Need a practical solution for recharging while off grid

[jpek]

I seem to be on a never-ending project of trying to figure out how to power my CPAP off grid. First priority is to have a backup for power outages -- possibly last many days. Second priority is to be able to go camping. I use a humidifier. That takes more power. Most recent measurements are that I use about 48 watts per hour, or about 333 for 7 hours sleep. This means that I will need a pretty high capacity battery and that I'll probably have to recharge it daily.

But how do I recharge it?

My primitive understanding is I can recharge by the following means (keep in mind that I'm almost completely ignorant about electricity and am not very handy):

• Solar panels, but I keep reading that these are not very efficient with lithium batteries and I don't have ANY idea how they would work with DIY batteries (which in any case seem beyond my level of competence to create). Solar panels also assume a sunny day and what if it's overcast? It doesn't seem like I'll be able to recharge the battery to full capacity on an average day with solar.

• From my car battery. I'm not sure how long this would take? Would I be running the engine of my car for an hour or more to do this? At least one poster advised me against this anyway because I would only be draining one battery to charge another.

• Generator. I really don't even know where to start with this. This solution has been recommended and in a way it seems the most efficient. I'm not very knowledgeable about generators and find the whole topic somewhat intimidating. A generator seems tricky and dangerous. It can't run inside. It has to be 20 feet away from the house but my outside property is very small and also exposed so that the generator could be easily seen and stolen outside. Even if not stolen I don't know where I would place it to be 20 feet away from the house. It requires gas or propane, which also has to be stored outside, also somewhat visible and possibly easily stolen and also explosive. Do I want to keep an explosive gas right near my house? How do I store it safely? And if I'm camping do I bring a bunch of gas or propane with me on my camping trip to feed the generator? I also don't know how long a generator takes to recharge a battery to capacity.

That's as far as I've gotten and that's as much as I know. None of these solutions seem workable to me, but there must be some practical way to recharge batteries in my situation? Please tell me what I'm missing or what I need to know. What is the solution here?

[Revived1]

This thread might help you.
viewtopic/t179440/I-need-a-light-weight ... 43772e38cf
It was posted a few days ago. If not, the same guy might come along and give you more info. that suits your situation.
I love camping, but now that I'm on CPAP, I'll be having to figure something out for power, myself, if I'm to have a good camping trip any time in the future.
Hope that thread helps.

[khauser]

Tough one.
Solar is a problem because the sun is sometimes behind clouds. You would need a moderate system that included a battery system of its own. Then you would not need a separate battery for the cpap though. The Tesla power wall is an example. This won't be cheap.

You can't recharge a cpap battery from a car battery. You'll end up without a charged car battery, so you'd have to run the car. Essentially your car becomes a generator. If you had the cpap battery, in this case a lead acid type, properly installed so that it could be charged at capacity it would charge fast on a short drive, i think. You would be logging the battery back and forth. You could look at li-ion car batteries, which are lighter, but they are very expensive.

There are small generators if you only need to charge the battery, eg: http://images.app.goo.gl/Z9uKmKR8HEBkrHdc9

I wouldn't know where to do this but a custom li-ion battery might be an option. But you'd still need a way to charge it. None of the existing cpap battery packs are going to power your system with humidifier all night.

[jpek]

You can't recharge a cpap battery from a car battery. You'll end up without a charged car battery, so you'd have to run the car. Essentially your car becomes a generator. If you had the cpap battery, in this case a lead acid type, properly installed so that it could be charged at capacity it would charge fast on a short drive, i think. You would be logging the battery back and forth. You could look at li-ion car batteries, which are lighter, but they are very expensive.

I am seriously thinking about getting a lithium battery because I don't have the technical know-how to rig up an acid one. (I know, there's a thread about that, but it's not geared toward people who've never worked with batteries or electricity.) But how long does it take to charge a battery like that, lithium or acid, on a drive? If I had to I would take a drive every day, or at least run my car, but for how long?

Also, in a real SHTF scenario gas stations may not be open, or I might not be able to get to them, so I wouldn't be able to run my car every day, but at least this solution would get me through less drastic scenarios.

There are small generators if you only need to charge the battery, eg: http://images.app.goo.gl/Z9uKmKR8HEBkrHdc9

This brings me right back to the question of where to store a bunch of gasoline, where to run the generator on my property, etc. (see my original post).

[khauser]

I am seriously thinking about getting a lithium battery because I don't have the technical know-how to rig up an acid one. (I know, there's a thread about that, but it's not geared toward people who've never worked with batteries or electricity.) But how long does it take to charge a battery like that, lithium or acid, on a drive? If I had to I would take a drive every day, or at least run my car, but for how long?

Also, in a real SHTF scenario gas stations may not be open, or I might not be able to get to them, so I wouldn't be able to run my car every day, but at least this solution would get me through less drastic scenarios.
<snip>
This brings me right back to the question of where to store a bunch of gasoline, where to run the generator on my property, etc. (see my original post).

