# Solar Powered Speaker

#### Kurtis Potier

May 24, 2016
6
I'm a student headed for college next year and am looking for a cool summer project to do so I can make something neat and learn a little along the way, my budget is around $80 plus the stuff I already have. I am interested in renewable energy and speakers, so I was thinking about a solar powered relatively portable speaker. I have the speakers I need already (quite a few sitting around, I will likely use 2 two way Boston acoustics computer speakers). I will make the enclosure as well or possibly modify the box of an old center channel that I have that seems quite good. I am getting the solar cells on ebay for$20 or less (getting quite a few for future projects), this amp seems to have good reviews: http://www.amazon.com/DROK-TDA7297-...59&sr=8-2-spons&keywords=mini+amplifier&psc=1
and seems to have plenty of power for my application. What I really need help with is the batteries and charging systems which I just don't have much knowledge on. What battery specifications should I use (mah/votage)? How can I charge them from the solar panels given that their output will vary a lot? I should also add what I expect from the unit. I'm looking for something to play music that is relatively small for a dorm room. I can put up to 9 solar panels on the unit which generate up to 1.8 watts each and .5 volts. (So, 16.2 watts, 4.5 volts). I realize the portability of the unit is a big question, but I am mostly doing this for fun and somewhat for functionality. Any help or suggestions are appreciated. Also, if you need clarification of anything please ask.
Thank you!

#### Gryd3

Jun 25, 2014
4,098
Just a warning, that the voltage from the panel will drop a LOT if you attempt to pull too much current.
That said, 16.2W may not be enough depending on the run-time and draw of the device you have.
The amplifier is 2x 15W channels, so if things were absolutely perfect, an hour charge time would give you a half hour of run-time with the volume cranked.
You should also look into using something other than lithium batteries for this project unless you plan to operate exactly at the voltage supplied by the batter(ies).
2x 3.7V batteries will need to be operated at 7.4V , if yo go too low, you will damage the batteries. Using NiCd or NiMh will give you more flexibility and forgiveness with charging, and because they are approx 1.2V each, you can use 4 of them in series.
Depending on how far you want to dig, you should also look into methods to 'balance' the cells... charging any battery type in series with other batteries can lead to them charging at slightly different rates. Keeping them balanced will be key to making sure the pack lasts for a longer time.

#### Kurtis Potier

May 24, 2016
6
I will definitely not go with lithiums then, one concern though, will my charge controller make the batteries safe to run to the amp since it is 12 volt?

#### Gryd3

Jun 25, 2014
4,098
I will definitely not go with lithiums then, one concern though, will my charge controller make the batteries safe to run to the amp since it is 12 volt?
Not on it's own. You need some kind of conversion...
Take the solar panels and 'boost' the voltage to charge a 12V battery... or take the batteries you have and 'boost' the voltage to 12V for the Amp.
One way or another, you will need to raise the voltage somewhere... (remember that current goes down when voltage goes up if you convert it with a 'boost' converter)

#### Kurtis Potier

May 24, 2016
6
Not on it's own. You need some kind of conversion...
Take the solar panels and 'boost' the voltage to charge a 12V battery... or take the batteries you have and 'boost' the voltage to 12V for the Amp.
One way or another, you will need to raise the voltage somewhere... (remember that current goes down when voltage goes up if you convert it with a 'boost' converter)
This charge controller : http://www.amazon.com/Docooler-Cont...204602&sr=8-5&keywords=solar+charge+regulator
seems like it boosts it to 12 volts to the batteries, then it has a load power out, which I am assuming would also be 12 volts, so I guess I use enough batteries to get to 12 volts then?

#### Gryd3

Jun 25, 2014
4,098
This charge controller : http://www.amazon.com/Docooler-Cont...204602&sr=8-5&keywords=solar+charge+regulator
seems like it boosts it to 12 volts to the batteries, then it has a load power out, which I am assuming would also be 12 volts, so I guess I use enough batteries to get to 12 volts then?
Looks good to me.
What kind of weight are you looking to get?
You can buy 12V SLA batteries . You would only need one, and would not need to worry about building a pack with multiple smaller batteries.
You can buy them in various sizes... from little ones in home alarm backups, to large ones for motorcycle/car batteries xD

#### Kurtis Potier

May 24, 2016
6
Looks good to me.
What kind of weight are you looking to get?
You can buy 12V SLA batteries . You would only need one, and would not need to worry about building a pack with multiple smaller batteries.
You can buy them in various sizes... from little ones in home alarm backups, to large ones for motorcycle/car batteries xD
Weight isn't really much of an issue, the thing will already have to be big to fit 4 speakers and two tweeters, plus the solar panels, I like the SLA idea, really simple and those things do last a long time, I found one that is has great dimensions for the project and has 2.3 amps, so it should last for at least 2-3 hours in the dark, assuming 10-15 watts average power from the amp. Thanks so much for the help, I'll post some pics of the progress, going to get the box modified for the new speakers this weekend and work on the rest as it ships

#### Gryd3

Jun 25, 2014
4,098
Weight isn't really much of an issue, the thing will already have to be big to fit 4 speakers and two tweeters, plus the solar panels, I like the SLA idea, really simple and those things do last a long time, I found one that is has great dimensions for the project and has 2.3 amps, so it should last for at least 2-3 hours in the dark, assuming 10-15 watts average power from the amp. Thanks so much for the help, I'll post some pics of the progress, going to get the box modified for the new speakers this weekend and work on the rest as it ships
Keep in mind the Ah rating on most batteries is overstated.
If you buy a 2.2Ah battery, aim to reliably use a little over half that. Your charge controller may have 'under voltage' protection for the load/battery which will cut the power to the device if the battery goes too low. SLA does last a while, but you still have to treat it nicely

#### BobK

Jan 5, 2010
7,682
Also, consider that an amplifier rated at 15W will draw about 30W to output 15W, unless it is a class D. I would definitely look for a class D amp. These would run maybe 17W to output 15W.

Bob

#### Kurtis Potier

May 24, 2016
6
Ended up actually finishing this one a couple of years ago, figured I would post the results. It's sounds great and the solar power tends to keep it charged well in the sunlight. Thanks for all the help!

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