CPAP on a battery

I love to camp and travel however sometimes we are without electricity. I bought a 425 power inverter and hooked it up to a car battery. This works great but I'm finding the car battery is heavy and hard to carry around. I'm asking if anyone has used a motorcycle battery or some other power source to run their cpap while out camping. I know their are some specialized batteries out there but the price is staggering. Any ideas? thanks

One of our members has a post on this subject. viewtopic/t114012/Choosing-a-Battery.html

Do check out the thread OkyDoky mentioned. If your machine can run off of 12V DC, you should be doing that instead of using an inverter. You'd just need a cable for that, or perhaps a DC to DC converter if it runs off of higher DC voltage. You're losing probably 30-40% in the conversion from DC to AC. You might want to fill out your profile with your equipment and we can tell you if it can run on DC. This extra efficiency may allow you to take a smaller deep cycle battery (or use what you have for a longer time without a recharge). In general regular car batteries are not good for this kind of service. Read the post mentioned, it talks about what type of battery is appropriate.

Awesome thread above but I have to ask a question in a slightly different direction... Assume I'm driving an RV that runs entirely on battery but recharges from alternator driving everyday. I don't use AC power much so I have a cheap 400W 12VDC to 120VAC inverter for nuisance AC needs. I don't care about efficiency losses since the battery easily recharges, so its not worth building a stepup PCB and custom plug to run CPAP when it can just use its normal 120VAC adapter.

Now, my question is whether this setup is still bad for the CPAP. I've been told that the almost certainly blocky sine approximation of the inverter may overheat / stress the CPAP's "laptop type" switching power supply transformer. Is this true or do you think various regulators in the chain would handle any such oddities?

wolfnrose wrote:Awesome thread above but I have to ask a question in a slightly different direction... Assume I'm driving an RV that runs entirely on battery but recharges from alternator driving everyday. I don't use AC power much so I have a cheap 400W 12VDC to 120VAC inverter for nuisance AC needs. I don't care about efficiency losses since the battery easily recharges, so its not worth building a stepup PCB and custom plug to run CPAP when it can just use its normal 120VAC adapter.

Now, my question is whether this setup is still bad for the CPAP. I've been told that the almost certainly blocky sine approximation of the inverter may overheat / stress the CPAP's "laptop type" switching power supply transformer. Is this true or do you think various regulators in the chain would handle any such oddities?

It would have been really nice if you mentioned the model, or at least the brand of your CPAP. I'll assume you have a newer Resmed, S9 or later. There are older models that do require a pure sine wave.

Although there claims of problems with "Modified Sine Wave" or MSW inverters, they invariably involve certain power tools or sometimes a bit of RF noise. Of course, anyone who paid a lot for a pure sine wave inverter will tell you it was necessary for piece of mind. Certainly the seller slept well after providing it!

I've spent extended periods living on battery power on a boat. All my inverters have been MSW and I've only had a problem once with a power tool. I watch TV and charge computers daily with power bricks and never had a problem. If you don't use a humidifier, you're only using 10-20% of the capacity on the power supply, so it probably won't even get warm.

However, If you do use humidity, you should be careful. Although the power supply should work just fine, the load on you battery is not trivial. If you use a high setting, that could be 30 Amp-hours. With an inverter, that load could be doubled. If you have a single deep cycle battery (about 100 AH), that's a significant load. Even with two batteries, if you add in an evening of TV or computer use, plus lights, etc. you're adding significant wear to the batteries. Even recharging underway could add a load to the engine. On my boat I only have 18 hp engines, so I have a switch to turn off charging while underway if I need full power. I'm sure you have a larger engine, but I've heard of overheating problems climbing hills, so the extra load of the alternator could have an affect.

One other problem, the failure rate on cheap inverters is high enough that I consider them disposable and always have a spare (or two) ready to go. Given the issues, I think of them as a necessary evil to be used as a last resort.

If you have a Resmed, you can get the 12V adapter for only $85. (Why would you even think making one yourself???) This would probably pay for itself in reduced wear on the system.

I just looked up your "also posted as amandah72" user and found you use a Dreamstation from Respironics. If that is true, you should get the 12V adaptor for $24. Using an inverter in this case is foolish!

Thanks for the fast response... My original post splattered and reposting from memory lost some info. I have no idea about the "also posted as" bit since I'm brand new here.

I had originally said that I use a ResMed airsense 10, which is 24 volts through an HP laptop style power plug. The reason I would make an adapter myself is that I can get a step up PCB for a couple dollars, as opposed to the $90 from Resmed. Just a convenience/complexity issue.

My trailer has 200mah batteries, a 650A alternator, spun by a 600hp motor. I current limit the house battery charge line not for engine loading, but to prevent charging too fast!

