Yet another camping question

[jenngirl]

I have spent many hours reading about the different battery power options for camping, and Im still a little confused, but I think I have some ideas, and want your advice. I use ResMed Escape 2 @15 with a humidifier. I will obviously only be using the humidifier as pass-over while camping, and will bring dry-mouth mouthwash and saline nasal spray to survive.
It looks like this is the BEST option, https://www.cpap.com/productpage/respir ... r-kit.html
but it costs almost $400 and I really can't afford that.

So I am thinking of getting this
http://www.batteryspace.com/12vportable ... ger3a.aspx

and this
https://www.cpap.com/productpage/DC-12-Inverter.html


Or this to just use the AC plug on my machine.
http://www.autobarn.net/vec026bd.html


l have access to both a car with a cigarette lighter or a traditional wall outlet during the day to charge. I will be camping for 3 nights.

Does any of this make sense? Will either of the cheaper options work?

Thanks for your help!
-Jenn

[BigNortherner]

First you should do the calculations to see how much battery capacity you need.

I rewrote this to be more informative, especially to emphasize that amp-hour capacity is at a certain voltage but you are talking of both direct 12vdc and running via an inverter at 115vac.


We are speaking of taking energy out of a battery to run your CPAP machine for several hours.

Energy capacity of the battery is commonly given as as amp-hours assuming a certain voltage. (If the capacity rating is in watt-hours you have to translate. So for example, 144 watt-hours capacity in a 12 volt battery is 12 ah since amps = watts divided by volts.)

So a rough calculation is dividing battery capacity in amp-hours by the current drain of your machine when operating at 12 volts.

For the humidifier you have to ratio the voltages to get to a common denominator of 12 volts which your battery is - so 115/12 times [its current draw at 115] gives you the draw of the inverter on the battery, roughly as that ignores inductance, and remember the inverter consumes energy itself so the demand on the battery is even greater).

I've run a Respironics bread-loaf RemStar Auto a few nights on a deep-cycle battery of full automotive size 27.

[BigNortherner]

Pedantic info on batteries:

Note that batteries deteriorate from use, thus there is value in having a good charger - Black & Decker make some sophisticated ones. That may be one reason the all-in-one batteries are pricey.
Also, for CPAP use you want a "deep-cycle" type of battery for regular use, not a car-starting type of battery. (Your CPAP demand is low output for a long time between charges, the "deep-cycle" battery will deteriorate more slowly - BUT also beware that batteries also deteriorate if sitting unused without being recharged periodically, and deep-cycle are worse for that than starting type. I don't recall what gel type are like.)

And of course you strongly prefer a gel battery to reduce spill risk, unless you can secure the battery so it won't tip over. ("AGM" or "VSLRA" type is fairly spill resistant as it is sealed up to the point that the pressure relief valve opens, however they are expensive - though I have not compared with prices of gel batteries as those are smaller than I wanted).

This gets complicated.

[jenngirl]

I looks to me that the two battery options I linked to are designed to provide long-term output. The black and decker one says it can power gps and game systems. So doesn't that mean it works just like a re-chargeable wall socket, and not like a car jump-start unit?

I'm so confused.

Thanks for the description of amp hours, that might help me some...

[imtired]

http://www.canadiantire.ca/AST/browse/5 ... ?locale=en

this is what i used. it is 50mah marine deep cycle. just to give you an idea i ran my S8 with the humidifier at 3 (half way up) and it lasted 6:28 before it died. with the humidifier off it ran for over 30:17. to run the humidifier you will need a pure sine wave inverter. im not sure how much of a difference pressure makes, but my machine normally runs 11-12cm. with the humidity on a lo setting i can normally get 3 nights out of my battery.

[BigNortherner]

Disregard my post on calculating duration until I clarify it and add a good example. (I can't see how to delete it, I will edit it later.)

Looking up the Respironics classic RemStar Auto (bread loaf) I see 3A max at 12 volts DC.
The humidifier takes 1A max at 100-240 volts AC, which is poorly stated as it will vary with voltage. I assume that is at 100vac thus its consumption will be roughly 9 amps max at 12 volts DC which your battery probably is, or three times the CPAP unit itself.

"jenngirl", regarding powering game and GPS units, I see that as just a normal use of the DC socket that unit probably has, assuming those devices can operate on 12 DC as GPS units for temporary use in cars can. I've used a starting power pack to power a laptop computer for a while, using the 12vdc socket that many have.

Perhaps you are thinking of a wall plugin unit that supplies DC to the GPS or game unit, but those units may come with a different cord and plug for car use

[BigNortherner]

"imtired", your duration numbers match mine approximately, for my Remstar bread loaf CPAP without humidifier, and would match its humidifier power rating if Respironics meant 1A at 115vac (considering your night was 8 hours gives 24 hours duration without humidifier, you got 1/4 of that with humidifier).

Good point about pure sine wave inverter, the CPAP device probably needs that which is the safe way given that you don't want to risk damage, a heater itself wouldn't but it your humifidier has control electronics.

