how warm/hot is safe for a transformer

Sceadwian said:

No transformer should be THAT hot unloaded.

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Just exaggerating
Well, um, it was barely loaded, but it was one of those cheap, ultra tiny and high-power ones!

I can't keep my hand on it for more than a second though!

audioguru said:

Transformers are not supposed to consume power, they are supposed to pass power.

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They pass power, and waste a little in the process!

Oh yeah, about the nimh battery and the charger, I have a 200mA,9volt charger for a nimh battery, and it gets darn hot too!
Good 'ol chinese crap!

Bad stuff waiting to happen! HUMBUG I TELL YOU, HUMBUGG!!!

Yeah ben but some are better than others. To keeps costs low chinese companies will stick right with the maximum temperature as they can get away with because copper is expensive, and a bigger or coil or better core materials would cost more for a higher efficiency transformer they'll go with a lower effciency one every time if it saves them a dime. Commercial or power company transformers will be close to 95% efficient, that cheap one that overheats at load might be 80 percent or lower, they don't care if they waste your energy, doesn't cost them anything.

the industry standard grade of lamination generates 5.3W/kg when running at 1.5Tesla
smaller transformers will have less losses as they weigh less, but less surface area to loose the heat from. it's reasonable to have half the losses on the core and half on the copper. so at tickover the transformer gets half as hot as it does when it is running.

a bit like starting the car but not driving, it's not doing any work, but it still gets warm.

as for efficiency, the 'transformers are the most efficient electrical components' only applies to big ones. small ones can be as bad as 50%

There is an infinite supply of free oil.
Everyboy loves to pull cartfuls of lead batteries uphill.
The bigger a power station is, the better for the environment.
the best wire for winding transformers is tungsten, because it doesnt melt easily.
A large methylated and nitric, please, I'm going to BURP at someone.

Sceadwian said:

Yeah ben but some are better than others. To keeps costs low chinese companies will stick right with the maximum temperature as they can get away with because copper is expensive, and a bigger or coil or better core materials would cost more for a higher efficiency transformer they'll go with a lower effciency one every time if it saves them a dime. Commercial or power company transformers will be close to 95% efficient, that cheap one that overheats at load might be 80 percent or lower, they don't care if they waste your energy, doesn't cost them anything.

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Yes, you are down right RIGHT!
Cheap Chinese Crap