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You don't need a heatsink on a wirewound 5W resistor.
The time delay is about 100ms to 300ms. The resistor does not have time to heat up the enclosing casing, never mind trying to heat up the heatsink.
If you have set your time delay for the bypassing relay to longer than 300ms then you have designed your soft start wrongly.
If you need 20r use two 10r 5W resistors in series.
If you need 40r use two 20r 5W resistors in series.
If you need 60r use three 20r 5W resistors in series.
I have used 7 off 20r resistors for a 140r limiting resistor to start a 100VA transformer with a T500mA fuse that does not rupture on start up. It would be cheaper to buy some specific resistors for these higher value resistors but I have a big stock of 10r and 20r 5W that do the job admirably.
The time delay is about 100ms to 300ms. The resistor does not have time to heat up the enclosing casing, never mind trying to heat up the heatsink.
If you have set your time delay for the bypassing relay to longer than 300ms then you have designed your soft start wrongly.
If you need 20r use two 10r 5W resistors in series.
If you need 40r use two 20r 5W resistors in series.
If you need 60r use three 20r 5W resistors in series.
I have used 7 off 20r resistors for a 140r limiting resistor to start a 100VA transformer with a T500mA fuse that does not rupture on start up. It would be cheaper to buy some specific resistors for these higher value resistors but I have a big stock of 10r and 20r 5W that do the job admirably.
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Thanks for sharing so much,
Is this circuit shared ?
Looks like it has some protection on board, nice.
Regards