My unferstanding of the potential harm is overheating the Resmed's ACtoDC brick, not the DCtoAC inverter. It also occurred to me, when you mentioned redundancy, that I actually carry smaller inverters as well... I have a jumper pack with a 200 watt and the truck has a 150 watt on the dashboard (although I suspect that one turns off with the ignition). It's always possible that the sine output of one of the smaller ones might actually be better quality or more efficient, being closer to be desired wattage. I may just have to play and see what it looks like, using the theory that "Electronics getting hot is bad."

The ResMED connector is Proprietary, DON'T use a generic connector.

bonjour wrote:The ResMED connector is Proprietary, DON'T use a generic connector.

So is the Respironics, at least the one for the DreamStation.

bonjour wrote:The ResMED connector is Proprietary, DON'T use a generic connector.

meh, it's reportedly easy enough to do.

wolfnrose wrote:Thanks for the fast response... My original post splattered and reposting from memory lost some info. I have no idea about the "also posted as" bit since I'm brand new here.

The "also posted as" is probably because your IP address has been recycled. If you create a user account it won't happen and you can identify your equipment.

wolfnrose wrote: I had originally said that I use a ResMed airsense 10, which is 24 volts through an HP laptop style power plug. The reason I would make an adapter myself is that I can get a step up PCB for a couple dollars, as opposed to the $90 from Resmed. Just a convenience/complexity issue.

Right. It doesn't work - its not HP style, its a proprietary plug that identifies how much power can be supplied.

wolfnrose wrote:
My trailer has 200mah batteries, a 650A alternator, spun by a 600hp motor. I current limit the house battery charge line not for engine loading, but to prevent charging too fast!

I'm guessing you mean 200 Amp-hours, not milli-amp-hours! Well, 600 hp is certainly plenty of power. If you're afraid of overcharging perhaps you should get a smart regulator.

wolfnrose wrote: My unferstanding of the potential harm is overheating the Resmed's ACtoDC brick, not the DCtoAC inverter. It also occurred to me, when you mentioned redundancy, that I actually carry smaller inverters as well... I have a jumper pack with a 200 watt and the truck has a 150 watt on the dashboard (although I suspect that one turns off with the ignition). It's always possible that the sine output of one of the smaller ones might actually be better quality or more efficient, being closer to be desired wattage. I may just have to play and see what it looks like, using the theory that "Electronics getting hot is bad."

I'm surprised you would be more concerned about damage to the power brick from a MSW inverter, but willing to trust the pump to a homemade power supply. The only way I would be remotely concerned is if you're running at top power, that is, using a humidifier on full. And that's the situation that calls out for the ResMed 12-24 converter.

And just curious, do you really travel every day? You never stop at a place for two or three days?

CapnLoki wrote:Right. It doesn't work - its not HP style, its a proprietary plug that identifies how much power can be supplied.

I'm sure I can replicate whatever it's doing, but extra signalling/voltage splits complicates things a little bit more... :-s

CapnLoki wrote: I'm guessing you mean 200 Amp-hours, not milli-amp-hours! Well, 600 hp is certainly plenty of power. If you're afraid of overcharging perhaps you should get a smart regulator.

Already there... I wasn't going to complicate the background, but I also have solar and 4KW gas-generator on this rig. The towing truck's charge line runs through the solar's charge controller, which is set to cap incoming amps to avoid boiling the batteries when I (usually) have plenty of time to charge at a slower rate. That said, I'm pretty sure there has to be some limiters already in place somewhere else in the truck, because (400+250 dual alternators) should never be allowed to put out all 9000W of power through most of the truck's wiring. Only had this truck for a year, but I'm not sure what (besides maybe a HUGE inverter to use the truck AS a 9KW generator?) would use all that power the alternators COULD put out.

CapnLoki wrote: I'm surprised you would be more concerned about damage to the power brick from a MSW inverter, but willing to trust the pump to a homemade power supply. The only way I would be remotely concerned is if you're running at top power, that is, using a humidifier on full. And that's the situation that calls out for the ResMed 12-24 converter.

I'd confirm correct voltage and amperage carrying, but otherwise have pretty good faith in my electronics DIYing. Probably foolishly overconfident...

CapnLoki wrote: And just curious, do you really travel every day? You never stop at a place for two or three days?

Strictly, I do stop occasionally, but it again muddies my question! I tend to use the trailer traveling cross-country (I *hate* flying since TSA and tiny seats make it miserable, and it's actually cheaper to drive my 6 tons 3000 miles!). Therefore, MOST of the time, I'm "boondocking"/pavement camping at Walmarts while in transit, or staying at state parks without hookups. Even if I run genny or collect solar to charge up during the day, I can't do either at night when running the CPAP, so it's still going to be running from battery power. If you're saying I'll run down my battery bank doing this for long and not charging batteries *somehow*, of course! Sometimes I'll plug in at a friend's house or client's site once "there", but having AC available at night is comparatively rare. I never cared much before, but I just starting using CPAP last year and going a couple nights without it DOES noticeably "feel bad" increasingly. I'm probably being cheap not springing the $90, but I like saving money anywhere I don't need to spend it IF my jumper-inverter will suffice.

