Voltage Regulator and Solar Panel

[Disco Dan]

I have a 12v solar panel that I need to step down to 5-6v

I have a voltage regulator 7805CT which when I connect to a 6v battery pack outputs 5v without a problem.

However when I connect the 12v solar panel to it the input voltage (output from panel) drops instantly to 2-3v and the output from the voltage regulator then is only 1.2ish volts. removing the voltage regulator from the solar panel the output from the panel jumps back 12v.

I tried connecting a diode to the +v feed from the panel (which dropped the voltage by 1v) but as soon as I connected the voltage regulator again it instantly dropped to 1.2v (output leg of regulator).

* I have checked the solar panel - no regulating circuitry that I could find and appears to be just two wires giving 12v (it is actually a panel designed to top up car batteries but I cut off the clamps)
* Voltage regulator appears to work fine with lower voltages inputted 6-8v was tried and output was 5v.

1) Do I have the correct voltage regulator? (rated for 12v)
2) Is the panel shorting out when connect to regulator?
3) Could the amperage of the panel be too low (I was using only ambient light on overcast day) that the voltage regulator has a cut off?
4) Have I damaged the voltage regulator? It has been used for a few projects and has been soldered to about 10 different breadboards and wires soldered directly to it over and over.

Attached image shows the how I have wired it up to the solar panel and the voltages it should output.

Appreciated any help! Thank you all in advance!

Daniel

 

[davenn]

The 12V from the panel you are reading will be its open circuit voltage its voltage under load will be quite a bit less

The 7805 needs at least 2V more on its input that its regulated output voltage
( that goes for all the 78xx series regulators)

do you have a spec sheet for the panel ?

Dave

 

[Disco Dan]

The 12V from the panel you are reading will be its open circuit voltage its voltage under load will be quite a bit less

The 7805 needs at least 2V more on its input that its regulated output voltage
( that goes for all the 78xx series regulators)

do you have a spec sheet for the panel ?

Dave

Thank you for your reply,

Under ambient light the solar panel only produces 0.03ma - I think this may be the problem, I need to test it in sunlight. Despite it reading over 12v prior to connection to regulator.

Only data I could find on the panel is here:

http://www.supercheapauto.co.nz/onl...W-Solar-Trickle-Charger.aspx?pid=292829#Cross

Regulator info:

https://www.sparkfun.com/datasheets/Components/LM7805.pdf

 

[davenn]

Yes, you must use it under sunlight, else all your tests are pretty meaningless

Dave

 

[Disco Dan]

I have attached images of my smaller Solar Panel attached to meter. This one is unregulated and gives off 6v.

It connects to a LiPo battery charger designed for solar power input that then charges a 2000mA LiPo battery. This then plugs into my iPhone and charges that.

This panel works with my charger (5-6v input required). However to compete with the mains adapter I was hoping for 500-1000mA at 5-6v.

 

[Disco Dan]

These photos show my larger 12v panel attached to the meter both with and without the voltage regulator attached.

Please excuse the crudity of the regulator lead, the wires to the plug were far too short to make it any tidier.

 

[Disco Dan]

Testing using the smaller panel - I attempted to charge my 2000mah LiPo battery and it was on the window sill all day in full NZ sun from dawn to dusk and was still not fully charged. I had to plug in the mains plug pack (which is 500mA) to finish it off.

Not ideal.

The original plan was for me to be able to charge the LiPo battery during the day then charge my phone off it in the evening or overnight. Having to plug it into the mains defeats the purpose!

Thanks again in advance!

 

[Disco Dan]

In addition - the spec sheet for the small solar panel states 330mA at 6v output.

I'm guessing it needs to be angled right at the sun rather than the 45 degrees I did my testing on.

Still not enough though.