General advice on building a solar garden led lamp

Thread Starter

elsmandino

Joined Mar 3, 2022
6
Hi there.

As a beginner to electronics and am reading all I can to get up-to-speed.

I am hoping that by getting advice on what I am doing wrong/right, with a project, it will help me a little quicker.

At the moment, I am thinking of building one of those garden solar lamps that comes on when it gets dark.

Where do I start in terms of what parts I will need?

I want to use a solar panel to charge a rechargeable 1.2v AA battery.

Does this dictate the type of solar panel I will need to buy?

Is there a maximum voltage and current that you can use to charge such a battery?

Thanks very much.
 

Tonyr1084

Joined Sep 24, 2015
6,894
Well, um, your solar panel is going to need to be a higher voltage than the battery. But you don't want to go too high because overcharging the battery can be a problem.

The garden variety lamps they sell in the big box stores has a small solar panel whose output - I don't know. But there's a COB (Chip On Board) that controls charging and switching the light on at dusk. When the solar panel drops to some specified voltage it switches the light on. There may be just a few other components on board. Likely a resistor to limit the current going to the LED itself. But again, I don't know for sure.

To build a light that charges from the sun then switches on at dusk - at least for me, I'd need the solar panel and chargeable battery. Then I'd need a photo sensor to detect when light level is sufficiently dark to switch the LED on.

You mention a 1.2V battery, that is either a Lithium Metal Hydride type battery OR a Nickel Cadmium type. The Ni-Cad is more charge tolerant than the Li-MH type. So depending on what type of battery you choose you may also need some sort of BMS (Battery Management System) to 1) prevent over charge rate (current); and 2) prevent over discharge of the battery. I mostly know this to be true of Li-Ion batteries. But before you proceed you need to have chosen the type of battery or batteries you intend to use. Then knowing the battery voltage profile you choose an appropriate solar panel and appropriate BMS. Once you have that down you then need to decide what capacity the battery can maintain over night (or for as long as you want the LED to be illuminated) and what brightness you can get out of your design. Once you have that stuff down you can then begin gathering parts.

Back a few months ago I considered a 12 volt car battery to be charged via solar panel and a series of 12V LED's to be strung along my driveway. It ended up being much cheaper and more reliable to just use a 12VAC transformer and a light sensor with internal relay to switch the lights on at dusk and off at dawn. OK, they won't work during a power failure. Oh well. I don't get many power failures around here, so - - - .

Good luck with your endeavor. Learning is always an exciting undertaking. Especially when you learn from failures. Spectacular failures are not so much fun, not unless you enjoy turning your dollars into smoke.
 

Tonyr1084

Joined Sep 24, 2015
6,894
Just grabbed one of my older solar lights from years of use gone by. It also has a photo sensor. The board with the COB also has a current limiting resistor and a 1.2V Ni-Mh 600mAh battery. Oh, and an old spiders nest. Don't know how important that last part is.
 

Audioguru again

Joined Oct 21, 2019
4,693
Modern solar garden lights use the 2V solar panel as the light sensor to replace an old LDR, and use a Ni-MH battery (it has no Lithium in it) to replace an old Ni-Cad battery. They use a QX5252F IC that has 4 pins to replace the old Blob-On-Board.

Since a white or blue LED needs about 3.2V then the IC uses a small inductor in an oscillator to boost the voltage from a run-down battery from its 0.9V to enough voltage to light the LED plus to switch the LED on when there is darkness.

You can buy the IC on ebay and a pack of 10 of them might have one that works or you can buy one solar garden light that is guaranteed to work for a low cost at a big box store. Years ago they used solar panels with a clear plastic cover that quickly became useless due to sunburn. New ones have a glass cover that lasts for many years. The Chinese Ni-MH battery is garbage, replace it with an Energizer Ni-MH battery that has high quality made in Japan (like Eneloop ones). Duracell have some of their Ni-MH batteries (with low mAh rating) with poor performance made in China.

So buy a solar garden light, take it apart then put it back together.
 

Attachments

dl324

Joined Mar 30, 2015
14,480
Where do I start in terms of what parts I will need?

I want to use a solar panel to charge a rechargeable 1.2v AA battery.
After you do your make versus buy analysis, you'll find that you can't compete with mass produced items. The last batch I bought was 10 lights for $15 at Harbor Freight. That was a sale price. I think the regular price was $20.
 

Audioguru again

Joined Oct 21, 2019
4,693
I bought solar garden lights at Walmart for $1.00CAN each which is $.80US. They have a glass covered solar panel but the garbage battery soon needed replacement. The solar panel is probably worth the price I paid so the battery, IC, inductor, LED and housing were free.

I replaced the simple white LED with a colors changing LED. Then I added a Schottky diode feeding the LED and a 0.1uF filter capacitor parallel with the LED.
 

DickCappels

Joined Aug 21, 2008
8,711
Maybe this will help you a little bit.

