Electronic – Power resistor dealing with quick high current surge

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I am currently working on a circuit to deal with the high inrush current of high value capacitors.

I'm calling this a 'capacitor adder' as the rest of the circuit (output load) is already powered while the caps are slowly charged over a current limiting resistor. The resistor is then shunted by a relay when the capacitors are (almost) fully charged.

my circuit

Falstad Link1

My question is concerning the wattage of the power resistor as the simulator shows power consumption of over 11 watts but in a short burst of about 1.1 seconds until it lowers to 1 watt. Does this mean only a resistor rated over 11 watts is suitable? I'm thinking because of the short time frame this will not give the resistor time to warm up and so maybe a 5w wire-wound resistor may be suitable.

Any other improvement I could make?

Thank you ESE community!

Best Answer

Any other improvement I could make?

There are resistors specifically designed to handle surges. In fact all will but, few have the information in their data sheet that allows you to make the right choice.

For instance, the Bourns CRS0805 range of surface mount resistors have a nominal power dissipation value of 0.25 watts but, the data sheet tells you that if the surge is no more than 1 second, the power can be a little over 1 watt. For 10 ms the power dissipated can be about 10 watts: -

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So, if you choose the right resistor you’ll get the info you need in the data.

I’m not saying this range is suitable for your needs of course; just look for resistors with surge handling capabilities and inspect the data sheet for the power vs duration graph.

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