how can i find the watts of smd resistance

[Xristakis795]

hi
in a pcb circuit of welding machine
i have three resistances smd 4.7 ohm burnt in series with std2nb80t4 also burnt
with hole on the middle
this mosfet is connected on primary of an transformer and it seems take dc voltage
how can i calculate the watts of smd resistances to be sure i have choice the right value
can i take from an older pcb smd resistance with the same size?
is right ?

[stj]

Re: how can i find the watts of smd resistance

you can only try to guess from the physical size

[sam_sam_sam]

Re: how can i find the watts of smd resistance

Or if there is a big enough pad you could external mount if you have any extra space in the enclosure ( just an idea )

I have done this with surface mount LEDs before you do have to take your time doing and do not be in a hurry

[jiroy]

Re: how can i find the watts of smd resistance

That's a long story and needs lot of efforts and spare time . Each company makes its catalogue and put its own specs ; sometimes they follow international standards and sometimes they create their own .

To add on difficulties , many small business companies do not even bother issuing catalogues , while some big companies on the other hand , make their catalogues discrete and difficult to get .

That's said , a respected catalogue would put the whole specs of a smd resistor , with even its diameters , L x L x H , including the pins diameters and kind of package , wattage , etc ..

If you know which company made the resistor and do have its catalogue , you're a king , otherwise Only a good knowledge and a high level understanding of Electronics study , plus a long experience , can fill all these gaps ..

[Xristakis795]

Re: how can i find the watts of smd resistance

ok
i want to thanks all for your useful advices

[petehall347]

Re: how can i find the watts of smd resistance

if you replace with one same size and ohms then you can measure volts across it and use ohms law to see if its ok for the circuit