Adding 'Oomph' to the Garden Solar Light





Introduction: Adding 'Oomph' to the Garden Solar Light

Tired of the feeble light from your Solar-rechargeable Garden lights? You can more than triple the light output with this new circuit. Works even with red or orange lights - as long as it runs off a single AA rechargeable battery!

Step 1: Remove the Old Circuit Board.

Cut the wires as close to the board as possible. We'll need the wires from the solar cell and the battery holder, so cut them as close to the circuit board as possible. If there are wires from a light sensor (colored Green here) we can cut those too - it's not needed anymore.

The board can go and join the others we removed from other projects.

Step 2: The New Turbo Circuit.

The new circuit uses fewer parts than the original but can deliver over 80mA, almost 4-times the current to a White or Blue LED while using about 250mA, which is double the efficiency of the original design.

We will need to use 1/2W LED, which are readily available on eBay:
here, or here. They each have slightly different products, but I've used both and they're both reliable.

The real star of this circuit is the driver transistor, FJN965, from Fairchild Semi. Capable of handling up to 5-amps of current in a TO-92 case, it will start at .9v and run the light until the battery drops to under 0.3-volts. You can get them from

Resistors, capacitors and inductors can be obtained from your local supply houses (eg Radio Shack, The Source), Sure Electronics, or at online surplus stores, like

The second image shows the layout using a Perfboard. S+ and S- indicate the wires from the Solar cell.

Step 3: Perfboard? or Try Just Winging It Freehand...

We will be using a 100mA white LED with a 140-degree spread. Start by slipping the leads through a scrap piece of perfboard to keep it upright.

If you want to follow the perfboard assembly, do that now, then solder the leads to the finished board.

The circuit is simple enough that the whole thing can be assembled freehand, which I will show you here.

Start by flipping the case over and bend the shorter (-) lead of the LED flat against the plastic. Then push it INTO the plastic by holding a hot soldering iron against the end of the lead until it melts it. Now it's SOLID!

Step 4: What IS This Sh*t???

Making our many legged creature.

Start by holding the 'C' lead of the 2N3906 to the 'B' lead of the FPN965 and soldering them together.

When you have attached the 2 capacitors and the diode to the transistors, this section is done.

Let me emphasize the need to COOL the parts after applying solder. The rule-of-thumb is to blow on the solder for TWICE as long as you apply heat. So if the joint took 2 seconds, cool it for 4 seconds. Heat is the second highest cause of failed circuits. (Number one is operator/designer stupidity.)

A few more images of the process of building our amorphous creature. Fine needle nose pliers are a must-have for little circuits like this. As is a GOOD soldering iron with a 1/16" or 1/32" tip.

Step 5: Attaching to the LED

I've trimmed and cleaned up all the little solder joints and I've bent into small hooks the 3 leads which require attachments.

Step 6: A Quick Test, And...


The green wires from the Light Sensor is left unconnected.

A 'feature' of this circuit is that once on, it will not be 'distracted' by flashes of light, from passing cars etc.

Here's another approach to make your garden light more effective - by adding Bling to the Oomph!

If you like this, see other LED ideas on my website:

Step 7: Another Option.

I have a light which sits on a gate surrounded by tall trees, with perhaps a max of 3 hours of sunlight in the afternoon. I added a small 2v, 30mA solar cell which is glued on facing West. It is simply added in series with the existing one. I also put a 2000mAH Sanyo battery in. Now even on overcast and rainy days, I get a good light showing the gate.



    • Woodworking Contest

      Woodworking Contest
    • Oil Contest

      Oil Contest
    • Make it Move Contest

      Make it Move Contest

    We have a be nice policy.
    Please be positive and constructive.




    So do I use the 2SD965 in place of the FJN965? This will actually be the first circuit I'll ever have built from scratch, so I'm very new to all the different parts and what they are called/do.


    Yes, they are identical. Fairchild had a licence to make them and decided to call them by a different name.

    So how much illumionation time do you get from a half-decent days sun????

    Hello QS; still love yer designs. I am having trouble geting yer OOmph circuit to start reliably. Could you please describe the mechanism that begins the whole converter process? I have read all the comments and replies; but no joy.

