For quite awhile now I have been using a dummy load made up of 5x 0r33 100W resistors (aluminum cased, wirewound). So the total resistance of the load is 66mΩ. The load is driven by mosfets, and the load is used to discharge batteries. What never occurred to me when I designed this, was that the power resistors I am using are wirewound resistors, therefore they will have an inductance. Unfortunately, I only have a cheap LCR meter and really can't get a good reading on the inductance of the resistors. Measuring 1, is says 2µH, but measuring 5 in parallel gives the same measurement. My understanding is inductive loads are like resistive loads in parallel, so the inductance should go down. Based on that, I say my meter is reading correctly.
This is the first circuit I designed using mosfets, and like I said, I took no precautions for inductive kickback. That said, there have been no issues thus far regarding damage to the mosfets, but that doesn't necessarily mean there will not be.
I am using 4x IPP013N04NF2S (
https://www.mouser.com/datasheet/2/196/Infineon_IPP013N04NF2S_DataSheet_v01_00_EN-3011955.pdf) in parallel to do the switching. The pwm frequency is 490Hz. The mosfets are heatsinked and I have an NTC measuring the temp at the junction of the tab and the heatsink. The temp gets up to about 45°C, so the mosfets are not running too hot.
I would like some help figuring out all the parameters I need to decide what I need in my future version of this. I've done a fair amount of reading and have read that some may use TVS diodes, some just say a flyback, some say maybe just a resistor (I'm using 5 in parallel). But regardless, I need to figure out how to calculate what I need.
Thanks