3 wire cord but no ground

[larrymoencurly]

No-name model SPP34-12.0/5.0-2000, 3-wire plug but no ground connection (or UL approval or EMI filter):

[ben7]

Re: 3 wire cord but no ground

No-name model SPP34-12.0/5.0-2000, 3-wire plug but no ground connection (or UL approval or EMI filter):

LOLOLOL!!!!

I love how its labled genericly, "Power Supply"

Try shorting the output and see what it does

[budm]

Re: 3 wire cord but no ground

If the construction for critical components are double insulated, then ground prong is not needed. Is there actual ground pin on this IEC AC Inlet?

[mariushm]

Re: 3 wire cord but no ground

I think there actually is ground, through that blue capacitor by the transformer. later edit: no i was wrong, it has to do with making sure there's no high frequency noise and radiation in the output cable .

The optical isolator is for feedback on the secondary side.


Here's a really crap psu : http://www.youtube.com/watch?v=T88ej...ature=g-user-u

And a reasonable one: http://www.youtube.com/watch?v=1F3Xl...ature=g-user-u

^ it explains about that capacitor near the transformer and being isolated and all that, why it doesn't need ground...

[larrymoencurly]

Re: 3 wire cord but no ground

If the construction for critical components are double insulated, then ground prong is not needed. Is there actual ground pin on this IEC AC Inlet?

There is a ground pin there (see attached pic), only it goes nowhere inside, but on eBay I've seen power supplies with AC inlets that fit 3-wire cords but lacked any visible ground pin. At least they weren't pretending to be safer than 2-wire.

How safe are non-certified transformers vs. certified ones?

I use the 3-wire 19VDC power adapter from an old Dell Latitude with my Toshiba laptop because it's grounded because I suspect it's safer. Actually Toshiba once told users of a certain AMD-based model to switch to 3-wire non-Toshiba AC adapters, not for safety but to prevent lockups and reboots from line noise. I don't know why their Intel-based laptops, like mine, weren't included in the notice.

[larrymoencurly]

Re: 3 wire cord but no ground

This AC adapter has been updated to make it even cheaper, although the output ratings remain unchanged. I think the basic circuit is the same (new one still has an optoisolator, but it's hard to see in the picture), but some parts were removed (output chokes), reduced in size (less capacitance, lower wattage resistors, TO-220 schottky diodes replaced with axials), or cheapened (regular resistor in place of flameproof, UL certified Y-capacitor now an uncertified one). The ground prong still goes nowhere, but they quit bothering to solder it, at least not properly.

The old AC adapter was made in China; the new one was made in "CHIAN".

[imp]

Re: 3 wire cord but no ground

Here's a really crap psu : http://www.youtube.com/watch?v=T88ej...ature=g-user-u

LOL! Why even bother to put some components inside? Worst I ever seen!

[eccerr0r]

Re: 3 wire cord but no ground

If one laptop PSU needs 3-prong then wouldn't all portable electronics need it?

In my opinion it almost seems all laptops require 3-prong unless somehow they can double insulate the output plug exposed contacts... as far as I know, most laptop PSUs are single insulated for the exposed plug contacts (namely, the main transformer). However somehow my eeePC 12V PSU is 2-prong and supposedly passes UL (but I have yet to open it to look at how it's insulated internally...)

[mariushm]

Re: 3 wire cord but no ground

The eeePC may need low enough power for the adapter to fit into another category of power supplies, when it comes to radiations and so on.

I don't own one and didn't have one go through my hands, but looking on Amazon for replacement power supply for eeePC it looks like it's 9.5v 2.315A ... that's just 22 watts... no problem.

[ben7]

Re: 3 wire cord but no ground

If one laptop PSU needs 3-prong then wouldn't all portable electronics need it?

In my opinion it almost seems all laptops require 3-prong unless somehow they can double insulate the output plug exposed contacts... as far as I know, most laptop PSUs are single insulated for the exposed plug contacts (namely, the main transformer). However somehow my eeePC 12V PSU is 2-prong and supposedly passes UL (but I have yet to open it to look at how it's insulated internally...)

My 65W AC adapter for my laptop has two prongs also.

[mariushm]

Re: 3 wire cord but no ground

The transformer inside is insulated, there's only a tiny capacitor coupling the dc side and ac side and that's for emi suppression, so the dc is basically floating.

