Hi - I have a small solar panel (~6v) and a little rechargeable battery back (12v, 1,2Ah).
I'm new to solar things, I was just hoping to make something that'd allow a lightbulb or two to be used for a few hours every day.
I read that the solar panel voltage needs to be about 2 to 3v higher than the battery's voltage to ensure it will charge, and will not damage. I'm just wondering if I should buy a second one of these 6v panels to run in series or get a bigger one.
Voltaje: 6v
Corriente: 0 - 330mA Voltaje en circuito abierto: 7v
Potencia: 2W
Dimensiones: 136 x 110 x 3 mm
Material: Silicio policristalino
(sorry it's in spanish, but you get the idea)
It says 7v in open circuit - does that mean that two in series would give me 14v and make it a very suitable match for this 12v battery?
While I'm asking solar things, is this battery really a good choice for what I want (just some lighting, maybe a phone charger)? Would it be possible to build a little charging controller with it?
jtbennett:
Hi - I have a small solar panel (~6v) and a little rechargeable battery back (12v, 1,2Ah).
I'm new to solar things, I was just hoping to make something that'd allow a lightbulb or two to be used for a few hours every day.
I read that the solar panel voltage needs to be about 2 to 3v higher than the battery's voltage to ensure it will charge, and will not damage. I'm just wondering if I should buy a second one of these 6v panels to run in series or get a bigger one.
Voltaje: 6v
Corriente: 0 - 330mA Voltaje en circuito abierto: 7v
Potencia: 2W
Dimensiones: 136 x 110 x 3 mm
Material: Silicio policristalino
(sorry it's in spanish, but you get the idea)
It says 7v in open circuit - does that mean that two in series would give me 14v and make it a very suitable match for this 12v battery?
While I'm asking solar things, is this battery really a good choice for what I want (just some lighting, maybe a phone charger)? Would it be possible to build a little charging controller with it?
I wouldn't connect the solar panel directly to the battery, you will need some kind of protection. Solar panels are everithing but constant. The voltage and current they provide varies over a lot of factor (sun, temperature...) and their MPP (Maximum power point) varies consequently.
Normally solar controllers are used they ensure that the battery is charged properly by obtaining the maximum amount of power from the solar panel. There are of two types: PWM and MPPT.
If you, for example, have panels with a higher voltage than the battery's nominal voltage you could overload the battery and it could explode.
Just buy a PWM solar charge controller (you can find chinese products for less than 20€) and you will avoid problems
Hello jtbennett,
Please note: A 12 volt gell cell or lead acid battery (sealed or not) has a
terminal voltage of 13.8 volts when fully charged. You can connect
solar panels in series for higher voltage. The solar panel specs are
for the panel in full sunlight: 7 volts out with no load, 6 volts out with
a 330 ma. load (2 Watts). I'm not sure if you need a diode between
the battery and the solar panel to prevent discharging when there is
not enough sunlight. The 330 ma. rating seems acceptable for battery
charging.
Herb
MBC99:
If you, for example, have panels with a higher voltage than the battery's nominal voltage you could overload the battery and it could explode.
Just buy a PWM solar charge controller (you can find chinese products for less than 20€) and you will avoid problems
If I get a solar charge controller, is there still need to worry about matching the voltage output of each of the components (battery and panel)?
herbschwarz:
The solar panel specs are
for the panel in full sunlight: 7 volts out with no load, 6 volts out with
a 330 ma. load (2 Watts). I'm not sure if you need a diode between
the battery and the solar panel to prevent discharging when there is
not enough sunlight. The 330 ma. rating seems acceptable for battery
charging.
Herb
I live in southern mexico in the yucatan, so it's extremely sunny and hot. I assume it'll be putting out the maximum voltage most of the day. I'm mostly wondering about matching the voltages of the battery and panel - how necessary is that if you have a charge controller?
This site says I need about 18v of solar input to properly charge a 12v battery using a PWM controller due to loss of power in the cables (wat? they didn't explain that very well).
So, technically, 3 of these 6v things would be suitable at full power - on paper. Would it be silly to get a 4th one and wire it up? Would that amount of excess voltage (6v theoretically) be enough to cause damage or wear on the batteries?
Or should I just buy a single, larger solar panel that puts out 18v max?
So, technically, 3 of these 6v things would be suitable at full power - on paper.
Yes, three will charge the cell. The panels might push 200-300 mA into the battery in full sun, so it would take 6-10 hours to charge a 1.2 Ah cell.
You need a diode (1N4001 or similar) between the battery and the cells, to prevent the cells from discharging the battery during cloudy or dark periods.
jtbennett:
I read that the solar panel voltage needs to be about 2 to 3v higher than the battery's voltage to ensure it will charge, and will not damage. I'm just wondering if I should buy a second one of these 6v panels to run in series or get a bigger one.
No, its 50% higher, not 2 to 3V higher.
The full-sun open circuit voltage of a panel to charge a 12V battery should be 18V or so. This
is about 36 individual cells in series.
This is partly because you won't get the open circuit voltage from the panel once you pull
current from it, and partly because on overcast days you will get about 15V open-circuit from the panel
anyway.
If a 15V full-sun open-circuit panel was used on an overcast day it would do nothing useful.
There is confusion as people sometimes sell solar panels by battery voltage, rather than open-circuit
voltage, so you have to read the specs carefully. Each cell develops about 0.5V open-circuit for
a silicon based PV panel, counting the cells will help confirm the ratings if there's a picture.
jtbennett: This site says I need about 18v of solar input to properly charge a 12v battery using a PWM controller due to loss of power in the cables (wat? they didn't explain that very well).
So, technically, 3 of these 6v things would be suitable at full power - on paper. Would it be silly to get a 4th one and wire it up? Would that amount of excess voltage (6v theoretically) be enough to cause damage or wear on the batteries?
Or should I just buy a single, larger solar panel that puts out 18v max?
As I explain above this is nothing to do with cables, its that open-circuit voltage is for zero current and
full sun, so it needs to be much larger than the battery voltage.
