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Frugal Mono Full-range, Solar-Charging, Battery-Powered "Ashiko" Speaker
Frugal Mono Full-range, Solar-Charging, Battery-Powered "Ashiko" Speaker
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Old 13th June 2012, 07:18 AM   #1
xpheolix is offline xpheolix  United States
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Default Frugal Mono Full-range, Solar-Charging, Battery-Powered "Ashiko" Speaker

Yes, thats right...another boombox post.
I'm thinking of making a portable music player somewhat in the shape of an old wooden bucket or a hand drum (Ashiko hand drum). I have many ideas for a much higher quality portable system, but want to build something more frugal for now to get a bit more accustomed to working with batteries and solar cells.

That being said, I've selected the GRS 8FR-8 Full-Range 8" Speaker Pioneer Type B20FU20-51FW from PE for the driver. I wish the Pioneer driver was still being made, but it is discontinued. The Goldwood GW-8003/8 8" is another option, but is more expensive and more importantly, less efficient by 4db/w. There are Visaton options that I'd like to work with, but shipping to the US is ridiculous. Unfortunately, this driver is 8ohms and not 4 which isn't as good for a portable system.

I've been looking at the20 Watt Bridged Audio Amp Circuit from Electronic Kits.com for the amp module. I would rather work with something from 41hz, but trying to not spend as much. This amp recomends 12-18v supply, and I'll be using a 12v SLA Battery. The driver is also 8ohms which means I'll get 10watts, maybe, from the amp at full power, but with 91db/1w efficiency it should be fine for this project. It also includes volume pot, which is nice.

I'm thinking of using SLA Battery: Sealed Lead Acid Battery 12V 7.0 AH from batteryspace.com. They are heavy, but cheap and 1 of these should be plenty for right now. This is where I have a few questions. I'd like to have an on/off switch between the battery and amp module, but I've read that you should also have a fuse as well. I'm fairly sure these amp modules do not come with fuses.The amp module says 2 amp supply. What amperage and what type of a fuse would I want and where in the circuit does it go? After the switch, but before the amp? I would also want to be able to charge the battery without using solar power only. So I would want to get a 12v smart charger, but is it alright to permanently leave the leads for the charger attached to the battery terminals? I wouldn't think this would matter unless plugged in, but not sure. Help please?

I was thinking of using 21 400mA 0.22W Commercial Solar Cell wired in series for 11.55V to match the battery. I'll cover the panels with plexiglass and I'll use a reverse blocking diode to prevent discharge through the panel. I'm not sure about whether I would need some form of charge controller or not? I'm thinking maybe I could get away without one, seeing as the discharge rate is around 2 amps max and the charge rate is 400ma with full sun and I'm using an SLA battery. Not sure though...could someone verify maybe?

I also want to include a 12v USB charger to charge ipods/etc from the battery/solar. Is there anything special about wiring one of these in the mix? I would think just wire it in after the on/off switch along with the amp?

Excuse the thrown together 3d model, but something like this:
Click the image to open in full size.
The Cabinet is sealed, not ported. Adding a port would be a bit awkward to this design and with the available volume and this driver, not much is gained from a reflex design. The biggest compromise is probably the available 400-450in^3 internal volume. This driver would love QUITE a bit more, but it is what it is. I want the cabinet this size, or close to it. The speaker could be set firing up for "360 dispersion" or laid on its side. I know the off-axis response wouldn't be the absolute best, but it'd work. There is a "holy brace" that supports the driver as well as the SLA battery. The solar cells would cover three panels which would act as the "top" when the speaker is laid down. The input terminals, on/off switch, volume control and USB charger in the grey square on the side. Thinking you could have a canvas shoulder strap at the top on two opposing sides and carry it like a hand drum. I got the inspiration from this neat little speaker that isn't in production yet, but will be soon: CHANT PORTABLE AUDIO SYSTEM

I've been reading a lot of posts here and elsewhere and I have a pretty good idea of what to do, but I know there are experienced people on here that could definitely make me feel better about the design. I have built a handful of speakers, but always passive designs. Keep in mind that for this project the main goals were cost, size, and longer battery life from solar charging. Please let me know if you notice anything wrong with my plan or have any suggestions! Thank you!

Last edited by xpheolix; 18th June 2012 at 07:24 PM.
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Old 13th June 2012, 09:23 AM   #2
sreten is offline sreten  United Kingdom
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Location: Brighton UK

You need about 14V total to charge a SLA to full power, 13.8V no load.

USB is nominally 5V and nominally charges 3.6V batteries. 12V will
just blow things up. You could use a 12V to 5V switching converter.

rgds, sreten.
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Old 13th June 2012, 02:51 PM   #3
xpheolix is offline xpheolix  United States
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alright, I'll add another 5 or 6 of the solar cells for 13.75-14.3v.
So something like this Car Usb Charger would not work stand-alone? hmm...unless something like the above would work or I found a fairly inexpensive 12v->5v step down regulator, the USB power may end up being too much for this project.
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