ETD49 Overheating

[badboy_6120]

It depends.

The best answer would be: if you want to limit temperature rise of a winding you have to limit copper loss for that winding.

For example, if you do a test with DC current flowing through the transformer then you can find that (just an example, I'm trying to guess) it takes 8 watts to rise the temperature of the windings by +30degC. With a fan, it takes 15 watts for +30degC rise.

Then if you have just two windings you can split copper loss equally between the windings.

Taking into account pri and sec voltage, current, copper resistance and winding length (you can use MLT aka mean length per turn) you can easily calculate minimum wire area.

Thank you for your helpful answer

what awg wire do you suggest I wind the transformer with???

 

[Jagd.Panther]

Thank you for your helpful answer

I edited the post and added an example to illustrate the idea.

what awg wire do you suggest I wind the transformer with???

What is your best transformer at the moment? I mean pri/sec turns, wire diameter (strand dia x number of strands), switching freq?

 

[badboy_6120]

I edited the post and added an example to illustrate the idea

Thank you

What is your best transformer at the moment? I mean pri/sec turns, wire diameter (strand dia x number of strands), switching freq?

Primary = 54x0.25mm >>> 18 turns
Secondary = 36x0.25mm >>> 18turns >>> Voltage without load=170V >>> voltage with about 1KW is 158V
Frequency = 40Khz
with 1KW load I have about 80°c in cores and winding after 1 hour
the flux density of transformer is about 1600 Gauss

Cores temperature in idle is about 69°c

 

[badboy_6120]

after 1 hour that SMPS was loaded with 1kW I place a pc fan in front of the transformer and it bring the core temperature from 80°c to about 50°c in less than 10 minutes but I'm afraid of temperature in the inner parts of winding

 

[badboy_6120]

I also measured the DC resistance of the Primary winding as you mentioned before (with Car battery)
with 10.6 A load I had 0.18V on the primary winding(18 turns) and that means I have 0.017 ohm resistance on primary (54x0.25mm) and DC copper loss of 2.65W in primary at full power (12.5A in primary)

and with 10.6A load the temperature of the primary winding didn't rise significantly ( about 5 to 10°c)

 

[badboy_6120]

Can anybody tell me the temperature of ETD49 or ETD59 (N87, N27 or N97) cores in idle condition with 1600 Gauss flux????

and anybody who has experience in more than 1kW SMPS, can tell me the temperature rise of their transformer in above 1kW without forced cooling???

 

[Jagd.Panther]

Hi Badboy,

Did you measure DC resistance of secondaries as well?

I haven't seen any SMPS for over 500w cooled by convection. All were cooled with a fan or even more than 1

 

[Jagd.Panther]

Can anybody tell me the temperature of ETD49 or ETD59 (N87, N27 or N97) cores in idle condition with 1600 Gauss flux????

I can do few tests in a week or two (I have few genuine ETD N97 cores)