cpap machine charging from Prius in campground?

I've left my Prius locked and running in a campground before, and it's worked well. But I was only powering a cooler for a short time, not a cpap machine, so the suggestions of getting an inverter and trying it at home first seem like good ideas. You may find an available outlet in the campground, so you could pack an extension cord just in case. A little note on the receptacle explaining the 'mission critical' use might not hurt, either, just in case someone else decides they need the outlet more than you do, since you're sleeping anyway and 'obviously' not using it.

 

did i forget to mention i've powered my uncles breathing machine and air mattress of my setup for 7 hours or so... including charging his wheelchair?.. the power was out for 10 hours or so... grid power switched back on around 4:30am that morning.

i've even used it while camping... that was only an amp or so

 

Make sure hubby reads the Harvard Press article that Evan points to in reply #7:

 

Leave the car ON ("Ready", exactly as though you were about to drive it away) in Park and the parking brake set. The car will start the engine as needed to keep the batteries all charged up. You can do this until it runs out of gas. That would probably take a couple of days if you start with a full tank. Test the setup in your own yard before taking it on the road.

 

The online source where I bought my latest CPAP machine (fax them the prescription) also has rechargeable battery packs that are compatible with various machines. I don't know if they have enough power/longevity for a humidification module.

This may be more convenient if you have daytime access to AC power for recharging.

 

12V x 0.8A = 9.6W. This is equivalent to one light bulb left on.

Suppose the car is IG-OFF and the inverter remains on for 8 hours. This will result in 6.4 Ah being taken from the battery. When new the battery's capacity is ~36 Ah. Normally you should not discharge the battery below 50% if you desire long battery life.

The bottom line is that if the 12V battery is fully-charged and in like-new condition, leaving the inverter on for an 8 hour period will be OK. However, if the battery is marginal then leaving the inverter on for that time may result in a no-start situation the next day. Hence you would be well-advised to make sure the inverter is off when not in use.

 

as richard has said.. leave the car ON in Ready mode.... with the car in park... parking brake applied too.

as for the inverter.. you'll only use it for camping and power outages. attach a quick-connect on the 12v side... this way, when you're done using it, you can unplug the entire unit... instead of worrying about shutting it off by a switch. it also allows you to take it out of your car whenever you want.

i recently disconnected mine. if i were to leave it on when i turn the car off, i would hear it's internal fan run... if my 12v starts to run low, it sets off an alarm. (audible outside of my car)

 

As mentioned earlier many campgrounds now have sites that supply 120V AC power (and running water). I would look into that as a hassle-free alternative.

If you go with the inverter route I would triple check that the Prius dash shows "READY" before going to sleep.

Good luck!

 

Thanks for all the info everyone. I'm the guy trying to install a 1KW inverter. Up till now I have been asking messages via my wife, jenbbay.

I'm still trying to figure out a few things.
1) Should I really put in the 150A fuse as the Xantrex docs demand or should I join the Darwin club?
2) Will the 10.5 volt cutoff on the inverter save the battery if I leave the inverter power switch on by accident? The consensus here seems to be that if I forget to turn off the inverter and go into non-ready on the prius, then the battery gets totally discharged. I wonder if anyone actually has had that happen?
3) Where can I get a 90A quick-disconnect, i.e. a socket and plug? I see 50A ones for 120VAC and 240VAC but no 90A ones (of course one for 120VAC would work fine for 12VDC as well because the insulation will be better than needed.) Digikey and Mouser don't seem to have it.

I went to West marine and they have all of this stuff but the $ is adding up. They want $350 for the inverter, but the web shows $250, which I can also get at Fry's (NorCal) too. The cables are $20, fuse $20, fuse block $30 etc etc. Maybe I should go down to 600W or less.

All this just for a CPAP driver.

Anyone have experience like this?

Thanks

 

Actually, this is not a good assumption, even though it is done frequently.

Many AC disconnect devices rely on the zero crossings of the alternating current to function properly. When the contacts break, they allow an arc to flow initially, with the expectation of extinquishing it at the next current zero crossing. For this reason, very many 120VAC fuses, circuit breakers, and disconnects do not have agency approvals for any DC, even 12VDC.

