# Help I want to run LED light by solar power & be dusk to dawn



## Tempest2 (Jan 5, 2013)

Hi All. I purchased a reel of LED lights off of eBay & I want them Powered by solar power & have the dusk to dawn option. I have been searching online & have just gotten more confused!!!

These are the details of the lights I got.
Product Specification
LED TypeSMD 3528 *Number of LEDs-300
Light Output*900-1100 lumen *Power*24W
Input Voltage*12VDC*Current*2A

I am trying to figure out how many solar panels I will need to run them? Size of the panels & what wattage or volts they have to equal too. What size battery? I do have some small garden solar power lights that i can take parts from & they do have the dusk to dawn feature on them.

Any & all information, help or advice you can give me would be greatly appreciated!
Thank you very much


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## konig (Jan 5, 2013)

You need to say how many hours you want the lights to be turn on, dusk to dawn varies over the year and were you live in the world.
Let say you live in Sweden like me, at this time of year it`s dark 18h a day. Your lights uses 24W, 24*18=432Wh. Battery size then is 432Wh/12V=36Ah.
If it`s dark 18h a day, you have sunlight for 6h. To produce 432Wh in 6h you need a 72W solar panel. And remember this under perfect conditions. Expect real life to be a bit worse.


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## SemiMan (Jan 6, 2013)

konig said:


> You need to say how many hours you want the lights to be turn on, dusk to dawn varies over the year and were you live in the world.
> Let say you live in Sweden like me, at this time of year it`s dark 18h a day. Your lights uses 24W, 24*18=432Wh. Battery size then is 432Wh/12V=36Ah.
> If it`s dark 18h a day, you have sunlight for 6h. To produce 432Wh in 6h you need a 72W solar panel. And remember this under perfect conditions. Expect real life to be a bit worse.



Expect real world to be much much worse.

Biggest question is how reliable you want this to be ... And where somewhat accurately you live as winter solar resources can vary over small distances.

A reliable solution could be 200 to 300 watts of solar panels and 200 to 300 amp hours of battery ... Unless you live fairly north in which case more is needed ... And less somewhat south.

Semiman


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## foxtrot824 (Jan 6, 2013)

I don't know if you are set on using the light you already have and depending on what you are illuminating a lower consumption light might be a good option for you to reduce the size of your panel array and battery bank. Bottom line will still come down to you need to put as much power into the system as you need to get out of it and then have a reserve for cloudy and cold days. To give you an idea of physical size (since you're talking about some small garden lights) a 60w solar panel is about (just a ball park size) 2'x2'. If weight is not an issue a sealed lead acid (SLA) battery is probably going to be a good choice for your setup. A car battery will work too but they don't like to be run down too much and they are not sealed so they can spill. You will also need a charge controller to regulate the power coming from the panels to the batteries. Some have build in controllers for the load like the SunLight 10, this will allow you to set it to run a set number of hours or dusk to dawn. I hope this helps.


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## Illum (Jan 6, 2013)

I wanted to make my own solar lamp too... but gave up after confronting reality one too many times in the last couple years. Initially it was meant to build a security light for the utility shed that illuminates all four sides using 4 LEDs total in a 4S1P configuration and operated at 350ma. Five PV purchases [from 5W to 50W], three charge controllers [from 3A to 10A], and ten lead acid batteries later [ruined quite a few 7s, 12s, and 35AHs] I gave up the idea of running anything on PV as a permanent fixture that draws in excess of 1A direct drive. Every year is the same, one too many hurricane/rain days and the batteries go kaput. If I'm not in Florida, those batteries might still be alive :shrug:
The most successful circuit I've came up with is driving a single CREE XPG at 700mA, using a LuxDrive buckpuck, switched by a relay triggered using a LTR-4206E IR detector, only drawback is that is relay is always "ON" [turns the buckpuck off] when daylights out, which siphons some power of of the battery when it should be recharging. 

*Sun Hours* "I have sunshine all day, but why is my PV not producing?"
Simple, depending on where you are located, sunshine intensity varies alot! As opposed to measuring "how many hours of sunshine there are" Theres a unit called Sun-Hours. Where I am at, It can be sunny all day, but on average I many only receive gain from only about 4 productive hours of sunshine. PV placement and angle will vary this as well.
*What this means*: If you insist on increasing your gain [by an okay margin], you'll need to invest in a solar tracking device that will align your PV for you. Otherwise, come up with an average for your PV's output. Buy that PV panel, tack it on a datalogger and a near depleted battery with a charge controller, record the gains at your planned installation site for about a week per month across the four seasons. Come up with a chart for your location, then take that information and redesign your plan with respect to the load you intend to operate. You'll find the numbers will be way off than you initially hoped for.

