How to fix arcing in the contactor in this circuit

Question

I am building the switching circuit using contactor to switch 300A over the contacts. My circuit is below:

When I run the circuit, the current is switching but I see arcing. See the scope below:

The red line in the scope is the voltage over the two contacts in the contactor, you can see when the contact is not fully closed, there is some current passing by.

Is there a way to solve this issue?

The contactor I have is not a coil actuated contactor, so the switching speed is way slower than the coil actuated, that leads to the arcing. I cannot make my contactor switch faster to avoid arcing so is there any other way I could implement my circuit? I have read somewhere that if I add a resistor in series with the buffer capacitor it would solve this case. Any ideas?

Answer 1

Switching 300A 30V DC with a mechanical switch will almost inevitably cause arcing, and unless the device is rated for that current will ultimately cause failure. As you say, if it is a slow mechanical action your problems will be worse.

Having said that, with correct design this is not an issue. I know from correctly rated 48V 1000A switch gear used in a telco environment, that you get a meaty arc when it opens, with magnets used to push the arc against ceramic "arc breakers" to cause it to extinguish cleanly. This gear is rated for 10K operations under full load.

If the concern is that you want clean control of the current through the load, then I'd suggest you avoid the mechanical switch, and use a suitably rated MOSFET instead, with careful application of snubbers.

There are devices more than capable of switching 300A, and if the load is resistive this will greatly help switch-off.