Where to tap for 12 volts

Ivan Vegvary wrote in news: snipped-for-privacy@googlegroups.com:

What's the draw on the CPAP machine? I suspect you'll run the car's battery down if you use it all night with the engine off.

Get a separate battery pack for the CPAP, or just leave the engine running all night. No harm will result from the engine running all night, but you'll use a couple of gallons of gas.

Does your ignition have an accessory position? It should work there.

Chas

You'll need to determine the current draw of the device if you want to pick an existing circuit. If you're adding a line with a fuse, and it sounds as if you are, then you can just run the line right from the battery or anywhere the positive cable of the battery bolts to. Ground in a car is the body so that's of no issue.

As for having battery power to start the car in the morning you'll need to figure out how much energy it's going to draw, current again.

Machine is rated for "3amp max. at 12V DC". Does that mean 24 amp hours for eight hours sleep? Seems like battery capacity should be ample?

Machine is rated for "3amp max. at 12V DC". Does that mean 24 amp hours for eight hours sleep? Seems like battery capacity should be ample?

You can still use the cigarette lighter outlet. Just stop the car, turn off the engine, then turn ignition on without starting it.

mg

"MG" wrote in news:muAav.64966$ snipped-for-privacy@fx12.iad:

now thats some really bad advice. dont just turn the key on without the eng running for any peroid of time. KB

It's not going to hurt anything with newer cars.

Back when cars had points you couldn't leave the ignition on or you would burn your points up.

With today's cars it's no big deal.

I know lot's of folks who use CPAP while traveling/camping. The common method for folks with tents or small campers is to use a jump box to power the pump, then let it charge back up the next day. Folks with bigger RV's just run off the house batts.

Yeah, all those other systems that "come alive" with the igniton on don't draw any current at all. Did we forget that he doesn't want 20 minutes of power, he wants 8 hours?

Then he can just leave the motor running. It won't use that much fuel at idle

This is a good point. Some vehicles have a cigarette lighter fuse that can be moved from an ACC to BAT position. In the BAT position, the cig. lighter outlet is always hot. Fewer things some on in ACC position than ON. But ACC can still be a battery killer.

Another 'always hot' circuit is the dome light. In some vehicles, the door switches provide the light a ground.

m6onz5a wrote in news: snipped-for-privacy@googlegroups.com:

Which is exactly what I said back on May 7th.

Thanks for all the replies. Rigged a cigarette socket with alligator clips and long wires. Direct to battery. Ran 10 hour test (only need 6 hrs. sleep) and car started fine. Ivan Vegvary

Free safety hint... put an inline fuse at your positive alligator clip. Always fuse anything connected to the positive battery post, at the post.

Thanks for the hint. Will do!!

Ivan Vegvary

What fuse would you recommend for this application? Thanks.

Depends on the anticipated load. The wire gauge also depends on the load. For a specific load, the longer the wire the heavier the gauge needed. There are charts for sizing wires to load and length. He's got a temp hook up. Does he need a weatherproof inline fuse? He would know better than me. If permanent hook up, go weatherproof.

Mostly, I like to know what would be the suggested amp rating of the fuse with a 36W maximum load.

For DC, Watts = amps X volts