WARNING to CPAP Users: PREPARE for the Unexpected - When the power goes out

[SuperSleeper]

I am currently using an APC modified 120V sine wave UPS, with a internal sealed VRLA 9AHr battery, which will give me a few hours of AC upon a power outage, according to the Resmed "Batttery Guide".

ResMed recommends only using lead-acid deep cycle batteries in their Battery Guide.  I'm wondering how  you came to the conclusion above?  A 9 amp-hour lead acid battery cannot be "fully" used up without major damage to the cells.  (meaning, if you have a grid power outage, you're not going to be able to get anywhere near 9 hours at a 1.0 amp draw and still have a good battery afterwards.  Why is that?   Because even on deep cycle lead-acid batteries, for good battery life,  you should not allow your battery to get much below a 70% charge (roughly 12.3 volts, open terminal).  If you run a lead-acid battery down to 30 or 40% of charge, you'll greatly reduce or even destroy the capacity of the battery.  Yes, you may be able to re-charge it and have it go back up to over 13 volts open-terminal, but an open-terminal reading is not the same as a reading done under load. That open-terminal reading gives you a false sense of security.  You'd have to get a 12-volt load tester to get an accurate reading.

For this reason, I would never get the "minimum" amp-hour battery that you can get away with.  You're not going to be happy with the result.  Most of the people here who claim that their small amp-hour battery or UPS worked for them "just fine" have not FULLY tested their emergency setup.  You might be able to get away with drawing down your lead-acid battery below a 50% charge for one night for instance-- and most people who say their system operated "just fine" by doing that-- those folks have NOT tried to do this more than one or two nights, for if they did, they would soon discover that their lead-acid battery had an extremely reduced capacity (meaning, they damaged their battery).  Keep in mind, the only way to properly test your battery capacity is with a good load tester, not a simple volt meter or open-terminal battery tester.  So it's easy to think you're okay, when in fact, you're not.

In addition, the amp-hour rating on a given battery is not necessarily the same thing across different brands or types of batteries.  For instance, you can't simply say "This battery has a 100 amp-hour rating".  Why?  Because there are different methods used to measure amp-hours.  You have to ask "Is that amp-hour rating for 15 minutes, 10 hours or 20 hours?"  Battery manufactures can easily bamboozle the public by claiming their batteries have more capacity than another similar battery.  The industry standard for lead-acid deep cycle batteries is to use the 20-hour rating when calculating amp-hour ratings.  Make sure you understand the difference and the  TRUE rating of your battery.

For good battery life, I'd recommend using a deep cycle lead-acid battery that is at least 3-4 times the "minimum" 20 hour amp-hour rating given in the Battery Guide for the desired run-time.  That Battery Guide is your minimum baseline - a minimum for safe operation of your ResMed CPAP machine.  It does not take into account the fact of potential damage to your battery if you discharge your lead-acid battery to low levels.  In other words, they're only mainly concerned with how amp-hours affects their machine, not how such operation will affect your battery.  Lithium-ion batteries can be discharged to very low levels and still be okay-- but that is NOT the case with lead-acid batteries, including lead-acid deep cycle batteries. In fact, if you look at the documentation from deep cycle battery manufacturers, they usually recommend you DO NOT allow your deep cycle battery to go much below 70% of full charge.

Personally, I use two 6-volt golf-cart deep cycle batteries hooked up in series, which raises the voltage to a 12-volt system.  Each of my two batteries has a 105 amp-hour rating at the 20-hour rate, which, when in series, has the same 105 amp-hours system-wide.  This system will allow me to use my AirSense 10 AutoSet (without a heated humidifier) for 2-3 nights without deep-discharging my batteries below the recommended levels.  And, since my batteries are connected to my solar panels via a charge controller, they usually charge back up to 100% if there's any sun at all during the daytime, even on relatively overcast days.  My batteries are similar to the name-brand Trojan brand golf cart batteries which come highly recommended by many Recreational Vehicle owners for instance.

Also keep in mind that leaving a live grid-powered lead-acid battery charger of any type (trickle or otherwise) on a battery that is actively powering a CPAP machine might very well damage your CPAP machine, unless your CPAP is designed for a wide range of voltages.  The 14.5 volts pushed into the circuit via a grid-powered battery charger doesn't just "go into the battery".  It goes everywhere the circuit goes, including your converter (if you use one) and CPAP machine if it can operate directly on DC power, assuming if it's on and attached to the battery.  So it's very unwise to use a live, plugged-in battery charger with a 12-volt battery that's also powering a CPAP machine at the same time (attempting to use such an arrangement like an Uninterruptible Power Supply).  If you attempt this, make absolutely sure both your CPAP and converter can handle voltage fluctuations, including the higher voltages associated with a grid-powered battery charger.

