Convert Emberjs recordArray model to JSON

Disclaimer: I am new to Ember.

With that being said, I am trying to convert an Ember recordArray to a JSON string so that I can send it to my server for processing.

I have the following Ember model:

Loads.Load = DS.Model.extend({
    pickupStartTime: DS.attr('string'),
    pickupEndTime: DS.attr('string'),
    pickupLocation: DS.attr('string'),
    pickupGeocode: DS.attr('string'),
    pickupWeight: DS.attr('number'),
    pickupTicket: DS.attr('string'),
    dropoffStartTime: DS.attr('string'),
    dropoffEndTime: DS.attr('string'),
    dropoffLocation: DS.attr('string'),
    dropoffGeocode: DS.attr('string'),
    dropoffWeight: DS.attr('number'),
    dropoffTicket: DS.attr('string'),
    commodity: DS.attr('string'),
    isCompleted: DS.attr('boolean'),
    shortPickupStartTime: function(){
        var time = this.get('pickupStartTime');
        if(time){
            var split = time.split(" ");
            return split[4];    
        }else{
            return " ";
        }
    }.property('pickupStartTime'),
    shortPickupEndTime: function(){
        var time = this.get('pickupEndTime');
        if(time){
            var split = time.split(" ");
            return split[4];    
        }else{
            return " ";
        }
    }.property('pickupEndTime'),
    shortDropoffStartTime:function(){
        var time = this.get('dropoffStartTime');
        if(time){
            var split = time.split(" ");
            return split[4];    
        }else{
            return " ";
        }
    }.property('dropoffStartTime'),
    shortDropoffEndTime: function(){
        var time = this.get('dropoffEndTime');
        if(time){
            var split = time.split(" ");
            return split[4];    
        }else{
            return " ";
        }
    }.property('dropoffEndTime')
});

I have the following action in my controller:

var self = this;

Ember.RSVP.hash({
   //loads is an array of records
   loads: this.store.find('load')
}).then(function (data) {      
   $.ajax({
       type: "POST",
       data: { Loads: JSON.stringify(data.loads) },
       url: "api/buildexcelsheet",
       contentType: "application/json",
       success: function (message) {
           self.set('uri', message);
       }
   });
});

When I run this action from the controller I get the following error:

Uncaught Error: Assertion Failed: TypeError: Converting circular structure to JSON

Since I'm new to Ember, I'm unsure as to what I'm doing wrong.

Any help would be greatly appreciated.

Thanks!