I've seen both methods of construction. I'm just trying to come up with some explanation as to where the heat is coming from.
A saturated core may get hot but this is the opposite phenomena that this thread is investigating.
I'm merely suggesting that the cause of the heat may be at the centre of the windings so that it is not felt on the outer copper layers.
A saturated core may get hot but this is the opposite phenomena that this thread is investigating.
I'm merely suggesting that the cause of the heat may be at the centre of the windings so that it is not felt on the outer copper layers.
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The fan did the job!It no longer overheats...even after pushing it hard the whole afternoon.The fan runs continuously,not temperature controlled.It isn't noisy either,i lubricated it real good...even if it was noisy,this bass is way too loud for it to be heard. I hope i wont get thrown out of the college hostel!
Thanks for your replies.Regards.
I don't agree. But there again I don't claim to know the interior temperature nor do I know why you are not searching for the reason for the overheating.
Trafo overloading?Shorted winding?...I can't tell.The rails remain at +/-49.7v even when pushed hard. I know am pushing my luck with this former.If it fails,i wont rewind it,i'll modify a pc psu.
Those were my first choices,i couldn't find any.Mj15003/4 are all fakes...nothing comes easy to a diyer in Kenya,apart from good ol' stuff from a radio shack.
The interior is always hotter than the surface. The heat is generated inside, and then conducted to the surface where you can take it away. The very reason that heat escapes from the outside by whatever means, means that the outside is always cooler than the inside.
Anyway, transformers often run fairly hot; but if you can't keep your fingers on the surface for 10 secs than it is close to 50 degrees Celcius and that's not really a healthy situation.
You can put in fans but that's just hiding a problem that'll blow up sooner or later, maybe literally.
So you need to fix the problem and not just the symptoms.
jan didden
Let's quantify the temperature. Measure the winding resistances with the transformer at room temperature (we'll say that's 25 degrees for the purpose of discussion). Run the transformer for 2-3 hours. Then power down, UNPLUG FROM MAINS, and measure the resistance again (making sure that the power supply filter caps are discharged!). Use the formula (Rhot - Rcold)/(Rcold x 0.004) to determine the temperature rise. Add the room temp to this to get the actual internal temperature. If it's more than 55-60 degrees, the transformer is too hot.
that will give some kind of average resistance and temperature for the whole winding. Some of that winding is near the cooling air and some is buried deep under other windings.
How can that useful average temp estimate be corrected to give a better indication of internal temperature?
If the Primary is buried under the secondary then that may give a better indication of highest operating temperature, but the EI core is also cooling the from the inside to the outside.
Transformers are designed to run hot, if CHEAP is your criteria. Typical modern (since mid 70's) transformers can run at a total temperature, that's internally generated heat plus ambient heat, of 130 degrees C for a mtbf of 300,000 hours. This is substantially hotter than boiling water.
Most transformers are not designed to utilize this ability because folks think it's too hot, if you can feel it as warm. It's actually too hot if it burns you upon contact with your finger tips. If the transformer had a shorted turn it would already have either burst into flame or just emitted molten material and smoke. In either case there would be NO DOUBT that you have a problem, due to the acrid, choking fumes filling your listening area.
If you assume that your transformers should all run cool, then purchase transformers with less than 3% no load to full load voltage loss. This will guarantee you a 45 degree C rise in your local ambient temperature, which will feel warm to the touch. It will also guarantee that your transformers will not be CHEAP.
Quit buying commercial power transformers that are designed to be as cheap as possible, they are going to be hot to the touch!
Bud
Most transformers are not designed to utilize this ability because folks think it's too hot, if you can feel it as warm. It's actually too hot if it burns you upon contact with your finger tips. If the transformer had a shorted turn it would already have either burst into flame or just emitted molten material and smoke. In either case there would be NO DOUBT that you have a problem, due to the acrid, choking fumes filling your listening area.
If you assume that your transformers should all run cool, then purchase transformers with less than 3% no load to full load voltage loss. This will guarantee you a 45 degree C rise in your local ambient temperature, which will feel warm to the touch. It will also guarantee that your transformers will not be CHEAP.
Quit buying commercial power transformers that are designed to be as cheap as possible, they are going to be hot to the touch!
Bud
Thermal resistance is a better term than thermal conductors. Not in concept but for understanding. Just as you have voltage across a resistor if you have electrical current flow through the resistor, you have temperature across a thermal resistor/conductor with heat flow through the resistor/conductor. That is the reason that the interior is hotter than the outside.
jan didden
That's how transformer builders do it.
The transformer in question only has 20 mm or so of winding depth meaning most of the thermal resistance will be in the body to air interface rather than in the windings, fan forced cooling still gives a noticeable improvement with winding depths over 100mm. AFAIR this material in covered in transformer design texts since the 40's
Now we have class H insulation.
Go with fan forced cooling, millions of welders and microwave ovens exploit this technique very sucessfully.
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