Battery Backup Setup for xPAP

Introduction

Objectives

As you may know from [CPAPtalk.com], I have problems with both obstructive and central sleep apnea. As a result, I use an [Auto Servo Venilation (ASV)] unit to provide therapeutic positive airway pressure. Due to the severity of the apneas, I can not sleep without it. Thus, I needed to build a battery backup system for my ASV unit.

This article only describes how I went about creating a Battery Backup Setup for my ASV unit. Since I've dealt with other xPAP devices, I also explored various options. I also explored how to minimize risks and how to define my requirements. Though you might find this interesting, I do not recommend you use this as a set of instructions on how to do this.

Notes

To do this project, I put together a checklist to help me wade through options, safety issues, and my own requirements.

Part of what I wanted was a modular design with which I could change components as needed.

Since others may ask, let me be clear. I do not have any financial stake in any of these components. I am just reporting what I, as an xPAP device user, decided I needed to help create my own Battery Backup Setup.

Since I will always need my ASV unit, and power can be an option, I wanted to have this setup stay in my bedroom. So the design had to address some very specific risks. Those include meeting various safety needs for myself, for my family, for my home and for anyone who might visit our home.

As you will see, I decided to not use the humidifer while using the battery backup. I did work through what I would need if I used a humidifer.

I also decided to use this setup only as needed. For example, if we might loose power during the night, I would plug into it for the night. But I would not always plug into the battery backup unit. That change would have presented different (and more costly) power requirements.

What This Article Covers

In this writeup of my article, I present my research for my battery backup setup. As I put this together, I put together the following sections. It's not perfect, but it highlights the process I went through to build my setup.

• Warnings and Disclaimers
• Checklists
• Battery
• Battery Charging
• Battery Box
• Shared Use Connector
• Other Connectors & Covers
• DC to xPAP Hookup
• External Links

Warnings and Disclaimers

This Wiki article describes how I went about building a battery backup system. I am not an expert in this. I do not pretend to be an expert. What I learned from my research is that there are serious risks in building a battery backup system. To help mitigate those risks, I methodically identify them and planned on how to minimize those risks.

But I do NOT recommend you use this to create your own battery backup system. This is not an article about how you can create a Battery Backup. It's just an article that explains how I went about doing this. If you use it to create a Battery Backup Setup, you do so at your own risk.

Remember, there is a lot of POTENTIAL energy in a battery. A battery converts electrical energy to chemical energy. That chemical energy can later be converted back to electrical engergy. The more powerful the battery, the more potential damage it can cause.

You have been warned.

Warnings

Don't believe me? The folks at SubSystm over at Revision3 put together a great video that shows how to hack a UPS to add more battery power:

http://revision3.com/systm/hackedups

I did not use that approach because it will not work well for driving an xPAP unit for several nights. Plus, I can better control the quality and risks using equipment I select that meets my safety and power requirements. That approach seemed to be safer, cheaper and more cost effective.

Electrical Danger

Since batteries provide energy in the form of electrical energy, there is an electrical danger with powerful batteries. The design I used takes precautions to avoid unintended and/or uncontrolled electrical discharges. The following image comes directly from the video by SubSystm and shows using a deep cycle battery to arc weld! Yikes!

As a result, the design I used minimizes the possibility of unintentional short circuits. It also includes a fuse to help shut down any uncontrolled release of energy. That could not be an option.

Explosive Danger

Batteries convert electrical energy to chemical energy. Well, if they are over charged, improperly handled, or have some problem, they can explode. The following scene from http://www.kd4bbm.com/ shows an image of a battery that exploded. That image shows the aftermath of a lot of energy that was released.

As a result, I designed my setup to minimize the possibility of an explosion, a hydrogen leak. It also seemed prudent to be certain the battery was well contained, but also allow the gasses to vent and not build up to an explosive level.

So, this helped guide my choice of battery and battery box.

Fire Danger

Though I choose a Lead Acid battery, Lithium Ion batteries also have their risks. Improperly made a Lithium Ion battery will catch on fire and cause serious damage. So, even the portable batteries have risks.