This simple flyback/blocking oscillator LED power supply was adapted to and built into solar powered garden light by a talented experimenter in the United States known as "mrpiggss". The method of switching the power supply off during daylight hours, thus allowing the rechargeable cell to recharge, was taken from a circuit design by Nick Baroni, of Willetton, Washington, and published on the siliconchip.com.au website. Here is the design from mrpiggss' workbench.

1646850092355.png
The 1.5 volt cell used in this picture was replaced with a 1.25 volt nickel-cadmium cell.

1646850110379.png
Actual values used in mrpiggss' circuit.

Mr. Baroni's original circuit used a BC547, but mrpiggss found that a BC547C (the version he bought) would work as Q1 but not Q2. In his version, mrpiggss used 2N4401 transistors for both Q1 and Q2, to keep the bill of material as simple as possible. He also noted that if R1 was 15k, the sunlight gating function would be more sensitive, thus keeping the LED power supply off until it was darker than when R1 is 22k.

The core for L1 came from ebay with no part number or supplier but it is the size of a penny and about 3mm thick. The wire came in a 3 pack of magnet wire from Radio Shack and and are pure copper. Being green in color and 30 gauge, the wire is easy to handle and wind. The cores have 40 turns, 20+20 (wind 20 turns, pull out the center tap, then wind 20 turns more). and removing the coating is easier than with really thin wire. The insulation on this wire can just be burnt off with a lighter, and it comes off just like magic. No scraping or sanding, although he use a small emery board to give it some tooth for soldering.

Another very nice method of removing the insulation from magnet wire came from Christian Daniel of Germany: To quote his email:
"Scratching away the insulation is difficult with thin wires, it's too easy to cut or weaken them. I prefer fine corund sanding paper. Or - for very thin wires - I use an Asperin(R) pill and press the wire with the tinned hot soldering tip on it : opacht ! Put your eyes and nose away ! The hot organic acid destroys the insulation and it can be tinne nicely."

The solar panel is a standard one-battery panel. it has no info on it but puts out 1.5 volts in full sun. No idea about the current rating.

D1 can be nearly any silicon or germanium diode, provided it is rated to handle the solar panel's output current into a short circuit. For most of the panels used in garden lights, this means basically, any diode you can buy. A low power Schottky or germanium diode would have a lower forward voltage drop than a small signal silicon PN diode. The 1N4001 series, as used by mrpiggss is a good choice as well because its large junction area results in a relatively low forward voltage drop.

1646850246225.png

This is the "circuit side" of the printed circuit board.
The components are mounted on the opposite side. It should be noted that
the basing for the transistors corresponds to the 2N4401, and NOT the BC547.
 

Thread Starter

elsmandino

Joined Mar 3, 2022
6
Thanks every so much for all your responses on this.

I think my electronics ignorance is holding me back a bit on this - just trying to get my head around everything.

As a starting point, say I have a 1.2v 750mah battery.

Sorry if this is a silly question but is there a minimum and maximum voltage and current I can use to charge this battery?
 

ci139

Joined Jul 11, 2016
1,821
The 1.2V if it's not the service-life average of the 1.6 ... 0.9 V would hint the NiMH or Ni-Cad , speculatively - the 750mA·h would exclude the Ni-Cad.
simplified :
  • The maximum voltage depends on particular NiMH battery model and a bit also of it's age/condition , temperature (is about 1.45 to 1.5 V)
  • The maximum current depends (as in prev.) on it's specific chemistry/construction & aging , on it's A·h capacity , on it's SOC (state of charge) and temperature (safe rate might be C/5 but is usually C/10 , C/20 , for the .75 A·h cell it's respectively - 150mA and 75mA , 37mA)
  • https://www.google.com/search?q=nimh+charge+profile
reading list ; https://www.researchgate.net/public...Conquer_Technique_for_High-Capacity_Batteries
 

Thread Starter

elsmandino

Joined Mar 3, 2022
6
Thank you - starting to get this now.

Just an example, then:

Say I bought this particular battery:

5035513 | Ansmann MaxE AA NiMH Rechargeable AA Batteries, 800mAh, 1.2V - Pack of 2 | RS Components (rs-online.com)

The data sheet (which I need to start getting into the habit of finding for everything I buy, from now on):

800mAh 5035513 LSD SOLAR 2pcs blister Sino (rs-online.com)

Confirms a charge voltage of 1.5V and that 80-800ma current is acceptable for charging.

This being the case, could I in theory (forgetting other components like diodes for the time being) connect one of these to the battery and it would charge it?

RUNCCI-YUN 4pcs 1.5V 0.65W 60X80mm Polycrystalline Micro Mini Solar Panel For Solar Power Energy, DIY Home, Science Projects Toys+8 pcs JST SM 2 Pin Male and Female Connector : Amazon.co.uk: Business, Industry & Science

The voltage of 1.5V matches and the output would vary between 0-300mA, depending on how much son the solar panel was receiving.
 

