A while ago I was diagnosed with the need for a CPAP machine, DVA very generously provided one with the ability to run on 12VDC as well as 240AC. As I now have a dog and a desire to stop independently of mains power I thought I'd get the 12 volt lead for the CPAP machine only to be told that they don't run on 12 volts reliably and I had to get an INVERTER.
Now Inverters I know not much about except that the elcheapo ones are not very efficient and draw far more current than needed for the job at hand.
I need 150 watts so do I get a 150 watt one (DSE cat M15104) with a 450 watt surge rating or do I go for a 300 watt one (DSE cat M15102). Many brands out there and I did an Ebay search and they are very cheap there but some are not to Australian standards so I will purchase one that is from a shop in Au....
Anyone have any recomendations?
My van has a 100 A/H battery and I calculate that I'd be drawing 15 -16 amps to get the 150 watts 240ac so that would give me around 4-5 hours practical use... Yes  - no??

I run an elcheapo 300 watt inverter, projecta from memory, I think you will find that the power draw from this size is very similar to the draw from a 150 watt, I dont use it much, the heaviest thing I run off the battery is the engel, then I run it directly off 12 volt glad to hear you are looking in to free camping at last

Basil,
can't help out with the invertor as I know nothing about them, but
what type of CPAP did they give you?
If and when you need replacement masks if DVA don't supply,give me a yell and i should be able to help out.

Basils wife reckons the masks arent big enough for him Gary, can you do something about that, poor cybil can still see his face hah!!!!!! HAH!!!! HAH!!!! HAH!!!, I'll just sneak out here shall I!

Basil, the guy that runs this web site ("Mr Val") is a friend of mine. I suggest you talk to him. He uses a CPAP machine and says that it uses 1A at 12V (that is 12W, not 150W).
http://www.motorhomesaustralia.net/
The next question that you need to answer is if the machine needs a pure sine wave inverter or a modified sine wave inverter. Some electronic stuff needs sine wave which is more expensive. 

In practical terms, a good qualiy 100ahr deep cycle battery  will only deliver 15A for about 3 hours if you want any decent life from it.

Let's know how you get on. You need to get this right.

Cheers,
Pete

Bit more info Basil. The power usage of the CPAP depends on the use of the humidifier. That is the bit that would use lots of power. Do you need to use the humidifier part? If you can't get on to Mr Val, let me know and I will contact him myself for you. Cheers, Peter

just made a quick call to the brother in law, he and his wife use these machines out in the wild, he said he runs his off the car battery (size unknown) through the cigarette lighter all night long without a problem, 

he has also used his on batteries without a problem, they last about a week, they do not have a humidifier on theirs, as this is only for congestion or if you cant stand the "dry air"

they have just returned from the great alpine way and the mount kosiousco national park, free camping when they could, and did not have any dramas with the positive ventilation breathing apparatis

Mine CPAP is a Resmed S8 Lightwieght... I need the humidifier, if you don't use it my mouth feels like I have eaten half of the Tanami Desert in the morning.
The thing has a 12 V inlet clearly labled and I made up a lead, attached it and it blew the internal fuse that took 6 weeks to have replaced. DVA are generous with masks etc, I use the nasal pillows thing.
I can sleep with out it, I only use it because I snore so It's a "marital aide" in a way......

yeah thats what the brother in law and his wife has them for (snoring) the dragon reckons I should get one, but could you imagine breaking in to his house and both wearing these things, be enough to race out again screaming