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'[EE]: current sensing on mains'
2006\05\20@093519 by Alessandro Queri

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face
Hello everybody.
I wonder if any of you can help me in solving this problem.
I have a stylish table lamp which i'd like to retrofit. The lamp is built
with a transformer permanently connected to the mains and a switch plus a
bulb on the low voltage side of the transformer. The bulb and the switch are
away from the transformer and I cannot put anything that side (remember, t
is stylysh... ;-( ). What happens is that transformer gets very hot and
after some time breaks even if not used. besides I don't like the
transformer to be always connected to the mains. I'm wondering if there is
any way limiting current on the mains side of the transformer and to sense
in order to switch the real power only when needed. I'd like to use all
semiconductors, all on the mains side, no secondary supply. Any idea? Hope I
made you understand the problem, my english is not that good.
Many thanks in advance.

Alessandro

2006\05\20@120307 by Harold Hallikainen

face picon face
It sounds like you've got a "wall wart" transformer running the lamp.
These are well known for their inefficiency and standby power
requirements. As such, they are about to be outlawed in California. I
think the simplest solution to the problem is to buy a new high efficiency
wall wart, which is generally a wall mounted switching power supply. These
meet the new efficiency and standby power requirements.

Harold


{Quote hidden}

> -

2006\05\20@124917 by Alessandro Queri

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Uhm... No, it was a huge transformer i once tried to substitute with a
switching PS.
The switching PS blew after few months of operation: the load is really
heavy when you switch on the lamp: the filtering capacitors were soon
damaged.
I think linear is better in this case.

Thanks!

Alessandro

> It sounds like you've got a "wall wart" transformer running the lamp.
> These are well known for their inefficiency and standby power
> requirements. As such, they are about to be outlawed in California. I
> think the simplest solution to the problem is to buy a new high efficiency
> wall wart, which is generally a wall mounted switching power supply. These
> meet the new efficiency and standby power requirements.

2006\05\20@175214 by William Chops Westfield

face picon face

On May 20, 2006, at 9:02 AM, Harold Hallikainen wrote:

> It sounds like you've got a "wall wart" transformer running the lamp.
> These are well known for their inefficiency and standby power
> requirements. As such, they are about to be outlawed in California. I
> think the simplest solution to the problem is to buy a new high
> efficiency
> wall wart, which is generally a wall mounted switching power supply.

Are switching wall-warts really that much more efficient in standby
mode than linear supplies?  Are they much more efficient than linear
supplies at the sort of standard currents such things provide (less
than 500mA)?  Or is this just another one of california's sillier
laws?

BillW

2006\05\20@182418 by Spehro Pefhany

picon face
At 02:54 PM 5/20/2006 -0700, you wrote:

>On May 20, 2006, at 9:02 AM, Harold Hallikainen wrote:
>
> > It sounds like you've got a "wall wart" transformer running the lamp.
> > These are well known for their inefficiency and standby power
> > requirements. As such, they are about to be outlawed in California. I
> > think the simplest solution to the problem is to buy a new high
> > efficiency
> > wall wart, which is generally a wall mounted switching power supply.
>
>Are switching wall-warts really that much more efficient in standby
>mode than linear supplies?  Are they much more efficient than linear
>supplies at the sort of standard currents such things provide (less
>than 500mA)?  Or is this just another one of california's sillier
>laws?

The limits are numerical, not related to technology, but they effectively
outlaw sale of the typical cheap linear wall-warts. Does that answer your
question?

http://www.energy.ca.gov/2005publications/CEC-400-2005-012/CEC-400-2005-012.PDF

See page 119.

They figure the measures, over time, will eliminate the need for several
new power plants.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


2006\05\20@191331 by Roy

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face
part 1 455 bytes content-type:text/plain; (decoded 7bit)

What is the voltage and current or wattage of the lamp?

Switch mode supply does sound like the answer.
_______________________________________

Feel the power of the dark side!  
Atmel AVR

Roy Hopkins
Tauranga
New Zealand
_______________________________________



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19/05/2006




part 2 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2006\05\21@045257 by Wouter van Ooijen

face picon face
> Are switching wall-warts really that much more efficient in standby
> mode than linear supplies?

AFAIK it's not the linear supply that is inefficient, it is the (cheapo)
transformer.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2006\05\21@054348 by Bob Axtell

face picon face
William Chops Westfield wrote:
> On May 20, 2006, at 9:02 AM, Harold Hallikainen wrote:
>
>  
>> It sounds like you've got a "wall wart" transformer running the lamp.
>> These are well known for their inefficiency and standby power
>> requirements. As such, they are about to be outlawed in California. I
>> think the simplest solution to the problem is to buy a new high
>> efficiency
>> wall wart, which is generally a wall mounted switching power supply.
>>    
>
> Are switching wall-warts really that much more efficient in standby
> mode than linear supplies?  Are they much more efficient than linear
> supplies at the sort of standard currents such things provide (less
> than 500mA)?  Or is this just another one of california's sillier
> laws?
>
> BillW
>  
They ARE more efficient... But even if all the walwarts in California
were unplugged completely,
it won't help California's power woes. Most of the power problems stem
from a braindead
legislature that tinkered with the power companies and when it was over,
there was nothing
but shreds.