This distinction is very important for systems that require permits and electrical inspections, such as home solar installations. But for projects without permits, a huge number of people get away with this substitution.

The other caveat is that 12V systems cannot tolerate as much voltage drop as 120V and still function as intended. But at 90 amps, you will know this by how hot the parts get during operation.

 

I am a CPAP user and I sometimes camp on motorcycle trips. I posted a note before about a possible solution using a seperate 12 battery.

Honestly I think using a 15 to 30 thousand dollar car to run a CPAP machine overnight is nuts. Why risk any damage to your car or even run it more than needed if you can get a battery backup for a couple of hundred dollars to do what you need?

Just my 2 cents worth and it ain't worth much.

Good luck,
Glenn

 

Please, please, please,...

Whatever you do, test it out extensively before leaving...and I'd also have a back-up source.

It's PURELY SELFISH, but I don't want to wake up and see headlines on FOX NEWS exclaiming, ....Toyota Prius suffocates man while sleeping......

 

You can buy a DC disconnect from a marine or RV store. Don't assume that AC devices will work well on DC systems.

Tom

 

I'm amazed at all the attention on this. Thanks.

I have just finished putting in a 1KW inverter (Xantrex) into the Prius by connecting 4AWG cabling through a 150A ANL fuse directly to the battery. The connection is difficult due to the thickness of the cable and the wimpiness of the connections to the battery, but it is conservative on my side so I don't see any problem. The 4AWG is capable of about 100A.

The ground wire from the battery is rather thin - probably only 8AWG or smaller. It is hard to believe that the battery can be recharged on an engine-on duty cycle of 5min/hr or some such low percentage of the time without requiring huge current to average it out. I don't remember where I heard about this 5min/hr but that is the basic idea. That huge current would have to be a multiple of the current I am drawing, which is about 80A at 1KW. So we would get 1hr/5min*80A = 960A. How does this work out?

The fact that the inverter is 1KW allows me about 15Ahr/90A = 10min of runtime without charging. I read about a guy or two who put in such an inverter and then ran power tools at construction sites or as emergency power to a house on an almost continuous basis, so again, the fast charging capability is needed.

Does anyone know how the charging can be at such a high amperage? The small ground strap makes it look improbable. The DC/DC converter seems necessary for this all to work out, so if that is the source of the power - the traction battery - then I should not connect the negative inverter to the negative on the 12v battery but instead to the chassis ground. The cable coming into the positive on the 12v battery is about 4 or 6 AWG, so that part looks OK.

Being a pure sine inverter - which is apparently required for the cpap's humidifier - bumped up the $ tremendously (0.5K$).

I hope this is clear. It is rather complex situation due to the various power sources.

There are indeed campgrounds with power, e.g. in Oregon, but we're going to the high Sierra where there aren't any. I could probably get away with separate batteries but there still needs to be wiring of various kinds for the recharge and we have to carry batteries around etc. The car would have to stay put during the daytime recharge, but we want to drive around. We are going for two weeks, so a single charge on the battery is insufficient. A single night requires about 3.6A*8hr = 28.8Ahr with humidifier, so only a big battery can do it if we want to stay to less than 50% state of charge.

The inverter serves in an emergency too.

 

The 12V battery is charged whenever the Prius is READY. Once the Prius is READY, it doesn't matter whether the gasoline engine is running or not, from the point of view of the 12V battery, since it is charged by the DC/DC converter within the inverter. The DC/DC converter maintains a constant ~13.8VDC when the car is READY, and that voltage level is what causes the 12V battery to be charged at a moderate pace.

You are right that the inverter negative cable should be connected to body metal in preference to the negative terminal of the battery, because the inverter will be obtaining power from the DC/DC converter, not the 12V battery. Good luck, hope you have sufficient time to test your inverter over a prolonged period prior to embarking on your vacation.

 

Adding to Patrick's comments, in Ready mode all of the 12V power comes from the HV battery via the DC to DC converter. Your CPAP machine will be powered by the HV battery, not the tiny 12V battery.

Tom