I believe you are actually talking about circuit breakers, not relays. A relay is triggered by an electrical current, often a low amperage connection will cause the relay to switch heavier contacts open or closed.
A circuit breaker is designed to handle up to a rated amperage, a draw of over than set amp load causes it to open and shut off power. If the circuit breaker controlled your converter/charger, it drew too many amps and the circuit breaker tripped. Perhaps your converter/charger was trying to desulfate your batteries, which can use as much as 20 v to 'fix' the batteries.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI