Is this iffy

[JohnW2]

Is that dangerous? I leave my laptop power supply unit plugged in (and turned on) all the time. As long as it isn't connected to the laptop, it remains flat cold.

If there is no, or little, load it should stay cold. If you leave any power supply powered up (even if with little or no load), there is a theoretical possibility that a component within it could fail, potentially causing it to 'burst into flames' (and maybe when no-one is around to see it happening). That's true whether it's a charger, a plug-in power supply for some AV/IT equipment, a TV/Sky Box, a boiler, washing machine, or anything else. However, in my personal circles, I've only ever heard of it happening once (when a colleague's unloaded laptop charger more-or-less 'burst into flames').

Kind Regards, John

 

[Adam_151]

They're flogging them in my local city.

... Whatever possessed you to go there?!

 

[RF Lighting]

Unfortunately they're 10 mins up the road and the next nearest is half an hour away, and they fully exploit this fact


Was having a bit of a play with my usb charger last night. It's a LAP branded euro modular one from screwfix. I leave the lead in all the time. It stays completely cold when not in use and warms up when actually charging. The standby current in negligible.


Standby

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• RF Lighting
• 24 Aug 2014
• 1

Charging

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• RF Lighting
• 24 Aug 2014
• 1

 

[JohnW2]

Was having a bit of a play with my usb charger last night. It's a LAP branded euro modular one from screwfix. I leave the lead in all the time. It stays completely cold when not in use and warms up when actually charging. The standby current in negligible.

Interesting! Is that the supply cable on the left? If so, it looks as if it gets surprising warm when the charger is in its standby state.

Kind Regards, John

 

[RF Lighting]

No it's a galv coupler. As it's a shiny surface what you can see is the reflection of heat from my body.

 

[JohnW2]

No it's a galv coupler. As it's a shiny surface what you can see is the reflection of heat from my body.

Ah, I see - thanks for clarifying. Your body must have been quite hot at the time

Kind Regards, John

 

[RF Lighting]

Emmisivity is the bit of thermal imaging that I still don't fully understand, but basically shiny surfaces appear hot when they are not really. For reliable readings of these you need to apply either black tape or matt paint.

 

[endecotp]

shiny surfaces appear hot when they are not really

Isn't it the other way around?

They have low emisivity, so they radiate less.

 

[RF Lighting]

No they reflect IR energy from other sources, and appear hot. You can see the coupling and plate screws in my first picture appear hot, whilst they are really the exact same temperature as everything else in the picture.

 

[JohnW2]

shiny surfaces appear hot when they are not really

Isn't it the other way around? They have low emisivity, so they radiate less.

No they reflect IR energy from other sources, and appear hot. You can see the coupling and plate screws in my first picture appear hot, whilst they are really the exact same temperature as everything else in the picture.

I think you're both right, in some senses, but that endecotp is somewhat muddling the concepts of emissivity and reflectivity - which, although somewhat related, can operate independently.

A highly polished metallic surface has a very low emissivity - so radiates very little of the heat that it 'contains'. Hence, if RF's socket and charger were in deep space, with no other significant heat sources around, his camera would therefore show the screws etc. as colder than surrounding materials (of higher emissivity) at the same temperature.

However, highly polished metallic surfaces also have a high reflectivity. Hence, if there are other heat sources around (like RF's body), his camera will see the screws as hotter than their surroundings (which have lower reflectivity), since the screws are reflecting a lot of the incident heat from his body, even though they are radiating very little of the heat which they 'contain'.

That's how I see it, anyway!

Kind Regards, John