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

[Crimson Nape]

I have been using this setup for over 3 years.  A check of the battery with a load type battery analyzer showed excellent health.  I also use the same type (and brand) battery tenders on my backup generator and lawn mower.  So far, being on the generator for 5 years unused, it fired it up without any hesitation.  I'll be a happy camper until it doesn't work.

- Red

[SuperSleeper]

I have been using this setup for over 3 years.

Red, do I understand correctly you've been using a Battery Tender to charge your 12 volt lead-acid deep cycle battery while that same battery is actively and simultaneously powering your CPAP machine via the ResMed DC converter while you sleep?  And that's what you've been doing for over 3 years?   (Never unplugging the Battery Tender from the wall outlet or the 12v battery while that same battery is also attached to your running CPAP machine via the converter)?  

Battery chargers have limited output current and usually apply a higher voltage when charging (anywhere between 14-18 volts) to make up for the series diode drop and any line losses. Pulling a good load from the battery while the charger is attached will likely trigger the over-current protection (best case) on a good quality unit, or cause failure for the cheaper brands.  Less risk if using a small trickle charger, of course, but it's always best to have a stable input voltages for a running CPAP machine, rather than voltages that go up and down due to the various cycles of common battery chargers.

While most 12 volt devices can operate in a relatively wide range of voltages - (11.x volts up to around 14.x volts),   going up into the 18 volt DC input range could easily damage equipment, unless there's a device in between the battery and the CPAP to control that charge.

But if this has seemingly been working for you for over 3 years, I would think that the only reason it hasn't damaged your CPAP is because of the quality charge controller circuitry in the ResMed converter device you're using to protect the CPAP.

That might work for newer ResMed devices (since they use the proprietary converter), but my older Respironics CPAP machines (old REMstar and System One devices) could operate on direct DC current (12-volt, no converter needed).  I would not recommend charging a deep-cycle lead-acid battery while powering those types of devices at the same time, because there's no circuitry to control the charge (like there would be using a ResMed converter).

[RayBee]

Battery Tenders typically trickle charge at only 1.25 amps. Then once fully charged they only feed a very light float charging current to keep the battery topped off at its optimal fully-charged level. Their design is specifically engineered to not boil out batteries, and are very gentle with lead acid batteries. Some of their chargers are designed to charge at 2, 5, 6 and 10 amps. But for automotive, deep cycle marine grade batteries or golf cart batteries, that's still pretty gentle. And they will also slow to their float charge current as the particular battery under charge exhibits the need. The rather low Battery Tender charge current results in a very gradual voltage rise until it goes into a float charge maintaining a specific maximum voltage.

They are an excellent choice for any lawn mower battery, and larger, to maximize a lead acid battery's life.

I doubt the OEM ResMed 37297 and the Chinese knockoffs would care much about battery fluctuations either. They would be designed as switching power supplies and are not prone to caring much about dirty input or variations in supply voltage. As would be the same with ResMed's AC power adapters. If one of these 12 to 24 v adapters fail, its probably a one-off bad apple. Having said that, I would only buy an OEM ResMed product. Downstream is too precious a commodity to be feeding it from a cheap Chinese power supply.

[SuperSleeper]

Agreed, Ray.  The ResMed converter (in these cases) is acting to protect the CPAP circuitry, since it can deal with those voltage fluctuations.  My precautions are against making a blanket statement that you can put a 12-volt battery charger on a battery that's actively powering a CPAP machine -- that is poor advice because it won't work in all cases.

Because first of all, it depends upon the specific battery charger and the output voltage.  Small "wall-wort" Trickle chargers are best of course, but you have to take precautions to make sure folks don't use any old 12-volt charger while attempting to power their CPAP simultaneously.

In addition, the Respironics CPAPs could be powered using direct 12-volt DC current.  There is no extra in-line converter or controller required on their devices, thus higher voltage inputs on those machines could damage them, because they don't have the same charge controlling-activity that the ResMed brand DC converter has, which provides for a degree of protection for the CPAP.

Also, I'm also concerned about the automatic  "desulfating" modes of these small trickle chargers-- it's my understanding that they use pulse technology to shoot higher voltages into the battery for desulfating purposes.  That pulsating voltage change could easily damage a medical device, if it's connected and operating at the same time, could it not?

I wouldn't think that widely-varying, rapid voltage changes associated with the pulse (desulfating) modes of these chargers can be good for electronic circuitry over the long-term.  I'd be willing to bet that actively charging a lead-acid battery while simultaneously operating the CPAP machine would likely void the manufacturer warranty as well.

[RayBee]

IMHO, the best battery choice would be a LiFePO4.

The Pro’s:
They don’t outgas.
They have exceptional longevity of 10+ years.
They are encased in heavy plastic housings like a gel cell.
They each have built-in smart charge/discharge circuitry.
They live happy long lives being discharged down to 20%.
Their voltage does not drop much - all the way down to 20%.
They are very lightweight.
They can be charged with standard gel cell chargers (but they won’t fully charge).
Their price is exceptional given all their Pro’s listed above.

