Crazed dad detonates device outside mom’s Brooklyn apt.

A deranged dad set off an explosive device Friday morning outside the apartment of the mother of his child, authorities said.

The device, described as a commercial-grade firework, was powerful enough to badly damage a door at the three-story home on Madison St. near Throop Ave. in Bedford-Stuyvesant, Brooklyn District Attorney Eric Gonzalez said at the scene.

The device was placed outside the door of the woman’s neighbor. No one in that apartment was harmed, police said. The woman was not hurt, nor was another adult and two children in her apartment.

The woman told police the disgruntled dad, who is in his 40s, was having a psychotic episode. But she did not elaborate on whether any tensions might have fueled the attack, police sources said.

“We can see him light the explosive device,” Gonzalez said, describing video that captured the 7:45 a.m. incident. “It blows out the windows. It damages an interior door — it blows in the door. ...This is a horrible act.”

The suspect drove off on a dirt bike but not before using a hammer to crack the windshields of about 14 vehicles on the block.

The device was examined by the NYPD Bomb Squad. Gonzalez described it as a “commercial-grade firework — but not a bomb in the traditional sense.” He sought to calm locals about the blast, which occurred on the eve of the 20th anniversary of the 9/11 attacks.

“This doesn’t appear to be related to 9/11 or any kinds of terrorism,” Gonzalez said.

“There seems to have been a domestic issue.”

Police said the suspect is Black and was wearing a blue shirt and blue shorts. He drove off sporting a black and green helmet.

Gonzalez expects a quick arrest.

“He will be brought to justice for what he did, but everyone inside, thank God, is fine,” he said.