Anyone know a simple and cheap solar panel setup to run a small boombox about 9-12V DC?

December 4, 2007 9:30 PM

Anyone know a simple and cheap solar panel setup to run a small boombox about 9-12V DC?

I need to power a small portable boom box (one of those that normally runs off of 6 C cell batteries) for an extended period of time for a public art project. I was thinking of using a solar panel but haven't been able to figure out all the complexities of using them. Does anyone know a simple and cheap ($50-$150) solution to this? I don't really care if the volume dips or if the sound stops playing at night. Thanks.

posted by Bengston to technology (3 comments total)

All Electronics three of the 60MM X 60MM X2MM should do it.
posted by hortense at 9:49 PM on December 4, 2007

Your boom box runs on batteries at 9V (6 C cells). Alkaline C cells have about 8.3Ah (Amp hours) of capacity. I suspect that the boombox probably runs about 6 hours at a reasonable volume on a set of batteries, but I don't really know. With that assumption, you will need ~1.4 Amps or ~13 Watts, which is actually quite a bit of power. However, you'll actually need a panel rated for more power than that. You won't get the rated power out of them on cloudy days, early in the morning, late at night, or during the winter. The normal method to power something with solar panels off-grid is to set up your solar panels and connect them to a battery (like a car battery, but specially designed for high capacity when discharged slowly) through a charge controller. If you are happy with the boombox only running during the middle of the day on sunny days, you could probably get by without a battery and with a solar panel rated around 20 Watts, but you'll still need something to regulate the power between the panels and the boombox.

You could probably do this in the $150 and somewhat higher price range.

You should also clarify the input voltage that the boombox accepts: does it accept 12V when plugged in? 12V will be cheaper and simpler, because it is more common than 9V. The boombox (or adapter, if it has an external wall wart) will also tell you how much power it can supply, which gives an upper bound for power consumption. If there is an external wall wart, can you measure the current draw when the boombox is playing at the volume you want?
posted by ssg at 10:31 PM on December 4, 2007 [1 favorite]

As ssg points out, the boombox requires significant current as well as voltage. The panels mentioned by hortense are only 40 mA. Working from ssg's assumption of 1.4 amps, you would need 35 of those panels in parallel just to get the current you need, and then it would still only be 3 V. If the volume is low and the boombox is efficient you can probably get by with less current, but as ssg says, I would try to measure the current draw before designing something like this.

Something like this panel might work. I would follow it with a simple voltage regulator circuit (LM317 or similar) to protect the boombox.

Another thing to consider is whether the boombox will start playing again on its own when power is restored (e.g., when daylight comes in the morning).
posted by exogenous at 7:55 AM on December 5, 2007