BTW: I have all KINDS of electric metering on my rig, and know that my CPAP draws a hard maximum 90W when running at full ("17" unitless, which I assume is Inch-Water-Column since it's NOT PSI?) pressure with humidifier (and presumably some heater -- which doesn't seem to allow below 65F no matter how cold I sleep). At 90Wx8hrs, 720Wh of my available 2400Wh bank. Even allowing max consumption and reserving 50% drain to protect the batteries, running all night seems pretty safe capacity-wise. If using the jumper, it has it's own 80Ah battery being patched in as well (though, probably more starter-type than deep-cycle...hmm... maybe better NOT to run that down so hard if not patched into main bank...).

Ah! Too much spit-balling, not enough data... :-S Maybe I'll just run from the jumper tonight for a couple hours, set an alarm to check temps and charges, and see how it's doing. No one has screamed "No, don't ever use an inverter with these units!", so it must work "well enough" for most people...

A little shopping may have answered my original question... ResMed actually sells a 150W MSW inverter for use with their own 12V lithium battery packs ($60 for the same inverter I get for $7... ahem!). They caution that the battery life will suck, but that it's fine to use their battery with their inverter to run their AC power brick to run the A10... So, not efficient, but their brick IS compatible with an MSW inverter without burning up. You'd really HOPE that's the case for a $1000 CPAP, but many laptop bricks don't like MSW and we are way-close in technology here.

That said, I think I do like the efficiency standpoint the more I think about it -- even if I CAN recharge my batteries every day, it's a shame having to waste solar or gas to do so... :-S

A little research finds a 150W step-up (boost) DC-DC converter for $3 delivered on aliexpress. I'd allow that overshoot since you don't want to run these boost converters at 100% of spec for long... so, $3 and whatever physical plug is needed replaces the $85 ResMed power cord... For $5 or so, you can even have a boost PCB with LED voltmeters to monitor you're not browning out / monitor the input battery voltage... that's a BETTER device for off-grid usage, at 1/16th the cost... Hmmm.... Gotta read that ResMed patent/spec link on the plug again...

wolfnrose wrote:A little research finds a 150W step-up (boost) DC-DC converter for $3 delivered on aliexpress. I'd allow that overshoot since you don't want to run these boost converters at 100% of spec for long... so, $3 and whatever physical plug is needed replaces the $85 ResMed power cord... For $5 or so, you can even have a boost PCB with LED voltmeters to monitor you're not browning out / monitor the input battery voltage... that's a BETTER device for off-grid usage, at 1/16th the cost... Hmmm.... Gotta read that ResMed patent/spec link on the plug again...

you'll need a 47k resistor (reportedly) between +24 and the center sense pin, else it'll turn it's nose up at you and ignore the power... much like my notebook doesn't like 90 watt power supplies with the exact same connector, runs but won't charge the battery... has to have the 170 watt ps. (same connector as the resmed machine, btw.

FYI, for other crazy people wanting to experiment with DIY 12V to 24V adapter:

$2.64 delivered, 150W boost converter:

http://www.aliexpress.com/item/150W-DC- ... 47286.html

$3.99 delivered, 100W boost converter with LED voltage displays (best if NOT using humidifier/heater):

https://www.aliexpress.com/item/DC-DC-1 ... 55003.html

Now I just need the plugs... I *think* it's a 7.4mmx5mm (gotta check when at CPAP), but if so here's a wired plug with (yes!) three wires... which I suspect are intended for just the 20-47K resistor bridging we've been discussing...

https://www.aliexpress.com/item/2015-DC ... 81485.html

If this works, it's literally $5 to recreate the $85 adapter...

wolfnrose wrote:FYI, for other crazy people wanting to experiment with DIY 12V to 24V adapter: ...

There was a recent thread here with someone who wanted to build a converter, including figuring out the third pin characteristics. After getting a disheartening response, he deleted his posts and moved the discussion to apneaboard where a few others helped design a board. A prototype was built and briefly tested, but as far as I know, no one actually used it for a night. As I've mentioned, the issue was not producing the 24V, its replicating the signal wire, which seems to identify the nature of the power supply. There have been differing opinions on how this works. Personally, although I understand the academic curiosity aspect of this, I see no need of a half-assed solution to a problem already properly solved, albeit somewhat pricey.