camping?

[wolewyck]

Hi all. I haven't been camping since diagnosis. I have a backup battery (made specifically for CPAP use) but am not sure for how many nights it might last, or if it could be recharged during the day from the car? And if the car has to be running to recharge it? Advice appreciated.

[HoseCrusher]

You need more information.

Find the capacity of the battery pack. It is usually given in amp hours or milliamp hours. Next you need to figure out how many amps your machine uses.

Knowing these values you can get a very rough idea of how long a battery pack will last.

For example if your machine uses 10 amps and your battery pack has a capacity of 10 amp hours, your battery will last 1 hour.

Charging the battery pack can be done just by hooking it up to the car battery, but will be quicker if you start the engine.

[underpressure]

Is it the new lithium ion from resmed. Or lead acid??? Humidifiers take up a lot of the power , turning down your humid can help increase your time. You can't recharge the lithium ion off the car but can from a wall plug in. The reg batteries can be charged off a cigarette lighter adapter. steve

[handyguy]

If it can be recharged from only a wall outlet, he could use a small inverter that operates from the car battery to produce AC for the charger. Depending on the current draw, there may be enough capacity in the car battery to work just fine.

[Ms Piggy]

Mine is all rigged up for this as we sometimes have power outages in bad winter weather -
I didn't rig it up so am no help, sorry. BUT this questions, like many others, has been
asked before so if you use the search thing at the top of the page you will find lots of info.
hope this helps.

[wolewyck]

The battery in question is the Respironics long-life rechargable battery pack (http://www.directhomemedical.com/long-l ... esmed.html), which seems to be lead-acid.

The specs mention 14.4 amp-hours. Not sure just how much my machine draws... I haven't found specs for it specifically. But I have found specs for older models (http://www.resmed.com/us/documents/batt ... ts-usa.pdf), which seem to suggest roughly a draw of 1.5 amps (at 12 V) without the humidifier, or ~4 amps with (ouch). If I understand correctly, it means I'd have maximum ~10 hours run-time without the humidifier-- not even 2 nights' worth. Does that seem right to you all?

I am still confused about whether I can recharge this from the car. This website (http://www.directhomemedical.com/long-l ... esmed.html) says "Recharging from 12V DC Power Sockets is not recommended." Another website ("Important Tips" tab in https://www.cpap.com/productpage/respir ... -pack.html) says "If you would like to charge the Respironics Battery Pack through a DC source, please order the 400 Watt DC to AC Power Inverter."

So... not sure if it's ok to use the car battery to recharge the Respironics battery (if not, why not?). Or if it is ok, I guess I need the inverter?

Don't know much about electricity, but I guess I'm learning a little...

[HoseCrusher]

OK, now you have to move from theoretical to the real world.

14.4 amp hours is most likely optimistic. If you figure about 80% of that, you will be much closer. 14.4 X 0.80 = 11.5 usable amp hours.

With a 1.5 amp load you end up with 11.5 / 1.5 = 7.6 hours of use.

The issue with charging is that there is some resistance involved. This means that if you hook up a battery at 11 volts to one at 12 volts, very little charging will take place. when you run your engine, your 12 volt battery is charged at just over 14 volts. As you can see you need a little higher voltage to "push" the charge into the discharged battery.

Using an inverter is a good way to go, but there is a problem with that too. Most inverters have a low voltage shut off to keep the battery they are hooked up to from becoming totally discharged. With the care shut off, the battery in the car that you are using to recharge your other battery can quickly drop in voltage to a point where the inverter shuts off before fully charging your other battery.

It is looking like your battery pack will give you one nights use, then you will have to run the car for about 3 hours to charge it back up and be ready for the next night.

Now, if you have 2 battery packs, you could go for 2 nights and then the charging system on your car has enough capacity to enable you to charge both battery packs in about 3 hours.

Sometimes that is not practical so there is another option. You can put another battery into your car. This should keep the voltage up high enough to enable you to charge without the car running. Some testing would have to be done to determine how many charges you can get from this particular set up. The downside to this is that when you finally start the car, it will take longer to bring both batteries up to a full charge.

Decisions, decisions, decisions...

I haven't checked this out, but the Provent nasal device may help enough while camping that you wouldn't need your xPAP machine for short trips. This would have to be checked out at home to see if it works well enough to keep you going.

[GumbyCT]

The specs mention 14.4 amp-hours. Not sure just how much my machine draws.

Is that spec what is written on the battery? If not look for the specs written on the battery.

I know the current is written on the bottom of the Respironics machines, check your machine for similar info. Keep in mind this is max draw and does vary with pressure, so it is NOT a flat line.

There are many variables in this equation like the condition of the battery, pressures, leaks, etc.

The very best thing you can do is to try your setup before you really need it.

Good Luck

[idamtnboy]

I am still confused about whether I can recharge this from the car.

So... not sure if it's ok to use the car battery to recharge the Respironics battery (if not, why not?). Or if it is ok, I guess I need the inverter?

Don't know much about electricity, but I guess I'm learning a little...

Good comments from Gumby, HoseCrusher, and others. Here's some of my thoughts based on my experience.

A CPAP can consume a surprisingly large amount of energy, especially with the humidifier, when compared to other everyday electronics like boom boxes and laptops.

To supply that energy via battery for more than just a few hours requires a surprisingly large battery capacity. That's why you will find recommendations for deep cycle batteries and lithium-ion batteries. In my first night of CPAP camping I totally discharged my pickup battery in one night. Had to jump it the next morning to start it.

Car batteries are made for very high, short duration, current draw, and those batteries should not regularly be discharged below about 50% capacity. Deep cycle batteries are made for moderate, long duration, current draw which makes them ideal for CPAP use.

Battery recharge rate is comparable to it's design discharge rate. A car battery can be recharged in a fairly short time because it will accept a high current push. A deep cycle battery takes a lot longer to recharge because it won't accept a high current push. I ran my CPAP, with humidifier running, for about 7 hours for each of 3 nights. The battery discharged about 1/3 of full charge each night. I have my pickup set up so I can recharge the deep cycle battery with the alternator output all going to the deep cycle. With the engine running at high idle for about 2 hours or more, the battery only recharged about 1/4 of full charge. So after 3 nights of use and two times of recharge the battery was down to about 1/4 to 1/3 charge. Now, a car battery can be fully recharged from dead by running the pickup for 2 hours.

As has been mentioned this issue has been hashed quite a bit. A search on battery should find you much of that discussion. As in all things CPAP, there ain't no simple answer. You'll just have to figure out what works best for you, and go that direction.