Solarpanel and charging

Thread Starter

FroceMaster

Joined Jan 28, 2012
541
Hi.
Have this solarpanel that generate 12-30v with no load,
How would be best to extract 5v 500mA from this.
Either with 7805 or zener diode, or any ???
 

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MikeML

Joined Oct 2, 2009
5,444
What current will the panel deliver in bright sun if it is connected to a 12V car battery (using the battery as temporary test load)?
What is the nature of the load? Does its current demand vary, or is it steady at 1/2A?
 

spinnaker

Joined Oct 29, 2009
7,815
Hi.
Have this solarpanel that generate 12-30v with no load,
How would be best to extract 5v 500mA from this.
Either with 7805 or zener diode, or any ???
A linear regulator is the wrong way to go. You will dissipate most of the energy in heat. What you want is a switching regulator. The easy way to go is to pick up on of those USB chargers for the car and hack it apart. They are designed for 12V in and 5V out. They usually use a 34063 which is an older switcher and not the most efficient. You could also pick up full modules from eBay or just build your own.
 

Thread Starter

FroceMaster

Joined Jan 28, 2012
541
Have used something like that.
I have no battery to 12v
I have solarpanel with 12v out and a battery 3.2v for windgauge.
Need to charge this battery
 

MikeML

Joined Oct 2, 2009
5,444
...
I have no battery to 12v
I have ... a battery 3.2v for windgauge.
Need to charge this battery
Ok, take the panel, connect it to a 20Ω resistor. Measure voltage across resistor in bright sun.
Try it with a 100Ω resistor.

What battery chemistry?
 

Thread Starter

FroceMaster

Joined Jan 28, 2012
541
Hi
Lithum ion.
He have tried to put a 3w 12v bulp over the solarpanel. 5.5 ohm. Voltage drop to 0.09v 2.96 mA.
 

wayneh

Joined Sep 9, 2010
16,102
In bright sun? That's pathetic. Perhaps you are not measuring the current properly? Post a photo.
 

Thread Starter

FroceMaster

Joined Jan 28, 2012
541
Correct done volt parrelel over the bulp. Amp in series.
Have no sun these days in denmark so use very bright light to light the panel up.
21.5v with no load.
 

wayneh

Joined Sep 9, 2010
16,102
Have no sun these days in denmark so use very bright light to light the panel up.
Ah, OK. It's difficult to get enough light to simulate sunlight.

Let's back up now and talk about what your goal is. You mentioned wanting 5V and 500mA from this? That's 2.5W of output power and obviously cannot happen at low illumination.

Your best bet is a buck converter that will allow your panel to operate at ~24V where it is most efficient. As long as you have enough light, the converter will provide a steady 5V at the output with a high conversion efficiency. You can find buck converters on e-bay. Many, many choices and very cheap.

It's still possible that your panel will not deliver enough power to meet your goal.
 

Roderick Young

Joined Feb 22, 2015
408
How large is the panel, physically? If the short circuit current is about 3 mA, that's a very small or weak panel. You might be able to trickle charge a battery by connecting the panel directly, with no other electronics.
 

tom_s

Joined Jun 27, 2014
302
20w max using a marine grade panel that size. personally, post #10 best option, i doubt you have marine grade panel.
 

Roderick Young

Joined Feb 22, 2015
408
apologies, google matches are so .....
only looked for the wattage rating, didn't check the size that was imperial :/

https://www.emarineinc.com/Kyocera-20-Watt-12-Volt-Solar-Panel-Fixed-Frame

on a good note, got the new transition glasses today :)
Ah, 14 x 20 inches, yes, that makes sense. Kyocera is also a reputable manufacturer.

If I were doing this, I would just get a small buck regulator based on the LM2596. You can buy them on eBay for not very much, for example: http://www.ebay.com/itm/LM2596-Buck-Step-down-Power-Converter-Module-DC-4-0-40-to-1-3-37V-LED-Voltmeter-/400802470941?hash=item5d51b05c1d:g:XyoAAOSwLa9UXJBL . There are even some with a built-in USB socket, if that's what you're trying to power. Search "lm2596 usb" and you'll find them.
 
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