Note your $200. battery is probably AGM technology, given it's "spiral wound" description (round cells inside it, which is a particular design of AGM), whereas a standard flooded lead acid battery might be half that price (depending on quality but definitely much less). Optima's spiral wound batteries would be better quality than Canadian Tire, for even more money. [I do not believe the "completely sealed" claim made by Canadian Tire, see my earlier post about relief valves.] Your battery may be a mixed-use battery as needed in some marine applications, a cross between automotive type starting use and pure deep-cycle use.

[nanwilson]

Hi Iamtired
Looks like we frequent the same CanadiaTire store.... they told me I could get by with an Eliminator 600A power pack. I thought it would be easier to haul 1 unit into and out of the rv, but I'm not sure now if it would be the best idea......................I'm REALLY confused now!!!!!!!
Cheers neighbour...Nan

[physicsbob]

Yes I would definitely recommend a deep cycle battery. I am currently using a 75 ampHour Deep cycle Marine battery, and I can get at least 24 hours (3 eight hour nights) on a charge using the humidifier on my M series machine. I use and would recommend using a "Float charger", these are designed to keep the battery fully charged and not over charge them. For a Deep discharge battery over charging them is worse than letting them go dead. I use this system to power my cpap for the last 2 months with the float charger charging the whole time. Next week I am using it to go tent camping where I expect to charge it every other day.

[BigNortherner]

"jenngirl", I may have mis-understood your point about the B&D unit. Some of the battery
power-packs meant for vehicle starting also have a "cigar lighter" type of DC socket that could
power devices that have the mating jack. That B&D unit you link to, more detail here http://www.blackanddecker.com/productgu ... =2#details, appears to have two on the left side of the front face. I've used mine a few times to run my laptop for an hour or so, using its manufacturer's DC power cord-brick, that's at least the draw of a typical CPAP unit without humidifier. However, they probably aren't optimized for that as their purpose is brief use to start the vehicle.
(The B&D unit is nifty in that it has recharger built in plus a light and air pump for your camping air bed.

The critical piece of data to calculate duration given amp-hours and voltage, or watt-hours, is the actual consumption of your CPAP device, which may vary significantly with pressure used. You need to get that information, or do a test which of course requires having a battery of known capability.

A year ago The CPAP Store was claiming "ResMed S8 Escape @ 10 cm H2O @ Sea Level, Ah Draw = 1.24 Ah" which is not in correct units - I assume Joe means 1.24 A. They claimed 9 hours from a 12.5ah battery for that machine draw (which calculates approximately correctly as 12.5 amp-hours/1.24 amps = 10 hours).

Note there is a run-time calculator on the page of the first battery pack you linked to, the
Respironics one. It shows over 14 hours for a Respironics Remstar Auto (no vintage specified).

They do not detail the battery design type, but given they claim no need to recharge for several months if sitting unused it isn't like a flooded lead-acid deep-cycle version, they say it is sealed, the charger is for lead-acid so I guess it is a gel type.

[BigNortherner]

Also, the S8 converter you linked to appears to be a conditionning unit to go from 12vdc to some other voltage, another efficiency loss and cost. In contrast, my Respironics Remstar Auto power cord is simple 12 volt DC cord with filter inline.

A question in my mind is how tolerant the CPAP machine is of low voltage. A 12 volt lead-acid
battery starts at well above 12 when fully charged but voltage drops as energy is taken out of
it.

Another variable is that capacity of a large battery is often rated at a current draw well above
your amp or three, such as 25 amps, so will actually provide more energy than the rating
indicates because at the lower draw less energy is lost in heating of the battery due to its internal resistance.

Note that some of the battery packs sold for CPAP use are lithium, which sounds more like a big version of a laptop computer battery - much more expensive than lead acid but lighter and
negligible concern about leakage.

[nanwilson]

Ok you guys, you are confusing the hell out of me. Just tell me if I did okay please.
I went to Canadian Tire this morning and bought a nautilus 10-2799-4 which has a 100 ah, for $124 aand an inverter. Did I get the right one????
Nan

[nanwilson]

IT WORKED LIKE A HOT DAMN!!!! Used the battery and inverter last night, turned off the humidifier and got 8 hours sleep. I have a battery charger, and I will use that to top up the charge after each use. I still need to get a meter,but thats cheap. Great investment for camping and emergencies
Cheers..Nan

[SleepyTiger]

Ok you guys, you are confusing the hell out of me. Just tell me if I did okay please.
I went to Canadian Tire this morning and bought a nautilus 10-2799-4 which has a 100 ah, for $124 aand an inverter.

Yes.

That battery can safely go 5 nights between recharges. (50% capacity).
That was a reasonable price for that battery and an inverter.

I'd need to know more about the inverter (pure sine vs modified sine wave) to know if you hit the right one,but it may not matter for your machine...

Sleepy Tiger

[nanwilson]

Thanks Sleepy Tiger
Its a modified sine wave inverter...does that make a difference?
Cheers...Nan