Is there any continuous 12 volt relays on cars?
Your only half right with your theory. To stop switch contacts melting. The relays function in this case is to handle current NOT voltage. A relay will not regulate! A standard ‘regulator’ will not help you here either as you are drawing too much CURRENT, voltage is set by manufacturer Your ‘device’ (go on tell us what it is) what current will it draw? Voltage must be to suit vehicle (12-13.5 volt) if your ‘device’ is drawing more CURRANT than your alternator can supply your battery will eventually become discharged. The ‘average’ alternator supply 50-60 amp, you can get an uprated one to over 75-90 amp. Any more than that then have 2 alternators ( maybe batteries also) fitted.