*PV Limitation*
Many manufacturers do not use real sunlight to test their panels, simply because of its inconsistency when subjected to weather. Therefore, a massive xenon lamp array is used that simulates 1 sun condition as close as possible, run it for several hours, then take an average. You cannot, should not, and must not base your load calculations solely on the values printed on the solar panel. Depending on surface contamination, wiring resistance, etc. you'll be lucky to get maybe 70% of that rating if you average the gain you would receive in a day.
*What this means*: Your solar panel should be larger than your existing calculations, which in term may require you to upgrade your charge controller, wiring, and mounting design as needed

*Lead acid Limitation*: ugh... where should I start..
Regardless of their capacity, you should de-rate their performance in regards to temperature. Sitting outside means there maybe drastic temperature fluctuations from dusk to dawn. Batteries like to cozy up, and will get lazy when cold. My experiments show that if its really cold their voltages reduce and may even refuse to charge until their temperature returns to a reasonable level. AGM SLAs are considered general purpose/stand by batteries. If it doesn't say Deep cycle on them, do not use it for PV applications... unless you prefer to operate your loads to consume only 40% capacity at max. [That is, say you lug a 35AH group U1 battery home, if its not a "deep cycle" battery, you would only be able to use 40%, or 35x.4=14AH on the C/20 scale, increase or decrease according to your load accordingly.] Battery contacts subject to galvanic corrosion if you use the wrong connectors, and subject to electrolytic corrosion if placed in a humid environment without protection. They tend to sulfate if partially discharged and your PV cannot recharge it back up in time [PV surface blocked by something or the sun blocked in clouds] you you may have to do some battery maintenance on the bad days. Some Charge controllers for PVs nominally float batteries at 14.4-15V... this is nice for FLA Lead Acids. but for SLA it will cause the small ones to swell and bubble. SLAs should not float above 2.35V/cell or approx 14.1V. FLAs are cheaper, but you'll have to vent hydrogen and go at it with a hydrometer every once awhile. You also cannot lean FLAs at an angle or any angle other than perpendicular to the ground. Battery is full at 13.8V, completely dead at 10.5V, since we are running only 40% out of the battery, your usable window is even smaller: between 12V and 13.8V. 
*What this means*: You'll need to protect your battery from the environment, additional materials like foam won't hurt, but it would increase the load on your parts budget. Lead-Acids are tolerant to mediocre charger designs, but its really more of a deadweight than anything else. Just like you, they'll need a tent and a sleeping bag on camping trips. 

*Runtime* "I thought it said it would run 12 hours?"
In the ideal world dusk sets at 8PM and dawn arrives at 6AM, which will give it a runtime around 10 hours. However, seasonal changes on top of meteorological effects may push your runtime beyond 15 hours.. if its rainy all day [or if you find a bird nest on top of your sensor] it may cause it to run 24/7. An LVD circuit may be necessary to prevent overdischarge, most LVDs do not cut off at 12V, so keep that in mind too. 
*What this means*: This would add more stuff on top of your circuit, and turns it tricky if you want to build a DC timer to go with it 

Okay, lets see about lighting your lights,
12V 2A.... ouch, so I have to assume that it has an internal driver that requires a constant voltage input of 12Vs and it has to be be capable of supplying 2A. It might not like to work with voltage fluctuations so you'll have to introduce in a DC-DC converter.

So your layout would look something like this:
[PV] --> [Charge Controller] --> [Battery] --> [DC-DC converter] --> [Load]

The cheapest DC-DC converter would probably the open frame MeanWell PSD-30A-12, ~$25/shipped
9-18Vin, 12V 2.5A out. Lets look at the efficiency numbers: http://www.mouser.com/ds/2/260/PSD-30-spec-34930.pdf
Efficiency 77%... just to be conservative lets say 70% without any thermal derating. Electrical efficiency in its simplest form is output over input. With a battery working voltage under load of 12.6V, your input from the battery into the DC-DC converter would actually be closer to 3A, increasing as battery voltage drops. 