Since Lithium Ion batteries cost more, last less time than a deep cycle Lead Acid battery, I chose the Lead Acid battery approach. Obviously an explosion can also lead to a fire. So, any design I used had to contain the battery when not in use.

Acid Danger

As if the other dangers were not enough, Lead Acid batteries use sulphuric acid. Improperly handled, that poses a very, very real danger. Besides the potential damage it might pose to my house, if it comes into contact with skin it will burn it.

Even the "dry" type Lead Acid batteries can present a risk of acid exposure. Once again, any design I chose must contain the battery. Use of Baking Soda - even in a battery box - may be a good method to neutralize any battery acid that might spill and/or leak from a battery. Of course, a battery box is essential to contain any battery acid.

Disclaimers

Do I really need to say more on this? Yes, I do. I present only what I did. If you use this, you do so at your own risk. If you ignore any safety concerns, you do so at your own risk. Even if you follow all the directions and have some unexpected problems, you do so at your own risk.

Though I offer how I reduced my own risk - and it's worked well for me, I can not guarantee I won't have problems tomorrow. And I certainly can not guarantee you won't have problems. So, you have been warned!

Checklists

I used the following set of checklists to help me figure the best choice for using a battery backup unit.

Do I Need a Battery Backup Setup?

The first question I needed to answer was "Do I really need a battery backup setup?". Might seem odd, but before I purchase something like this, I want to be certain it will be a good use of my funds. And whatever I purchase, I want to be certain it really meets my needs.

But let's face it, I also need to be honest so I don't waste my money.

Frequency of Power Outages

Some of the questions, I asked my self (and answered) included:

• [__] Do we loose power more during more than one season of the year?
• [__] Does the power stay off for more than a few hours?
• [__] Do we have severe weather that might cause problems?
• [__] Does the power flicker more than a couple times per year?
• [__] When the power flickers is it more than a few times at night?

Essentially, I want to answer if this battery backup system would cost me more than some alternatives. For example, I might want to honestly answer:

• [__] Could I go to a hotel instead of having a battery backup system?
• [__] Could I go to a friends house instead of having a battery backup system?

Duration of Power Outages

• [__] Has my area lost power for more than a few hours?
• [__] Has my area lost power for more than one day?
• [__] When power flickers does it do so more than once?
• [__] Have we lost power long enough to need to throw away food?

Causes of Power Outages

Of course, these questions are related to the frequency of loosing power. So, do we loose power:

• [__] ...during thunder and lightening storms?
• [__] ...when there are ice storms?
• [__] ...whenever we experience heavy winds?
• [__] ...from other severe weather or events (tornadoes, hurricanes, earthquakes, etc.)?
• [__] ...as a result of accidents on nearby roads?
• [__] ...due to contruction in the area?

Power Available Elsewhere

What options do I have for alternatives? So, during the length of the power outage, could I:

• [__] ...go to a hotel?
• [__] ...use an RV that I own?
• [__] ...stay at a friend's house?
• [__] ...use a generator?

So, Do I Need a Battery Backup Setup?

Here were my answers to these questions:

Frequency of Power Outages

• [_Y_] Do we loose power more during more than one season of the year?
• [_Y_] Does the power stay off for more than a few hours?
• [_Y_] Do we have severe weather that might cause problems?
• [_Y_] Does the power flicker more than a couple times per year?
• [_Y_] When the power flickers is it more than a few times at night?

We loose power two to three times per year. At the most we loose power for a couple days. And when that happens it is due to very severe weather.

• [_Y_] Could I go to a hotel instead of having a battery backup system?
• [_Y_] Could I go to a friends house instead of having a battery backup system?

I could go to a hotel or friend's house. However, I do not drive. So I would not have immediate access to these resources. Additionally, I would not go to a friend's house in the middle of the night. Thus, the hotel stay due to a power outage would cost about one have the cost of a battery backup system.

Duration of Power Outages

So, how long do we loose power in my area:

• [_Y_] Has my area lost power for more than a few hours?
• [_Y_] Has my area lost power for more than one day?
• [_Y_] When power flickers does it do so more than once?
• [_Y_] Have we lost power long enough to need to throw away food?

