I got the same Problem with the RAMPS 1.4a which is manufactured and assembled completely by myself
When I use first, the fuse (big yellow one MFR1100) blown away and doesn't work for a while and after few hours it started working (checked with Multimeter) it seems it uses more current, (I always use couple or more wires to solve current related issues!)
Later I worked with that but it cannot push more than 70 deg C @ 12v DC for Heated bed
Now I am Using 24v DC, but the fuse is rated of only 16V !
Let me check how long it can run, well I am thinking to bypass the resettable fuse to the glass fuse rated @ 15amps and so we can supply more current for big heated platform!
When I use first, the fuse (big yellow one MFR1100) blown away and doesn't work for a while and after few hours it started working (checked with Multimeter) it seems it uses more current, (I always use couple or more wires to solve current related issues!)
Later I worked with that but it cannot push more than 70 deg C @ 12v DC for Heated bed
Now I am Using 24v DC, but the fuse is rated of only 16V !
Let me check how long it can run, well I am thinking to bypass the resettable fuse to the glass fuse rated @ 15amps and so we can supply more current for big heated platform!