The Warlock Ram helmet trigger the Voidwalker's health regeneration effect after punching anything and then has to wait five seconds for the effect to cooldown before triggering it again. The health regeneration start immediatly and will be canceled right away if damage is received just like usual. Putting a cooldown just like that to the Sunbreaker healing effect might be enough (it could be a 3 second-long cooldown if 5 seconds is too long).