charge battery with solar panel

[knarf.be]

Hi,

I want to charge a 6v lead battery with a solar panel.
Specs solar panel:
5w (Voltage drops to 4v)
Voltage max in sun 9.5v
Voltage in shade 8-9v
Battery specs:
4 Ah
6vLead sealed

What is the best option to charge the battery? I want a system with a verh low voltage drop, and im using a ge diode to protect the solar panel.
Currently I'm planning to use a lm7807 low drop and diode, vin is 7.5 and higher, vout is 6.6v.
Anyone other ideas? Please let me know

[SeanB]

1A Shottky diode in series with the panel and connect across the battery. 5W panel will not overcharge the battery, it does not put out enough to drive the battery to the point where it will generate gas. It would be better to use a second panel in parallel to increase the current though, the panel is just too small to get any useful power out of it.

[commerou]

Hi
I want to charge a 12v lead acid battery with a 12v 13w solar panel, do I require any kind of circuit or could I just hook it straight up?
 

[knarf.be]

Hi
I want to charge a 12v lead acid battery with a 12v 13w solar panel, do I require any kind of circuit or could I just hook it straight up?

You always need a diode, and thanks to seanb, I know now it has to be a Shottky.

But for 12v you better use a cheap off the shelf charger. (These aren't available for 6v) Just look on ebay.
As far as I know it will destroy your battery without a descent charging circuit.

[Kevin.D]

Hi
I want to charge a 12v lead acid battery with a 12v 13w solar panel, do I require any kind of circuit or could I just hook it straight up?
 

Depends on the capacity of the lead acid battery .But for a car battery size (~60Ah) you can usually leave upto 10 Watt's max size panel on permanently without a regulator , but for  13 Watt panel I would use a regulator if it's conected permantley to prevent overcharging

[SeanB]

With a car battery ( especially as you can check water level) the 13W panel is ok, it will keep the battery close to full charge and will only need checking every month for water level.

[ivan747]

Just a tip. Diodes have a smaller voltage drop at higher temperatures, so don't heatsink them more than necessary! In fact, you may even want to place the diodes in the sun to heat them up. And don't use a 1A diode for a 1A solar panel. Why? Because it is operating at its maximum rating. Its lifespan will be shorter and it is more likely to fail. Also the voltage drop will probably be higher.

[ZOMGVTEK]

A car battery won't mind a 10W trickle during daylight hours. Lots of panels, especially smaller ones, have diodes built in, so that might be unnecessary. Just something to be aware of. You run into this a lot more with cheap 12V panels, since they typically have battery charging in mind.

[knarf.be]

It may be possible to charge it with 9v without problems, but I think it wil lower the battery life.
For now I've got a simple lm317K and a few resitors, and it seems to work fine, but there is a voltage drop of 1.5V. And if i have to use a si shottiky, there will be to much voltage drop.
I attached some photo's of the circuit, using a 5W 10 Ohm resistor as battery replacement.

[commerou]

Thanks for all the replies, as mentioned by ZOMGVTEK the solarpanel is made to the purpose of charging batteries from caravans, but mine would'nt charge anything, I guess I'll have to check all swithes and wires again.