Ugh! I can not guarantee that it won't last just one night. I don't sleep without my ASV unit, so to get the rest I need, I need to plan on two nights. Beyond that amount of time, I should be able to arrange alternatives to either charge my battery or sleep elsewhere.

Causes of Power Outages

When we loose power, it is now most frequently during storms:

• [_Y_] ...during thunder and lightening storms?
• [_Y_] ...when there are ice storms?
• [_Y_] ...whenever we experience heavy winds?
• [_Y_] ...from other severe weather or events (tornadoes, hurricanes, earthquakes, etc.)?
• [_Y_] ...as a result of accidents on nearby roads?
• [_N_] ...due to contruction in the area?

We used to lose power due to construction. But that's been several years since that happened. Most of our power outages are due to weather events. Though power is normally restored within a day, we sometimes loose power for more than a day.

When we do lose power for more than a day, it's typically due to severe weather. And when that happens, we lose power for several days at a time. So, my battery design had to handle those long events.

Power Available Elsewhere

What options do I have for alternatives? So, during the length of the power outage, could I:

• [_Y_] ...go to a hotel?
• [_N_] ...use an RV that I own?
• [_Y_] ...stay at a friend's house?
• [_N_] ...use a generator?

I have a generator. But normally we can not use it at night. I can charge a battery during the day, if needed. I can go to a hotel. I can stay at a friend's house. But I won't go to a friend's house when the power loss starts, since it is often late at night. And with the cost of hotels in my area this is not a cost effective solution.

What does this mean to you?

Probably nothing. You may have a completely different set of requirements and needs. Your situation is your own. But I try to show how I went through the process of trying to determine my needs. If you add your own questions, if you consider your own situation, you can tailor the process to your needs. Just don't expect my questions to be completely applicable to your situation.

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Battery

Deep Cycle Battery

Of course at the core of the unit is the deep cycle battery. There are many options of battery that can be used. I recommend the following links to provide an excellent FAQs for batteries:

• Battery FAQ - http://www.windsun.com/Batteries/Battery_FAQ.htm
• Battery Tutorial - http://www.batterystuff.com/tutorial_battery.html

Resmed also provides a battery guide at the link below for their flow generators. It also includes some basic information about batteries. It is well written and easy to understand.

• Resmed Battery Guide - http://www.resmed.com/us/assets/documents/service_support/battery_guide/19825_battery-guide_glo_eng.pdf

Why use a Deep Cycle battery?

To quote from the WindSun website (above):

Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. This gives less surface area, thus less 'instant' power like starting batteries need. Although these an be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge.

So, the deep cycle battery can last 4 to 8 years and be reused over and over and over.

Other choices include AGM deep cycle batteries and Gelled deep cycle batteries. From my research I found that a standard deep cycle battery provided the best price performance. As I noted, I've used one for about the past 10 to 15 years without problem, so I am sticking to that for this design. That is, during the past 10 to 15 years I used two different deep cycle batteries. I just purchased my third. So, the design works well and lasts a long time.

Note: It is best to purchase a sealed, maintenace free deep cycle battery.

What about UPS units?

Well, they can be an option. Some xPAP units require more power than most UPS units provide. Larger UPS units (though more expensive) can be used to power more current xPAP units.

What about portable batteries?

These certainly can also be used. However, the cost of those batteries are prohibitive for the power requirements of my ASV unit. Thus, I selected a deep cycle battery to keep my unit going for a couple nights.

What about car batteries?

Standard car batteries should NOT be used. They typically are designed to provide a quick boost of energy to start an engine (cold cranking amps), instead of being designed for deep cycle operations. A deep cycle will often ruin such batteries after one or two times they are used.

How much power do I need?

ResMed provides a handy Battery Guide to help understand how to hook up and use battery backup for your ResMed unit.

ResMed Battery Guide - http://www.resmed.com/us/assets/documents/service_support/battery_guide/19825_battery-guide_glo_eng.pdf

For instance, I use a ResMed VPAP Adapt SV Enhanced unit. To use this unit without a humidifier, I need to use a modified sine wave Inverter. That inverter must provide at least 150W sustained output. If I use a humidifer with my ASV unit, I need to use a pure sine wave inverter with at least 300W sustained output and upto 500W peak output. See page 7 of the battery guide for more information.