Bottom line in all this is:

1) It's best to use a lead-acid deep cycle battery to power CPAP off-grid (using a DC converter, rather than an DC-AC inverter, as mentioned by Red, above).

2)  Never actively charge ANY battery (lead-acid, AGM, Lithium, or others) while at the same time powering your CPAP machine, unless it's UPS that's designed for that very function, or on a solar powered system with a good charge controller.  But keep in mind, most household/home office UPS devices are woefully inadequate for powering CPAP for any length of time due to the low amp-hour rating of the batteries that go into UPS devices.

3)  If you use a Lithium-ion battery, NEVER leave it plugged in and charging unattended (for fire safety).

4)  While you can discharge a Lithium-based battery to lower levels, you cannot do that with a lead-acid battery often without damaging your battery.

[snorin2]

Thanks Super for the excellent comprehensive analysis. In my case, I am bothered mostly by "blips" in the power supply: 1 second to 20 seconds. My Resmed starts up again but it takes 2 minutes to reboot after the power interruption and I think that wakes me up. So I set up an entry level UPS. It solves my immediate problem but I'm of course looking for a solution to a longer power outage. I was really interested in one of those mini UPS's that work only on 12 volts (no inverter) but there is no info on how they work (or whether they actually have some electronics to actually switch the electric route). I suspect that they just charge all the time and the CPAP might just take the juice from the battery as needed.

Anyway, given the posts showing the fire hazard of lithium, I think we (I) should be looking at lead acid, particularly at home where you don't need to move battery very much. I think other posters have had good success with a lead acid battery continuously kept up to charge with a QUALITY automatic battery trickle charger while the battery is hooked up and sending juice to the CPAP and I have heard that this system doesn't kill the battery. Personally I am not prepared to use it though until I can get a handle on the risks.

I thought the DC to DC converter was good from somewhere around 10.5 volts to 22 volts although my memory on this is probably bad. Just as the AC to DC converter is pretty robust I thought the DC to DC converter was as well. What do you think? What about all the people continuously using their phones while they are charging them up--mind you those are lithium batteries. I am a rookie with this stuff but it would be nice to find out exactly how this charging system works if your using the CPAP at the same time.

[SuperSleeper]

All I'll say is that there is a reason for the special circuitry inside of a UPS.  It's designed to protect your equipment from quick voltage surges and spikes that can come from an increasingly unstable electrical grid, or power line instabilities (for instance a lighting strike nearby, or the sudden on-off-on-off nature of some blackouts or low voltage brown-outs).

Even though the ResMed converter can operate using two separate in-bound DC voltages (12v or 24v), it's designed to operate on relatively stable lead-acid battery voltages, not large swings or rapid fluctuations in voltages that can occur with a grid-powered battery charger, especially the common pulse-type 12-volt chargers designed for lead-acid batteries.    You could easily damage your CPAP machine should there be a failure of the converter to clamp down a voltage spike in a timely manner.  And the ResMed converter is not designed to operate like a UPS.

It's much, much safer to fully charge your battery, then unplug it from the grid, and then plug in your CPAP (with converter if it needs one) to the battery supply (without being connected to battery charger during operation).

The only situation where a "battery charger" can safely be attached to your battery while simultaneously powering your CPAP is when there is a device controlling the outbound current to the CPAP (ie- a UPS-like device, or a DC solar charge controller in a solar-panel/battery setup).

That's all I say for now - if you decide to attach your CPAP in any way to a grid-powered 12-volt lead-acid battery charger while it's in operation, you may end up with a doorstop when Mr. GridSpike comes to visit your home.  

[Regular Joe]

I have a Portable Outlet UPS model PO-160UPS. So far, it's worked well. We had one outage around Christmas, and it worked perfectly. Never knew the power was out. It was only about two hours though.

[SuperSleeper]

I have a Portable Outlet UPS model PO-160UPS.  So far, it's worked well.  We had one outage around Christmas, and it worked perfectly.  Never knew the power was out.  It was only about two hours though.

That PO-160UPS is a Lithium-Ion battery, with a built-in UPS circuitry, designed for CPAP use for $359.   This unit is okay for when the power goes out for roughly one night only on most standard CPAP machines operated without a heated humidifier.   Lead-acid systems will give you multiple nights if what you're looking for is longer-term power outages.  

