Do You Have Backup Power?

by Bill Norman on Tue, 2009-09-01 11:37

Tips for vent and respirator users for dealing with power outages

Home power often bites the dust when storms or other unpredictable influences play havoc with power lines and neighborhood transformer boxes. For people who use electrically powered respiratory equipment, this can be a life-threatening occurrence — unless there’s a reliable secondary source of power at the ready.

Note: Vents and positive-air-pressure devices (like Philips Respironics’ BiPAP) contain delicate electronics that can be damaged by hooking them up to the wrong sort of power source. Always consult your vent manual or contact the manufacturer whenever creating a backup power system.

Internal and external power

Pulmonetics battery will run vents about three hours.

Most vents contain an internal battery that keeps them operating if the electricity goes out. Internal battery life varies greatly, from about 25 minutes in VIASYS Healthcare’s TBird Legacy vent, to up to 11 hours with the Puritan Bennett 540’s lithium ion battery.

Some units have no internal batteries, like the Respironics BiPAP Harmony S/T, ResMed’s Sullivan Comfort and the AIROX SmartAir ST.

Most manufacturers advise against relying on a vent’s internal power source for any longer than necessary, and many offer supplemental external batteries that are larger and heavier than their internal counterparts. These batteries, generally providing 12 volts of direct current (DC), usually come with battery chargers and are kept plugged in so they’re ready for use on short notice.  These backups are useful not only during power outages but also when traveling.

Manufacturers generally offer a range of external battery/charger options. For example, Pulmonetics offers five battery/charger options for its LTV 800 vent, with battery life ranging from three to nine hours. Prices run from about $540 to $1,050. Another Pulmonetics option is its Universal Power Supply, which serves as a full-time source of 110 power for the vent, but also contains a battery that’s kept charged as the current flows through it. If the house power goes down, the UPS automatically switches to battery power so the vent doesn’t experience any down time.

Comparison shopping

Deltran Battery Tender supplies just enough power to keep batteries topped off.

A 12-volt battery suitable for powering a vent often can be bought at a local battery shop or auto parts store for much less money than from vent manufacturers. (Batteries suitable for this purpose vary widely in size, weight, configuration, capability, portability and cost. Lighter-weight batteries usually cost more than their heftier counterparts with the same power capability.)

Manufacturers often advise against making such buys, guaranteeing only their own batteries and chargers, and sometimes indicating that other batteries may be harmful to the vent.

Nonetheless, many budget-conscious vent owners do buy and use their own back-up 12-volt DC batteries, chargers and other equipment (see “Sine wave power”).

To connect an external battery to a vent, consumers need a cable with adapter (obtained from the manufacturer) that plugs into the vent, and two inexpensive clamps to attach the other end of the cable to the battery terminals/posts.

A word of caution: Cable clamps must be attached to the proper positive and negative battery terminals to avoid damage to the vent’s electronics. If unsure about the proper connection, check with the vent manufacturer.

Bob Mauro, motivational speaker, artist and writer (author of Sucking Air, Doing Wheelies, PublishAmerica, 2005), saves his old wheelchair batteries, and now has seven in his collection. Even when they’re no longer able to power his chair, they have sufficient remaining energy to power his vent for six to 10 hours each. “We get about two to three [power outages] a year,” he said of his home in Levittown, N.Y. “Each usually lasts three to five hours. Once when the Northeast coast went out, it was out 22 hours.”

Battery construction

A Samlex inverter turns 12-volt battery power to pure sine wave energy.

Consumers generally can choose among three battery types: flooded, gel cell and absorbed glass mat. All three are readily available at typical battery stores. The right one for your use will depend on cost and where the battery will be used.

Flooded batteries (common for automobile use) are usually the least costly, but they contain acid that can spill out if the battery turns over. They also give off hydrogen gas, so they shouldn’t be used indoors, including in a bedroom, unless the space is well ventilated (even when the power is out). They’re not recommended for travel.

Gel cell batteries have had silica gel added to their acid so it’s the texture of thick jelly. The battery is sealed, and even if broken, the acid won’t run out.

In absorbed glass mat (AGM) batteries, the acid is contained inside boron-silicate glass mats, and the battery is sealed, as well. Although they cost about the same, their rugged construction means AGMs can withstand shock and bumping better than gel cells, and can be charged up more rapidly.

Batteries also should be of the deep-cycle type, which means their electric charge can be drawn down (60 percent or more) and they can be recharged many times.

Keeping batteries charged

Some vents require higher quality pure sine wave power.

