# [SOLVED]Inductor temperature rise

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#### bowman1710

##### Full Member level 3
Hi Guys,

What is the easiest way to calculate the temperature rise of an Inductor at a given DC current (e.g @ 40 deg the current would be ???A) I have calculated the DCR and the power loss at the max current but dont know how to transpose this information into temperature.

Thanks

Hi,

sure, it depends on size and cooling.....
Is it potted or unpotted, air flow or vacuum, or water cooled?
In a box or not?

Klaus

The missing link is thermal resistance of inductor to ambient. Estimate numbers are given by core and inductor manufacturers, but the exact value depends on how the part is mounted.

sure, it depends on size and cooling.....
Is it potted or unpotted, air flow or vacuum, or water cooled?
In a box or not?

Well I have my toroid core

That will be fitted unpotted in a box with minimum air flow if at all.

The missing link is thermal resistance

I tried calculating this but didnt know how it related with the current

"Dividing the temperature rise due to Irms current (e.g. 40°C rise) by the power required to generate that rise (Power = DCR × Irms2):

Rth (in °C/W) = 40°C ÷ (DCR × Irms2)"

The coilcraft articel is assuming that you have a component with specified current rating and DCR. Knowing the temperature rise the rating is based on, you can calculate a Rth value.

But you are apparently making your own inductor and don't have respective data. So you can't "calculate" Rth.

You can either determine it by a measurement, or try to find Rth specifications for inductors using a similar core and winding size. I just checked the Epcos Ferrite tool, unfortunately it gives no thermal data for toroid cores.

Inductor will have DC and AC Losses. DC losses will depends on DCR of Inductor and the rms current flowing through it. AC Losses will depends on Frequency of operation, Core ..etc. Once we have DC and AC losses. Find out total losses. Most of the inductor datasheets will give Current Vs temperature rise characteristic. Check with WE they have an EXE which will give more details. or any mfg like Vishay/Coilcraft/cooper-busman etc

Well I have my toroid core

That will be fitted unpotted in a box with minimum air flow if at all.

I tried calculating this but didnt know how it related with the current

"Dividing the temperature rise due to Irms current (e.g. 40°C rise) by the power required to generate that rise (Power = DCR × Irms2):

Rth (in °C/W) = 40°C ÷ (DCR × Irms2)"

This formula works for low frequency ESR losses but does not include Eddy current losses in the core at high f.

Core and winding losses, and an estimate of the resulting temperature rise, can be calculated for Coilcraft’s power inductors using the web tool :
Thermal resistance will be greatly dependent on air flow. The wire is also thermally insulated with any electrical insulation.

Ok then guys,

I found this

which seemed to have all my answers.

Another thing, how do I know the Isat of the inductor I am making for a given DC, is there a way to calculate the current at which it will go into saturation?

the isat you get by equation isat = (Bsat. Area.N) /L

where
Area = min core area cross section
N = number of turns
L = inductance

this equation is got by equating

V = L.di/dt

and

V = N.d(phi)/dt

..equate right hand sides and do B = PHI/AREA

I am assuming that you are using a standard ferrite with Bsat = 0.3T

But welcome to the subject of saturation/heating of ferrites, which is shrouded in industrial secrecy

• bowman1710

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