Not much to kill you from the secondary side of the adapter and onwards. Also, laptops usually only use a high voltage to charge the batteries, otherwise there's just a tiny area on the pcb where you get more than 5v in the laptop.

Even if you short something, it's theoretically not deadly, so there's no risk for human.

But of course, there's a lot to argue about low voltage/high voltage, low current/high current and so on ... you may get your heart fibrillating or damage your tongue if you put your tongue on the 19v dc jack of a laptop charger.

[eccerr0r]

Re: 3 wire cord but no ground

Oh... I think I just thought of why it's OK for transformers are OK. The varnish on a transformer's primary counts as one layer of insulation, a plastic guide and tape to separate the primary and secondary will be the main insulation, and finally the varnish on the secondary would be a third... that should qualify, so maybe this is fine not to have a ground after all as long as the transformer is designed this way. (I would hope that varnish would not be the only insulation separating me from doom!)

The wiring from the mains plug and the primary circuitry itself still needs to be double insulated...which typically isn't too hard... So I think for power bricks it mostly should be fairly safe to have no ground as long as it's designed properly.

And BTW...the eeePC PSU is a 3A 12V, so 36W, so very well might be a special class. Some other PSUs I have:
Scanner: 24V 1A -- GROUNDED!
Big HP laptop power brick: 12V 5A -- Grounded!
Iomega PSU: 5V1A+12V0.75A - Not grounded
LCD: 12V 4A -- Grounded.

I guess the scanner might be an anomaly?

[tom66]

Re: 3 wire cord but no ground

The reason no ground is used is because there are two separate insulating layers PLUS the ground isn't needed for EMI.

Ground is very useful for getting rid of EMI because it is easy to couple most of the noise into it. Live and neutral approximate ground at high frequencies.

This is why some products do not have an earth: including one is more expensive, so they'd rather make it such that one isn't needed. For lower power products, that's possible.

[momaka]

Re: 3 wire cord but no ground

My 65W AC adapter for my laptop has two prongs also.

I have an old 95W Sony VAIO "power brick" (it really is) with only 2 prongs.
I also have a 12V 1A 3 prong SMPS from my D-Link DCM-202 modem.
Go figure ...

[larrymoencurly]

Re: 3 wire cord but no ground

The reason no ground is used is because there are two separate insulating layers PLUS the ground isn't needed for EMI.

Several years ago, Toshiba issued a technical bulletin about some of their laptop computers acting wierd because EMI got through their ungrounded AC adapter, and their suggestion was to substitute a grounded Targas brand adapter. That was back when Targas adapters were UL or CSA approved.

[ben7]

Re: 3 wire cord but no ground

Several years ago, Toshiba issued a technical bulletin about some of their laptop computers acting wierd because EMI got through their ungrounded AC adapter, and their suggestion was to substitute a grounded Targas brand adapter. That was back when Targas adapters were UL or CSA approved.

I've never had that problem

[lti]

Re: 3 wire cord but no ground

I've never had that problem

It was only a certain series. See post 5:

I use the 3-wire 19VDC power adapter from an old Dell Latitude with my Toshiba laptop because it's grounded because I suspect it's safer. Actually Toshiba once told users of a certain AMD-based model to switch to 3-wire non-Toshiba AC adapters, not for safety but to prevent lockups and reboots from line noise. I don't know why their Intel-based laptops, like mine, weren't included in the notice.

[larrymoencurly]

Re: 3 wire cord but no ground

Several years ago, Toshiba issued a technical bulletin about some of their laptop computers acting wierd because EMI got through their ungrounded AC adapter, and their suggestion was to substitute a grounded Targas brand adapter. That was back when Targas adapters were UL or CSA approved.

I've never had that problem

It was for some of their A2xx series Satellite laptops, only those with AMD CPUs (A215?).

[ben7]

Re: 3 wire cord but no ground

It was for some of their A2xx series Satellite laptops, only those with AMD CPUs (A215?).

Ah, thats older than mine. Good to hear xD

(mine is a L645D from 2010, AMD Phenom II triple core CPU )

[Colt45ws]

Re: 3 wire cord but no ground

Once I took my old Dell laptop on a trip and forgot the power adapter, so I bought one of those "green" adapters from WalMart that purported to be compatible.
It made the computer HOT. Like AC voltage hot. Any metal components I would get a tingle off of like if I rested my hands on the palm rest. So I returned it and got another one. It did the same thing! I couldnt figure it out. It wasnt full 120VAC, obviously, but it was well enough to feel.