Inverter vs. Hooking directly to 12V

If the 1.8 amps is the current draw at 12V, no problem plugging it into the lighter socket, which is fused at 10 amps. As you note, you'd want to keep the car in Ready mode to avoid running down the rather low capacity 12V battery.

You'll see in other threads here that an inverter connected directly to the 12V battery can supply about 800 watts of AC power. An inverter plugged into the lighter socket should be about 100 watts maximum.

 

If the question is should I run a CPAP off the 12vdc directly (using an adapter) versus running it through a 12vdc to 120vac inverter first then through my standard CPAP brick power supply, then I would always run off the 12vdc directly. It would pull less current overall since the 12v inverter is inefficient, wasting power internally. You should be able to run 1.8 amps off a cigarette lighter receptacle. I believe the Prius outlet is fused at 10 amps.

It is difficult to estimate exactly how inefficient any given inverter solution is short of actually measuring the DC amps used in both scenarios. Measuring would be fairly easy for someone with enough knowledge to wire-in a 10 amp DC meter. However the direct 12vdc solution is likely to be 20-50% better (lower amps).

By the way, are you sleeping in your car? Usually CPAPs are used when sleeping. Of course the outlets are off when not in Ready and the car engine will periodically run when in Ready.

 

Just want to make sure that you're not planning to run a 300 watt inverter off the lighter socket!

 

I would worry about Carbon Monoxide poisoning. Some do this on purpose to achieve a suicide. Usually 100w inverters are considered to be the biggest you should connect. At least 9 amps on the 12v and probably 10 on full load with a 100w.

 

With such a small load the engine will run only infrequently for a couple of minutes at a time. There are a number of threads on sleeping in the Prius, and as far as I know we've never lost anyone.

 

As other mentioned, 1.8 Amp at 12 Volts DC is fine. But we need to be clear that 1.8 Amps at 120 Volts AC won't work, because the 12V->120V inverter will overload the 12V socket.

No, 300 Watts will overload that 12V outlet.

Modern emission controls have sharply reduced (though not eliminated) this risk. Because of this, numerous attempted suicides by this path have failed.

 

You could park a Prius in a closed garage and stay in there with it, you'd probably last a couple days before the monoxide built up enough in your system to kill you. Seriously, not an issue.

 

There is not an IF with the HVAC. You need to have the fan running at least a notch or two above low and all the windows closed and recirc. off .......to keep a slight positive pressure in the cabin.

And are you sure that the 1.8 amps is at 12 volts ? That's only about 20 watts and sounds rather low.
If it is 1.8 amps at 110 vots, that's about 200 watts and sounds more reasonable.
200 watts at 12 volts would require about 16 amps.

 

Yes. The required 16 amps FAR exceeds the fuse on the ligher socket.......if the quoted 10 amp fuse is correct.

AND it is a pretty high load to be putting on the battery and charging system too.
Might not be a good idea overall.

 

In the Prius, acc-mode should not be used for long periods; the small aux battery runs down more quickly than a regular battery, and deep-discharging significantly shortens its life. I have found that ready-mode works well for running accessories, and tends to shut itself off after a period of inactivity.

 

Does the rear 12v outlet have a different load rating than the front?

 

1.8 amps at 110V is about 200 watts. This is a relatively trivial load on the charging system, which has a 100 amp fuse and has been used by quite a few PriusChat posters to run a 1 kilowatt inverter.

 

Where would be the best point to attach a high-load connection, like for a large inverter, the battery?

 

Yes, if you check the various threads here on this (which reached a peak after Hurricane Sandy in 2012), you'll find quite a few with hookup details.
Using car as generator for house power | PriusChat
Anybody have a POWER INVERTER for emergency use installed on their Prius? | PriusChat

This web page created by a PC member is quite comprehensive:
Running an Inverter off a Prius for Backup Power | Peak Prosperity

As noted, the maximum that can be drawn at the 12V battery, with the car in Ready, is about 1000 watts. Any more than this and you need a direct connection to the traction battery, which has also been done very successfully.

In Japan, Toyota is offering current models with a built-in AC power outlet, which eliminates the need to do it yourself.

 

A simple way to do it for periodic use might be to get something like this:
400 Watt Continuous/800 Watt Peak Power Inverter
12V Power Inverter - 1500 Watts Max

Just clamp it on the battery posts when you need it, and as others have mentioned keep the car in Ready mode. You might also want to do some searching online to see if anyone has had issues using your machine on these cheaper modified sine wave inverters.