I was curious if someone could explain why solar panels that charge a
12V system put out 19V? I used a multi-meter to check the voltage on my
panels and was at first alarmed that they output 19V but then upon
looking online I discovered that it's fairly common. Anyhow, was
wondering if someone would be game to explain why they make many solar
panels to output 19V (instead of a more common charging voltage such as
14.5V)?

Thanks,
Todd
--
http://gabrito.com
http://windandtides.com
http://gearandboats.com

Just a wild guess, but probably because the amp output is so small,
that it relies on the voltage to push what it can make though.

at almost no amps the 19v won't hurt a 12v battery.


wrote:
I was curious if someone could explain why solar panels that charge a
12V system put out 19V? I used a multi-meter to check the voltage on my
panels and was at first alarmed that they output 19V but then upon
looking online I discovered that it's fairly common. Anyhow, was
wondering if someone would be game to explain why they make many solar
panels to output 19V (instead of a more common charging voltage such as
14.5V)?

Thanks,
Todd
--
http://gabrito.com
http://windandtides.com
http://gearandboats.com

wrote in news:1168660902.921941.207290
@a75g2000cwd.googlegroups.com:

I was curious if someone could explain why solar panels that charge a
12V system put out 19V?

Two reasons:

1 - Any charger must put out a voltage that exceeds the charging voltage,
up to 15V on a lead-acid battery, in order to force the current through
it backwards to charge it.

2 - All chargers have internal resistance that is effectively in series
with the charging power source. IN a solar cell, this is quite a high
series resistance. This inherent series resistance manifests itself when
the cells are charging near their design specification by making them so
hot they'll burn your hand and it turns the cells brown over time from
the heat. If they didn't have this, you'd never have to replace them.

So, here we have this circuit:

inherent
power source------series resistance------battery

When you take the battery off, you're measuring the power sources natural
output voltage, 19V. As your meter draws no current through the series
resistance, that resistance drops no voltage and you read 19V. But, if
the power source had no overhead of voltage and was, say, 15V, the
instant the battery started to draw charging current, the voltage drop
across the series resistance would drop the charging voltage below the
battery voltage and there'd be no charging current to speak of. But, at
some design level, if we had a 19V source, we could drop 19-14=5 volts
across the inherent series resistance at the design current output of the
solar panel. 19V is about "normal" for any size panel. The physics just
works out that way. Big panels have less series resistance than small
panels, so put out more current. The bigger the cells, the lower their
inherent resistance.

Keep the voltmeter across the solar panel and hook up a tail light bulb
across the panel. The 19V will drop drastically pulling the current from
the bulb through that resistance in the panel. If you use an ammeter to
measure the bulb current at this measured voltage you can calculate the
actual resistance of the panel, the voltage difference between no bulb
and bulb on, divided by the bulb current = the panel's resistance. If
you track the panel over time, you'll find the panels resistance
INCREASES over time until its useful output current finally drops to
useless when the cells are all cooked brown from the current....self
destructing, planned obsolescence....just like a GM car..(c;

That's why...

Larry
--
Extremely intelligent life exists that is so smart they never called
Earth.

Solar panels are made up of individual cells. Each cell puts out x volts and
enough cells are installed to typically output 15-19 v AT OPEN CIRCUIT. Note
the shouting. Every panel has an amp vs voltage curve. At open circuit
conditions the amperage is zero. The maximum wattage (power) point on the
curve (volts x amps) is about 15-16 v. If one fewer cell were installed this
curve would be x volts lower and too low to effectively charge your battery.

If you simply connect the panel to the battery, the battery will load the
panel down to about 13 v which is below the maximum power point. But it is
still pretty high. Maximum power regulators load the panel to its maximum
power point and then convert the voltage down to about 13 volts to charge
the batteries. This typically can increase power by 10-15%.

David

On 12 Jan 2007 20:01:43 -0800, wrote:

I was curious if someone could explain why solar panels that charge a
12V system put out 19V? I used a multi-meter to check the voltage on my
panels and was at first alarmed that they output 19V but then upon
looking online I discovered that it's fairly common. Anyhow, was
wondering if someone would be game to explain why they make many solar
panels to output 19V (instead of a more common charging voltage such as
14.5V)?

