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Author Topic: 5v usb battery modification, help!  (Read 1862 times)

trials_modder

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5v usb battery modification, help!
« on: May 04, 2006, 12:30:54 AM »

I am trying to modify the 5V usb battery design http://www.hackaday.com/entry/1234000270029372/ used to power small usb devices, by replacing the battery with a 12 V, 500mA AC to DC transformer. Only problem is, the transistor (LM7805) gets extremely hot as I test the circuit using a resistor and a small LED. Why is the transistor overheating?
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trials_modder

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Re: 5v usb battery modification, help!
« Reply #1 on: May 04, 2006, 12:43:56 AM »

ok, so i had the power supply and the LED coincientally hooked up backwards so I was forcing current the wrong way.
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trials_modder

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Re: 5v usb battery modification, help!
« Reply #2 on: May 04, 2006, 08:18:14 PM »

new problem - the circuit is supplying the 5 volts to recharge a zen micro via usb, and the micro indicates it is charging. however, it doesn't and over time the transistor gets hot. what now?
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trials_modder

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Re: 5v usb battery modification, help!
« Reply #3 on: May 04, 2006, 08:48:05 PM »

ok, so the zen appears to be charging and the transistor keeping cool as long as the player is not playing any songs at the same time. perhaps i should find which component is not supplying enough current, and start my own blog (seeing i'm just posting to myself :P)
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pinkpanther

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Re: 5v usb battery modification, help!
« Reply #4 on: May 04, 2006, 09:21:10 PM »

I would say do yourself a favor and invest in a high quality multi-meter if you're going to be doing things like that ;).  If you already have one, then just ignore me. 
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trials_modder

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Re: 5v usb battery modification, help!
« Reply #5 on: May 05, 2006, 01:48:39 AM »

ah once again, new problem. seems the thing won't really charge either way, even if its indicating that it is. leaving it plugged in and off for two hours didnt get the battery charged at all. the LM7805C transistor i used is rated for 1A, and the wall wart 500mA, so I don't think current draw is the problem. anyone know if theres something i'm missing to charge the creative zen micro? (plugging the zen into a computer with the computer's power off charges it)
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Skylined

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Re: 5v usb battery modification, help!
« Reply #6 on: May 05, 2006, 02:27:57 PM »

Check twice, do once.

You should better start from zero, without any hurry, and as I've said, checking twice, doing once. ;)
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trials_modder

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Re: 5v usb battery modification, help!
« Reply #7 on: May 05, 2006, 03:58:01 PM »

no, this has happened before, but it was using a 9 volt battery instead of a wall wart. i thought it was because the battery could not supply the current needed to recharge the battery.
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viridius

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Re: 5v usb battery modification, help!
« Reply #8 on: May 05, 2006, 04:04:22 PM »

Did you try swapping in a new 7805?  You might have killed it when you hooked it up backwards.
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