Whenever Denki exceeds his wattage limit, he loses his ability to discharge energy, with his entire personality changing into that of a giggling idiot for a certain period until he reverts back to normal.

Why does kaminari go yay mode?

The brain consumes energy at 10 times the rate of the rest of the body per gram of tissue. ... Denki's brain is capable of producing electricity to electrocute, and his body is strong enough to handle a specific voltage of electricity. Let's talk about the drawbacks, his "Yay" mode.

How long does kaminari stay dumb?

If he exceeds his wattage limit, Denki short-circuits his own brain, turning himself dumb for a one-hour period and being unable to activate his Quirk, or even do anything for that matter, until he recovers, although he does appear to retain minimal awareness of his surroundings.