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want to find (smart) battery charger w/ 5vdc input

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Jazzi View Drop Down
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    Posted: 17 September 2016 at 8:20am
I would like to build my first battery powered portable boombox.  This will be a gift for my company and I'm trying to make it user friendly and able to function with common off-the-shelf cables and accessories since I fear a really specific charger or cable would get lost.  I also need the charging circuit to be somewhat smart and shut itself off instead of overcharging since the users will not know anything about how it works.

To that end, I want someone to be able to plug it into any USB port (or any USB phone charger) to charge the battery.  So I would like to find a battery charging circuit that will work off of 5vdc input with as little as 0.5A of input current.

At first I thought about using the 18650 lithium battery board from sure-electronics, but it looks like I need a 15v+ power supply to charge that system.  I don't think that is compatible with what I'm trying to do.

Then I thought about using one of the lead acid batteries from eXpertPower like the 5Ah model, but it looks like the maximum current they are rated to supply is 1.5A which is almost enough but I'd like to send up to 30rms to my speaker.

I'm not really sure where to go from here.  I think a lithium-ion solution would be great, but I don't know of one that can be run in parallel like the sure-electronics board to provide 12v but can also be charged with a 5vdc source.  I think the lead-acid battery system is cheap and simple, but also don't know how to charge it (intelligently) from a 5vdc source.

Maybe one of you can guide me a bit?  Even if you show me some websites that would carry stuff like this, I can search a bit on my own.  All I know right now is parts-express, sparkfun, sure-electronics.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 18 September 2016 at 7:42pm
I wouldn't lose too much sleep over the idea of a charger cable getting lost. 5v DC charging is fiddly if you're restricted to off-the-shelf components. You would need a DC/DC boost converter at least, either in the charging circuit or just charging a big 5v battery bank and boosting that into the amp. I don't know enough about these to advise so maybe someone else can.

One possible workaround would be to get a 12v wall charger, but try and find one of the ones, like a laptop charger, where it has a 3 pin plug lead that is separate from the inverter box, then you could carefully mount it inside the box, adding perhaps 200 grams to your system weight, and provide the system with an easily replaceable cable which anyone could pull a replacement for off of an old laptop charger if they lost it.

That's one slightly clumsy but possible way to do it.

I also think the battery provider you've chosen is being very conservative in their rating. A 5ah lead acid battery will handle a 30 watt amplifier with no problems at all. It's possible it might not be comfortable with a continuous 30 Watt sine wave for hours on end.

I find the 7ah lead acid batteries tend to provide the best value for money, for a little more weight than the 5ah. £11.99 delivered from eBay http://www.ebay.co.uk/itm/NP7-12-12v-7Ah-Ultra-Max-Lead-Acid-Rechargeable-Battery-NP9-12-NP6-12-/130918310649?hash=item1e7b56e2f9:g:HD8AAOSwxH1UAIe4





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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 18 September 2016 at 7:56pm
By the way: 
Originally posted by <a href=http://www.powerstream.com/SLA.htm%5d target=_blank rel=nofollow>http://www.powerstream.com/SLA.htm http://www.powerstream.com/SLA.htm wrote:

The typical charging voltage is between 2.15 volts per cell (12.9 volts for a 6 cell battery) and 2.35 volts per cell (14.1 volts for a 6 cell battery). These voltages are appropriate to apply to a fully charged battery without overcharging or damage.

So if you can find a laptop style wall charger in that voltage range you should have a pretty foolproof charging system and a user replacable/serviceable cable.
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