Obviously, it’s important that backup batteries are ready to go on short notice. Some battery chargers offer a quick-charge capability, but that’s not a wise option for extended periods. Much more preferable are trickle chargers (available at auto parts stores, electronics shops and from some vent manufacturers), that can be left hooked up to the batteries for long periods. This is the type that Mauro uses. Small portable chargers can be had for $50-60.

A variation on rapid and trickle chargers is the battery charger/tender. The device, which sells in the same price range as the other types, contains a microprocessor. Once it has fully charged a battery, it tapers off on the charge and maintains just enough input to keep the battery topped off.

As when selecting backup batteries, select a charger whose output in amps at least equals the amp rating of the vent. Chargers with smaller amp output can charge batteries with higher Ah ratings (see box), but may require hours more to do so.

Sine wave power

The 110-volt alternating current that comes from a wall outlet is characterized by pure sine energy. When viewed on an oscilloscope screen, the energy shows as identical, uniform sine waves.

Power from other sources, such as DC batteries and some portable generators, can produce modified sine wave power that appears as blocky, ragged or jerky waves, not smooth and even like pure sine power.

Some vents require pure sine energy to protect their sensitive internal electronics. Others don’t. Asking the manufacturer if pure sine power is required is the only way to be sure.

This video demonstrates the proper way to connect respiratory equipment to a back-up battery. MDA thanks Mike O'Dower of Walgreen's Home Care in Tucson, Ariz., for providing the equipment shown. O'Dower reminds customers to periodically use back-up batteries (even those on battery chargers) to ensure they're fully charged.

If using a DC battery to power a vent that requires pure sine power, it’s important to connect an inverter between the battery and vent. The inverter converts DC power to pure sine AC power that the vent can safely use. Inverters are usually sold at battery shops, some camping/RV supply outlets and on the Internet.

Many vents use between 200 and 400 watts of electricity, so when purchasing an inverter (typically costing $150 and up), make sure it can produce at least as much wattage as the vent requires. Wattage ratings are included in the vent’s tech literature.

The family car

A multitude of devices can be plugged into the cigarette lighter receptacle of cars, boats and planes to tap the vehicle’s 12-volt DC power. In many cases that includes vents.  Check with the manufacturer to be sure.

Some vent makers sell a plug, wiring and connector to link up the vent to a vehicle through its cigarette lighter receptacle. A convenient way to keep the vent powered up while traveling, it’s also an option during power outages. Cord length is usually limited to about 12 feet, however, meaning it may be tricky to reach a vent user inside a home.  When getting power this way, it’s necessary to start up the car every hour and let it run for about 15 minutes.


Gasoline- and diesel-fueled electric generators come in many sizes, from small portables to large permanently mounted units located adjacent to homes. Costs range from less than a hundred to thousands of dollars.

Because vents use relatively little power and backup batteries can keep them going for days, a generator may not be needed at all, unless appliances and other equipment in the home need to be powered.

In all cases, generators must be operated outside because they give off lethal carbon monoxide exhaust. Although large generator systems may “kick in” automatically if an outage occurs, most portables must be started by hand with a pull-cord.

Advising utilities and emergency responders

Electric utility companies can sometimes select which areas will be without power when they intentionally cause “rolling black-outs” to reduce electrical demand. If a company has been advised in advance that electrical power is critical, it may be able to avoid including that person’s home in a black-out region.

Police and fire personnel also should be advised in advance that a person with ALS at a specific address may require special assistance or life-support equipment during evacuations.

Ampere/hour (Ah) capacity tells how many amps of electrical current a battery can provide in a given period. With a little calculating, the Ah reveals how long a given battery will power your specific respiratory device.

  • Determine your vent’s amps requirements (listed in the manual and sometimes on the vent itself). Most vents operate at between one and five amps.
  • Identify the battery’s Ah rating (listed on the battery).
  • Divide the Ah rating by the vent’s amp rating. The resulting number is approximately how many hours the vent can operate on that battery.

For example:
Vent amps = 5    Battery Ah = 100    100 ÷ 5 = 20 hours operating time.

Note: Battery age, air temperature and degree of charge can reduce efficiency, so err on the side of caution and reduce the final figure by about 25 percent (20 x .25 = 5; 20 – 5 = 15 hours.)


Information: Amp and wattage requirements of the respiratory device; whether it requires pure sine energy; what kinds of external power sources/connections are recommended by the manufacturer.

A power source: Charged external batteries, a generator, or a vehicle with an outlet plug.

Proper connections: The correct adapter plug/cable for the respiratory device; battery connectors; and possibly an inverter to convert the current to pure sine energy.

Bill Norman
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