You called it, Bill, just another crackpot law.

--Bob

2006\05\21@070510 by Tony Smith

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{Quote hidden}

But think of how many plasma TV's you'll be able to run!

Tony

(Seriously, I'd ban those first!)

2006\05\21@105806 by Bob Blick

face picon face
On 21 May 2006 at 2:43, Bob Axtell wrote:
> They ARE more efficient... But even if all the walwarts in California
> were unplugged completely,
> it won't help California's power woes. Most of the power problems stem
> from a braindead
> legislature that tinkered with the power companies and when it was over,
> there was nothing
> but shreds.

I thought about replying rather than dashing off a nasty little
message immediately. Please take this OT if you are going to diss
California or discuss politics.

Thanks,

Bob

2006\05\21@111612 by Spehro Pefhany

picon face
At 10:50 AM 5/21/2006 +0200, you wrote:
> > Are switching wall-warts really that much more efficient in standby
> > mode than linear supplies?
>
>AFAIK it's not the linear supply that is inefficient, it is the (cheapo)
>transformer.

The transformer is inefficient in standby (it could be made better, but
it would cost more for better core materials to reduce the core losses).

If a linear supply is followed by a linear regulator, then even more power
is wasted (as much as half under typical full load conditions), whereas
the SMPS may not require any extra regulation or perhaps just a bit of
LDO regulation.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


2006\05\21@115951 by Bob Axtell

face picon face
Bob Blick wrote:
> On 21 May 2006 at 2:43, Bob Axtell wrote:
>  
>> They ARE more efficient... But even if all the walwarts in California
>> were unplugged completely,
>> it won't help California's power woes. Most of the power problems stem
>> from a braindead
>> legislature that tinkered with the power companies and when it was over,
>> there was nothing
>> but shreds.
>>    
>
> I thought about replying rather than dashing off a nasty little
> message immediately. Please take this OT if you are going to diss
> California or discuss politics.
>
> Thanks,
>
> Bob
>
>  
Sorry, Bob, you are right.

--Bob

2006\05\22@032613 by Alessandro Queri

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part 1 378 bytes content-type:text/plain; format=flowed; charset="windows-1250"; (decoded 7bit)

It's 12V 35W.

I tried a switching PS but it blew after few months. When suddenly connected
the lamp is like a short circuit and the capacitors after some time went
dead.

From: "Roy" <roy.hspamKILLspamihug.co.nz>


> What is the voltage and current or wattage of the lamp?
>
> Switch mode supply does sound like the answer.



part 2 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2006\05\22@085440 by Vasile Surducan

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On 5/22/06, Alessandro Queri <.....piclistKILLspamspam.....tiscali.it> wrote:
> It's 12V 35W.

Theoreticaly such load can't create problems if:

1. there is no short circuit on the secondary (to the lamp)
2. the transformer is well dimensioned (it must have at least 40-50W,
so you can't use a small wallwart)
3. the primary coil has enough wires, so with the secondary circuit
open, must be less than 20-40mA in the primary.

or

4. the transformer is a switching one and well designed (it's sourcing
a small current when is on stdby)

If the bulb it's a halogen lamp and there is no ceramic socket and the
wires are not insulated with silicone, than almost sure you have a
"variable" short circuit near the socket. For a standard transformer
the effect is damaging the primar coil by hot (assuming the secondary
is well dimensioned and insulated).

Vasile

2006\05\22@123536 by Peter

picon face


On Mon, 22 May 2006, Alessandro Queri wrote:

> It's 12V 35W.

Any good reason for not using a smpsu meant for halogens ? I used such a
smpsu for many years to operate two 20 Watt halogens in a desk lamp.
Never had trouble.

Peter

2006\05\22@150111 by Alessandro Queri

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face
Thanks Peter and thanks also to Vasile.

The switch mode I had was not that good, but I wasn't able to find a better
one. Actually it was a portable computer one, rated 5A.
Problem is that commercial smpsu for this application have LIVE wires and
the lamp has exposed metal arms to carry power.

Ale


{Original Message removed}

2006\05\23@104714 by M. Adam Davis

face picon face
Well, you've got a lot of good information from others trying to help
you avoid the "hard" solution you seem to want.  If you still want to
try to do this the hard way (rather than simply getting a better power
supply) then read on...

