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 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

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.

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.

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.

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

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.)

Thanks to all those who answered with helpful advice. To those who
warned of dire consequences of overcharging, I don't think we have to
worry about that with the relatively small currents here. Keep in mind
I'm not designing a mil-spec system, but a solution for someone who
currently has to drag his batteries (physically) to be charged
regularly; this should make life better for him.

[1] Yes, I know, advertised power output: the actual output (under load)
is probably close enough for our purposes here.


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.

wrote:

On Fri, 27 Feb 2009 11:48:47 -0600, "Pete C."
wrote:


wrote:

On Fri, 27 Feb 2009 11:10:46 -0600, "Pete C."
wrote:


wrote:

On Fri, 27 Feb 2009 09:04:44 -0600, "Pete C."
wrote:


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.


Just for openers, the output voltage for the panel is more like 18
volts. And it only puts out 45 watts under perfect and optimal
conditions in a Laboratory. In real conditions you may get 30 watts
output from it for a period of a few hours on a sunny day.

The output voltage of the panel varies with the load on it.

The rating used to sell it is the output without any load applied.

No, it isn't as there is no power (power as in Watts) output with no
load applied, only open circuit voltage (closer to 24V).


The advertised ratings are puffery, and are calculated based on
unloaded voltage and theoretical output derived by calculation.


This is
where the MPPT tracking controllers come in, finding and tracking the
sweet spot where the panel can produce the highest power (wattage). At
any rate, the straight P/V=I gets you into the correct charge controller
current rating with some conservatism.

Yeah, if by "conservatism" you mean, "divide the rated output by about
2"! LOL

Most Solar panels sold by bargain outlets have specious specs.

Have you actually used the panels in question? If not hold your babble
until you have.

This is a subject I am VERY familiar with. The only babble I've heard
so far is from someone who believes advertising copy.

I'd do some measurements on the panels, however there is a severe lack
of sun today. Perhaps on the weekend if I get bored.

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.


--
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

wrote:
On Fri, 27 Feb 2009 11:10:46 -0600, "Pete C."
wrote:

wrote:
On Fri, 27 Feb 2009 09:04:44 -0600, "Pete C."
wrote:

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.

Just for openers, the output voltage for the panel is more like 18
volts. And it only puts out 45 watts under perfect and optimal
conditions in a Laboratory. In real conditions you may get 30 watts
output from it for a period of a few hours on a sunny day.
The output voltage of the panel varies with the load on it.

The rating used to sell it is the output without any load applied.

This is
where the MPPT tracking controllers come in, finding and tracking the
sweet spot where the panel can produce the highest power (wattage). At
any rate, the straight P/V=I gets you into the correct charge controller
current rating with some conservatism.

Yeah, if by "conservatism" you mean, "divide the rated output by about
2"! LOL

Most Solar panels sold by bargain outlets have specious specs.

What specious are you and what kind of specs do you wear?

TDD

On 2/27/2009 6:59 PM The Daring Dufas spake thus:

wrote:

Most Solar panels sold by bargain outlets have specious specs.

What specious are you and what kind of specs do you wear?

That should be "what *species* are you?". Like homo sapiens, a pretty
specious species that sometimes wears specs.


--
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

David Nebenzahl wrote:
On 2/27/2009 6:59 PM The Daring Dufas spake thus:

wrote:

Most Solar panels sold by bargain outlets have specious specs.

What specious are you and what kind of specs do you wear?

That should be "what *species* are you?". Like homo sapiens, a pretty
specious species that sometimes wears specs.


What!? You never heard of Norm Crosby?

TDD

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.