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

[spystyle]

Hello from Maine

I have an LCD photo frame, I get a kick out of those. I bought it for almost nothing because it didn't come with a plug and it's a little beat up.

It calls for 5 volts and 1.5 amps. I have 5 volt adapters in my box of AC adapters but none fit!

I also have a USB cable.

if I knew where to solder I think I could power the photo frame from USB

Care to give me a clue based on these pics?







I know one of these points near the plug is +5v and another is ground, but I don't know which one and I don't know if I'd kill the LCD if I solder it wrong-ly

Thanks,
Craig

[Franco B]

I don't think USB will be an option as you only have ~0.5A to play with from USB.

What are the specs of the 5v adapters? as long as they provide >1.5A you should be able to hack one of those. You can determine the polarity using a multimeter.

I will let someone else who actually knows something about electronics to tell you where to solder You will most likely be soldering to two pads which come off that socket (not the mounting ones if thats what they are) but you need to know which is + and which is - as the pin can be + or - and vice versa for the barell

If it was me though I would take a look at the PCB and see if I could see any common paths to/from those which may point towards a ground.

Then again I would probably get it wrong and fry it so as I said, wait until someone who knows what they are on about chips in

[Kevin Mullins]

I don't think USB will be an option as you only have ~0.5A to play with from USB.

I'm no EE, but that was the FIRST thing that crossed my mind as well.
@500ma vs. 1.5A is a helluva difference.

[spystyle]

Aha, so USB has 0.5 amps - that explains why my "laptop sata hard drive to USB" adapter has two USB plugs, to make 1.0 amps.

You can stack USB plugs to add amperage, apparently.

I think I need an EE guy as a neighbor

[MonMotha]

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.

[spystyle]

Thanks

EE-HERO to the rescue

[Ond]

The simplest way IMO?  Assuming one of your 5V adaptors is rated at 1.5 amps (it will be printed on it) just solder a plug that fits the socket onto the adaptor.  Plugs in various sizes designed for that purpose with screw on barrel covers are available at most electronic hobby stores.  You can twist the wires on intially to the plug to check the polarity is correct before soldering.  I keep a range of plugs in my parts for this purpose to reuse those pesky bricks that seem to pile up when I'm not looking.  This is neater than soldering directly to the pads on the board.  

Thinking about it though, very few 'general purpose' 5V bricks are rated at 1.5A (most are at or less than an 1 amp) The exception to this is PS units designed to provide power to external drives.  Good hunting!

[shardian]

You need to run power directly from a +5 tap on the power supply. DO NOT power a device that big from the USB bus.

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). Put you DMM on continuity test and put one lead on the pin, and the other lead on each solder point until you find the correct one.

Just to be sure, most DC things have a plaque that says the voltage and amps requirement, then below that have a simple diagram that shows a dot with a "c" around it. It will denote if either the dot or the "c" is positive or negative. If that diagram isn't on the device, the pin is positive.

[danny_galaga]

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)

Out of curiosity, why would it be any safer?

[Ond]

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)

Out of curiosity, why would it be any safer?

Yeah I wondered about that too......

[spystyle]

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

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.

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

have fun!
Craig

[Samstag]

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)

Out of curiosity, why would it be any safer?

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]

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)

Out of curiosity, why would it be any safer?

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. 

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

[Samstag]

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)

Out of curiosity, why would it be any safer?

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. 

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

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]

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)

Out of curiosity, why would it be any safer?

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. 

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

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.

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

[spystyle]

Hey Monmothma,

Care to identify the polarity of this one ? It's a 12v IDE to USB adapter, I want to solder a molex to it



Thanks!
Craig

[crashwg]

The one closest to the jack (and the one on the same pad) are ground, the one below is +.

[spystyle]

Thanks

I would have deduced that from looking at the other one, but I thought maybe this plug was different so it would be reversed polarity - I guess not.

I need to go to EE skooL

Have fun!
Craig

[spystyle]

Dear EE guys, I need your brain power again

Can "HJR-3FF-S-Z" (HJR-3FF) relay be used to make hacked power strips ?

Here is the datasheet :

http://www.datasheet.co.kr/datasheet-html/H/J/R/HJR-3FF_TIANBOGANGLIANELECTRONICS.pdf.html

They are really affordable, like $1.10 each :

http://www.ebay.com/itm/3-x-Mini-Relay-SPDT-5-Pins-12VDC-10A-120V-Contact-USA-Seller-Free-Shipping-/221040166504?pt=LH_DefaultDomain_0&hash=item3377054668

I currently use "275-218"

http://www.radioshack.com/product/index.jsp?productId=2049722

And that's nearly 10 bucks each.

Here is how I solder the pins :



"White" is AC white wire
"Black" is AC black wire
and "PC" is 12 volts from a computer

When the computer is turned on, the 12 volts activate the relay, and white is connected to white, and black is connected to black.