Audioguru again

Joined Oct 21, 2019
4,693
Elesmandino, the datasheet for your AA Ni-MH batteries is more than 10 years old. Newer batteries are better and different.
Ansmann and other manufacturer websites show a new small AAA Ni-MH cell that is 800mAh.

Most solar garden lights with the popular QX5252F IC use a 2.0V solar panel, not 1.5V because the voltage drops with load current and a diode (blocks the solar panel from draining the battery at night) reduces the voltage.
My solar panels have four 0.5V segments but the Chinese one from Amazon has only three 0.5V segments.

My cheap solar garden lights use good solar panels with a glass top, not cheap Poly and are 40mm x 40mm. Poly solar panels were used years ago and have a limited lifetime caused by UV sunburn. They say 5 years but they are already sunburned after the first summer.

The charging current from a solar panel is rated when in summer sunshine at noon pointing directly at the sun and drops in the morning and afternoon. Some solar panels have a "short circuit" fake current rating. A solar panel is never used when shorted.
 
I bought a bunch of $1 solar garden lights with glass solar array. You can't beat that price.
I'm told the 30x30mm array of 3-1/2 cells on glass is Cadmium Telluride. It's strange the 4th cell is 1/2 size of the others.
In full sun, I measure Isc=20mA and Voc=2.3V and the load single LED YX805 IC 270uH draws about 4.2mA, so I would say it can charge at ~18mA in full sun. The AAA "600mAh" battery, well it's a bit cheap. So these perform poorly.

I also have a few different Ikea Solvinden solar lights, they don't work well. One has two solar cells/3 LED's under a dark white cone, and it doesn't charge much. The other indoor light has the solar cell pointing up to the sky and my ceiling does not have much sun lol. I ripped out the solar cell and pointed it sideways for window sun. I have schematics for the Ikea lights as well.

But overall, it's fun to do the math on how much sun you need to recharge and the sizing of battery/solar array/LED for something to work most of the time.

I just tried a 2.3V 200mA 50x80mm panel, and it worked much better as we can have weeks of cloud during winter. Next is an upgrade to AA.
 

Thread Starter

elsmandino

Joined Mar 3, 2022
6
Thanks for sticking with me on this - must feel like Usain Bolt teaching someone to walk.

It also did not help that I even managed to misspell "sun" in my last post, which is particularly worrying.

Anyway, it looks like I need to do a bit of shopping and try building some stuff.

I note that my best bet is to go to some cheapy stores and try to find some lights with glass solar panels.

I shall also order some QX5252F components to play with.

I also understand that I shall need an inductor as well - which one do you recommend?

I have watched as many solar light videos (and joule thief videos) as I can and I think I understand the basics of how boost converters work, now.

With regard to the battery, is 800mAh enough or should I get something bigger?
 

Audioguru again

Joined Oct 21, 2019
4,693
I have many cheap solar garden lights and the newer ones all came with a glass-covered solar panel, a QX5252F IC and a little inductor that looks like a 1/4W resistor with inductances from 47uH (bright LED) to 150uH (dim LED). They all came with a very poor quality Chinese AAA battery that I replaced with a high quality Energizer American 800mAh Ni-MH AAA cell. Most of the solar garden lights were purchased at Walmart and they all worked, none needed to be returned. Solar garden lights from some cheapy stores are junk.

I have never bought solar panels, the QX5252F IC (maybe fake untested ones are sold online separately) or the inductors.
I think you should buy a package of some solar garden lights at a home products store to get good parts.

I replaced the white LED in many of my solar garden lights with a colors-changing LED and added a series 1N5817 Schottky diode then a 0.1uF ceramic filter capacitor marked 104 parallel to the LED.
 

dl324

Joined Mar 30, 2015
14,480
Thanks for sticking with me on this - must feel like Usain Bolt teaching someone to walk.
I don't see how you're going to be able to build anything with the fit and finish of a commercial product for anywhere near the $1-2 you could purchase them for.

Is this just a cost-and-looks-be-damned learning exercise?
 

DickCappels

Joined Aug 21, 2008
8,711
Chill... sometimes people build things to enhance their understanding or just because the have a desire to do it. I have made many things I could buy but building something and using it, maybe for years after can be very satisfying. I made a neon night-light for the hallway in my fathers house (there were no LEDs at the time). It ran for decades before it was replaced. You can't buy that kind of satisfaction.
 

ErnieM

Joined Apr 24, 2011
8,294
Chill... sometimes people build things to enhance their understanding or just because the have a desire to do it. <snip>
In my case I have some garden lights I particularly like, and since I cannot find anything close to them I have rebuilt them several times over. Sometimes just the battery or holder, sometimes the electronics, sometimes the solar cell too. I have a huge stock of control boards with LEDS bought off EBay a few years back. I helped thy guy out when I messaged him that his NY address was coming up as somewhere in Europe and refusing my PayPal payment, so he doubled my order for free.

If the solar cell is out I buy another light and start disassembly.
 
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