How to feed data in time tag from angular controller

I am using time field in html and want to feed data from angular controller

<input type="time"  ng-model="bt_time" class="form-control" style="width: 20%" required>

I want to feed data from controller

$scope.bt_time='12:30';

But I am getting error

Error: [ngModel:datefmt] http://errors.angularjs.org/1.6.5/ngModel/datefmt?p0=12%3A30