    I am using 2SC3202 specd at 2A: schottky diodes both places; and a 2N2907 with 22uH. Help

    1 reply

    Hi OldGuy,

    Very briefly, the circuit starts when the PNP begins conducting, which turns on the NPN, and this starts charging the coil. At the same time, current is drawn through the 150pF capacitor, which further increases the drive to the PNP and, subsequently, the NPN. When the capacitor is charged, the drive is cut off, and the magnetic field built up in the coil collapses and cause a voltage to appear across the ends. This voltage is placed in series with the NiCd battery to turn on the LED. Simultaneously, a small portion of this voltage is diverted through the diode (D2) to charge the 1uF cap. This provides about 3.5v to drive the PNP, which improves the brightness and efficiency. The cycle then restarts.

    As far as your circuit, double check the specs for the transistor you're using - the datasheet I have rates the C3202 for 500mA, not 2A. And the gain at that level may be a tad low. This may be offset by reducing the 1M-ohm to 720K, which will likely help with the startup reliability. If the output is low, you can try to increase the drive to the NPN (by going down to 680k), but remember you are already pushing the transistor to its operating limits. Fwiw, the FJN965 is also available as the 2SD965 on Ebay  The 2SC2500 also works here.

    Another thing I'd watch for is that the pinouts for the 2SC series is different from the BC series, which is different from the 2N series!

    Good luck!

    Here is a spice simulation of the new turbo circuit. I have substituted an FZT849 for the FJN965 being the closest type available in the simulator (8 amp) and I needed to reduce the 1meg resistor down to 100k before it would operate properly. I also found that increasing the 1 microF cap to 2 microF in the peak detector arm improved its voltage stability but takes slightly longer to startup.

    However, I also found that this circuit will not start if the voltage is below 1.1 volts (!). It should work down to at least 0.8 volts to be usable.

    ltspice simulation3.jpg
    2 replies

    Can you emulate a circuit to use a lithium instead and i can wire up 6 solar cells in series instead of the normal two? Id like to have the batteries cycle from 3.9v to 3.2v if possible. I just do not know how to use that program.


    Even if SPICE is getting close to real-world performance, it's not a valid emulation if you substitute a part that has less than 1/2 the gain of the FJN- / 2SD965. The 2SC2500 is also acceptable.

    Your observation about the 10uF cap is a valid one - it does improve the operation somewhat.

    This circuit was designed to make use of the power curve of the NiCad cell, so operation below 1-volt was not a consideration. However, for other applications, substituting a Schottky diode for the 1N4148 / 1N914 will allow the circuit to start at 0.7-volt and continue running until 0.4-volt.


    Any diode that can handle 150mA or more is suitable here. I've used the 1N4148 and they're still running after 5 years. If you can afford Schottky diodes they are even more efficient.

    Hi, great article. I have this exact problem. The Northern Ireland weather is almost always cloudy and overcast. How many hours will the battery drive the LED for?

    Is this my solution? or is there a better way for me to get my solar lights working in the garden right into the next morning but making sure the battery gets a good charge on a cloudy day? Many Thanks

    2 replies

    MrDiy88 - I'm no expert, but I upgraded mine with solar panels that put out more mA than the one that came with it. Mine came with a 40, I upgraded to a 225. They run all nite long now.

    See "Solar Walkway Lights Solar Panel Replacement" by Vlorbschnat on this site (Instructibles)


    Hello there!

    It's always questionable whether a battery is being charged on overcast days. In the northern latitudes, even on sunny days, it is necessary to point the solar cell in a southerly direction, angled approximately 35-degrees to get the maximum exposure to sunlight.

    A good rule of thumb is that typical solar cell will produce about 50mA to charge the NiCad under full sunlight. So that translates to about the same operating time, since the JT here uses about 50mA while operating. So basically, you'll need 10 hours of sunlight to run the light through the night. Less sunlight? Less time.

    That's the reason I developed alternate circuits, notably the 'reverse' Joule Thief and the Blinking Joule Thief. Both are attempts to wring a bit more operating time out of whatever sunlight we see each day.

