Run Boombox off 12v DC for longer runtime?

[kman]

Hi, I'm new to solar so please let me know if this is the wrong place.

I have a sony boombox I'd like to run off a battery (deep cycle) for a while, and a solar panel to recharge the battery.

An idea is the boombox will run longer if I run it off 12v DC instead of hooking up an inverter, right? The box takes 8x D cells (12v) so I think I could run it right off the big battery's current?

I'd imagine I could use clips to connect the battery right to the contacts, or better yet make a little fake dowel battery connected to a 12v cigarette lighter plug? Only problem is I'm not certain how to hook it up to the battery and I'm afraid to fry it!



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Oh, the bottom of the boom box says 120v 60hz 30w and 12v DC. Can that help me figure how long it can run off the battery (battery is 115 amp-hours)?

I know the formula is watts = amps * volts, but I don't know if the 30w figure is common to both AC and DC voltage. But if so, I figure on 12vDC it's pulling 2.5 amps, think that's right for an average-size sony boombox? I somehow doubt that means I can run it for 22 hours (bringing it to 50% charge), but that would be great if so!

[Mike90250]

12 D cells is 18V, so a 12V battery may behave poorly.

8 D cells would be 12V . Standard AAA -D batteries are 1.5V, rechargeables are 1.25V

[indalecio.feng]

Yes, for sure you could use longer than with inverter.

From battery to inverter you will save 10%.

From inverter to your 12DC which is the source of the sony boombox, you will save another 10% to 15%.

[kman]

12 D cells is 18V, so a 12V battery may behave poorly.

8 D cells would be 12V . Standard AAA -D batteries are 1.5V, rechargeables are 1.25V

My bad, just a typo, which I've now fixed. Yes, it takes 8 D batteries, so 12v is correct.

[kman]

Yes, for sure you could use longer than with inverter.

From battery to inverter you will save 10%.

From inverter to your 12DC which is the source of the sony boombox, you will save another 10% to 15%.

That's what I figured. Any thoughts on how to wire it up? (specifically, which wire where, oy!)

[Mike90250]

12V - OK.
Well, does you box have a DC power input ? That would be the safest method. other wise, you have to look at the little springs, and contacts, and figure out which 2 have a power wire that leads inside to the box. You can tell the polarity of them, buy the end of the battery that's supposed to go there.
I would use an clip, and just clip it on to the contacts. and put a 2 or 3 amp fuse at the battery - even a small battery can start a fire if the clip comes off.

[kman]

12V - OK.
Well, does you box have a DC power input ? That would be the safest method. other wise, you have to look at the little springs, and contacts, and figure out which 2 have a power wire that leads inside to the box. You can tell the polarity of them, buy the end of the battery that's supposed to go there.
I would use an clip, and just clip it on to the contacts. and put a 2 or 3 amp fuse at the battery - even a small battery can start a fire if the clip comes off.

I wish it had a DC input. I probably wouldn't have needed this thread if it did.

Sadly, only AC, and the battery compartment (which is thank goodness, 12v).

As long as it's safe to connect the deep cycle battery directly to the stereo (figuring out the polarity is still going to be the tricky part, I think), I was thinking perhaps a pair of "fake" D cells, made from a piece of appropriately-sized wooden dowel. Run wire through the middle, which snakes out of the battery compartment, and connects to a male cigarette lighter plug. I already have a pair of battery clips that terminate in a female cigarette lighter-type jack, so plug it in normally, and no special fear of short circuits and fire, right?

Just to be clear, as long as the polarity is correct (and fire danger is reasonably prepared for), there shouldn't be any danger to the boombox from connecting directly to the big honking battery, right? It's just a lot more capacity, otherwise not so different from the 8 D cells it normally uses?

So the big question remains, how can I connect it? I looked closely at the battery compartment, and it's a pretty odd setup compared to the other, easy-to-track battery layouts. There is a circuit board running along the top and bottom. The bottom appears isolated, just continuing the circuit. The top board extends into the chassis, and a small surface-mount jack plugs in and goes deeper into the box. Clipping off the spring is easy, but I don't see an easy way get a tap off the other side (positive, I guess?), since only two small bars are exposed on the accessible side of the circuit board that runs along the top. Hard to explain, but look closer at the photo in my first post. The visible contact board at the top of the photo is the one I'm talking about.

[kman]

That back circuit panel has actual circuits on the back that go off to the side into the box. I was finally able to carefully work it somewhat free, but couldn't fully disconnect it without disassembling the box more than I want to, but I pulled it up for a photo of the circuit on the back (which I outlined for extra clarity):



On this end, the middle pair float separately, joined on the other end of the battery compartment only. It looks like the only two critical contacts are the outside pair... those seem to be the only ones that actually connect in to the plug inside the stereo. Not sure why there are four separate wires coming out of the plug just inside, though, hopefully they all join together inside somewhere and aren't actually 4 separate circuits.

So here's my idea:



The red "batteries" are a wooden dowel similar in size to a D cell, with a bolt and/or washer in the end, connected to a wire leading out of a convenient access slot to the lighter plug. The rest of the battery compartments would be empty. As long as the socket is connected properly (and securely) to the battery, there should be no way to accidentally mis-wire the stereo. Right?

Any idea which is positive and which is negative on the cigarette plug? (center vs. outer ring)

[Mike90250]

Any idea which is positive and which is negative on the cigarette plug? (center vs. outer ring)

Cars in the 50 States, generally are negative ground, and the outer shell of the lighter is - The center pin is +

[kman]

Just wanted to post back a quick thanks! I wired up my stereo as indicated in the graphic and it works great! I'll post back a photo when I get a chance.

Of course, after all that work I ended up going out and buying an amplified speaker from Roland that uses a tiny fraction of the power that the Sony boombox does (300 milliamps vs ~2.5 amps!), and still has adequate sound for my immediate needs. Oh well... it'll still be great for shorter-duration trips.