Backup battery for cpap

Hey everyone, I’m really hoping to get some help with this one.

Like many people I suffer from sleep apnea and use a cpap machine to make sure I keep breathing.

I honestly fear not sleeping with the machine and fear a power outage.

I know I can buy a UPS but from the research I’ve done they only last so many minutes until the power comes back on. I’ve just gone 14 hours without power due to downed power lines and didn’t sleep out of fear and not being able to use my cpap machine.

I’d love to get some help making an inline battery backup so that if the power goes off the machine keeps working for upto 8 hours. I want this to be completely open source and hopefully cheaper then anything on the market as prices for backup batteries specifically for cpap machines start at $400.

If anyone has ideas or is able to help in making this become are reality it would be greatly appreciated

So the cpap that my mate uses when camping runs off a 12v 7.5ah gel cell battery.

I am assuming that yours plugs into the wall only?

if it runs from 12v then its a very easy fix, you just attach a gel cell battery and a float battery charger. While plugged in to 240v it charges the battery and keeps it topped off while you use it, but when the 240v goes out, it then runs from the battery.

As I understand it, one of the 12v 7.5ah lithium batteries lasts 1.5 nights use for a cpap, so you have plenty of wiggle room with just one battery, but you could simply wire in 2 to give you a 3 day runway without power.

If it is a plug in type only, then that gets harder and you would need to go down the inverter route and that means bigger, heavier and more expensive, and as you have pointed out, they dont have long run times due to the inefficiencies of converting 12v or 24v to 240v.

That all said, this is a medical device that can be a life or death situation, I am not sure that I would be comfortable cobbling together a solution even if it was just for my own usage, if it wasnt a battery powered unit.

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So this is the power brick for my machine so it’s 24v and 3.33A. It has a barrel jack on it so to build something that it can have uninterrupted power and not switch off to switch over is my goal

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So 24v makes it more expensive and 3.3A input means it will chew through batteries fast.
ie those Jaycar LiPo batteries at $75, you’ve need two of them and that would only run for a couple of hours.

It’s going to get real expensive, and real large and heavy, real quick.

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Hi Barrie
How long does that $400 back up battery last. Once you start costing deep cycle or lithium batteries up to 80 or 100 Ah the $400 might not seem that expensive, especially if it is purpose built to fit into your machine for dedicated back up. Both deep cycle and lithium also require specialist chargers but I think lithium batteries in 12V flavours have the clever bits built into the battery pack. I haven’t come across lithium in the 24V range and I don’t know how you would go about charging them. Someone else may have some experience here.

Andrew’s comments regarding Medical Equipment have a lot of merit and I would keep that in mind when thinking about non dedicated equipment.
Cheers Bob