EDIT: I'm a moron for only testing the 12v line on my car without the engine running, and thus assuming it was regulated.
TL;DR : Put a 3.5" hdd in my car, powered by + - 12v from cigarette lighter lines. Blew two 10A fuses in a row on my Radio's line, but the cigarette lighter was still receiving power each time. I turned the HDD off and put a 7.5 A fuse in, and everything was fine. Why is this setup causing me to blow fuses on a totally different line?
Yesterday I embedded a 3.5" hard drive (in a Rosewill enclosure) into the glovebox on my 2001 CRV, so I could keep my music and video library in my car. The hard drive receives power from the 12v cigarette lighter jack on the center console (I just spliced into the lines). I made a little USB Y cable, that has one female USB A port for the drive to plug into, a male USB Micro B jack that plugs into my Android phone, and a male USB A jack that is ONLY connected to the 5v + and - lines of the cable, which plugs into USB car charger that I have plugged into my cigarette lighter.
The cigarette lighter is cable of supplying 10 Amps. The entire setup only draws 2 A for the drive, and the USB charger is only capable of supplying 750 mA, so all together the setup draws 2.75 A MAX, well under the jacks capabilities.
The whole setup worked fine, other than the fact that it takes a little while for the phone to recognize the drive, which can get a little annoying if you're starting and killing your engine a lot.
Or at least it WAS working fine. I decided to take a little detour down a cliff road (think canyon road) on my way to my destination (for locals, it was Blowhole/Sandys Makapu'u road), and was driving somewhat spiritedly in my little grandma mobile. Everything was fine, until I hear a pretty loud POP and see a flash of light come from my interior fusebox, as my deck went black. "DAMN, blew a fuse".
HOWEVER, my USB charger was still receiving power (indicator LED on its face was lit up), and my phone still played music, leading me to believe the hard drive was still being powered too. From this, I deduced that the Radio was on its own fuse, and that my setup had nothing to do with the fuse blowing. I assumed that it was just a freak occurrence.
So I arrive at my destination, change the fuse, and embark back home. I took the cliff road again, only this time I WASN'T driving "spiritedly". Fuse blows again. At this point, I start to wonder if maybe my setup really did have something to do with the fuse going, since I had blown two fuses within maybe like 20 minutes of my car being on.
I pull into a gas station and swap the fuse, but this time I was all out of spare 10 A fuses. I turned the harddrive to OFF and popped in a 7.5 A fuse, and made it home without blowing another one.
So, at this point, i'm somewhat torn. I'm led to believe that my little jerry rig HDD setup has something to do with this fuse blowing problem, since I stopped blowing fuses once I turned the drive off.
On the other hand though, I have a feeling the hard drive setup has nothing to do with it, because the hard drive only draws 2 A of power, which means I would have blown that 7.5 A fuse by now because there'd still be over 8 A of current left over. The only explanation for this, is that the USB port of the hard drive draws a lot of power, so turning off the drive alleviates 2 A + whatever the USB port draws.
But even still, why on earth would both the drive and the phone still be working after the fuse goes out?
Anybody have any ideas?