How can I run a CPAP in my tiny van?

[BigT]

I just got off the phone with both CPAP.com and Philips Respironics. CPAP couldn't answer my question, but they gave me a contact number for PR, where I got the answer I needed and, given what I've been reading on the CPAP sites, expected to get.

The guy I spoke with said that 6.67A is the maximum amperage the unit would draw with the humidifier attached and that 2.0 - 2.2 Amps would be the average Amp draw I could expect *without* the humidifier. They quote 3 Amps just to be safe.

Now I'm getting quotes of as little as 0.35A (average) from members of a CPAP forum who have the same model machine that I have and have tested it with a meter.  
If this proves to be true, I'm looking at as little as 2.8 Ah for 8 hours of sleep!  That's a lot better than the 53.3 Ah, per night, numbers I was getting originally. This is getting better all the time! 

It means that I could run a single 160 Watt panel (to save space) to a 12V 80Ah AGM and still have plenty of Ah left over to run lights, a 12V fan and maybe charge my Macbook Air.
The 160W/80Ah set-up would mean a 2:1 Watt:Ah ratio, which from what I've read here seems to be the way to go.  

I plan to order a plug-in Amp/Volt/Watt meter from Amazon and run some tests of my own.  

This is really good news! 

 

[offroad]

BigT - without a watt meter I am running my Cpap on just a used car battery and a150 watt inverter. Plenty of juice.

 

[BigT]

I'm looking at AGM because I don't want to have to vent the battery and there's no room for it under the hood. Cutting holes in my van is not an option.
I also don't plan to run an inverter and will be charging it solely off solar. More and more I think adding a 12V fridge would be a good idea, if I can find a really tiny model that doesn't suck down much "juice".

 

[muddy]

Bumping this thread as I will be setting out shortly with my CPAP.

One thing I noticed was that my CPAP used a lot less power than the max wattage given in the specs when I measured it on the Kill-A-Watt. Your pressure may be much lower than the max pressure, whether you use a humidifier or not (and its settings if you do), and how many mask leaks you have might impact power usage significantly.

 

[BigT]

Thanks for bumping the thread!  My CPAP doesn't have the humidifier and I generally run the machine between 8 & 20 (it's automatic).  

When I first started this subject I thought it was going to run at 6.67A all the time, but eventually learned that was not the case.
Thanks for adding your input, and please feel free to keep us updated on how it goes!    

I've gotten a little (little?!) stalled on my solar project while waiting for Amazon to restock the 160W Grape panels, but I did manage to start building a battery box that will be mounted behind the drivers seat.  I figure I can at least mount an AGM back there and keep it charged off a plug-in 120V charger for now.  Better than nothing.  

The extra space behind the box is to address the problem of my camp toilet falling over in turns.  The plan is to attach it behind the battery box using a low-sided, topless (duh!) box made of 1" x 6".  It's going to wipe out some floor space, but I don't have a lot of options since I'm not willing to cut a hole in the floor of my van.  

 

[GotSmart]

My single 100w panel gives me more power than I could use with my CPAP, cooker, water heating device fan, computer, cell and lights.  If I upgraded with more panels I could put in a freezer.   

 

[muddy]

Yeah, the humidifer is probably the biggest draw. I need mine, here in my air-conditioned and dry house, but I'm hopeful that I will be able to turn it off when I'm not in a climate controlled environment.

 

[BigT]

My single 100w panel gives me more power than I could use with my CPAP, cooker, water heating device fan, computer, cell and lights.  If I upgraded with more panels I could put in a freezer.   

What's the Ah rating of your battery and is it an AGM?

 

[muddy]

Did my first test run just now. CPAP works and didn't get fried by the battery power, so next test is doing a full nights sleep and seeing what happens.

 

[BigT]

What kind of battery did you run your CPAP off of for the test?

I'll be picking up a 92Ah, Northstar, AGM pretty soon, but I'll be keeping it charged off a 120V plug-in charger for a while until I find the panel and charge controller I want.

 

[muddy]

I'm using two Trojan T105s

 

[muddy]

Well, last night went perfectly. I was kinda nervous about all this before I really started learning about batteries and solar power. Seemed like most people travelling with CPAP used either shore power or weren't staying away from 110v power for too long.

 

[BigT]

I found this on a battery site while looking up the Trojan T-105..

5-Hr Rate 185
10-Hr Rate 207
20-Hr Rate 225
100-Hr Rate 250

Can someone please explain this?  It seems the Ah goes up as the "rate" increases, but I have no idea what that means.   :huh:

 

[LeeRevell]

Read up on Puekert Factor. Basically as you draw more power in a shorter time, the battery's apparent capacity goes down. Somewhere back in Sternwake's dissertations, some of which I have begun copying and saving (Thanks, SW!) he explains this. Wiki has an article on it too, but they use a lot of tech-speak.
Essentially if you use a lot of power quickly, the battery doesn't last as long and will need recharging sooner. Hope I have that right.......

 

[GotSmart]

What's the Ah rating of your battery and is it an AGM?

I got lucky and found four Fullriver 224 AGM used for $220 a year ago.  

I just looked those up and they are going for $300 each!  

Ask at the battery shops.  Those places that specialize in batteries only.  I went in looking for two T105's, and was shown a pallet of the 224's.  At 1/2 price. ($55 each)  Shop around and you just might get lucky also.  

I charged them off the alternator while driving befor I got my solar.

 

[BigT]

 Shop around and you just might get lucky also.  

The luckiest I've gotten, so far, is to find a Northstar 92Ah AGM for $150.  They're usually around $350.  
Not sure how old it is, though, (blue top vs grey top) so I don't if it's really a good deal or not.

 

[VanLifeCrisis]

I believe pepple use the 20Hr rate when they talk about amp hours ratings on batteries

 

[SternWake]

The 20 hour rate is the standard.

A hundred amp hour battery earned its 100AH rating under a 5 amp load. It provided 5 amps for 20 hours until battery voltage dropped to 10.5v which is considered 100% discharged.

And yes you can discharge a battery below 10.5v, and no you should not, ever.

The 100AH battery, being discharged at a rate higher than 5 amps, will not have 100AH total to provide. The higher the discharge current, the less capacity it will have to give.

Also, if the amp draw is under 5 amps, the 100AH battery actually will have more than 100Ah total capacity to give.

But the capacity penalties for going over the 5 amp draw, are not rewarded as fairly when going under the 5 amp draw.

Peukert can be a little &(tch, and different batteries have different Peukert components, and good luck finding the manufacturer's peukert component to plug into a calculator.

Also the PK component changes for the worse as the battery ages, so not only is an older battery being cycled deeper as it has less capacity, Peukert is punishing the remaining capacity much harder, causing the battery to be cycled even deeper. This is why batteries seem to fall over a cliff at some point. Most people never see that ledge coming though. They just skip along singing the 'works just fine' theme, and freak out when the cliff edge was one step behind them.

http://www.csgnetwork.com/batterylifecalc.html

 

[BigT]

I've got a Yakima rack on the roof of my van, but half of it is taken up by a set of kayak saddles, leaving me with an area 20" wide.  Length is only limited to the length of the van.  
Now that I think about it, my kayak is going to shadow the panels unless I park facing east or west.  :/

Well, at least I've solved the "not enough room on the roof" issue.  I just picked up a set of wider crossbars that are 20" wider than the originals, giving me a lot more room for panels.    
Eventually I hope to pick up a Thule "Hullavator" for the kayak.  It's a system that allows you to lower the kayak down next to the vehicle, resulting in unobstructed access to sunlight.  

It's going to mean pushing the kayak pretty far to the right, but it's worth it for added room I'll be getting.  

 

[BigT]

Anyone heard of these? http://www.mlsolar.com/infinium-300-watt-72-cell-bifacial-n-type-mono-cystalline-panel/

Not sure of the price yet (I'll call them tomorrow or just stop by their shop). Not sure what "N-Type" means.
I do like the dimensions, though. 6' X 39". That would fit nicely on the roof of my van.
Would 300 Watts require an MPPT charge controller? I'm leaning toward going that way anyway.

Last question: Would 300 watts provide enough initial charge rate to allow for complete charging of a 92Ah AGM without the need for a wall charger or alternator hookup?