Opening a wall wart that has no screws ;)

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starhawk

[H]F Junkie
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OK, I bought a wall wart on eBay for the purposes of pulling it apart and reverse-engineering part of its circuitry. (It's a long story.) Of course the damn thing is epoxied or sonic-welded shut. It's a 5v 1.05a rated lump so there's not much danger of electrocution -- I'm not stupid enough to try to dismantle it while it's plugged in!

I should probably mention that I'm about as subtle as a 16lb sledgehammer and as patient as a 5yr old full of M&Ms :p I'm also rather bullheaded.

How do I open this damn thing without becoming impaled on a utility knife or otherwise severely injuring or killing myself?
 
One technique I've heard of is to freeze it (so the epoxy hardens) then whack at the seam with a hammer. I've never done it myself, so I can't testify as to its effectiveness, but you can't do much harm.

And if you do manage to break it beyond repair, you can always skip down to your local goodwill/salvation army/Deseret Industries and pick up another super cheap wall wart.
 
One technique I've heard of is to freeze it (so the epoxy hardens) then whack at the seam with a hammer. I've never done it myself, so I can't testify as to its effectiveness, but you can't do much harm.

And if you do manage to break it beyond repair, you can always skip down to your local goodwill/salvation army/Deseret Industries and pick up another super cheap wall wart.
 
I freeze them, then take it out and slap it good with the handle of a screwdriver or miniature ball peen hammer all around the glue joint, then go at it with the butterknife and screwdriver, works on battery packs too
 
This is the wall wart in question: http://www.ebay.com/itm/390556788902

Short version of the long story: I have a MiFi 4620L from Verizon, and this particular model of MiFi likes to chew up chargers and spit 'em out. Got a fairly nice 2a Phihong USB charger from DigiKey (first order from Digi EVAR) and two weeks later it was dead and smelled like bakelite. Hmmm.

Solution: figure out what in the charger tells the MiFi how much juice it can pull, and put together a 3a 5v charger from a 7805 and that nifty "add a power MOSFET and some other stuff and you can pull as much as the transistor can handle" circuit from the 7805 datasheet (*IF* I can figure out the math correctly for once!). The MOSFET is likely to be an IRF510 sourced from my local Radio Shark ;)
 
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This particular wall wart, which is the charger that is sold with the MiFi, is rated 5v 1.05a.
 
Funny I didn't see this till now.

It doesn't say. It's a microUSB plug so the rating's implied.
 
starhawk said:
Solution: figure out what in the charger tells the MiFi how much juice it can pull,
Click to expand...

time to grok the principle of impedance

The impedance of a circuit, in the case of DC and nonreactive AC loads measured in Ohms, determines the ratio of potential to kinetic energy in the system.

Voltage is potential energy. Amperage is kinetic. Both must be present for any work to be done.

A low impedance load will allow more current to flow than a high impedance load for a given voltage.

What I am getting at with the physics lecture is that nothing in the charger tells the MiFi how much to pull. The impedance of the MiFi determines how much current WILL flow at a given voltage. Ohms = Volts/Amps, Amps =Volts/Ohms, Volts = Ohms x Amps; all equivalent expressions.

It is possible that something is wrong inside the radio causing it to present an unduly low impedance. It is also possible that you have just had a run of bad luck with your supplies.

A real cheap way to get going again would be to paperclip an old ATX supply with lots of capacity on its 5V rail and feed the radio off of that.

I would be quite interested to hear the actual measured current.
 
Not what I was talking about.

Apple USB chargers have a voltage divider on the D+/D- lines of the connector that tell the attached iDevice what the charger is rated for.

I'm sure there's something analogous on the MiFi -- it'd be bloody stupid of them not to have that.

I just need to know how it works, and that involves opening a real Novatel charger.

Hence this thread asking how to open the charger.
 
That does seem a bit... brutal.

Is there a gentler way than going all smashy smashy on cold wall warts?
 
starhawk said:
That does seem a bit... brutal.

Is there a gentler way than going all smashy smashy on cold wall warts?
Click to expand...
You could use a small laser to slowly disintegrate the epoxy.
Try and transport the unit out of the epoxy mold.

or

Freeze and smash the crap out of it, might be your best bet to see the insides
or look for a schematic of it.
:p
 
starhawk said:
Silly me, but what about an "exacto" (hobby) or utility knife...?
Click to expand...

You'll poke your eye out kid...jk

I'm not talking smash, you freeze it to get the glue brittle then carefully smack it all around the seam to fracture the joint, then start with the cutting and prying
 
...oh...

I was just having visions of the PCB getting wrecked, not just the housing. Guess that was a little misplaced.

How long should it sit in the freezer?
 
till it ain't going to get any colder, couple hours at least, and often you can actually save the housing, not as pretty perhaps, but usable
 
And if you manage to destroy the housing, you could just pot the whole mess in two-part epoxy resin. That way you can even *see* the insides as they work! :D
 
I'm here. With *a* picture. But first, the news...

