trekwars2000 wrote: ↑Sun Jul 29, 2018 12:55 pm
Okay, I read the first 4 pages and think I've got most of what needs to happen for the setup. First a background and then I have some questions:
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Congratulations! Even I have trouble getting through the first four pages!
So you've posed a nice problem that starts with a few "meta-problems": first, all of the answers are guesses - there are just too many variables to get the best answer on the first try, and you'll know a lot more after your first trip. Second, all of the issues seem stacked against you. Let me enumerate:
Your pump is probably the least efficient of the common models. You don't mention pressure, but at 10 the ResMed guide says 0.92 amps, which means about 7 amp-hour for a night, compared to 4 for a Respironics. And high altitude that will make that go up a bit more. The big hit is humidity, and, if its cold you'll have rainout and may need the heated hose. (Physics problem to ponder - how much less energy does it take to vaporize at altitude?)
So if we assume 7 amp-hours for the pump, perhaps double that for the humidifier (more on this later). So that's 14 AH a night. That is pushing it for two nights on the 35 ah battery, but may work. The quick answer is give it a shot for a two night trip. Or, get a second one and see how it goes for 3-4 nights. If by "tent camping" you mean the car is close to the tent, I would consider a 100 AH AGM battery (about $170 prime) which should give you plenty to spare. I lean towards overkill when it comes to batteries. I like the 2 battery approach especially if you're lugging them around, but with two you never quite optimize the usage. On my boat I have 4 batteries but jumper them together as one bank.
Charging from the car presents a few issues. First, a battery will only accept a certain amount of charge. Deeply discharged its about 25% of its total capacity, and it goes down from there. Thus, the 35 amp-hour battery may start accepting 9 amps, but it will fall to 6 or 7 amps quickly. And the last 15% will be so slow you won't want to do it. For boaters, the common protocol is to discharge to 50%, then charge up to 85% in about 90 minutes, so you're actually using about a third of the capacity. (Tesla owners have the same issue and adopted a 80-20 protocol.) Having a bigger battery means that when you do charge, you can charge much faster.
Car charging has another issue - the regulators are either dumb and won't give you the added boost and safety of a good multi-stage charger, or they are overly smart and try to economize if they think they can save a drop of gas by turning off (turning on the lights may defeat this). Also, regulators don't turn on at a low idle - you might have to rev up to 1200 or 1500 to get the volts up. Definitely test with a volt meter. If you try charging through a cigarette socket remember that they may be fused at 10 amps.
So my advice is try to get a big enough battery for the whole trip, and bring jumper cables just in case. That will cost a few bucks but simplify life in the long run - you certainly don't go camping just so you can idle your car for a few hours each day. (BTW, the boat moored next to me yesterday morning started running his engine at 7 AM to charge - pissed me off but not enough to launch the dinghy and row over to complain!)
On humidity - I never use it on the boat or when travelling to humid areas, but I certainly took it on a trip to Palm Springs. Camping at altitude is a problem - you should check the dew points and night temps where you camp because the Relative Humidity may not be not be that bad at night. A dew point of 50 degrees is low on a hot day, but humid on a cold night. You certainly want to try to get by on the lowest possible setting. On my Respironics 560 I think I got it down to 4 AH a night by using a setting of 2 and no heated hose. You could experiment at home by cranking the A/C for a night to simulate the environment. The are other options, like the new lozenges that stimulate saliva, or the non-powered HME gadgets that go on the hose. And there might be a different mask that helps. You might find you can do away with power humidity, which would simply your life!
A battery box is nice - there are a few with sockets and usb, etc that might make everyone happy. But whatever you do, make sure the terminals are protected from shorts.
A BatteryTender is great for maintaining all batteries, and charging smaller ones. If you get a 100 AH you might want a larger charger so you can get a full charge in a finite amount of time. And the cables and quick connectors that come with the BT are very handy.
There are probably ways that you could tap into the power of your hybrid - but in the long run the "overkill" solution is only $100 more than the minimal solution, so why bother even going there? I can't count the number of times I've thought in retrospect, "I would have gladly paid $100 to avoid that hassle!"
), I have multiple 12V, 130W cigarette lighter plus in my car. Not sure if they would be useable in anyway.