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How hot should a transformer get?



 
 
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  #1  
Old July 29th 08, 06:23 AM posted to uk.d-i-y
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Posts: 21
Default How hot should a transformer get?


Apologies if this is not strictly a DIY question. I cannot think of better forum to ask.

I recently bought a cheap and cheerful LCD TV for our camper van. It can run off 12 volt DC or 240
AC, with a supplied transformer. The transformer looks like the type you get with a laptop - a
separate oblong black box.

When working from the mains the transformer gets hot - very hot. Last night we watched 2 hours of
telly and when time came to put it all away I could hardly pick the transformer up. It was almost
too hot to hold.

I am worried about a potential fire risk.
Is this normal? How hot do they normally get?


Thanks - Adam
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  #2  
Old July 29th 08, 06:48 AM posted to uk.d-i-y
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Posts: 9,132
Default How hot should a transformer get?

On 2008-07-29 06:23:56 +0100, Adam Lipscombe said:


Apologies if this is not strictly a DIY question. I cannot think of
better forum to ask.

I recently bought a cheap and cheerful LCD TV for our camper van. It
can run off 12 volt DC or 240 AC, with a supplied transformer. The
transformer looks like the type you get with a laptop - a separate
oblong black box.

When working from the mains the transformer gets hot - very hot. Last
night we watched 2 hours of telly and when time came to put it all away
I could hardly pick the transformer up. It was almost too hot to hold.

I am worried about a potential fire risk.
Is this normal? How hot do they normally get?


Thanks - Adam


It shouldn't get to that kind of temperature. I would return it. If
the replacement is as hot, then select another product.



  #3  
Old July 29th 08, 09:02 AM posted to uk.d-i-y
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Posts: 9,423
Default How hot should a transformer get?

On Tue, 29 Jul 2008 06:48:56 +0100, Andy Hall wrote:

When working from the mains the transformer gets hot - very hot. Last
night we watched 2 hours of telly and when time came to put it all away
I could hardly pick the transformer up. It was almost too hot to hold.


It shouldn't get to that kind of temperature. I would return it. If
the replacement is as hot, then select another product.


Agreed. Are there any ratings on the "transformer"(*) and on the TV? What
was the power source when you were using it 12v or 240v? It's not 100%
clear if the "transformer" is needed for 12v operation.

(*) I have "transformer" in quotes as quite often these days they are
really small switched mode power supplys rather than a lump of iron and a
couple of coils. Normally easy to tell as iron is quite heavy, circutry
not. I'd be surprised if a SMPSU would run down to 12v though most have a
lower voltage limit somewhere above 50v.

--
Cheers
Dave.



  #4  
Old July 29th 08, 09:54 AM posted to uk.d-i-y
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Posts: 6,490
Default How hot should a transformer get?


"Dave Liquorice" wrote in message
ll.net...
On Tue, 29 Jul 2008 06:48:56 +0100, Andy Hall wrote:

When working from the mains the transformer gets hot - very hot. Last
night we watched 2 hours of telly and when time came to put it all away
I could hardly pick the transformer up. It was almost too hot to hold.


It shouldn't get to that kind of temperature. I would return it. If
the replacement is as hot, then select another product.


Agreed. Are there any ratings on the "transformer"(*) and on the TV? What
was the power source when you were using it 12v or 240v? It's not 100%
clear if the "transformer" is needed for 12v operation.

(*) I have "transformer" in quotes as quite often these days they are
really small switched mode power supplys rather than a lump of iron and a
couple of coils. Normally easy to tell as iron is quite heavy, circutry
not. I'd be surprised if a SMPSU would run down to 12v though most have a
lower voltage limit somewhere above 50v.

--
Cheers
Dave.



Almost all are switchers, and it's not that uncommon for them to run very
hot - especially if they are not particularly well ventillated. It's why
they fail so regularly. Just to be on the safe side, it's probably worth
checking back with the shop where it was bought, but you are unlikely to
find that it really is a problem. There is very little that could cause a
switcher to run hotter than it was designed to. Any faults that switchers
develop, tend to kill them dead, or stop them starting up in the first
place. Most are pretty well protected against excess current draw, and if it
is the right power supply for the TV, then that should not be an issue,
anyway. Check that it is CE approved, and by all means check with the shop,
but you will probably find that it's 'normal', if not desirable ...

Arfa


  #5  
Old July 29th 08, 10:23 AM posted to uk.d-i-y
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Posts: 21
Default How hot should a transformer get?

Hi

Sorry my mistake: Its is a small power supply rather than a transformer.
Its only for 240v AC operation - there is a separate cigar lighter type supply for 12 volt.


Adam




Arfa Daily wrote:
"Dave Liquorice" wrote in message
ll.net...
On Tue, 29 Jul 2008 06:48:56 +0100, Andy Hall wrote:

When working from the mains the transformer gets hot - very hot. Last
night we watched 2 hours of telly and when time came to put it all away
I could hardly pick the transformer up. It was almost too hot to hold.
It shouldn't get to that kind of temperature. I would return it. If
the replacement is as hot, then select another product.

Agreed. Are there any ratings on the "transformer"(*) and on the TV? What
was the power source when you were using it 12v or 240v? It's not 100%
clear if the "transformer" is needed for 12v operation.

