# How to calculate free wheeling current value

In the below mentioned circuit which is used for automotive EMR braking. We are facing freewheeling diode burn out (FR607 is currently being used).

We are still clueless about the cause. But as per design this is a 6 A rated diode with surge value of 300 A which according to my design team is well enough. But we suspect that this ampere rated diode is not OK. We need to find the maximum freeweeling current in this circuit. How to calculate this current value. The coil resistance is 0.8 amps. Load of the circuit is 30 amps and the supply is a 24 V DC battery source 200 Ah.

• 1. Resistance is not measured in amps. 2. Coil inductance matters so I don't know why you bothered to measure coil resistance without trying to find its inductance. 3. Battery amp hours does not matter. I think your design team needs to do some studying on what happens when you interrupt current through an inductor. Figure out the current devay waveform. Find out what the current at the beginning of the decay, at the end, and how long it takes with the L/R time constant. Calculate, simulate, or solve the differential equation. Commented Dec 27, 2019 at 4:40
• Welcome to EE.SE. I have inlined the image for you and fixed the missing capitalisation. You could improve your question by adding a properly formatted link to the diode datasheet. How long and how frequently can the diode handle that current? Commented Dec 27, 2019 at 4:40
• Dear Nguyen yes it's actually 0.8 ohms. Just a typo sorry. Commented Dec 30, 2019 at 7:16