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Old 12-04-2016, 01:44   #1
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Small Solar kit for LED lights Calculation

If I wanted to add a self-contained solar power kit (not attached to battery bank) to run LED lights at night. How can I calculate required solar panel and battery?

The lights will be 30 x .6W = 18W.

Would a 20Watt solar panel, charge controller, inverter, and 12V 20Ah battery work? The lights would be on a timer from 8PM until 3AM?

A = w/v so A = 18/12 = 1.5A
1.5A x 7hours = 10.5Ah of use/night.

According to https://www.batterystuff.com/kb/tool...alculator.html A 10watt solar panel should be enough.

Couldn't I use a simple $14 150W car power inverter?
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Old 12-04-2016, 06:38   #2
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Re: Small Solar kit for LED lights Calculation

18 Watts of lighting for 7 hours = about 126 Watt hours.

For safety, figure on getting at most 5 hours of rated wattage out of your solar panel. So for 126 watt hours, you would need a minimum of 25 Watts of solar to replace those Watt hours each day.

126 Watt hours = about 10 Amp hours, so you would be drawing a 20Ah battery down to 50% overnight if it fully charged during the day. If you get one really cloudy day, you will run your battery down a lot more than that. That's not good for battery life.

Personally, I'd be looking at a 40 Watt panel and about 40 Amp hours of battery storage to provide the necessary margins for bad weather with that load.

Why the inverter? Are you looking at putting 110/220 Volt lights in? You'd be better off running 12 Volt LEDs.
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Old 12-04-2016, 08:35   #3
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Re: Small Solar kit for LED lights Calculation

A few questions to clear things up. What kind of LED's? Is this a string of LEDs like a rope light or individual LEDs? What is the operating voltage of the LEDs? From your calculations it looks like 12V , if so why the car inverter?

As StuM pointed out a 40W panel would be best and unless you use an MPPT controller with the panel the full rated wattage will never go into the battery, but now were talking some serious $$$.

Don't know your application but how about this? I'm using a string of outdoor solar holiday LED lights for cockpit lighting, turns on at dusk and off at dawn, comes wired to a 4x4" box that has the solar panel, batteries and light sensor. Not very bright though, but it was less than $10 on Amazon.

Hope that helps.
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Old 12-04-2016, 08:57   #4
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Re: Small Solar kit for LED lights Calculation

Go with at least a 40 ah battery and go 50 watt solar panel they are usually a bit cheaper to purchase than a 40 watt one now what are the lights for? For deck lighting it may be better to do like me and go for some 20 lumen solar pathway lights fully self contained. About $20 USD each.
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Old 12-04-2016, 09:26   #5
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Re: Small Solar kit for LED lights Calculation

As a huge generalization, many (most) LED's are 12v DC. However, if you buy them from a household supply store they come with a 115v AC to DC converter. It's the little black box with a plug on it. Depending on their intended use, it often makes sense to buy them this way rather than buying from often overpriced marine stores. It's normally a simple matter of cutting off the converter and wiring your LED's directly to a 12v DC supply. It is a waste of energy to convert them to AC and then run them off a DC battery using an inverter. However, unless you want a particular lamp or fitting that has caught your eye, it's often just as easy to buy them at 12V DC.
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Old 12-04-2016, 15:52   #6
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Re: Small Solar kit for LED lights Calculation

Quote:
Originally Posted by Privilege View Post
As a huge generalization, many (most) LED's are 12v DC. However, if you buy them from a household supply store they come with a 115v AC to DC converter. It's the little black box with a plug on it. Depending on their intended use, it often makes sense to buy them this way rather than buying from often overpriced marine stores. It's normally a simple matter of cutting off the converter and wiring your LED's directly to a 12v DC supply. It is a waste of energy to convert them to AC and then run them off a DC battery using an inverter. However, unless you want a particular lamp or fitting that has caught your eye, it's often just as easy to buy them at 12V DC.
Yep, I've got a 5m multicolour strip of them under the bimini for cockpit "mood lighting". Came with a 110/220V AC -DC converter. We just tossed the power pack and wired the strip directly into the existing cockpit light (with the addition of a selector switch on the light).
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Old 12-04-2016, 19:16   #7
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Re: Small Solar kit for LED lights Calculation

Yes, good idea. I didn't realize most LEDs were 12v. I don't need the inverter. I'll definitely hook up a little larger system to protect the battery.
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Old 13-04-2016, 21:21   #8
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Re: Small Solar kit for LED lights Calculation

https://www.emarineinc.com/Portable-...Battery-Tender

Not sure this isn't just about me but maybe it will help Linda.
I committed to a pair of these with my tax return to help keep the batteries going with a pretty light load ( some interior LEDs and LED navs)

Yet to install...just got them but should fit the bill in conjuction with my two group 27 AGMs. Love the portability though I will have to be careful that they are properly "tied down" when in use.
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