(*) I have "transformer" in quotes as quite often these days they are
really small switched mode power supplys rather than a lump of iron and a
couple of coils. Normally easy to tell as iron is quite heavy, circutry
not. I'd be surprised if a SMPSU would run down to 12v though most have a
lower voltage limit somewhere above 50v.

--
Cheers
Dave.



Almost all are switchers, and it's not that uncommon for them to run very
hot - especially if they are not particularly well ventillated. It's why
they fail so regularly. Just to be on the safe side, it's probably worth
checking back with the shop where it was bought, but you are unlikely to
find that it really is a problem. There is very little that could cause a
switcher to run hotter than it was designed to. Any faults that switchers
develop, tend to kill them dead, or stop them starting up in the first
place. Most are pretty well protected against excess current draw, and if it
is the right power supply for the TV, then that should not be an issue,
anyway. Check that it is CE approved, and by all means check with the shop,
but you will probably find that it's 'normal', if not desirable ...

Arfa


  #6  
Old July 29th 08, 11:55 AM posted to uk.d-i-y
external usenet poster
 
Posts: 6,490
Default How hot should a transformer get?


"Adam Lipscombe" wrote in message
...
Hi

Sorry my mistake: Its is a small power supply rather than a transformer.
Its only for 240v AC operation - there is a separate cigar lighter type
supply for 12 volt.


Adam



I expected it was, so all I said previously, still stands

Arfa


  #7  
Old July 29th 08, 01:23 PM posted to uk.d-i-y
external usenet poster
 
Posts: 19,386
Default How hot should a transformer get?

In article et,
Dave Liquorice wrote:
I'd be surprised if a SMPSU would run down to 12v though most have a
lower voltage limit somewhere above 50v.


Eh? Both my current phone and the last one had SMPS. The current one tiny
and weighs less than a normal plugtop.

--
*Everybody lies, but it doesn't matter since nobody listens*

Dave Plowman London SW
To e-mail, change noise into sound.
  #8  
Old July 29th 08, 01:34 PM posted to uk.d-i-y
external usenet poster
 
Posts: 8,464
Default How hot should a transformer get?

On Jul 29, 10:23*am, Adam Lipscombe wrote:
Hi

Sorry my mistake: Its is a small power supply rather than a transformer.
Its only for 240v AC operation - there is a *separate cigar lighter type supply for 12 volt.

Adam


Yes. If it runs that hot it wont last too well. But as long as it
lasts 1 yr you probably have no comeback. If its an expensive brand
name, you would. If you want it to last longer you could stick it in a
metal biscuit tin with a small fan.


NT


Arfa Daily wrote:
"Dave Liquorice" wrote in message
ill.net...
On Tue, 29 Jul 2008 06:48:56 +0100, Andy Hall wrote:


When working from the mains the transformer gets hot - very hot. Last
night we watched 2 hours of telly and when time came to put it all away
I could hardly pick the transformer up. It was almost too hot to hold.
It shouldn't get to that kind of temperature. * I would return it. * If
the replacement is as hot, then select another product.
Agreed. Are there any ratings on the "transformer"(*) and on the TV? What
was the power source when you were using it 12v or 240v? It's not 100%
clear if the "transformer" is needed for 12v operation.


(*) I have "transformer" in quotes as quite often these days they are
really small switched mode power supplys rather than a lump of iron and a
couple of coils. Normally easy to tell as iron is quite heavy, circutry
not. I'd be surprised if a SMPSU would run down to 12v though most have a
lower voltage limit somewhere above 50v.


--
Cheers
Dave.


Almost all are switchers, and it's not that uncommon for them to run very
hot - especially if they are not particularly well ventillated. It's why
they fail so regularly. Just to be on the safe side, it's probably worth
checking back with the shop where it was bought, but you are unlikely to
find that it really is a problem. There is very little that could cause a
switcher to run hotter than it was designed to. Any faults that switchers
develop, tend to kill them dead, or stop them starting up in the first
place. Most are pretty well protected against excess current draw, and if it
is the right power supply for the TV, then that should not be an issue,
anyway. Check that it is CE approved, and by all means check with the shop,
but you will probably find that it's 'normal', if not desirable ...


Arfa


  #9  
Old July 29th 08, 01:59 PM posted to uk.d-i-y
external usenet poster
 
Posts: 10
Default How hot should a transformer get?

Dave Plowman (News) wrote:
In article et,
Dave Liquorice wrote:
I'd be surprised if a SMPSU would run down to 12v though most have a
lower voltage limit somewhere above 50v.


Eh? Both my current phone and the last one had SMPS. The current one tiny
and weighs less than a normal plugtop.


Input not output Most that I have come across seem to stop working at
around 80V
  #10  
Old July 29th 08, 06:50 PM posted to uk.d-i-y
external usenet poster
 
Posts: 19,386
Default How hot should a transformer get?

In article ,
Steve Lupton wrote:
Dave Plowman (News) wrote:
In article et,
Dave Liquorice wrote:
I'd be surprised if a SMPSU would run down to 12v though most have a
lower voltage limit somewhere above 50v.


Eh? Both my current phone and the last one had SMPS. The current one
tiny and weighs less than a normal plugtop.


Input not output Most that I have come across seem to stop working at
around 80V


Ah. But there's no reason why an SMPS can't work from any voltage - I've
got a handy little circuit that produces 12 volts with an input of 3 - 30
volts.

--
*Remember, no-one is listening until you fart.*

Dave Plowman London SW
To e-mail, change noise into sound.
 




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