I assume you mean both the converter reverse polarity fuses are blowing? Usually they blow if the battery terminals are hooked up in reverse, or can also blow if the converter 12vdc output wiring bus is shorted accidentally; or if the overall load connected on the converter 12vdc bus output draws more than the reverse polarity fuse rating (usually 30 or 40 amp depending on rating of converter). On many coaches there is also a re-settable 50 amp breaker between the converter 12vdc output and the coach battery/ use-store latching relay. Sometimes that breaker will trip open as well depending on where the overload occurs. Another exciting situation is when folks incorrectly hookup their “add on” inverter 120vac output to feed the main coach ac breaker panel (via an add on transfer switch – so shore and inverter output don’t connect together) which also feeds the coach converter......so in effect you have an inverter running off coach batteries powering the 120vac input of the converter which is also charging the coach batteries........so very quickly fuses/breakers will usually open/trip.
So any physical load changes or electrical work being done when your fuses blow? Have the correct sized fuses been used to replace blown fuses? Are coach batteries in good condition/state of charge?
Javelin thank you for your answer.
The only unusual thing that the two events have in common is very discharged coach batteries. I have brought them back up to full charge this time with an outside charger. That might have been the issue. The two fuses are next to each other on the 12 volt distribution panel and are 30 amps each. I think the converter is 40 amps. I wonder if this difference is the issue.