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Quick question for EE guy, 5volt, USB, soldering, etc (solved)

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spystyle:
Thanks all for the replies, this has been solved by this post :


--- Quote from: MonMotha on July 09, 2010, 03:45:23 pm ---You physically can stack USB plugs and add the currents, but it's totally against the spec the way all those stupid adapters actually do it.  You only are supposed to get 100mA (0.1A) until you "enumerate" to the OS and request more.  They never do that on the second plug.  It works because most PCs don't have (or need) full per-port power management and tend to just limit each port to a little over the maximum.

Stacking them in parallel works in this case because you're pretty much guaranteed that all the USB plugs on a machine actually hook up to the same power supply internally.  Don't try it with switch mode bricks.  They'll "fight" each other as each one will have a slightly different regulation point.  Linear bricks (the bigger, heavier ones with bulky 60Hz transformers) would be a bit more forgiving.  I'd recommend just finding a single supply capable of sourcing whatever you need.

It looks like the two pads for the power jack connected together near the "side" of the jack are probably ground.  That would be typical of a "tip positive" DC barrel.  The remaining pin in the center is the positive input.  You can probably just buy a suitable brick or use a "universal" one.  It the picture frame is well designed, it'll tolerate a reverse polarity situation (though it might not work).  Don't count on it being well designed, though.

--- End quote ---

I will use a 5v 3a wall plug that I can cut and solder :)

have fun!
Craig

Samstag:

--- Quote from: danny_galaga on July 10, 2010, 12:10:09 am ---
--- Quote from: shardian on July 09, 2010, 08:51:15 pm ---

As for where to solder: Most of those plugs have the pin as positive, and the outside as ground. That way when the wall wart plug is just sitting there, the positive terminal is hidden inside the plug ( safety issue)


--- End quote ---

Out of curiosity, why would it be any safer?

--- End quote ---

On it's own it's no safer than the reverse, but since the negative is usually "common", protecting the positive side in all equipment prevents shorts when two different units touch.  Just like AC wiring in your home, you designate one wire as hot and the other "ground" even though they're both 120v potential. 

danny_galaga:

--- Quote from: Samstag on July 10, 2010, 06:05:10 pm ---
--- Quote from: danny_galaga on July 10, 2010, 12:10:09 am ---
--- Quote from: shardian on July 09, 2010, 08:51:15 pm ---

As for where to solder: Most of those plugs have the pin as positive, and the outside as ground. That way when the wall wart plug is just sitting there, the positive terminal is hidden inside the plug ( safety issue)


--- End quote ---

Out of curiosity, why would it be any safer?

--- End quote ---

On it's own it's no safer than the reverse, but since the negative is usually "common", protecting the positive side in all equipment prevents shorts when two different units touch.  Just like AC wiring in your home, you designate one wire as hot and the other "ground" even though they're both 120v potential. 

--- End quote ---

Ah, ok. It's the common convention thing. Like all shoe retailers displaying only left shoes...

Samstag:

--- Quote from: danny_galaga on July 16, 2010, 09:54:35 am ---
--- Quote from: Samstag on July 10, 2010, 06:05:10 pm ---
--- Quote from: danny_galaga on July 10, 2010, 12:10:09 am ---
--- Quote from: shardian on July 09, 2010, 08:51:15 pm ---

As for where to solder: Most of those plugs have the pin as positive, and the outside as ground. That way when the wall wart plug is just sitting there, the positive terminal is hidden inside the plug ( safety issue)


--- End quote ---

Out of curiosity, why would it be any safer?

--- End quote ---

On it's own it's no safer than the reverse, but since the negative is usually "common", protecting the positive side in all equipment prevents shorts when two different units touch.  Just like AC wiring in your home, you designate one wire as hot and the other "ground" even though they're both 120v potential. 

--- End quote ---

Ah, ok. It's the common convention thing. Like all shoe retailers displaying only left shoes...

--- End quote ---

A little like that, except that accidentally touching a left and right shoe at the same time is unlikely to be fatal.  Except during a really big sale, maybe.

danny_galaga:

--- Quote from: Samstag on July 16, 2010, 09:05:52 pm ---
--- Quote from: danny_galaga on July 16, 2010, 09:54:35 am ---
--- Quote from: Samstag on July 10, 2010, 06:05:10 pm ---
--- Quote from: danny_galaga on July 10, 2010, 12:10:09 am ---
--- Quote from: shardian on July 09, 2010, 08:51:15 pm ---

As for where to solder: Most of those plugs have the pin as positive, and the outside as ground. That way when the wall wart plug is just sitting there, the positive terminal is hidden inside the plug ( safety issue)


--- End quote ---

Out of curiosity, why would it be any safer?

--- End quote ---

On it's own it's no safer than the reverse, but since the negative is usually "common", protecting the positive side in all equipment prevents shorts when two different units touch.  Just like AC wiring in your home, you designate one wire as hot and the other "ground" even though they're both 120v potential. 

--- End quote ---

Ah, ok. It's the common convention thing. Like all shoe retailers displaying only left shoes...

--- End quote ---

A little like that, except that accidentally touching a left and right shoe at the same time is unlikely to be fatal.  Except during a really big sale, maybe.

--- End quote ---

Well, I suppose accidentally shorting out a 9V feed isn't exactly life threatening either  ;D

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