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Old 29th May 2005, 01:33 AM   #1
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Lightbulb portable, battery-operated 30W+... mission impossible?

Hey all,
Here's the deal- I'm looking to produce in excess of 30W from batteries... without carrying car batteries or a backpack... and I'm not insane. Maybe.

On the battery front, I think it's feasible if I use the Li-Poly packs commonly found in R/C gear. They're capable of serious discharge rates- 10 amps or more, continuously (http://www.hobby-lobby.com/lithium-polymer.htm). It's also worth noting here that the system won't need to operate continuously for long periods, and I really don't care if I only get half an hour of sporadic use out of it.

Sound quailty is not critical- the system will use a contact transducer, and the losses on that side will be monumental compared to a little electrical chatter.

My primary concern is electrical efficiency for thermal reasons. Imagine wearing a device that's in near-direct skin contact... and dumping however many thermal watts into your immediate vicinity. Active cooling is, clearly, a must- but the less required, the better.

Other useful bits of info:
-incoming signal will be line-level audio
-I have a fair bit of electrical experience, and am surrounded by those with more
-I have access to top-quality single/double-sided etching in house

Thoughts? Suggestions? Designs? Total madness?

Dick
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Old 29th May 2005, 03:10 AM   #2
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you are planning to do something evil

anyways you should be able to do it with a 12 volt battery pack and a TDA 7375 or something like that . it is 2x 35 watts to 4 ohms. if you are using it (for what mysterious purpose) intermittantly. an old p3 cooler(with 12v fan) would do fine
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Old 30th May 2005, 04:49 PM   #3
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Yah, if by "evil" you mean "insanely cool". I'll toss you guys a link the the Flickr once I get it all together.

On the 7375, though- I read the spec sheet, and I don't see a mention of whether or not the signal needs to be preamped... set gain of 26 dB, so that might encourage me to use one, but is it required?

Thanks for the advice!
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Old 30th May 2005, 04:54 PM   #4
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What about one of those cheap class d amps that everyone and his dog is modding?
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Old 30th May 2005, 10:15 PM   #5
djk is offline djk
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The most power you can get from a 12V battery without an inverter is about 12W at 4 ohms, and that is with a bridge amp.

The Philips TDA1562Q IC bootstraps the supply voltage to 24V and then runs a bridge amp in class H for the highest efficiency, it can push a clean 40W into 4 ohms without an inverter.
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Old 31st May 2005, 08:38 PM   #6
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Just to show my ignorance....

Doesn't W = A x V? Therefore, wouldn't the maximum wattage be based both on the voltage level and the amperage?

From another perspective, V = I x R... so, assuming V = 12, R = 4 (which was not a stipulation of my particular problem), then I = 3. Substituting back into the wattage equation, then W = 3 x 12 = 36W.

Continuing, how can the maximum of 12V be 12W, but the max of 24V be 40W?

What's more, R/C batts are available in a wide range of voltages, so I'm not limited to 12.

This all leads me to believe that I'm not particularly concerned, unless there are some other, nonmathematical reasons for the 12=12, 24=40 rule.
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