Installing a Cree LED into a cheap solar landscape lamp. How do I go about it?

There wasnt enough room in the heading to type out my question pertaining to this potential project. Here's my dilemna. I have never modded anything by adding a modern star mounted LED to it. This is the typical inexpensive outdoor landscaping lamp, with the solar cell on the top and a basic 5mm LED inside. They come in packs of 6 or boxes of 24 or more for not much money. I know how the various LED's used for flashlights perform, but when it comes to finding an LED for a lamp application where the light will be dispersed 360 degrees downward, I dont know which LED would fit the bill. Also, I have never wired an LED mounted onto a star, so I dont know exactly how.

Next, about the circuitry...... Can I simply wire the new Cree LED(whichever I choose) using the same wiring and circuitry as is used for the stock 5mm LED setup? I'd imagine that the new LED will be brighter and more efficient than the old LED, but I would like to definitely increase the brightness over where it is now, which isnt much BTW. They arent very bright. I'd say a 200-400% lumen increase would be nice. Will I get that anywhere near that level of increased luminosity using the stock circuitry, considering that the new LED is more efficient and brighter?

As far as the stock solar cell is concerned, I would imagine its not going to be good enough for this project. I would like to try adding a larger, round solar cell that covers most of the top of the lamp, instead of just a small area in the center of the top lid. I assume I should be able to find a solar cell that generates more energy per cubic inch versus the stock cell, no?

Here's problem #2. I have done multiple google searches to figure out how to do a project like this, but I cant find squat. I am doing this more out of curiosity than anything else. If it works well, maybe I'll make more of them. I dont want to spend a fortune on each one. Lets say $5 - $8 for the LED with star, .50 cents for replacement wiring if needed. I dont know how much solar cells cost, but lets estimate $15 for a circular cell approx 4" in diameter. Lastly, the circuitry. I dont know about that. Will I be able to buy a small, basic circuit for this project that will provide the correct current, voltage, wattage, etc, and be able to maybe cut off the lamp after approx 7-9 hours of run time?

What do you think? Will it work, whats involved, can I re-use some of the existing parts? Or, do you know of a good site where I can read up on how to do projects like this, in laymans terms?

First, most of these solar outdoor lights are very low quality to start with. From the solar cells, to the control circuitry to the actual leds they don't have a long design life. Some use actual silicon solar cells, others use glass. The glass cells may last 2-3 years, but deteriorate quickly in comparison. The silicon ones last much longer. I have some silicon ones that still work fine after 10 years or more. If possible, choose one that is silicon.

You can, in fact, remove the existing white led and replace it with a Cree or other high brightness led. Yes, you will get more available light. But there are trade offs. If the original led gave 8-10 hours of light (when fully charged) the replacement high brightness led might only give you a couple of hours. Also the control circuitry may work well with 30-50 milliamps of current for the stock led, but may die quickly when faced with the current demand of a high brightness led. The high brightness led may also over heat as the available current to it may be great enough to cause it to get too hot. Heat sinking may be necessary to prevent this.

The bottom line is that, yes, you can do what you are describing but be prepared to experiment and buy additional components if your experiments are not successful.

Genes;4345665}\ said:

The bottom line is that, yes, you can do what you are describing but be prepared to experiment and buy additional components if your experiments are not successful.

Click to expand...

This!!

Ive asked my *** off on this forum, and learned so much from everyones help!

Ive never opened up a solar lamp, but have U ? what battery is installed from factory- voltage wise

Thats gonna make a difference in light output. most "high output" crees want 3+volts per led' and adequate amperage to hit Decent lumens

The battery is usually a single or double, AA NiCad or NiMh. Some of the newer ones (from Home Depot) use a single Lithium Ion (various sizes). Almost all use some sort of DC to DC converter to insure a semi constant voltage to the LED as the battery voltage drops. They usually don't use constant current. Some of the DC to DC converters will turn off the led when the battery voltage drops below a certain point. This protects the battery and prolongs its life. Others have no protection and the batteries will have very short lives. I have replaced the leds and converters in many of these with more sophisticated converters and control circuits. I have used Micro Chip PICs programmed to do all sorts of things from simple flashing to driving RGB leds in various patterns. I have some that flash rapidly and are used as driveway makers to keep people from driving into the creek next to our drive. I have some that use amber leds with PICs that look like candles burning. These always attract attention at night in the summer as I have them around our pool. The big issue is battery life. It doesn't take too many dark days and long nights in the winter to totally drain and ruin a battery. You have to make sure that some protection against total discharge is included or you will be replacing the batteries on an all too frequent interval. Overcharge is rarely an issue, but "over discharge" happens all the time. These things are cheap, so go buy some and start playing with them.

I use the Costco inexpensive Solar lights which do include low voltage cutoff.
One sort of neat feature is that when I walk the dogs late enough on a winter's evening that the lights have gone out, I can just hit the solar cell on top with my flashlight beam and they come back on again for a couple of minutes before turning off again. In a pinch, just tapping them sharply will do the same thing.
I think they use Li.
I also have a multi-head unit with a larger panel that uses a larger LiFePO4 cell which you can get replacements for at Home Depot.

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A more efficient LED will deliver more lumens, but you need to consider the relatively low levels of energy you're dealing with in the first place. The stock low-power 5mm LED is likely receiving 20mA or less. All the circuitry is designed around this low power - either through package thermal envelope or by design to limit current. Putting a more-efficient power LED in there may well result in more lumens, but it will likely be a just-noticeable incremental increase in lumens that comes at the expense of runtime, component lifespan, etc.

All the inexpensive solar lanterns I've seen have difficulty enough running for 4 hours after sunset anyway due to cheap solar cells, NiCd batteries, and control circuitry. It seems that once someone reaches the point that they demand performance they buy some low-voltage wired system such as Malibu.

There simply is not a way to get a bright light from a small solar cell. To drive a 1 Watt Cree or equivalent LED for a few hours is going to easily require a 1-2 foot sheet of solar panels! a better idea is to use a motion activated solar light:
http://www.amazon.com/dp/B0052SF0LO/?tag=cpf0b6-20

DIY for a light like this is not worth it, buy the unit instead.

Solar powered lights are called accent lights and are not to be confused with actual, y'know, lighting. Heh. They have to be dim and have a AAA rechargeable battery inside that can barely last through the night. I use LED rope lights instead from Orangetreetrade:
http://www.orangetreetrade.com/shop/white-led-rope-light-kits-c-159_163_301.html

the New LED strip lights also work a treat for lighting decks and stairs:
http://www.amazon.com/dp/B003G9408K/?tag=cpf0b6-20

To improve the light duration could you upgrade the battery in one of these cheap garden lights? If the original battery is a low capacity NiMH AA cell, could it be replaced with a Li 14500 cell? A protected battery would last longer as it would avoid over-discharging. Would the solar cell in these cheap things be enough to charge it? And would the DC-DC converter be able to handle the 3.x volts of the Li cell?

Thanks, Mike

You can change out the battery to a higher capacity cell. This will usually give you more light runtime during the summer months, but most of the solar cells are simply too small to fully charge one of the larger capacity cells during a typical winter day.