Then based on the pressure setting of my unit, I can determine the size of the battery that I need. On page 13 there is a table titled "AutoSet CS2/VPAP Adapt powered with inverter". My unit uses an ending exhalation pressure (EEP) of 7. To be conservative, I will choose 8 from the table. So, to last 8 hours WITHOUT a humidifier, my unit needs upto 26 amp-hours. To last 8 hours WITH a humidifier, my unit needs upto 58 amp-hours:

How long will power be out?

In my area the power rarely is out more than 2 days. In fact, most of the time power is out only for a few hours. However, 2 days provides enough leeway to handle most emergencies.

So, with 2 nights of service but without a humidifier, I will need over 52 amp-hours (AH) from a deep cycle battery. Thus, I purchased a deep cycle battery rated at 55 amp-hours.

What if I had a ResMed S8 AutoSet Spirit II?

In that case, I probably would want to use a DC Converter. If my average treatement pressure was 16, then per the ResMed Battery Guide on page 15, it indicates I would need only 15 amp-hours to run the unit for 8 hours.

So, to last two nights, I would need a deep cycle battery rated for 30 amp-hours.

What about other units?

Other units by other manufacturers require a little more calculation. ...*** To Be Completed ***...

Where to purchase a deep cycle battery?

I found my deep cycle battery at Batteries Plus [1]. You can also find them at many automotive stores as well as Sears and other stores with automotive departments. Be careful that you purchase a battery that is a deep cycle battery. Rembmer that in this case, cheaper is probably going to be just that - cheaper. It is worth paying more for a battery that will last longer and not die in the middle of a power outage.

Battery Charging

With standard lead acid batteries and especially deep cycle batteries that are only periodically used, it is important to keep them charged to maintain their chemistry and charge. If left uncharged for a prolonged period of time it irrevocably damanges the battery.

To maintain this charge, you can periodically maintain the charge. For example, once a month charge the battery. However, if time elapses and the battery is not charged, damage can be done.

It is possible to maintain a trickle charger. However, unless it is designed to stop charging the battery, if left on too long a trickle charger can over charge a battery and thus permanently damage a battery.

Instead, the easiest and best way to maintain the charge on a battery is to use a Float Charger. This maintains the charge on the battery, but stops charging once it senses the battery is fully charged. For more information on trickle and float chargers, see the wikipedia article - http://en.wikipedia.org/wiki/Trickle_charging

Though others are available, I chose the Battery Tender Jr. charger:

It is available at:

http://www.batterytender.com/

Since I only rarely see power outages, the Battery Tender Jr delivers an adequate charge rate to maintain my battery. If you anticipate you will use the battery more frequently, or want to always remain plugged into the battery backup unit, then a more powerful Battery Tender unit will be needed.

Additionally, one of the advantages of the Battery Tender models is that they use the SAE automotive connectors. So, you can easily add an extension cord to the unit, such as those found at http://www.powerlet.com/:

Battery Box

There are several key disadvantages to batteries in the bedroom.

First, one of the disadvantages of lead acid batteries is that they do contain acid! Even sealed batteries can leak. That's certainly not somethng that I want uncontained within my bedroom.

Second, it is possible pets and/or little fingers might want to explore the battery. These batteries contain a good deal of power and might hurt those naive, inquisitive fingers and noses. So, sealed and protected makes the most sense for a battery in the bedroom.

Finally, though it probably won't occur, left uncovered and unsealed, it is possible clamps may be knocked off of the battery. Again, this can damage the battery and possibly cause other problems.

For for all three reasons an ounce of prevention is worth a pound of cure! And to do this, I chose a plastic battery box, such as the following image:

It was available at the [url=http://www.batteriesplus.com/]Batteries Plus[/url] store, where I purchased the battery and the Battery Tender Jr.

I also specifically chose a flat top to allow me to modify the top to make it that much more modular than with the rounded top.

To Be Continued ...

External Links

Resource on Batteries and Similar Projects

• Example of hacking a UPS
• etc.

Resources on Battery Backup for xPAP devices

• ResMed Battery Guide
• etc.

Resources for Deep Cycle AGM Batteries

• Batteries Plus
• etc.