Con’s:
Some might think they are a little pricy.

My dream system if I were to cobble one together would be…
Get an inexpensive power checker and check your CPAP’s power usage over several nights. They are $20 and up.

Base the LiFePO4 size on the load measured plus some overhead margin, say 20%+. Consider your hours needed (or several nights if camping for instance).

Get an appropriately sized LiFePO4 battery. I’m approximating for my ASV with using the heated line and humidifier, I would need a 50AH battery. About $140+. I rarely go over 6-1/2 hours per night.

I’d match it up with a LiFePO4 charger of 10 amps. About $60+. (20% of battery capacity is fine - plus or minus - don’t worry about it.)

Then I would find the best price for an OEM ResMed 12 to 24 volt supply. $75 or so.

All-in, maybe $300+ with tax.

Down-size the battery and charger accordingly if you don’t use the heated tube and heated humidifier.

Another benefit with the LiFePO4 battery is that since they have their own built-in smart charge/discharge circuitry, you can increase your run time by paralleling another battery with the first. And they don’t have to be the same capacity. So if the 50AH doesn’t provide enough run time, slap on a 20AH and you have 70AH total. They will cohabitate just fine together. And the charger will be fine too. It will just take a little longer to charger the added battery, so in this scenario, maybe 7 hours instead of 5 hours for well discharged batteries.

Of course all of this would be applicable for my ResMed ASV. I think my scenario is kind of a power hog. You can size a system with the power usage monitor and perhaps size it accordingly for a certain number of days, or hours,  depending on your needs. And just add more batteries for more hours or days accordingly. Increase charger size if needed. (Probably not necessary thought.) It’s all just a numbers game from there - what you need or want, and what you can afford.

I like reading about what people are actually using. But I’d like to see more specifics of what machine it is and settings used. Using (or not) a heated hose and/or heated humidifier. If so, state the settings used. How many hours tested. How many days tested. Number of days used between charge cycles. How long your system been in service. I’m sure I’m missing a few things.

Reference ResMed Battery Guide

I’m specifically not posting links to products because the links will probably not work at some point in the future. So do some research of the stuff mentioned above and find your best price versus quality.

[SuperSleeper]

Yep, although I have no first-hand experience with them, from what I've read, I'd trust Lithium Iron Phosphate (LiFePO4) over Lithium-Ion for sure. 

In fact, at the end of the lifespan of my current deep cycle lead-acid batteries for my solar panel system, I'm going to be looking at LiFePO4, assuming they've established a long-term clear record with those types of applications.

LiFePO4 isn't going to start your house on fire when charging unattended, and longer lifespan as well.

The only potential issue I see is a problem with the world supply of Lithium in general, due to a number of economic/political issues and the fact that there's been a huge increase in Lithium-based battery usage around the world, further affecting supply chains.

But, it looks like a great option.

[snorin2]

Have there been any fires with the LiFePo4 batteries?
I am guessing that the LiFePO4 fires are similarly difficult to put out?
Are they used in electric vehicles? laptops? scooters?
I was looking forward to using them for my next CPAP battery system but the "fire" posts have made me nervous about Li batteries.
Do I gather that your enthusiasm does not extend to charging at the same time as being used for the CPAP even with the "safety" charge/discharge built in features referred to. The Jackery customer service definitely says not to do it. I'm guessing they were covering the Li battery product.
Having read the "fire" posts, I would feel uncomfortable in leaving the battery (perhaps unatttended from time to time) or all day to charge and then plugging in every night

[SuperSleeper]

Do your own research regarding fire safety, but from what I understand the LiFePO4 batteries are much safer than Lithium-ion batteries in terms of fire risk.

LiFePO4 has been used more recently in a wide variety of applications, including electric vehicles.   They've been around since the mid-1990's, while Lithium-ion was developed about 4-5 years prior to that.

Probably the reason that the Jackery customer service says don't charge their Lithium-ion battery system while simultaneously actively powering a device is because they don't want to be held responsible for any potential damage to your device, and their product isn't really designed for that type of operation.

[RayBee]

I have no problems with the safety of LiFePO4 batteries. Most fires with lithium batteries stem from charging them on non-lithium specific chargers. And some lithium batteries just simply fail - very few that is. Since lithium ion batteries are packaged in a thick clear plastic wrap, they will puff up when unhealthy for whatever reason - age, misuse. The bare cells have no such charge/discharge built-in protection. I use lithium ion batteries in my radio control model helicopters. And they are the standard battery of choice in millions of radio controlled model aircraft. Millions are in cell phones, laptops and tablets across the world. We don’t give a second thought about charging those devices unattended.

Let us say that there are 0.00001% (pick a very small number) of these batteries that catch on fire for any reason and burn down a house. I’m not saying that’s the actual percentage, but what’s going to make the news? You’re never going to read about the billions of lithium batteries that live long useful lives, only the one that burned a house down.