    I'm a fan of the blinking JT circuit since it can multiply run times by a factor of over 3, meaning I get 3 days of "reserve" for each day of sunlight.

    Let me know if this answers your q!


    Can you help me with this?

    I have purchased the Moonrays globe type thru Walmart @ $12 to $15 each. After about 8 months some of them are developing the following problem: the Circuit or the Photocells are going bad. What I mean is that the "Moonray" brand 1.2v AA NI-Co batteries will not recharge in the unit. When I swap in a regular AA (for test purposes only) the light will glow. When I insert the suspect battery into another unit, it recharges fine and works well. This is the 4th one to exhibit this problem, and since I am heavily invested into this unit (I have about 40 of them operating around my property) I want to be able to repair them. I can upload a pic of board if that will help.


    This may be a bit off-topic, but I was having a problem with solar powered lights not lasting through the night. I was using the type with one Ni-CAD or NiMH cell. I put an ordinary AA alkaline battery in one and found it burned brighly all night. What is more, the lights have continued to operate this way for over two weeks. I can only conclude one of the following (1) there is enough energy in a non-rechargeable to outlast a rechargeable or (2) As in some of the advertised devices that recharge alkaline batteries, the solar cells in the light provide a sufficient recharge to keep the battery going. (3) The rechargeable batteries that come with solar lights are of inferior quality. I I tend to go with option (2). Has anyone else done this?

    2 replies

    dawp: This is VERY dangerous. Your solar panel is probably not going to be able to tell it's an alkaline, and your alkaline has been CHARGING! Heck, even most chargers don't have a safety mechanism to prevent charging alkalines. Lucky for you, the solar panels are only drip-charging the alkalines. Eventually, it'll burst, maybe within the year, and cause a nice little mess inside your light's battery chamber. It could potentially cause a fire or explosion as well. That's unlikely due to the speed at which it's charging, but I have to tell you it's possible. There's whole discussions about drip-charging alkalines. It's dangerous for those who don't know what they are doing, and there's a reason why commercial companies say NEVER to do it.

    The effect you are seeing is that alkalines have a lot more energy density than rechargeable batteries. It's a bit of a trade-off. Plus, since you've been drip-charging the alkaline, it's lasting even longer than it otherwise would. Considering even efficient circuits are still going to draw 100mAh or more, were it not charging, it'd have died within the week.

    Also, please view webgiant's response with extreme skepticism. Amp hours are a measure of energy, not power. And as I mentioned, alkalines are typically higher energy density than rechargeables, with the exception of lithium ion, which I'd highly recommend against using outside. Lithium catches fire with a nice giant green flame when it gets wet, and can explode if in high enough quantities.

    The option you have not considered, regarding your solar lights not lasting through the night, is that the sun falling where you have your solar lights did not fully recharge the original battery. Based on the solar cell size and composition (generally amorphous, which is less efficient than mono/polycrystalline silicon), most garden lights, even in full sun all day long, will still not charge the battery enough to last all night long. Solar garden lights are intended to provide light for about four to six hours in full sun, less in less sun.

    As an alkaline battery is charged in a completely different circuit than one used for NiCd or NiMH batteries, what is more likely happening is that your garden lights are simply running off the battery without the solar cell being involved, other than to shut off the light in the daytime. A full charge battery, such as an alkaline, can keep a single LED light on for 1-2 weeks, especially if it only runs at night, without recharging the battery. The LED "throwies" you may have seen on Instructables run for 1-2 weeks on a similar non-rechargeable battery, and they don't shut off in the daytime.

    A fully-charged rechargeable battery has at least the same, if not more, amp-hours of power (amperage) than a regular non-rechargeable battery. With solar garden lights you get what you pay for, so rechargeable batteries in cheap solar lights will probably be cheap as well. Some of them last for years while others do not last very long at all.

    Hello; on my lamps I have also glued a new cell at 45 degrees facing south to get more light especially in winter. The problem may come from overcharge in summer if the new 2000mAh battery you put is Ni-Mh.I think It would not be possible to put even a simple TL432 shunt regulator, because end of charge on NiMh is difficult to detect with easy circuit. You can see the lights I fixed on my site, just for images because it is in french:.


    Plenty of 2SD965 on ebay.