Assuming we are still in the ideal world, 10 hour runtime, and your battery would produce exactly what the specs read. Your outside temperature will always be 77F. You'll need a 55AH battery at minimum. Why? Isn't 3x10 only 30AH?
Here, follow me: http://www.batteryspace.com/prod-specs/SLA_12V55Ah.pdf
Scroll down to the discharge characteristics chart under the dimensions. You see the two curved lines on the far right? Those are curves using load current of 4.95A and 2.75A respectively. If we are drawing an average of 3A from the battery, then the 3A curve should fall between those two curves. Say we want the load to cut off at Vbatt=12V, you'll see the invisible line drawn for 3A falls directly on the 10 hour vertical line. In the most ideal settings, this would still only serve as a benchmark minimum. If it was me, I'd invest in a 70AH battery, where the battery voltage is nearly flat on its way out. 10 hour runtime over 3A is about 30AH before losses. So for example lets say we'll give it a charging overhead of 5AH, then from that it is determined that we will need to charge back 35AH of juice the next morning [or else your battery is X_X by tomorrow morning]. "12V" PV are actually rated with its output voltage being about 17V. So a 10W panel does not put out 830mA at 12V, instead it puts out 580mA at 17V. Assuming 5 hours of productive sunlight in one day, (35/5 = 7) your PV array must be at least [7x17=119] 120W to break even. Since days are rarely ideal, I'd go for 150 or even 200W. If your setup site is not facing south or is tree lined, you might have to go higher. 

For your system if I was to build it: 
[PV]: 4x Epcom 50W $500
[Controller]: Morningstar SS-20L-12V SunSaver 20 Amp with Load LVD, $100
[Battery]: Concorde PVX-690T, $250
[DC-DC Converter]: Cincon EC9B-12S12, $50
[Load]: Your light, runtime not exceeding 10 Hours
[Misc]: Manual battery charger, meters, disconnects, fuses, grounding stuff, lightning arrestor, dusk to dawn relay, hardware, etc etc... $100

Total investment I would probably plan for would be around $1000, 
My advice? Go for a smaller load like <500mA:shrug:


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## SemiMan (Jan 6, 2013)

Illum said:


> [PV]: 4x Epcom 50W $500
> [Controller]: Morningstar SS-20L-12V SunSaver 20 Amp with Load LVD, $100
> [Battery]: Concorde PVX-690T, $250
> [DC-DC Converter]: Cincon EC9B-12S12, $50
> ...




Thanks Illum, I am normally the one trying to put reason into solar lighting. You saved me a lot of typing, but even your setup as recommended will not cut it most of the time as the battery is too small. It may work for a night or two, but even in hot climates, a night or two of reserve is not enough. In cool climates or those with a lot of cloud cover, 5, 6, 7, 8 days is not unrealistic. That means your battery gets discharged and sits discharged (without the lights on) for long periods of time. There goes your expensive Concorde battery.

No need for the DC-DC though, those LED strips will run right off the battery.

In terms of cost, far better to get a 230 watt panel for about $200-250 dollars and an MPPT controller. Total expenditure is a lot less and you end up with far more power.

Semiman


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## Illum (Jan 6, 2013)

Concorde batteries have been on my "dream list" but I have never found a need to acquire one. Most of the batteries I've bought are regular AGMs mainly just to test system feasibility. They have always strapped down with an umbilical though, where when the battery voltage reaches a certain level [~11V], a relay will connect the wall charger to charge the cell back up. No system I have built to simulate a real life environment operated flawlessly over a week, at some point the load current will overrun the gain and the battery goes kaput. Overengineering is always a sound decision, but over redundancy makes the system very very complicated.

Where do you find a 230W panel for $250... and better yet where do you find one thats not designed for a 24V system? 
Come to think of it, an 24V system might be more economical in terms of smaller wires/fuses/breakers... but it will require the DC-DC converter to run anything below 24V [or rather, 28V]


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## SemiMan (Jan 6, 2013)

Actually I pay less than $250 for 230 watt panels, and you can readily find them online for that price. sunelec.com will have clearouts for even less.

Actually most 230W panels are not suitable for a 24V battery system as the voltage is often not high enough. They are good for 12/18 volt systems. MPPT controllers are essentially smart DC\DC converters and will handle the voltage conversion from the panel to the battery.

24V systems can certainly cut the wiring requirements down as the losses are 4x less, but not between the panel and an MPPT controller.

I have used quite a few Concordes. Good batteries, but there are others out there that are approaching that quality. They will sulfate just like any other battery if not treated well.

Depending on what you are doing, 11V may be too low. At low loads, that is a virtually 100% dead battery. 

Generally people grossly undersize the batteries for solar as they don't realize that just because the sun is up, does not mean you are getting much charging. When one looks at solar energy maps, it is an average value, not a minimum, and that average is over many days (and years for that matter). 

Semiman


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## Slotguy (Jan 6, 2013)

I am fortunate enough to live in Solar Zone 5 (The Colorado river valley in Arizona). I have found that to power 5 to 6 XPG based security lights at 700 Ma apiece, that i need a minimum of a 40-45 watt PV panel and a 35 amp hour battery. This is dusk to dawn this time of year. Keep in mind that it never freezes and temps in the summer can reach 125 F. However, a cloudy day will make a hour or so on a car charger necessary. If the need arose to totally automate this type of system, some type of low voltage detection would be required. 
I had planned to use a relay to cut out the input from the PV panel and apply a DC voltage to the Charge controller. Something like a 19 Volt Laptop power supply would suffice. Currently I am working on a project to make a single 1 watt floodlight run on solar power, dusk to dawn and have found that the Battery is the limiting factor. Even a 26550 at 4200mah will not run all night with the circuit I am working with. I have settled on 4 C type Nimh batteries at 5000 mah apiece and a simple relay circuit and am seeing good results. This time of year is the best time to test theses devices in the northern latitudes.