Can I get a clue from an EE ?

Thanks
Craig

[Mysterioii]

It says it's rated for 10A at 120VAC so if you need less than that, yes.  Assuming you actually get what it's rated at and not random Chinese knockoff junk.

BTW reading back through this thread I saw what I believe is some well-meaning misinformation from 2 years ago...  When talking about why coaxial power plugs generally have the power contact on the inside...

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.

Hot and ground/neutral/return are not equivalent and are not at the same potential.  You protect the hot pin in case for example you're making another path to ground like say you're plugging the thing in while standing barefoot in a puddle.  If you're like a little kid and you're holding the plug wrong, you'll just touch ground and everything's fine.  Same reason appliances have chassis ground.  You ever encounter a stove, oven or microwave with the chassis ground hooked up backwards?  Touch it while you touch the kitchen sink and you'll know it.  When properly grounded that won't happen.

In your house wiring hot and neutral are NOT both at 120v potential.  Apparently this is a common misconception?  Get a multimeter, stick one probe in the center ground terminal, then probe the hot and neutral ones.  The hot one will read about 120VAC and neutral will (quite sensibly) read zero.  Unless someone wired the outlet backwards.  I really hope people aren't wiring up there plugs backwards thinking they're interchangeable.  For driving an old appliance with a simple AC motor yeah it might seem like they're functionally interchangeable but there's a big difference.

You will hear the argument that "current flows both ways in an AC circuit", and that's true, but only one side (the hot side) is driving the current.  Imagine a garden hose with a pump on one end and the other end just dangling off into the grand canyon, just big reservoir for air just like earth ground is a huge reservoir for electrons.  Air can be flowing back and forth in the hose at any point in time... the current is going both ways.  Now cut the hose...  The sucking and blowing (huh huh) is only taking place on one side, the pump side.  That's hot.  The other side of the hose... nothin'.  That's neutral.  One of them is safe to hold up to your eye socket, the other one wouldn't be a good idea.  You should be able to stick a bare wire in the neutral terminal and hold it in your mouth then stick another wire in the ground terminal and hold it in your hand and be just fine.

[spystyle]

It says it's rated for 10A at 120VAC so if you need less than that, yes.  Assuming you actually get what it's rated at and not random Chinese knockoff junk.

Hey thanks for chiming in

Can you tell me how I'd wire it ?







I'd guess like so :

4-1 = black
2-5 = PC (12v)
3 = N/A ?

And therefore only 1 wire from the power strip needs to be interrupted ?

I need to go to EE skool

Thanks,
Craig

P.S. Also your correction was very interesting

EDIT :

Pins 1 to 4 are "normally closed", and pins 1 to 3 are "normally open"

So for a power strip hack =

1-3 = black
2-5 = PC (12v)
4 = N/A

... and try to keep it under 5 amps Or buy a better relay.

[MonMotha]

You should be able to stick a bare wire in the neutral terminal and hold it in your mouth then stick another wire in the ground terminal and hold it in your hand and be just fine.

For the record, don't do this.  It's common even in residential environments to get several volts between neutral and ground due to voltage "drop" across the neutral from the current flowing on it.  The ground (ideally) has no current flowing on it, so it doesn't see the same drop.  In industrial and commercial buildings, the situation is even nastier.  There's only one bond point between neutral and ground (where the power enters the facility).  The neutral and ground are then bussed to each sub-panel separately.  You can easily end up with 20-40V difference between neutral and ground in these environments.  It'll certainly give you quite a wake up if you touch both of them, especially on your tongue

"Ground" should always be touch-safe.  That's the whole point of it.  It's the current sink of last resort and should always be at local earth potential.  Neutral is bonded to earth ground at your main panel, but things can start to diverge from there.  Hot of course is 120Vrms relative to neutral (and hence approximately 120Vrms to ground, since neutral and ground are "about the same").  The only real difference between hot and neutral is that one of them is hooked up to a big metal spike driven into the ground, but the implications of that difference are pretty far reaching, and the entire electrical safety code is designed around this.

As for the relay in question, there's no way I'd use that tiny little relay for this purpose.  One, I don't like the pinout structure - it requires having 120V too close to the isolated 5V for my comfort.  I also don't really trust that tiny thing with 10A.  Heck, I'm not sure I'd trust it with 5A.  Your wiring description is correct, though.  If you want some cheaper relays, check out places like Jameco.  They've got some surplus stuff that can be way cheaper than Rat Shack.

[Mysterioii]

Haha yeah I admit I was being melodramatic...  my main point was that hot and neutral are not interchangeable even though I have come across several conversations over the years where people seem to believe that they are.  Making contact with the neutral conductor should be much safer than touching hot on a properly wired outlet but hopefully nobody would lick one based on my rant.