Two hours in the freezer and plenty of tack hammerage did nothing. I hit and it laughed at me. I got it open with a utility knife and (eventually) a flathead screwdriver. Then I discovered something that *really* pissed me off...

Novatel lied to me. They outright fucking lied.

I have an email from them where they explicitly say (in the rather unique Calcutta dialect of English) that there's *some* sort of communication along the D+ / D- lines of the USB connector.

FUCKING BULLSHIT.

There are exactly TWO wires going from the charger PCB into the cable for the MiFi. One is red, one is black. THAT'S IT. It's a fucking BLIND charging system -- the MiFi just hopes the charger can supply an amp and that's as far as it gets -- which is really bloody stupid because of exactly what would happen if someone plugged a bog-standard "ordinary" cheap shit USB charger -- 5v 500mA rating -- into the MiFi -- the charger would die quickly and spectacularly -- and quite likely take the MiFi with it. Ow.

So here's the insides of the charger --> http://i.imgur.com/NEnTtdv.jpg
 
I was going to suggest just taking a dremel cutting tool to the seams but I see you got it open.

Awwww, that's a cute little transformer. No wonder it has a crappy rating. :p They sure don't make stuff like they used to. I used to open these bad boys up all the time when I was a kid. It was more transformer than PCB.
 
The really cheap ones are. But something like what this plugs into needs a switch-mode supply with at least a little quality to it. (Apparently not much, tho.)
 
def switch mode, they rectify first thing before the transformer, the xfmr can be small because it is operating well above 60Hz.

I actually do think that the banging helped you out, looks like shiny broken glue in some areas, that is about as clean as they ever come apart.

I would forget the sensing BS and just hack up a monster 5V supply for the thing
 
Planning on it. 3a should be enough... that's 1-1/2 times the maximum the spec allows ;)

I'm thinking of using this circuit (image below), although I'll need some significant help with the 'rithmatic because 1+1=27 happens all too often around me ;) I can't math for shit. (I used to know a math prof with a T-shirt that said, 2+2=5, "for extremely large values of 2". Yeah, like that.) Input would be 12v. I have a couple 12v wall warts, although none rated for 3a.

YqqFUyp.png


Image is a screenshot from here, page 30/57 as numbered in the datasheet (not by the PDF reader) --> http://www.st.com/web/en/resource/technical/document/datasheet/CD00000444.pdf

I'm thinking I'll try out one of these with it --> http://www.murata-ps.com/data/meters/dms-78xxsr.pdf
That way I don't have to "invest" in a laptop-style brick that can step wall current down. Wait. Could I use an actual laptop brick with this? I have a "generic replacement" HP one for my mother's tc4200 that's such a pile of electroturds that it won't even stay in the laptop... it's rated 18.5v 3.5a. That's ~65w which is more than overkill for this... ;)
 
was me I'd just hack the red wire off an old ATX supply, but I'm lazy that way
 
Red Squirrel said:
Awwww, that's a cute little transformer. No wonder it has a crappy rating. :p They sure don't make stuff like they used to. I used to open these bad boys up all the time when I was a kid. It was more transformer than PCB.
Click to expand...
Back in the day, we didn't have switchmode power supplies, so the transformer *had* to be big. Nowadays, we're in better shape. Heck, Apple fit a whole 500mA USB charger in a 1" cube for their phones/ipods, and it's a quality piece of hardware.

starhawk said:
Planning on it. 3a should be enough... that's 1-1/2 times the maximum the spec allows ;)

I'm thinking of using this circuit (image below), although I'll need some significant help with the 'rithmatic because 1+1=27 happens all too often around me ;) I can't math for shit. (I used to know a math prof with a T-shirt that said, 2+2=5, "for extremely large values of 2". Yeah, like that.) Input would be 12v. I have a couple 12v wall warts, although none rated for 3a.
...
That way I don't have to "invest" in a laptop-style brick that can step wall current down. Wait. Could I use an actual laptop brick with this? I have a "generic replacement" HP one for my mother's tc4200 that's such a pile of electroturds that it won't even stay in the laptop... it's rated 18.5v 3.5a. That's ~65w which is more than overkill for this... ;)
Click to expand...
Yes, you could use an old laptop brick, but instead of using a linear regulator (which can waste a lot of electricity), get an MC34063-based buck converter, and it'll save you a lot of energy. (Incidentally, when searching ebay for such a thing, I ran across this.) Search for "buck converter" on ebay. Or just buy a higher-rated (1.5A or whatever) 5V wall wart on ebay--you can get 'em for under $5 shipped.
jojo69 said:
was me I'd just hack the red wire off an old ATX supply, but I'm lazy that way
Click to expand...
I heartily endorse this recommendation.
 
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Looking at these two supplies --

http://www.ebay.com/itm/120821112060
http://www.ebay.com/itm/121080478637

The 2nd one is definitely overkill. Since the pictures may be inaccurate, I've a message into each seller to confirm that each supply will run on 120v AC. Next question for them will be how long they can operate between shutdowns in a 70 F environment, without having issues.
 
