Electronic – Using multiple current sense resistors in parallel to handle a high current measurement with cheaper resistors


I am measuring the current going to a motor using current sense resistors; however, in order to get a resistor that can handle the proper power, the price goes up way too much. My question is, can I use multiple lower power rated resistors in parallel to measure the same current value? In other words if I need 10W single resistor, I would break that up into five 2W resistors in parallel with the same value.

They would all have to be the same resistance value/tolerance and the power margin would need to overcome the tolerance of the resistance. Seems mathematically fine, but wanted to see if there are any gotchas here?

Best Answer

You should be fine if you are careful about the physical layout. In theory, five equal value 2 watt resistors in parallel will be able to dissipate 10 watts However, if the resistors are physically close to each other, each one could heat up the others so that their temperature could exceed a safe value even if the total dissipation does not exceed 10 watts. I would consult the data sheet for these resistors to see what the mounting requirements are especially as to how close to heat sources they can be.