Author Topic: Solar charger with LM7806  (Read 7163 times)

kje

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Solar charger with LM7806
« on: May 07, 2012, 08:37:37 AM »
Here is some pictures of my solar charger project. I`m trying to connect a 9V 2W solar panel, schottky diode 5819, LM7806 regulator, on/off rocket led switch,  digital voltmeter, 4 AA 1,5v rechargable alkaline batteries and a USB.

The USB will be for load (smartphone charging), but I haven`t connected the USB yet so I don`t know if the solar panel are charging the batteries now... From the solar panel I soldered in a diode to prevent the batteries from discharge into the solar panel. After the diode I use a LM7806 regulator to step down the voltage to 6v so it can charge the four 1,5v batteries which is 6v in series. On the 7806 regulator I added a boiler plate flange for cooling. From the regulator it goes to the on/off switch which has three points; 1) power, 2) load and 3) ground. The voltmeter is for controlling the status of the batteries so I don`t overcharge them. Is the wiring correct so far?

« Last Edit: May 07, 2012, 08:48:26 AM by kje »

MJLorton

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Re: Solar charger with LM7806
« Reply #1 on: May 08, 2012, 03:46:58 AM »
Here is some pictures of my solar charger project. I`m trying to connect a 9V 2W solar panel, schottky diode 5819, LM7806 regulator, on/off rocket led switch,  digital voltmeter, 4 AA 1,5v rechargable alkaline batteries and a USB.

The USB will be for load (smartphone charging), but I haven`t connected the USB yet so I don`t know if the solar panel are charging the batteries now... From the solar panel I soldered in a diode to prevent the batteries from discharge into the solar panel. After the diode I use a LM7806 regulator to step down the voltage to 6v so it can charge the four 1,5v batteries which is 6v in series. On the 7806 regulator I added a boiler plate flange for cooling. From the regulator it goes to the on/off switch which has three points; 1) power, 2) load and 3) ground. The voltmeter is for controlling the status of the batteries so I don`t overcharge them. Is the wiring correct so far?

Hi kje,

From what I can see your wiring is correct. I'm very happy to see you have got this project off the ground and posted the pictures. That solar panel looks like the same type I have....does it have a plastic protective film on it? If so I would remove it so that it works better.
If you take it all out into the sun do you see the voltage rise on the voltmeter?
The circuit (like mine) lacks the charge control to prevent over charging but as you said you can monitor the voltage in the mean time.

This is a brilliant start, please post progress.

Cheers,
Martin.
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

kje

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Re: Solar charger with LM7806
« Reply #2 on: May 09, 2012, 11:29:00 AM »

Hi kje,

From what I can see your wiring is correct. I'm very happy to see you have got this project off the ground and posted the pictures. That solar panel looks like the same type I have....does it have a plastic protective film on it? If so I would remove it so that it works better.
If you take it all out into the sun do you see the voltage rise on the voltmeter?
The circuit (like mine) lacks the charge control to prevent over charging but as you said you can monitor the voltage in the mean time.

This is a brilliant start, please post progress.

Cheers,
Martin.

Thank you Martin. I found out a voltage regulator is kind of wasteful since it will convert the difference between the voltage in and voltage out to heat. So I will use 3 cells (4,5v), charged by the 9v panel, connected to a step up converter to provide the 5v for my USB devices. I might consider paralling two sets of 3 cells. Still 4,5, but, twice the capacity. I`ll get more energy from the cells using the step up converter than using a voltage regulator. I have to order the parts.

In the meantime I tried to build a simple solar charger with just the diode and a 7805 regulator I had. This is without batteries (see picture below). Everything is glued on the panels backside. I measured 4,88v in bright light without any load. It didn`t charge my USB speaker. I measured 4,33v voltage when my USB speaker was connected. When I connect the speaker to my laptop a red light indicate charging, but when I connect it to the solar panel its a blue light (like when it`s on) wich gets stronger or weaker depending on the light. I guess that means it give power to the speaker but not enough voltage for charging? Any thoughts about why this didn`t work?

I also made a second simple version of the solar charger, but with the 7806 regulator (the left one in the picture). This version didn`t manage to charge the USB speaker either (you can see the speaker to the left in the picture as well). I measured 6v from the USB without any load, but with the speaker I measured 4,38v (almost the same as the first solar version). My hope was this version would have higher voltage as I used the 7806 regulator...

