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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Sun Sep 05, 2010 11:46 am Post subject: OT Wall warts |
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I have a device that requires a 5 VDC power supply. It is assumed that it will be connected to a PC with a USB port for power. However, it will be remote mounted so I will need a external power supply for it. I have many used wall warts in the 6-12 VDC range. I was thinking of modfying one to output 5 VDC. But in the process of testing them to make sure it works first I discovered that with no load, they output way more than their rated output. The 6 VDC one I have outputs 11.6 VDC and all the 12's are in the 16-18 VDC range. Every DC wall wart I've tested is way high with no load.
I tested the output of the USB port to 5.2 VDC. Should I just try the 6 volt one or modify it to put out a little less.
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Chip
A Barco is only a AmPro with training wheels
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Ile
Joined: 09 Mar 2006
Posts: 1491
Location: Jyväskylä, Finland
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zaphod
Joined: 16 Jun 2006
Posts: 2002
Location: Cloverdale
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| Posted: Sun Sep 05, 2010 3:28 pm Post subject: |
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for the price of a wallwart you can get a USB power supply that plugs into the wall and lets you power in a USB device. i've even seen them sold as apple power supplies for travellers. i have one that supplies a couple of USB ports and a 110 outlet.
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Sun Sep 05, 2010 6:35 pm Post subject: |
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OK, it shows a 33uf cap on the input and a 0.1 cap on the output.
I don't have a 33uf cap nore does the shack. Can I just hook uo a 22 and 10 uf in parallel for 32uf and be close enough?
The circuit looks simple enough hook the +12VDC to terminal 1. 33uf from 1 to 2 (2 being ground or -), terminal 3 is +5VDC out with 0.1uf from 3 to 2. -12VDC or common connects to #2 and ends up being the neg or commong for the +5 out. Correct???
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Chip
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Das444
Joined: 22 Dec 2006
Posts: 145
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| Posted: Sun Sep 05, 2010 7:02 pm Post subject: wall wart |
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Hi
What about a phone charger? My Samsung Rogue has a 5.0V USB port on the wall charger. Just a thought
Dan
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Ile
Joined: 09 Mar 2006
Posts: 1491
Location: Jyväskylä, Finland
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| Posted: Sun Sep 05, 2010 7:40 pm Post subject: |
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| stefuel wrote: | OK, it shows a 33uf cap on the input and a 0.1 cap on the output.
I don't have a 33uf cap nore does the shack. Can I just hook uo a 22 and 10 uf in parallel for 32uf and be close enough?
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That is fine, or use 47uF if you have one.
| stefuel wrote: | | The circuit looks simple enough hook the +12VDC to terminal 1. 33uf from 1 to 2 (2 being ground or -), terminal 3 is +5VDC out with 0.1uf from 3 to 2. -12VDC or common connects to #2 and ends up being the neg or commong for the +5 out. Correct??? |
Sounds right, but if you have 6v transformer use it. Regulator heat more when dropped voltage goes high, same thing with current. Also check needed current from device, it cant be more than 1A with this chip (with 2V dropping).
It's also good to have some heatsink if that device take more than little current.
http://www.radioshack.com/product/index.jsp?productId=2102856
Chip have build in thermal protection, so you wont burn it though.
Some of these regulators have voltage on base (cant remember if this have), so also heatsink will have same voltage.
If that is problem you need also mica insulation sheet.
http://www.radioshack.com/product/index.jsp?productId=2102859
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Sun Sep 05, 2010 10:18 pm Post subject: |
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No voltage on the base (at least on the rat-shack version). It is common to 3 which is ground.
Tonight (if I can drag my son away from Nintendo) I will conduct science class by teaching my son how to design and etch a small circuit board. Not many kids these days would ever get the chance to see how that's done (at home).
Hopefully this will be some of the only chemicals he ever experiments with 
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Chip
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Mon Sep 06, 2010 2:21 am Post subject: |
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Well that was fun. It took him a couple of minutes to catch on to what I was trying to show him. We did the fist one huge so he could understand it better. then I said now make it again only really small 
He drew it and we etched it together. I drilled the holes and soldered it up. I told him that some of the parts have a + or - a couple of percent so don't expect it to be exactly 5VDC when we were done. Damn 4.99VDC 
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