archangle,(time=1323072399) Wrote:Don't neglect to add a fuse as close to the battery as possible.I wanted to add to archangle's warning here on making sure you have a FUSE on any 12-volt power wiring coming from battery...
The reason you need a fuse is SO YOU WON'T BURN YOUR HOUSE DOWN. Seriously.
If you have no fuse (usually placed on the positive wire and close to the battery), and if there is a short of any type along the length of the 12 volt wire, your 12-volt battery will just keep pumping out power and your wiring will HEAT UP RED HOT, melt any wire insulation and could very easily heat up enough to start a FIRE.
Adding a fuse of the proper amp rating will disconnect the power immediately when there is a short. Make sure not to use a slow-blow fuse either.. you want the fuse to disconnect the power immediately, not slowly. Fuses are cheap, houses aren't.
If you're only operating a CPAP machine on the battery (and no other appliances), you should get by okay with a 10 or 20 amp fuse. CPAPs draw varying amounts of amperage, depending upon what the highest pressure is and whether or not you're using a heated humidifier. If you have a ResMed machine, you can find this out by looking at their Battery Guide. Find out what is the max amperage your machine will use and then get a fuse that is a few amps above that.
Also, use the heaviest gage of copper wire that you can afford. The thinner the wire, the more resistance to electricity and the more it heats up as current flows through the wire. Also, the heavier the wire for 12-volt systems, the more distance (of wire) you can use without significant voltage drops.
The reason you want your fuse close to the battery is so that less of the wiring is subject to heating. Ideally, it would be safest to have only an inch or two of wiring between the fuse and the battery.
Serious stuff and I'm glad Archangle added this information.!
A cheap glass fuse holder might look something like this:
That type of fuse holder uses standard glass fuses like this:
Apnea Board Administrator