fan in circuit-breaker box is cycling every 10 seconds

The cooling fan runs, when the converter/charger is under heavy load. If it runs on/off continuous, I would check battery condition. May need new battery, or water added to battery. Water way too low, likely need new battery.

The converter itself could be failing, some are better than others. What model do you have?

Are you running any device, that may cause converter to overwork?

Jerry