Power outages

Quick version:
I have a battery backup design very similar to the elegant and very safe design posted here (this is a great post: see the link below):
viewtopic.php?f=1&t=49115&st=0&sk=t&sd=a&hilit=battery

Has anyone just left their CPAP and Humidifier plugged into the battery 100% of the time with the battery float charger plugged in at the same time? Basically the CPAP and Humidifier are running off of the charger with the battery acting as a buffer.

Long version:
I live in the north west area of the United States and recent ice storms and heavy rains have caused power to be unreliable at times. I hate waking up to a dead machine. That is really unnerving. Usually, I wake up with no air, and fumble around for the 12 volt plug. I disconnect my humidifier and hook the CPAP to the battery and go back to bed. If the power is still out, I start my generator in the morning and power my home. During that time, the charger returns the battery to a normal level. I turn off the generator at night and go on battery backup for the duration of the night. I repeat this until we are back on commercial power once again.

Basically I am looking for an uninterrupted night. If the power goes out, the cpap and the humidifier go for a few hours on battery bakup. When power is returned, the charger picks up. I wonder if my proposed activity will cause a problem with the battery. I am unsure if the charger can keep up with the drain imposed by the CPAP and the humidifier when commerical power is available.

Check this thread. He is running through his all the time for the same reason, but his UPS would know if the power was on or not. Might be a better option for you.

viewtopic/t74956/viewtopic.php?f=1&t=73 ... ry#p671658

My ears were burning

If you want to go the 12V route, the Battery Tender http://www.amazon.com/Battery-Tender-02 ... 734&sr=8-1 is a good choice for maintaining the battery. But you might also consider recycling a computer UPS with a dead battery, and just take the 12V battery leads out of the case and connect them to a deep cycle 12V battery in a vented box. It's important, though, to disable the buzzer on the circuit board of the UPS or it will keep you awake when it goes off.

viewtopic/t74956/viewtopic.php?f=1&t=73 ... in#p671485

I forgot to mention that I am using 12 volts direct current and not an inverter.

The concept is excellent, but there are some tricks in practice.

There might be some safety risks with any homegrown "live" battery charger system like this. The power supply for the CPAP machine is designed to be used with medical equipment and presumably has adequate safety precautions built in. The car battery charger may be UL listed, but it's listed for connection to a car battery, not to medical equipment. I doubt any safety professional would approve it being hooked up to a "live" CPAP machine. Suppose the battery charger fails and dumps 120V AC between the negative battery terminal and ground.

There's some risk with any kind of battery charger that something could go wrong and it would put too much voltage, or some kind of voltage spike, into your machine and do damage or make it not work right. The battery itself will tend to smooth out the voltage, but I've seen some pretty lousy battery chargers in my time.

The wrong battery charger will greatly shorten the life of your battery. Many of them are not really made right for 24/7 connection to the battery, despite manufacturer's claims.

The Battery Tender Jr. only puts out 0.75 Amps. This will probably not run the M Series CPAP. It's adequate to keep the battery charged when you're only hooking the CPAP to the battery when power goes out, but the CPAP may suck more juice out of the battery in 8 hours than the charger can put back in 24 hours. Your battery charge would slowly droop over several weeks, eventually leaving you with a dead battery.

Basically, you need enough amp hours from the charger in 24 hours to make up for the amp hours the CPAP draws in 8 hours. Then add in some safety margin.

It might actually work with the Battery Tender, Jr., but it would be close. We'd need to know what the current draw is for your CPAP. What's your pressure, and are you powering the humidifier off of DC?

If I were building something like this, I'd use a Schumacher SE-1-12S. It does 1.5 Amps. I've used these for years on marine batteries I have. It might not have enough current, but It's got twice the current of the battery tender Jr.

Thank you all for the advice. For now I will keep the system in place as standby power that requires manual cpap hookup. In the event of a power outage I can switch onto battery power.

I agree the larger charger is better if you're running every night off of a battery. The advantage of the computer UPS is that you don't need a separate charger and inverter.

The important thing is that you don't connect your battery to something like a 6-amp charger because terminal voltage can be quite high and might cook your expensive CPAP. However I would hope that the designer would have included a voltage regulator on the DC input in order to keep that from happening.