What I am saying is that we as intelligent people, using lithium batteries correctly are getting way too excited over something that is statistically likely never going to happen. Your chances of getting struck by lightening is probably higher.

Early on, lithium ion batteries were given a bad rap due to fires. But the few that get notoriety are very few. Spectacular and devastating results occur when they do burst into flames, but if used correctly and charged per manufacture’s specifications, the chances of a spontaneous fire are very remote.

In the model aircraft world, there are special fireproof bags you can buy to put your battery into during charging. Others use a metal ammo can. Most all modelers remove them from their aircraft for charging. The model radio control hobby world was probably one of the most misunderstood and abusive to lithium ion batteries. Most critical were new modelers with old-school nickel based chargers and not realizing that they can’t use them on lithium batteries. That’s almost a guaranteed fire. It happened all too often early on.

Ok, sorry for getting lost in the weeds. But I thought I’d share a little side project I’m putting together. It is a set of three solar powered attic vents. Home grown, not store bought.

I got a 255 watt solar panel and am going to power three 12 volt, 80 watt, 12-inch fans made for car radiator use. I’m using a Victron Energy SmartSolar MPPT 100V 20 amp solar charge controller. (Click here for Victron Energy Manual) My battery is a 12 volt 20AH LiFePO4. I am using an Arduino and five INA226 voltage-current-power monitors on the solar panel, battery and each of the three fans. The Arduino will also monitor attic temperature at several points and control the whole system. My own little personal experiment dabbling in the solar powered world of things.

Anyway, this little project would be perfectly adapted to powering an off-grid CPAP system. Scale it up to power whatever else you can think of. By the way, the 20AH battery is amazingly lightweight.

Also, on another note. I have a Liftmaster 8500 garage door opener with Liftmaster 475LM battery backup. The Liftmaster 24 volt backup had two 12 volt 4.5AH gel cells in it. I was replacing them every four years like clockwork. I just replaced them again but with LiFePO4 batteries. The will live happily on the Liftmaster gel cell charging circuit, but will never fully charge. However, for the same physical size, I got 6AH batteries. That coupled with the fact that they will discharge comfortably to 20%, I think my overall number of operation cycles will be a little more than that of the original gel cells. And they should last well past ten years too.

[SuperSleeper]

I agree that when being charged with a solar charge controller, this greatly reduces the risk of trouble, since solar charge controllers are designed for exactly the situation we've been discussing-- (safe charging while simultaneously powering a medical device).

That's why a lot of people have a small solar-powered system with a quality charge controller.  I use the Morningstar SunSaver Duo 25A PWM Solar Charge Controller.  It can control two separate battery banks.  I think my initial system with that controller for a 12-volt lead-acid battery was less than $300 total, and it was much, much safer than any Lithium-Ion setup that's constantly being charged with grid power 24/7.

Any grid-tied system is going to introduce more problems, as I see it.  Those problems can be overcome, but one has to know exactly what's going on and how each component of the system is interacting with the other.  That's why I love a separate solar-only system.  No need to provide extra safety equipment and circuitry (other than in-line fuses) to avoid the greater issues as when a charger is plugged into grid power continuously.

And given that there's such a wide variety of battery chargers out there - and plenty of confusion to go with them all - for most folks, it's going to be good advice in most cases to tell them to avoid charging a battery while simultaneously using it to operate a medical device that's critical to their health-- unless they have a system that is checked and double-checked for compatibility and safety, or they have the personal knowledge and experience to properly set up a system like that to ensure no damage is done to their CPAP.  Some people have used a less-than-safe setup with some "success" simply because of random luck, rather than because of knowledgeable planning and safety measures.

As far as the Lithium-Ion fire risk, it is real, and not as uncommon as you would think.  Not all small fires get reported in the news, and even a small Lithium-Ion battery fire can go from very, very small (and non-news-worthy) to very, very large in a few minutes if no one is at home to put out the fire.  The point is, if it's you who has their house burn down due to a Lithium-ion battery fire, your chances of losing your house just went up to 100%.  And those who take precautions and safety measures, and use safer types of batteries and charging systems are less likely to burn their house down, of course.

I would completely avoid continuously charging a grid-tied Lithium-Ion battery system unattended.  If you're going to use Lithium batteries for that type of system, definitely go with LiFePO4 for safety over Lithium-Ion.

It would be interesting I think -- since insurance companies live and die by their statistical risk analysis -- to call up one's homeowner's insurance company and ask them if you have a large Lithium-Ion emergency battery bank continuously charging unattended on grid power, will that void your homeowner's fire policy if a fire is started by that system, or are they completely "okay" with an insured person doing that?  (and would they be willing to put that in writing?)  I have feeling they'd have major issues with that.

As always, just my opinion, but I lean towards the safe side of things when it comes to fire risk, due to witnessing a few home fires in my area recently, mostly caused by electrical issues, one of them three houses away a couple of weeks ago.

But, your mileage may vary, as they say.