even boil the battery too
much. A Harbor Freight 120 ma. 3 inch by 12 inch panel would work, but is this
salt water ??

greg

True trickle charging is only to maintain the battery at full charge
by compensating for the battery's own rate of self-discharge. A true
trickle charge rate will not recharge a battery.

A solar panel for charging AND maintaining a typical marine battery
will need substantially more available power, and a smart regulator.
There is no $100 "magic pill" for this job. The 1 AH panel Dennis
mentions will hardly ever, if at all, put out it's full rated output
for more than a few minutes under perfect conditions. Most solar
panels are rated VERY optimistcally. In any case, you need a
regulator.

I call trickel charging on the order of 5-10 ma. 100 ma. will cause bubbling of
cells, and is absolutely the max I would use without a smart
controller. It would take at least 8 hours to replenish a 5 second 600
amp starting current @ 100ma. Plus some.

greg

wrote in message
...
On Mon, 21 Apr 2008 09:27:12 -0400, "Ed"
wrote:



A friend, who is an engineer, informed me that I am wasting my time. He
says
I need 12Volts from the solar panel to charge a 12 volt battery. Thus
the
7.2V will not do it.



Who's right, the manufacturer or my friend?


Neither. You need over 13 volts at a minimum to charge a 12 volt
battery.
100
milliamps isn't going to do squat, either. Also be aware that solar
panels
are
rated under ideal conditions, and you will likely NEVER see anything
close
to
the rated output. The panel you describe will actually DRAIN the
battery.


All of the small trickle charger solar panels (from decent companys) have
a
blocking diode that won't allow the panel to drain the battery.

All? Really? Are you sure? Is that safe to assume? Do you have a list
of these "decent" companies? Are there companies that are decent but
are not on your list? Are there companies on your list that are
otherwise decent but sell one or two panles that do not have a
blocking diode?

The specific company the original poster mentioned does NOT state that
their small panels have a blocking diode. Hmmm. They also state that
the small panels will not CHARGE a depleted battery.

:')

Any panel without a charge controller or a blocking diode WILL drain a

battery when the sun goes down so that makes it worthless.



A list of decent comps? No, but if you buy from West or another reputable
dealer you can return them if they prove to not have a diode.

Any panel without a charge controller or a blocking diode WILL drain a

battery when the sun goes down so that makes it worthless.


I have already noted the problem. In fact, I was the one who brought it
up. I
have now added the additional information that the company the poster was
specificaly interested in seems to be hiding some important information.
Do you
have anything USEFUL to add, or do you just like to see what you wrote
appear on
your computer screen for the thrill of it all?



A list of decent comps? No, but if you buy from West or another reputable
dealer you can return them if they prove to not have a diode.


Wow! That's useful! I'll bet with a little thought, you could tell us how
to
save the rainforests, too. Thanks so much! You've been a tremendous help.
Give
yourself a pat on the back.



Call me when you have installed your first MW of solar power... some of us
actually work in this industry and are too busy to do basic research for the
masses... Your only value add has been comic releif....

"John" wrote in
news:x5KdnbpZbNocRpbVnZ2dnUVZ_jydnZ2d@caribsurf:

A friend, who is an engineer, informed me that I am wasting my time.
He says I need 12Volts from the solar panel to charge a 12 volt
battery. Thus the 7.2V will not do it.




Your friend would be wrong. Solar panel have quite high internal
resistance. Measure the temperature of unloaded solar panels just
sitting in the sun, then hook them up to a battery and let them charge
the battery until their rising temperature settles down. Note the
intense temperature increase in intense sunlight due to this internal
resistance loading the output voltage.

It is for this reason, that the open circuit voltage of solar panels is
usually many volts ABOVE, not below, the 13.8V (not 12) of a fully
charged lead-acid battery whos float voltage at charge is 14.2VDC.
Solar panels I own are all in the 18-19V open circuit range, allowing
for a 4-5V drop in panel output voltage at rated load.

Look at old panels and you can see where the current came from. Around
the edge of each solar cell, the silicon still has that gun blueing
color. Where the current comes from inside that diameter, heavily
charging solar cells are all brown, cooked by the current IIR drop that
causes the heat. The brown color hides the active part of the cell from
the sun so its output goes to pot, so to speak, as time goes by.

Your house battery needs about 5V higher than float voltage to
overcharge your battery. I say overcharge because the 19V solar panel
will go right on cooking the battery, very slowly converting its water
into hydrogen gas and free oxygen to rust the plates as the ever-
lowering electrolyte becomes much more concentrated sulphuric acid,
eventually eating the bottom right off the plate stacks if you don't
constantly pour more DISTILLED ONLY water into it. Therefore, make SURE
you also buy a CHARGE CONTROLLER, which limits the charging to 14.2V and
prevents the cells from cooking the battery while you are ashore. .1A x
6 hours per day = 18.6AH/month. It's amazing how that sneaks up to a
full 1.280 specific gravity full charge when the boat is shut down with
its loads disconnected.

The 7.2V would make a nice Sellphone charger....(c;

Larry,

Reread what you just posted.
You said his friend was wrong:
He says I need 12Volts from the solar panel to charge a 12 volt
battery. Thus the 7.2V will not do it.

but then confirmed he was right. :-)
The 7.2V would make a nice Sellphone charger....(c;


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Larry" wrote in message
...
"John" wrote in
news:x5KdnbpZbNocRpbVnZ2dnUVZ_jydnZ2d@caribsurf:

A friend, who is an engineer, informed me that I am wasting my time.
He says I need 12Volts from the solar panel to charge a 12 volt
battery. Thus the 7.2V will not do it.




Your friend would be wrong. Solar panel have quite high internal
resistance. Measure the temperature of unloaded solar panels just
sitting in the sun, then hook them up to a battery and let them charge
the battery until their rising temperature settles down. Note the
intense temperature increase in intense sunlight due to this internal
resistance loading the output voltage.

It is for this reason, that the open circuit voltage of solar panels is
usually many volts ABOVE, not below, the 13.8V (not 12) of a fully
charged lead-acid battery whos float voltage at charge is 14.2VDC.
Solar panels I own are all in the 18-19V open circuit range, allowing
for a 4-5V drop in panel output voltage at rated load.

Look at old panels and you can see where the current came from. Around
the edge of each solar cell, the silicon still has that gun blueing
color. Where the current comes from inside that diameter, heavily
charging solar cells are all brown, cooked by the current IIR drop that
causes the heat. The brown color hides the active part of the cell from
the sun so its output goes to pot, so to speak, as time goes by.

Your house battery needs about 5V higher than float voltage to
overcharge your battery. I say overcharge because the 19V solar panel
will go right on cooking the battery, very slowly converting its water
into hydrogen gas and free oxygen to rust the plates as the ever-
lowering electrolyte becomes much more concentrated sulphuric acid,
eventually eating the bottom right off the plate stacks if you don't
constantly pour more DISTILLED ONLY water into it. Therefore, make SURE
you also buy a CHARGE CONTROLLER, which limits the charging to 14.2V and
prevents the cells from cooking the battery while you are ashore. .1A x
6 hours per day = 18.6AH/month. It's amazing how that sneaks up to a
full 1.280 specific gravity full charge when the boat is shut down with
its loads disconnected.

The 7.2V would make a nice Sellphone charger....(c;