From this Amazon listing:

BATTERY LIFE- Portable Outlet CPAP battery is really the best in the market because it has a battery timing of 7 to 9 hours for a home-based CPAP system and 12 to 18 hours for a travel system, NOTE: With heated tube and heated humidifier turned OFF

Lithium-ion systems are fine if you want to accept the fire risk of using a larger grid-attached Lithium-ion battery.  Keep in mind that these are substantially larger-capacity batteries than your cellphone or mobile device, and can produce larger fires if something goes wrong (see video in my previous post).  If you use this system while it's attached to the bedroom outlet, definitely have a smoke detector and ABC fire extinguisher in your bedroom and never leave this unit plugged in to charge unattended or when you're away from home.  With these Lithium systems, you're trusting that the manufacturer had really good quality-control and excellent components in their circuitry and wiring.

Most of the discussion and recommendations I've given thus far have been to suggest lead-acid deep cycle batteries rather than Lithium-ion.  They're much safer and will give more run-time for multiple nights for the same amount of money.  And I've also warned against using a standard 12-volt lead-acid battery charger while it's attached to an operating CPAP machine (in an attempt to approximate a UPS).  It's not designed for that like this PO-160UPS is.

But if you don't mind the risk, and are only looking for a simple system to cover short-term power outages (one night or so), then this system might work for you.

Are you starting to get the idea that I don't trust charging Lithium-ion batteries unattended?  

[snorin2]

thank you Super: very good point about those pulses in the battery chargers.  I'm back at the starting point. I would like a simple and inexpensive solution to a longer battery charge --like everyone else.  I am not good with electric stuff; do you think I could rewire the entry level UPS to a larger battery? I  would like to avoid paying the premium for a large battery UPS.

[jerrykur]

Useful thread. I am in Northern California. We are seeing wave after wave of heavy rain, flooding, and power outages. We have a battery backup for the house, but I am new to CPAP (3 months) and worried about the effects power dying while on CPAP. Now thinking about adding a small UPS to my CPAP setup.

[Crimson Nape]

UPS systems will shut down all connected devices when it runs out of power.   Based off your hazard description, power outages could easily last longer than 20 minutes.  

Since you have a Resmed, it would be to your advantage to get a deep cycle lead acid battery, a 12/24 Dc-DC power supply, and a battery tender.  Battery tender devices are a little different from battery chargers and will maintain a longer battery life.  With inflation, you can probably expect to spend around $200 to $250 USD for this setup. You can use this power configuration all the time without any problems. If the power should fail, you may never know it until you awake.

- Red

[WakeUpTime]

I'm always living in fear of any sustained power outage.  Luckily, my outages are only about 3X/year and last 6-12 hours.  I resort to no-sleep and the zombie effect for the next day, along with taking another day or two to get back to a traditional CPAP sleep.  I have another benefit in that I have a somewhat independent work schedule these days.  Zombie living, with a few hours off nightly CPAP, makes for a mistake-filled day.

CPAP therapy needs to be seen as vitally more important than merely an effective sleep aid.  In my experience, for most, it is a life sustaining medical device.  Going off CPAP for a period of time, for many, is damaging to their body's internal functions (later hatching as other issues) and dramatically affecting basic brain functions (reaction times for driving, memory, etc.).  

Most probably know that they can search Amazon comments for specific words.  When looking at purchasing a specific backup power device, it's insightful to search for all the comments from purchasors who included the term "CPAP".

Some areas have had terribly lengthy power outages, and lately in areas outside of traditionally problematic outage regions.  It's amazing that most don't think of their CPAP in their Emergency Preparedness Plan.  Having a backup plan (backup device, backup energy source) is extremely important.

Thank you to those posting their CPAP backup strategies.

[SuperSleeper]

Since you have a Resmed, it would be to your advantage to get a deep cycle lead acid battery, a 12/24 Dc-DC power supply, and a battery tender.  Battery tender devices are a little different from battery chargers and will maintain a longer battery life.

Hmmm.. This is essentially attempting to use such a system as a crude UPS.     I wonder if the circuitry in a CPAP would be able to withstand the voltage variations for longer periods of time when attached to a battery that's actively attached to a grid-tied Battery Tender.  

I'd be interesting in hearing from someone who has actually used a Battery Tender with this kind of lead-acid battery setup for a long period of time (over two weeks for instance).  I wonder if such folks experienced any issues or damage to their CPAP machine?  Battery Tenders are basically trickle chargers with some additional circuitry, usually including a desulfation mode which has large voltage pulses.  They claim it's okay in most cases to attach them to actively working systems, but most of their references refer to automotive use, not medical devices.