Re: the relay....  Yes sorry, I'm skeptical too, hence my "Assuming you actually get what it's rated at and not random Chinese knockoff junk" comment.  I should have been more clear with my skepticism.  I'll buy LEDs and stuff like that off of ebay but for something like a relay that's going to be carrying mains power I'd be more careful.  If you can find it at a digikey, mouser, newark etc. then I would trust it for sure.  However MonMotha you said:

there's no way I'd use that tiny little relay for this purpose

If you look at the spec sheet, this relay is 2cm x 1.5cm x 1.5cm, that's pretty small but not exactly tiny.  The spec sheet makes a point that one of it's selling points is a small footprint.  Yes, it's meant to be through-hole soldered on a board and I prefer the socketed relays like the first ones he was using, it's much easier to swap one out if it goes bad.  I did a search on mouser.com for industrial relays with a 12Vdc coil voltage capable of handling 120 VAC at 10 amps or more and found several, both socketed and through-hole.  Here's a panasonic one that's almost the same form factor as the one he's looking at:

http://pewa.panasonic.com/assets/pcsd/catalog/js-catalog.pdf 

Again, would I be skeptical?  Maybe.  With mains voltage I'd probably pay a little extra and get them from a big distributor and not off of ebay.  But if I did get them from a known-reliable source then yes I'd have faith in the specs.

[DaOld Man]

It says it's rated for 10A at 120VAC so if you need less than that, yes.  Assuming you actually get what it's rated at and not random Chinese knockoff junk.

Hey thanks for chiming in

Can you tell me how I'd wire it ?







I'd guess like so :

4-1 = black
2-5 = PC (12v)
3 = N/A ?

And therefore only 1 wire from the power strip needs to be interrupted ?

I need to go to EE skool

Thanks,
Craig

P.S. Also your correction was very interesting

For your case, you want to connect the black wire from the 120 vac plug to the pin #1 and the black wire from the power strip to pin #3. White from plug and white from power strip connect together.
Pins 1 to 4 are normally closed, and pins 1 to 3 are normally open. The power strip will turn off when the relay is turned on if you use pins 1 to 4.
Also, in US anyway, breaking the neutral wire (usually white) on the power strip is not necessary. Just control (or break) the black wire with the relay, no need in doing more work than you really need to.

Edit: I would not use the small relays with the pins, simply because it is going to be tough soldering a #16 or #14 AWG stranded wire that is on the power strip to those small pins. That relay is designed to be mounted on a PC board, where the pins on the relay go through solder pad holes on the PC board.
It can be done but it is not desirable. Plus (due to heavy gauge wire sucking up the heat), you will have to use a hot soldering iron to get a good joint, and that relay may not like the high heat.
I would go with the "cube" relay from radio shack, it has terminals that you can solder a bigger wire to fairly easy, although you may have to drill out the holes in the contacts for the bigger wires of the power strip to fit.

[spystyle]

Thank you all for chiming in

I appreciate it

Craig from Maine

[DaOld Man]

I picked up one of those relays today, and the socket to go with it.
I had a metal 6 outlet surge protected power strip, so I cut a hole in the side of the strip and mounted the socket.
I then wired it so that the first receptacle by the on/off switch is always hot and the other five are turned on and off by the relay. I cut the hole for the socket with a jig saw, got in a hurry and it looks uglier than I like, but it will work.
Made a few scratches too, but thats life I guess. It will be hidden inside the arcade cab anyway.
Now if the relay fails, it will be very simple to unplug it and plug in a new one.
Parts List:
Radio Shack #275-0220 10 Amp relay socket -- $2.99
Radio Shack #275-0218 10 Amp DPDT 12 VDC coil Relay -- $9.59
Power strip: I bought it a few months ago, I chose it because it had an easily removable back, and it has standard "house type" receptacles, so I knew it would be easy to hack. I think I got it at lowes, for around 10 bucks.

You might find the relay and socket on the web a lot cheaper, but I wanted it quick.
I tested it with a 9 volt transistor battery to turn relay on and off, and plugged a toaster and a hot air gun in the outlets.
I found out that the toaster (rarely used) is broke, it would not turn off (on its on) after several minutes, so by finding this out, this project could have saved my house from a toaster fire.
The modified power strip works like a charm. Just another part for the Little Rage!
Anyway, here are a couple of pics.

[spystyle]

Awesome, I build them like that as well.

Though I've never actually bought a socket.

I'll try that

Keep up the good work

[DaOld Man]

Awesome, I build them like that as well.

Though I've never actually bought a socket.

I'll try that

Keep up the good work

Thanks, BTW, the toaster is in the garbage now. I guess people should test those things ever so often, this one got hot enough to set off the smoke alarm, but it was probably burning off dust. But a 10 dollar toaster is not worth the risk of burning down the house.