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## Illum (Jan 6, 2013)

SemiMan said:


> Generally people grossly undersize the batteries for solar as they don't realize that just because the sun is up, does not mean you are getting much charging. When one looks at solar energy maps, it is an average value, not a minimum, and that average is over many days (and years for that matter).
> 
> Semiman



well said, but space is sometimes the biggest limitation. Batteries doesn't get exponentially more expensive the bigger they get, but space sometimes is.


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## Steve K (Jan 7, 2013)

Just a quick vote of appreciation to Illum for going through his analysis and write-up! It takes a fair amount of effort to do it, and can usually only be justified as a labor of love. Nice work!


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## AnAppleSnail (Jan 7, 2013)

Steve K said:


> Just a quick vote of appreciation to Illum for going through his analysis and write-up! It takes a fair amount of effort to do it, and can usually only be justified as a labor of love. Nice work!



What, you don't get your checks in the mail after helpful posts? 

I think that instead of treating this light load as a 24W output, it's a string of LEDs with a resistor in. This means that its current draw drops with voltage. My experience with these strings take minimal current below 9v. This isn't enough to save a lead-acid battery on its own nor does a de-rated battery experience much voltage drop to decrease the output current for the LED string. Even one 'run' of this LED strip will be quite bright at night, especially for under-roof lighting. Just think of the bugs you'll attract!


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## RoGuE_StreaK (Jan 7, 2013)

AnAppleSnail said:


> Just think of the bugs you'll attract!


Sorry getting off topic here, but I read a post yesterday elsewhere where someone thought their LED light didn't seem to attract any moths like incan etc.; has anyone noticed a qualifiable difference?


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## SemiMan (Jan 7, 2013)

Slotguy said:


> I am fortunate enough to live in Solar Zone 5 (The Colorado river valley in Arizona). I have found that to power 5 to 6 XPG based security lights at 700 Ma apiece, that i need a minimum of a 40-45 watt PV panel and a 35 amp hour battery. This is dusk to dawn this time of year. Keep in mind that it never freezes and temps in the summer can reach 125 F. However, a cloudy day will make a hour or so on a car charger necessary. If the need arose to totally automate this type of system, some type of low voltage detection would be required.
> I had planned to use a relay to cut out the input from the PV panel and apply a DC voltage to the Charge controller. Something like a 19 Volt Laptop power supply would suffice. Currently I am working on a project to make a single 1 watt floodlight run on solar power, dusk to dawn and have found that the Battery is the limiting factor. Even a 26550 at 4200mah will not run all night with the circuit I am working with. I have settled on 4 C type Nimh batteries at 5000 mah apiece and a simple relay circuit and am seeing good results. This time of year is the best time to test theses devices in the northern latitudes.




Certainly a much easier spot to run solar in then where I live. Most people doing solar lighting don't want to have any sort of AC backup and hence you need substantial battery resources, even in some part of Arizona though obviously not nearly as bad as where I live (Canada). On the other hand, our batteries tend to last longer as we don't experience the very hot weather that tends to cook lead-acid batteries.


If you are using a 40-45W panel, I am guessing you are using a PWM charge controller. A laptop supply would not work with a PWM controller. Laptop supplies are fixed voltage and PWM controllers for all intents and purposes short the power source to the battery. It is highly unlikely your laptop supply will be happy with that for any period of time. If you have an MPPT controller it will probably work, though I find some controllers attempt to determine if there is a real panel connected and will not work with a power supply unless you add some resistance. You could run a constant current LED driver into the PWM controller as well.

Semiman


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## Illum (Jan 7, 2013)

Steve K said:


> Just a quick vote of appreciation to Illum for going through his analysis and write-up! It takes a fair amount of effort to do it, and can usually only be justified as a labor of love. Nice work!



heh, thanks... thats my share of observations tinkering with this stuff. As Semiman have noted, there are many things I have yet to get "right"


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## SemiMan (Jan 7, 2013)

If anyone is trying to get a solar light set up running for Non-Commercial Purposes only (or commercial and interested in paying for assistance or partnerships), PM me and I will try to help you out. I do some of this for a living so I know the pitfalls and will try to help. I will emphasize non commercial only as it is one of the ways I pay the bills 

Semiman


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