Both lithium (depending on chemistry) and lead acid batteries can be charged with relatively high current. A random search finds this example: http://www.lithiumion-batteries.com/pro ... attery.php. I am NOT advocating this battery, this is just an example. This battery can take a charge of 100A (similar to a car battery). It's a 300AH battery, and if you could charge it with 100A it would take 3 hours to charge from flat. Your car can NOT deliver 100A to a second battery without seriously upgrading the charging system in it. So your talking money to go this way, lots of it.

What I am saying here is that there is NO simple answer to this. There are forums around that cater to off-grid living. You're far more likely to find the experience you need for this task at one of these. The fact that you want the power for your xPAP isn't material ... you need power in an off-grid way. I think you are limiting yourself to the wrong crowd by looking here for that answer.

Gas storage: You'd also have to figure out how to get the gas to the storage. Generators exist that run from LP or natural gas, so if you have the ability to get that delivered that's an option.

Google "off grid power forum". The first one in that list for me is http://diysolarforum.com/forums/off-gri ... advice.13/

[Janknitz]

I bought a battery system that charges either by plugging it in to a wall outlet or the car charger or you can hook up a solar charger (I haven't gotten one yet). It lasted perfectly for one night with no humidifier, but I don't think it would make it for two nights.

Take a look at a Heat Moisture Exchange adapter for about $5 at CPAP.com for when you don't have the power to run the humidifier. I'm not sure I would have made it all night running a humidifier, but I'm fine without it.

There are bigger battery generators that last longer than a single night--they get bigger and more expensive as you go up. I saw a one at REI that looked great but it was over $200.

I live in California and last year during power outages, the noise and smell of exhaust from our neighbors' generators convinced me I don't want a generator. I do want a solar panel to recharge my battery system. In our area of California we are pretty much guaranteed to have enough sun to charge it during the summer when I would need it most. Maybe not in a foggy, coastal area though.

[SleepGeek]

jpek, I think you would do better to first focus on one problem at a time. I read a post on here some years ago about using a jump start battery for backup DC power. Since I already had one I gave it a try and have been using one for over 10 yrs now. Maybe you already have one.

[khauser]

jpek, I think you would do better to first focus on one problem at a time. I read a post on here some years ago about using a jump start battery for backup DC power. Since I already had one I gave it a try and have been using one for over 10 yrs now. Maybe you already have one.

Hey SleepGeek ... I am curious at what pressure you machine is, and whether that includes a humidifier. For that matter, what machine do you have?

I tried the jump pack, and it lasted all of 3 hours, and that was without humidifier....

[SleepGeek]

I'm using a Dreamstation Auto BiPap @18/13 , while it does have a heated humidifier, always use any humidifier in passover mode when on DC. I have even added a Fisher & Paykel humidifier in line to increase the passover mode moisture. Esp if you are indoors in an air conditioned environment.

[khauser]

I'm using a Dreamstation Auto BiPap @18/13 , while it does have a heated humidifier, always use any humidifier in passover mode when on DC. I have even added a Fisher & Paykel humidifier in line to increase the passover mode moisture. Esp if you are indoors in an air conditioned environment.

Huh ... I guess the DreamStation is much more efficient than the System One, or you have a larger jump pack, or both. Good info, thanks

[SleepGeek]

I guess the DreamStation is much more efficient than the System One

I have used a System One in the past. As mentioned when on DC do not power the humidifier. When I first started I needed the heated humidifier but learned to sleep wo the heat.
I have been known to use the jump starter right at my bedside using it like a UPS. but wo the power alarm. Nice to sleep right thru any power interruptions. What is there to do once the power goes out but sleep anyway.

[HoseCrusher]

Jpek, Here is a place to start from...

When you drive somewhere, how long does it take to arrive and how much gas do you use?

Example, if you drive 4 hours and go 200 miles and use 8 gallons of gas, you now have an idea of how to use you car to recharge your battery.

At idle you use less gas than driving. So to start you know that 4 hours will use about half a tank of gas while driving. Simply at idle recharging your CPAP battery will most likely use less fuel, but you now have a starting point to figure out your particular situation.

If you are able to store a tank of gas, you can now figure out how many times you can recharge your battery back up.

Please note that this is a place to start from. Additional testing may skew results far beyond what the initial result indicate.

[Goofproof]

Using your car to recharge your battery is a poor choice, even more now days since all your car computers are in charge and very costly to repair. Some cars have $ 3 to 4 thousand dollars of computers built in. They aren't very power friendly. The days of $ 50 Gen and Alt, are past, now cars require a $ 2,000 computer to replace a $ 8 switch.

A gas generator and a battery charger are the best option or solar if big enough and you have time. The best way to charge a battery with your car, install a 110 volt inverter and use a battery charger to charge the battery, a battery starts quickly charging when low and charges slower as it builds up charge. Jim

Hook the wires up incorrectly, and the Magic Smoke will get out~