[spystyle]

Hey, for $1.10 I figured I'd give it a try.

The little relay works So far ...





Here is how it's wired for a power strip hack =

1-3 = black
2-5 = PC (12v)
4 = N/A







I see this type of power strip selling for like $5 each :

http://www.walmart.com/ip/Philips-2pk-6-Outlet-Surge-Protector-White/17127152

... add $1.10 for a relay.

So the hacked power strip would be less than $7 after tax. 

That is very cheap LOL

Thanks for the clue, I didn't know how to wire it before asking.

I'll report how long it lasts and how much amperage it was used with.

Cheers,
Craig

p.s. I realize this isn't very tidy - I just hacked it together with the idea I may have to replace the relay if it fails. So that can be handy as it's sticking out.

[DaOld Man]

Looks good!
What you have in it is cheaper than a smart strip, and I think a relay would be much more reliable than the smart strip.
Thanks for keeping us updated.

[spystyle]

I wonder what is inside these relays ? I bet we could replicate it on a small breadboard.

I might attempt to dismantle one of these relays, I have 2 more

(they are bought in packs of 3)

Have fun!
Craig

[krick]

I wonder what is inside these relays ? I bet we could replicate it on a small breadboard.

Relays have a mechanical switch inside.  That's what causes the click.  I don't think there's any way to make them much smaller.

Has anyone tried wiring up a USB plug so that the relay is triggered by your PC turning on? like this... EcoStrip 2.0 - USB Controlled Power Strip

It would require a relay that could be triggered by 5v or less though.  Probably a pain to find.  Most I see are 12vDC triggered.

[spystyle]

Aha, thanks for chiming in

We'll see how it holds up

[MonMotha]

Most 6V rated relay coils work well enough at 5V.  A lot of them even have 5V/6V written on them.  They're definitely available.  They'll mostly be the smaller packages (and hence current ratings), though.  It can take a surprising amount of current at only 5/6V to move the larger contacts needed for high current relays.

[spystyle]

Interesting, I think I found one for less than 70 cents each LOL :

http://www.ebay.com/sch/i.html?_nkw=%22SRD-5VDC-SL-C%22+%225+pcs%22&_sacat=0&_odkw=SRD-5VDC-SL-C&LH_BIN=1&_sop=15&_osacat=0&_from=R40

When coupled with this $5.50 power strip :

http://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l2736&_nkw=4+OUTLET+POWER+STRIP+WITH+12%22+CORD+AND+CIRCUIT+BREAKER

... the completed strip is only $6.20 each to make LOL

And it can be powered through USB or Molex.

That apparently includes a breaker too. Here is the breaker from my recent hack :



I bet those are good to have

OK, have fun!
Craig

[spystyle]

OK, I figured out how to make a "smart strip" for like $4.50 Ultra-cheap.

This one is 5v so it can connect to USB or 5v molex.

This relay "SRD-5VDC-SL-C" can be had $3.99 for 5 (79 cents each)

http://www.ebay.com/sch/i.html?_nkw=%22SRD-5VDC-SL-C%22+%225+pcs%22&_sacat=0&_odkw=SRD-5VDC-SL-C&LH_BIN=1&_sop=15&_osacat=0&_from=R40

And this power strips from walmart "pps1060r/17". It cost only $3.27 and has a 15amp breaker, so it doesn't seem to be missing anything.

http://www.walmart.com/ip/Philips-Power-Sentry-6-Outlet-Cord-Strip-2.5/21109368

Here is a pic of the price from my local walmart (Auburn Maine) :



So, $3.27, 20 cents tax, 79 cents for the relay =  $4.26 ultra cheap "smart strip"

Pretty funny huh ? I am soldering one up today to USB :

http://pinouts.ru/Slots/USB_pinout.shtml

If you go with USB, and don't have any USB wires laying around, a USB extension cable can be used (99 cents)

http://www.ebay.com/sch/i.html?_nkw=usb+extension+cable+-retractable+-mini+-webcam+-splitter+-connector+-micro&_sacat=44932&_odkw=usb+extension+cable+-retractable+-mini+-webcam+-splitter+-connector&LH_BIN=1&_osacat=44932&_from=R40

OK, have fun
Craig

EDIT :

Dang ! The computer I tried to use this with has "always hot" USB, apparently. In other words, the USB is constantly outputting 5 volts when the computer is plugged in, regardless if the computer is on or off.

So I have to connect it to the computer's 5volt molex rather than a USB cord (male)

EDIT 2 : Well the $4.26 ultra cheap "smart strip" was a success But I had to connect it to 5v molex, I was not able to connect it to USB.

However, I consider a sub-five-dollar "smart strip" to be a milestone in thrifty-hacking

EDIT 3 : OK, here are pics of the $4.26 ultra cheap Smart strip". This time I was more precise and did not lose a socket.