« Last Edit: May 09, 2012, 07:48:48 PM by kje »

MJLorton

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Re: Solar charger with LM7806
« Reply #3 on: May 10, 2012, 07:33:21 AM »

Thank you Martin. I found out a voltage regulator is kind of wasteful since it will convert the difference between the voltage in and voltage out to heat. So I will use 3 cells (4,5v), charged by the 9v panel, connected to a step up converter to provide the 5v for my USB devices. I might consider paralling two sets of 3 cells. Still 4,5, but, twice the capacity. I`ll get more energy from the cells using the step up converter than using a voltage regulator. I have to order the parts.

In the meantime I tried to build a simple solar charger with just the diode and a 7805 regulator I had. This is without batteries (see picture below). Everything is glued on the panels backside. I measured 4,88v in bright light without any load. It didn`t charge my USB speaker. I measured 4,33v voltage when my USB speaker was connected. When I connect the speaker to my laptop a red light indicate charging, but when I connect it to the solar panel its a blue light (like when it`s on) wich gets stronger or weaker depending on the light. I guess that means it give power to the speaker but not enough voltage for charging? Any thoughts about why this didn`t work?

I also made a second simple version of the solar charger, but with the 7806 regulator (the left one in the picture). This version didn`t manage to charge the USB speaker either (you can see the speaker to the left in the picture as well). I measured 6v from the USB without any load, but with the speaker I measured 4,38v (almost the same as the first solar version). My hope was this version would have higher voltage as I used the 7806 regulator...

Yes....those voltage regulators are ugly in that regard and hence that's why I did not use them in my small projects. But, you have moved onto an excellent idea now by considering the step up converter. You could also think about linking the two cells in series and using a DC-DC converter to step down to 5 volts. This is the approach I was taking with my solar powered Kindle case....but that is still a work in progress. It will be interesting to see how effective the step up is so I look forward to hearing the feedback once you have it together.

In terms of the solar USB and the speaker...I think you are correct about there not being enough power....but perhaps it's not the power but the voltage specifically. The USB specification is for about 5 volts so you need to at least meet that.....and then have enough current.

Your second attempt  with the 7806 would have the same issue. I would stay with the 7805 if you are trying to directly power USB. As there will be losses through the regulator I would connect the two solar cells in series so you will at least get the right voltage out of the 7805 after losses. That may have a better chance of getting the speaker to enter a charge state.

Cheers,
Martin.
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

kje

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Re: Solar charger with LM7806
« Reply #4 on: May 22, 2012, 05:06:00 PM »
Both the simple versions of the solar charger are successfully charge my Nokia phone and my friends Samsung Galaxy in the sun. :)

Barryg41

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Re: Solar charger with LM7806
« Reply #5 on: May 22, 2012, 09:30:14 PM »
I don't know if you are just wanting to build your own circuit, but would something like this solar boost converter do what you want to do?

It's a converter that is CC and CV that is fully configurable for charging and load use with notification LEDs on the pcb.

http://www.ebay.com/itm/Solar-Wind-Energy-DC-Boost-Buck-Converter-Constant-Current-Voltage-Charger-Power-/280883522203?pt=LH_DefaultDomain_0&hash=item4165f66a9b#ht_4628wt_902

Cheers

birrbert

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Re: Solar charger with LM7806
« Reply #6 on: June 20, 2012, 05:55:23 AM »
Hi!

I just wanted to check in and ask whether you managed to make progress in the past month or so?

Also, did you check the Voltage and Amperage requirements of the speakers? OK, we know that it needs 5 Volts, since it's a USB speaker, but a USB port can deliver up to 500 mA. Maybe the speaker needs 400 mA and the solar cells provide only 300 mA. Don't pay attention to the figures because I have no idea about the Amperage requirements of your USB speaker, but maybe this is the phenomenon that's causing the trouble (plus low voltage, as Martin said it too, since you mentioned that the output is only 4.88-4.33 Volts).

I, myself, am trying to understand how Voltage and Amperage work together to power different devices, because I believe that's the key thing I'm missing at the moment. The problem is that there are so many situations that it's confusing me. Hopefully Martin can shed some light with the new episode of the Electronics tutorial series.

By the way, you wrote "charge my USB speaker". Does this mean that your speakers have batteries and they are not directly powered from the USB port?

edit: if a voltage regulator converts excess voltage into heat, then what does a DC to DC step down converter do with the excess voltage?
« Last Edit: June 20, 2012, 07:10:27 AM by birrbert »
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