Thanks,
Todd

That's "no load" voltage. It will change as the light goes down as
well. (you can still see 12v even if it's raining- you just don't have
much current generated with which to charge a battery). Also, don't
forget to subtract .7v for the blocking diode that's going to be in
series with your batteries.
19v seems to be a magic number for power generation at this level.
Alternators put out something like that too before it hits the
regulator pack. Also, this number will be high when a panel is brand
new and decrease a 1 - 11/2v as the panel breaks in. All perfectly
normal. It takes a higher voltage to charge a lower one and I suppose
a spread like that takes aging and panel shading into consideration as
well. Not sure if the internal resistance of a panel changes with
overhead vs angled sun position or not. The difference between the 19v
generated and the voltage state of your battery is thrown away in
heat, either in the battery or the panel so they can't make this
number too high.
The discouraging thing about solar panels becomes sickeningly obvious
when you hook up a multi meter and wave the shadow of your hat over
even just one of the cells. The amperage output drops by two thirds.
For a single 5A panel it makes your $400, plus the cost of mounting,
wiring and monitoring look rather foolishly spent.

On Sat, 13 Jan 2007 08:25:10 -0800, "David&Joan"
wrote:

Solar panels are made up of individual cells. Each cell puts out x volts and
enough cells are installed to typically output 15-19 v AT OPEN CIRCUIT. Note
the shouting.

Yes, I did.
"An ideal solar cell may be modelled by a current source in parallel
with a diode"
http://en.wikipedia.org/wiki/Solar_cell

Every panel has an amp vs voltage curve. At open circuit
conditions the amperage is zero. The maximum wattage (power) point on the
curve (volts x amps) is about 15-16 v. If one fewer cell were installed this
curve would be x volts lower and too low to effectively charge your battery.

If you simply connect the panel to the battery, the battery will load the
panel down to about 13 v which is below the maximum power point. But it is
still pretty high. Maximum power regulators load the panel to its maximum
power point and then convert the voltage down to about 13 volts to charge
the batteries. This typically can increase power by 10-15%.

David

On Sat, 13 Jan 2007 08:38:40 -0800, ray lunder wrote:

On 12 Jan 2007 20:01:43 -0800, wrote:

I was curious if someone could explain why solar panels that charge a
12V system put out 19V? I used a multi-meter to check the voltage on my
panels and was at first alarmed that they output 19V but then upon
looking online I discovered that it's fairly common. Anyhow, was
wondering if someone would be game to explain why they make many solar
panels to output 19V (instead of a more common charging voltage such as
14.5V)?

Thanks,
Todd

That's "no load" voltage. It will change as the light goes down as
well. (you can still see 12v even if it's raining- you just don't have
much current generated with which to charge a battery). Also, don't
forget to subtract .7v for the blocking diode that's going to be in
series with your batteries.
19v seems to be a magic number for power generation at this level.
Alternators put out something like that too before it hits the
regulator pack. Also, this number will be high when a panel is brand
new and decrease a 1 - 11/2v as the panel breaks in. All perfectly
normal. It takes a higher voltage to charge a lower one and I suppose
a spread like that takes aging and panel shading into consideration as
well. Not sure if the internal resistance of a panel changes with
overhead vs angled sun position or not. The difference between the 19v
generated and the voltage state of your battery is thrown away in
heat, either in the battery or the panel so they can't make this
number too high.

This is incorrect as well. See my other post. All available current is
shunted by the diodes when open circuit, making heat. A lower battery
voltage reduces the wasted current but of course reduces the power
input to the battery and an excessive number of cells is money spent
for nothing.

The discouraging thing about solar panels becomes sickeningly obvious
when you hook up a multi meter and wave the shadow of your hat over
even just one of the cells. The amperage output drops by two thirds.
For a single 5A panel it makes your $400, plus the cost of mounting,
wiring and monitoring look rather foolishly spent.

You must have it charge through a regulator.
Batteries can accept high charge until surface of plates is charged then
they will accept a lower charge
wrote in message
oups.com...
I was curious if someone could explain why solar panels that charge a
12V system put out 19V? I used a multi-meter to check the voltage on my
panels and was at first alarmed that they output 19V but then upon
looking online I discovered that it's fairly common. Anyhow, was
wondering if someone would be game to explain why they make many solar
panels to output 19V (instead of a more common charging voltage such as
14.5V)?

Thanks,
Todd
--
http://gabrito.com
http://windandtides.com
http://gearandboats.com