I'm assuming you are in a country that uses 120VAC - trade 120VAC for
whatever you use where suitable.

1.  Assume all the circuitry *has* to be on the mains side - we cannot
connect anything to the secondary of the transformer.

For this solution to work you *have* to use a transformer for the lamp
power supply.  Plug in a switching power supply and it simply won't
work.

Use a small 120VAC to 12v transformer to give your circuit 12VAC.  Use
a DPDT relay that will allow you to connect the lamp mains wire to
either mains OR the output of your 12VAC transformer.

Your circuit, should you choose to build it, will normally power the
lamp from the 12v transformer.  It will sense the current draw on the
lamp transformer through use of a current sensing transformer (wrap
magnet wire around one of the lamp transformer wires) and, probably
using a couple or window comparators, determine whether the switch is
on or off.

If the switch is on then your circuit will switch the relay so the
lamp transformer is powered by mains.  It will then measure a much
larger current draw.  When that current falls (the light was switched
off) then your circuit will switch the relay so the lamp is running
off the 12v again.

If it sounds more complex than purchasing a good transformer that
won't burn out, that's because it is.

If this is a halogen light then you'll probably find that the
lightbulb socket contacts are oxidized, and need to be replaced.  This
bad contact is one of the reasons your transformers are having such
trouble living long lives.  It could also be that you're buying cheap
transformers, which compounds the problem.  If the bulb breaks
frequently then you'll also find that shortens the life of the
transformer considerably.  Putting a suitable rated transorb or gas
discharge tube after the transformer may help the bulb burning out
situation, but the bad contacts can only be helped by a bigger, better
transformer or by replacing the bulb holder contacts once a year or
so.

-Adam

On 5/20/06, Alessandro Queri <EraseMEpiclistspam_OUTspamTakeThisOuTtiscali.it> wrote:
{Quote hidden}

> -

2006\05\23@124554 by Peter

picon face


On Mon, 22 May 2006, Alessandro Queri wrote:

> Thanks Peter and thanks also to Vasile.
>
> The switch mode I had was not that good, but I wasn't able to find a better
> one. Actually it was a portable computer one, rated 5A.
> Problem is that commercial smpsu for this application have LIVE wires and the
> lamp has exposed metal arms to carry power.

Not true. The commercial smpsu for halogen lamps with EC rating does not
have live wires.

Peter

2006\05\23@134701 by Vasile Surducan

face picon face
On 5/23/06, Peter <plpspamspam_OUTactcom.co.il> wrote:
>
>
> On Mon, 22 May 2006, Alessandro Queri wrote:
>
> > Thanks Peter and thanks also to Vasile.
> >
> > The switch mode I had was not that good, but I wasn't able to find a better
> > one. Actually it was a portable computer one, rated 5A.
> > Problem is that commercial smpsu for this application have LIVE wires and the
> > lamp has exposed metal arms to carry power.
>
> Not true. The commercial smpsu for halogen lamps with EC rating does not
> have live wires.
>
> Peter

 True Peter. As long LIVE means "no isolation" like two telescopic
antennas used to carry low voltage/high current and sustain the bulb
too. Crazy invention.
 If the things should be such simple on 5Ghz like bulb problems, what
a gorgeous day should be for me...

Vasile



> -

2006\05\24@085625 by Tony Smith

picon face
> > > Problem is that commercial smpsu for this application have LIVE
> > > wires and the lamp has exposed metal arms to carry power.
> >
> > Not true. The commercial smpsu for halogen lamps with EC
> rating does
> > not have live wires.
> >
> > Peter
>
>   True Peter. As long LIVE means "no isolation" like two
> telescopic antennas used to carry low voltage/high current
> and sustain the bulb too. Crazy invention.
>
> Vasile


Hey, don't knock it!  Why rummage around for a 12+ voltish AC
transformer when you can just put a couple of alligator clips on your
lamp?

Some of them are noisy buggers, so you can test your power filtering
too!

Tony

2006\05\25@171028 by Alessandro Queri

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face
Thanks guys,
I finally found an expensive switching PSU ;-)

Alessandro

----- Original Message -----
From: "Tony Smith" <@spam@ajsmithKILLspamspamrivernet.com.au>
To: "'Microcontroller discussion list - Public.'" <KILLspampiclistKILLspamspammit.edu>
Sent: Wednesday, May 24, 2006 2:55 PM
Subject: RE: [EE]: current sensing on mains


{Quote hidden}

> --

2006\05\26@143631 by Peter

picon face


On Thu, 25 May 2006, Alessandro Queri wrote:

> Thanks guys, I finally found an expensive switching PSU ;-)

Why expensive ? I paid $10 for a small one (about 1x1x2 in.) that was
good for up to 12V 50W halogen.

Peter

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