Don't use AC Circuit Breakers on DC

I tested a few circuit breakers rated for AC using my car's 250V DC battery. I used my load tester to limit the current to about 27A. I found that with a resistive load, the breakers successfully interrupted the current but failed safely after 5 or 10 switching cycles. Since I didn't have the equipment to limit the current to 50 or 100A, I used one of the windings in an isolation transformer to make the load more inductive and sort-of simulate a higher fault current situation. With this additional resistance, the current dropped to 23A. The results were quite scary:

A Vynckier Series E circuit breaker interrupted the current once and caught fire on the second attempt. The fire only went out because I used my (400V 250A DC rated) contactor to turn off the current, you can see the flash on the left when it switches off.

A People DZ47-63 circuit breaker interrupted the current but destroyed itself in the process. Inside you can see the switching element is significantly shortened and the casing burnt:

It's important to note these tests represent abuse of the circuit breakers, if you ask them to switch AC they will likely give years of trouble free operation. The key is that 50Hz AC current falls to zero for long enough that the plasma cools, when the voltage rises during the next cycle, the arc can't re-establish without the plasma. With DC, the current doesn't stop and the arc just keeps burning.