What do you look for in a portable battery backup for medical devices (like CPAP)?

You'll need a backup that supports the DC output voltage of your CPAP. Longevity depends on your CPAP pressure, humidifier settings and hours used. Both Amazon ads have charts estimating CPAP longevity for the backup.

Maxoak CPAP backup/$298/Amazon - 297 watt-hours, cannot handle refrigerator power usage -

Anker PowerHouse 767 backup/$2000/Amazon - 2048 watt-hours, can handle refrigerator power usage for multiple days -

If you want 3 days on your CPAP you should be considering a generator to charge the battery backup.

First thing to do is determine the load you will have.

OK - the typical heated CPAP device will consume 100 watts per hour if heated. I am going for the extreme case for safety.

a) Assume you will use it 8 hours per day, for three days. b) Assume a 10% self-discharge rate for (3.3% per day). c) Assume that you will want 200% of necessary capacity - that is, discharge the back-up device to no lower than 50% to avoid damage to the batteries.

3 x 8 x 100 x 2 = 4,800 watts.

Allowing for losses, and self-discharge as-noted. You will need a device capable of supplying 48 amp-hours at 120 VAC.

Without redundancy (dangerous). your typical 1500 watt UPS will operate at roughly 3 hours per 100 watts, without damage, and run in the $500 - $700 range. You will need eight (8) of them to meet your most basic need. And have to change them twice (2x) per night. Or, you could spend $3,500 for a single unit that could run for all of eight hours at 100watts.

Get a generator. Be wise in your fuel selection. You will have four (4) choices: a) Gasoline: Gasoline generators are amongst the cheapest of options, and even a relatively small one will run all critical functions in the typical household including your refrigerator, some lights and the CPAP. It will burn something on the order of 1.3 gallons of fuel per hour. So, you will need to store 30+ gallons of fuel on-site, and fill it as needed. At night. Or 94 gallons and run it 24/7. Gasoline devices tend to be either large, powerful and noisy, or small, quiet and low power. Anywhere from $400 - $1,000 will get you there. No transfer switch, strictly a manual device. c) Diesel fuel: This would be a whole house device, and if installed with the proper transfer switch, and with a large tank, you could get up to a week with such a device. But they are not cheap. You would start around $1,500 without installation or a transfer-switch. So, figure $3,500 absolute minimum installed. And that would be for a Chinese-origin device. A decent Kohler device would be about $4,500 installed. d) Natural gas: If you have a reliable source of natural gas - about the same installed cost as a diesel - and no fuel limits. By far, the cleanest, lowest maintenance option, and least expensive to operate. e) Propane: As above, but you would need a large propane tank with the associated issues.

The issue with medical devices is that one does not want to screw around with 'good enough' - as that 3-day issue might turn into a 4 or 8 day issue.

Peter Wieck Melrose Park, PA

On Tue, 4 Jul 2023 at 01:02:03, Ed P snipped-for-privacy@snet.xxx wrote: (my responses usually follow points raised):

The portable AC power inverter battery backup from the utility is free.

And it fits in the bedroom closet and can be used in the bedroom. The generator is not.

It's a "ResMed AirSense 10 Autoset" so the load is whatever that uses. Probably something like special 24VAC at probably something like 3.75 Amps.

At least that's what it says for the 3-wire DC output for the CPAP machine.

Peter's response applies. Ignore it at your own risk.

And "free" is not what you told us: "They offer the following portable battery backup units, where I want the most bang for the buck"

Fine, argue. We're trying to help.

Ok, now for the help you need. The manual for your device shows the power requirements as:

90W power supply unit AC input range: 100–240V, 50–60Hz 1.0–1.5A, Class II 115V, 400Hz 1.5A, Class II (nominal for aircraft use) DC output: 24V 3.75A Typical power consumption: 53W (57VA) Peak power consumption: 104W (108VA)

The last two lines are the most pertinent for you.

Next, the manuals for the backup devices in the link you provided give the following capacities in ascending order:

yeti 500 505 wh yet1 1000 983 wh ecoflow 1008 wh yet1 1500 1516 wh yeti 3000 3075 wh yeti 6000 6010 wh

The yeti 6000 will last longest. They're using the symbol wh to indicate total power in watts that the device can provide over time. For example, the yeti 6000 should be able to provide

100 watts for 60 hours if their number is correct.

I hope that helps you understand the electrical specs. As regards the specific use of these devices with your CPAP, I can only quote the specs from the manuals. I have no personal experience with any of the devices.

Ed

Ed: You are trying to nail Jell-O - I suspect this individual is a reincarnation of Jimmy Neutron, a notorious troll of long standing. Also a big fan of Harbor Freight and using a cell-phone to set wheel camber.

100 watts for 60 hours = a flat battery. Just a note to the effect that doing this even a few times to any UPS will destroy it. Let Mr. Gilliver find that out on its own. Certainly not from any suggestions received here.

Peter Wieck Melrose Park, PA