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12v LED lamp+ Solar panel+ 12v car battery? Answered

I am new to electricity beyond a basic circuit, so I am at a point of being unsure about my current scheme for a relatively bright light that runs off a battery which recharges via solar power and doesn't go dead due to the continual recharging during the day and effective use of electrical energy. I do not know whether resistors, transistors, power inverters, or any other equipment is beneficial or necessary. I am also unsure of a high quality, relatively cheap solar panel that is compatible with the 12v battery and the 12v LED bulb (if anyone has any advice for that). I drew up a diagram of my possible setups, labeled 1, 2, and 3. Option 1 is the basic setup without any additional hardware. Is one of these setups correct, and the most effective way to go about my objective? If not, how can I modify it to be the proper setup? Thanks :)


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Best Answer 8 years ago

There are lots of considerations with solar:

Currently, the CHEAPEST you'll find silicon photovoltaic cells is around $3-5/watt. Keep that in mind. Fully assembled panels range from 7-20 dollars/watt.

Batteries, particularly 12volt (lead acid) batteries don't like to be overcharged. After they are fully charged they tend to take the extra energy and convert it to heat, and self destruct. This is bad. You want what's called a charge controller -- it detects when the batter(ies)y are full and dumps that excess to a dummy load or just disconnects it to protect the battery. Charge controllers come in many shapes/sizes/voltages - Ive found one for small sized builds (a few car batteries) for around $20.

Batteries should be "Deep Cycle" -- regular car batteries are designed for short bursts of high load (like a car starter motor), where deep cycle batteries are designed for long slow drains. that long slow drain can hurt a regular battery because it causes degradation of the plates inside the battery. Long story short, you can run a deep cycle battery low without damaging it as much.

Inverters are handy because they allow you to run household AC electronics off of dc battery power. They are rated in watts.


What does all of that mean? You need to decide how much you want to use, and that will determine how much/many of the above you need. Do you need lots of power for short times, little power for a long time, or somewhere between? You can look up how much solar power you can generate 'per watt of solar panels' annually for your location based on your. With that calculation you decide how many watts of solar panels you need.
More batteries = more storage and more burst power, but slower charge for a fixed input.

tyranasaurus tyler
tyranasaurus tyler

Answer 8 years ago

Thank you for your answer,
In terms of solar panels, http://www.buy.com/prod/mini-solar-power-monocrystalline-silicon-10w-18v-battery-charger-solar/225147888.html would something like this be good? It is 18v; will that mean anything (good or bad) for the 12v battery?

In terms of batteries, I found a honda 12v true deep cycle here: http://www.amazon.com/Honda-150F-TTR230-YTX5L-BS-Battery/dp/B005D9UVTS Is this the right type of battery, and will it be compatible with everything I'm trying to do with it?
This is the charge controller I found: http://www.amazon.com/dp/B0006JO0XI/ref=asc_df_B0006JO0XI1851675?smid=ATVPDKIKX0DER&tag=hyprod-20&linkCode=asn&creative=395093&creativeASIN=B0006JO0XI Will it be sufficient?

Is the inverter vital, or just convenient/beneficial?

My main intent is to be able to power this bulb http://www.amazon.com/gp/product/B004IHQHJY/ref=noref?ie=UTF8&s=hi&psc=1 for up to 8 hours, anywhere from once a week to daily. An added bonus would be the capacity to power 2 five inch oscillating fans for the same amounts of time that the light would be on.

Thanks again for your help. And a preemptive thanks to anyone else who takes the time to answer. :)


Answer 8 years ago

remember that in order to charge a battery you have to put out more voltage than said battery.

Solar panels are often rated for 18+volts because that's in FULL direct sunlight, a cloud means it drops well below that. 10 watts is kinda small, you might require multiple of those.

the battery seems good. 12v 5Ah (60-watt-hour)

the charge controller @ 7 amps/14 volts = ~100 watts...seems reasonable but a bit big.

Inverters just let you run AC electronics, so if you only want to run a dc led lamp, then you don't need one. They're convenient for using things like laptops.

Calculating your power usage is as easy as multiplying.
that is a 3 watt LED light bulb.
for 8 hours,
it would use 24 watt-hours., or just under half the capacity of the battery.

Now, random numbers: say you get 8 hours of direct sunlight per day you have 8hours * 10 watts in panel = 80 watt hours per day of charge, acceptable for this setup. Remember EVERY step in the process is less than 100% efficient so you need to consider that more is usually better.

May I recommend that is a bit expensive for an led bulb, and many online etailers have better deals that include shipping for a price like that. I always recommend dealextreme.com -- just read the reviews and don't expect miracles for speed in the free shipping :D


6 years ago


I have a 37.5W Solar panel,

15A MPPT Charge Controller 12V/24V Auto Switch BOC (Bought from Ebay: http://www.ebay.com/itm/261392830593) &

100A DC 12V Lorry Battery.

I'd like to use this Panel for 12V DC LED Bulbs.

Are these items are Compatible. Can I use these?

Can I use Computer UPS as a Inverter. Is Possible?