Determine Fuse Rating

**brownaa82** · 11-14-2009, 08:15 PM

Folks, I have a Carnetix P1900. I'll be running a Mac Mini and a Lilliput EBY701. The Mini power adapter runs at 120W @ 18.5V and the EBY701 needs less than 10W @ 12V.

If my calcs are correct that is about 7.32 amps. That seems very small compared to what I was imagining it would be.

Can someone confirm that this is correct? I am trying to determine the correct fuse and wire size running from the battery to my P1900 and from the P1900 to the Mac Mini and Lilliput.

Thanks.

**pulsarsimon** · 11-15-2009, 01:19 AM

120W = 10Amps @ 12V
so 10A fuse is ok, or 15A if you never want it to blow.

**DarquePervert** · 11-15-2009, 06:59 AM

The fuse is to protect the wire.
You want the fuse to fall between the maximum power draw of your equipment and the maximum power the cable can handle.

Your amperage calculation is spot on, and the recommendation of a 10A or 15A fuse is, as well.

**brownaa82** · 11-15-2009, 11:51 AM

Originally Posted by pulsarsimon

120W = 10Amps @ 12V
so 10A fuse is ok, or 15A if you never want it to blow.

Maybe I'm thinking of this wrong, but the wattages I described above come after the P1900. Therefore the amps being pulled from the battery should be the sum of the amps being pulled from the PSU.

Code:

Mac Mini
120W @ 18.5V = 6.5Amps

Lilliput EBY-701
10W @ 12V = 0.83Amps

Total Amp Draw
6.5Amps + 0.83Amps = 7.33Amps

The Total Amp Draw from all of the equipment connected to the P1900 should also equal that pulled from the battery (+ inefficiency of equipment, but not counting that here).

Maybe that gets me, by coincidence, to the same fuse you described (10Amp).

**cjrokke** · 11-15-2009, 12:42 PM

Originally Posted by brownaa82

The Mini power adapter runs at 120W @ 18.5V

Correct me if I'm wrong, but you fuse what the car supplies (12V)

**brownaa82** · 11-16-2009, 04:42 PM

Originally Posted by cjrokke

Correct me if I'm wrong, but you fuse what the car supplies (12V)

Definitely. I'm trying to figure out if you add up the amps being drawn by each piece of equipment, then get the fuse. Presumably the fuse would be installed as close to the (-) terminal on the battery as possible.