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Chances are the sellers won't be able to give you the answer to the second question--they're probably just resellers for some OEM. Rather than dealing with a chassis-mount power supply, why not just get a wall wart off ebay for less money?
 
I want something that's very durable and can run for 14+ hours at a time.

As for the wall warts... I spent $20 (incl shipping) for a Phihong 2A USB wall wart and it burned out in at most two weeks. I don't want to repeat that. Further, the cheap USB and 5V wall warts on eBay are "rippletastic" as my tech shop friend would say -- they have almost no filtering and put out something a little closer to AC than I'd like. Besides, most of them don't have the current capability I want.
 
This is old news. VERY old news :p the wall wart I opened was put back together and served in its intended duties for a couple weeks before expiring. Apparently Novatel doesn't believe in anything more than intermittent-duty warts :rolleyes: that's fine in the city where you can drink and eat all sorts of things while browsing email -- but I don't live in the city. I'm at least a half hour's drive from cities like that.

The Phihong adapter lasted a similar length of time and met a similar fate. I opened it and found no sign of obvious damage, but nevertheless it was dead so out it goes.

As for "chinese" anything -- it matters very little, in my not-so-humble opinion, where a device was built. 99.9% of the problem with modern technology not lasting long enough to drain a soda can... is design. Money is more important than functionality. If a company can build an item for $75 and sell it for $100 and have it last for ten years, or they can build it for $35 and sell it for $50 and have it last for two years, they'll build it for $35, sell it for $100, and slap a two-year warranty on it and proceed to line their coffers with insane amounts of money -- and if you want it to last longer, you can either buy elsewhere (ha! everyone does it that way) or build it your own damn self (which inevitably costs $150 or more).

Look up "planned obsolescence" and you'll find the root of exactly what I'm talking about. Basically (IIRC it started in the '80s), some rather overly bothered economist, who should have the Dunce Cap of the Galaxy permanently glued to his head so people know to stay the fuck away, he thought that there was an actual danger inherent in factories building eg refrigerators that were designed to last a few decades. He thought that meant that someday nobody would buy any more refrigerators. Now if people had done the sensible thing and ignored this idiot, we wouldn't have a problem because everything would still be built well. But they listened. So now everything has to be designed to last five years or less (usually a lot less) and build quality is horrible on even the supposedly "best" stuff.

I'd love to have, for instance, a Fifties-era Frigidaire in my kitchen. May not be terribly efficient, but I can ignore that because it'll quite likely live longer than I will. That was before this "planned obsolescence" BULLSHIT so it's built right. I can NOT come even CLOSE to saying the same, lifespan-wise, about the ~2010 Whirlpool that's in my kitchen right now. That will most likely sputter and clunk to a spectacular halt sometime in the next five years, because it's not built for quality, it's built to die after a period of time to make me go out and buy another because theoretically people buying major appliances every five years keeps the economy going. (I hope I've clearly communicated what I think of that idea. Jesus H. Christ.)

Designed under the influence of a stupid economical idea that makes no fucking sense whatsoever is the problem. The little oval "Made in China" sticker is --at best-- a side effect. If you want shit that works, junk this "planned obsolescence" crap, for the entire globe. Or, buy everything you can that's pre-1980s and what you need that you can't buy, make yourself.

/rant
 
that power supply i linked you is very old... old linear lambda, power one, etc power supplies are very reliable... if you blow those up there is something else happening
 
...and terrifically inefficient because it's linear. Reliable, hell yes, but I have to be able to afford my electric bill as well :p

A pity one can't seem to find continuous-duty USB-able switching power supplies.

EDIT: well... hmmm... I'm inclined to try it just for the retro appeal, but $26 incl shipping for basically a USB wall wart...? Plus it'll need a housing, primarily because I have a cat. I'll think about it and I'll also talk to Mom. Guessing that this is similar to a 7805 on serious steroids, in that it takes in as many amps as it puts out?
 
fwiw... I went through similar with my Slingbox Pro. It uses a 4amp 5v supply. Near impossible to find 5V AC adapter in that amperage. I ended up using a Dlink router ac adapter which was 5V 2A with it fine.. for a while. Then died.

I eventually ended up going with this and haven't had an issue in the 8 months I've been using it.

4AMP 20W USB Charger

it came with all kinds of power connectors to connect other devices etc.
 
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If you can, measure the current draw on the device, either using a multimeter and a jig, or one of these. As long as it draws below 2A, I'd just pick up a quality tablet usb charger that puts out a solid 2A, that should be enough.

Ken Shirriff did a good test and writeup on how shitty generic usb chargers can be: http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html

I picked up a couple of the HP Touchpad chargers when they were clearing them out. $5 each for a USB charger that puts out clean 2.4A was too much of a bargain to pass up :D
 
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