Battery Backup Design (V2)

Hose_Head wrote:... A few suggestions for additions ...

Great ideas! And really easy to implement. I'll add them into the edits in the upcoming week. I might even make a short version of the installation instructions to allow a mechanic to use it. I don't have to tell them how to do pieces, but it will help make certain they do it pretty consistently and don't take short cuts.

Then I would have a set of instructions on how to the system once it's back at home.

Great ideas!

Wouldn't it be a good idea to add this to the CPAP Basics thread?

mollete wrote:Wouldn't it be a good idea to add this to the CPAP Basics thread?

Personally, I don't agree that it should be added to the CPAP Basics thread. One of the beautiful things about John's post is that it draws together in a single post all of the things needed to set up a workable battery back up. It becomes less useful when the post is diluted with discussion of other topics. However I agree that a cross-post reference in the CPAP basics thread would be an excellent idea. That way, a newbie reading through the "basics" thread will be aware of and have a link to this thread on battery backup.

Good day
I have a Res Med auto set S 9 with the H5i heated humidifier. We full time in an RV and do not have a built in generator and it is not always appropriate to use a portable generator. We have two Kirkland batteries that are each 95 amp hours. We have a modified sine wave 400 watt inverter. The TV area plugs are on the inverter. Would it be appropriate and safe to take an extension cord to the CPAP set up.
Thanks in advance for any help offered

TrickyB1951 wrote:... I have a Res Med auto set S 9 with the H5i heated humidifier. We full time in an RV and do not have a built in generator and it is not always appropriate to use a portable generator. We have two Kirkland batteries that are each 95 amp hours. We have a modified sine wave 400 watt inverter. The TV area plugs are on the inverter. Would it be appropriate and safe to take an extension cord to the CPAP set up. ...

Yes. However, depending on the length of the extension cord and if you are going to use the humidifier, you might want to upgrade from a simple "lamp" extension cord to a utility extension cord.

While this type of extension cord will work:



It will be safer / better to use a sturdier extension cord:



Specifically, you will want an extension cord with 16 gauge wires. It's not strictly necessary, but it personally makes me happier, especially if you are going to be running a higher resistance load, such as when the humidifier is running.

Hope that helps.

The cord I was going to use was a builders extension cord that my husband used for 13 mp tool. Thank you!!

We have had another look at the inverter and it is specifically a Superex AC toDC inverter square wave 400 watt. It looks as though it is a heavy gauge extension cord that runs from the inverter to the plug. Do we need to check anything else??

To the best of my knowledge you are in good shape. You might want to try it before you travel. That way if you encounter a problem you can address it before you need it.

JohnBFisher wrote:Yes. However, depending on the length of the extension cord and if you are going to use the humidifier, you might want to upgrade from a simple "lamp" extension cord to a utility extension cord.

The "utility" type cord is also less susceptible to fraying, etc.

Whatever cord you use, be careful about how you route it, check frequently for nicks, fraying, etc.

Reminds me that I need to check my cords as well.

Great job John. The only suggestion is to add a section on fusing. I see in the pictures you do have a fuse in the battery case but make no mention of it. In mine I currently have two fuses. one inside the battery box and a smaller on for the leg powering the cpap.
I agree with you that not recommending the Battery Minder not be hooked up while using the battery to power the cpap. I currently do this, as I exclusively run off the battery, but I have modified the battery minder. As It tended to get hot while the cpap was operating so I added a large heat sink to the case where the output transistor is located. I also have overly extensive house, and cpap surge protection that most normal households do not have.

Nice work and information. Especially for those that need easy to implement emergency power. All people need emergency power and especially for us who need medical equipment. I chose to go the whole house generator route but even that is not bomb proof. What if the generator breaks, the transfer switch malfunctions, fuel issues or other. This is one of my battery stacks in my basement. I currently have four of these and they charge off alternative power and the grid. Thus no matter if the sun is shining, the wind blows, or not; when the power goes out, these kick in if the generator doesn't. If anyone is willing to pay the shipping and feels confident doing home projects with batteries that will blow the corner off our house if you screw up drop me a p.m. as I occasionally have a few extra serviceable deep storage batteries in inventory. FYI, a rack like this will make your local news if you screw up and dead short it. For most folks the simplest and safest is to go to a real computer supply store and buy a UPS in the 1,300 to 3,000 VA range. 150 bucks will buy you a lot of safe and easy to use backup power.

Tricky,
Why not buy the battery adapter kit for the S9 and run it straight of the batteries. To step the voltage up to 120v AC from 12v using an inverter when the power supply for the machine is going to step it back down to low voltage DC is adding a lot of complication to the issue. Plus I am not a fan of square wave inverters. If it were a modified sine wave as you originally posted or a true sine wave then I would not worry. Expensive electronics and inexpensive square wave inverters do not belong together. If you run straight off the batteries a buck and boost transformer would be a nice safety feature in case your batteries saw excessive voltage drop.

hueyville wrote:... Why not buy the battery adapter kit for the S9 and run it straight of the batteries. ...

I assume you mean the DC to DC converter for the S9. Resmed does not allow any other DC to DC connection for the S9. The S9 converter helps ascertain the S9 unit has the correct voltage throughout the discharge time.

I just got an interesting question that I thought I would share with folks. The question was, could a solar panel be used to charge the battery? The answer is sure, but it might be more expensive than you anticipate. However, it would allow you to be off the beaten path and away from power. However, it would pretty much require a stationary camp where you could setup the solar panel, battery tender controller for the solar panel, as well as the battery.

Will it be very portable? Perhaps not. The size of the panel and setup gear would tend to make it more appropriate to an RV parked at a camp site.

As an example of this type of calculation, let me point you toward a sample q&a where they talk about the solar panel needs for charging a battery that can run a computer. It provides a good example:

http://answers.yahoo.com/question/index ... 511AAPnboW

Let's assume you need to determine how much wattage the solar panel needs to supply to charge a deep cycle battery for a Resmed S9 Autoset unit with humidifier.

First, use the battery guide from Resmed:

http://www.resmed.com/assets/documents/ ... lo_eng.pdf

Second, use the calculators at the following URL to calculate the various values needed:

http://www.rapidtables.com/calc/electric/index.htm

Third, assume you use Humidifer setting 3 and the average pressure is 12 ... (see page 19 .. this assumes you use the converter rather than the inverter. The battery requirement is GREATLY reduced, which drops the size of the solar panel to a reasonable size.) .. Then the battery size for just 8 hours of use is 29 amp hours. Thus, you will need to determine the size of the solar panel to fully recharge the battery.

Some of the calculations are:

(1) The current draw is 2.39 amps at 12V. (The converter up converts that to 24V power for the unit). This means that the setup will draw 2.39 amps per hour times 8 hours .. or 19.12 amp hours). So, with a 50% reserve for a deep cycle application, you need 29 amp hour batteries.

(2) To calculate the wattage needed during sunlight time, you will need to calculate the wattage that will be drained and then needs to be recharged. To get this we change amps to watts or 2.39 amps at 12 volts (dc). Thus with P(W) = I(A) × V(V) we have P(W) = 2.39 amps x 12 volts or 28.68 watts. Then we calculate the Energy consumed in killo-Watt hours (kWh). This is calculated as E(kWh) = P(W) × t(hr) / 1000. Substituting our values 28.68 watts and 8 hours, we have E(kWh) = 28.68(W) × 8(hr) / 1000. With a result of E(kWh) = 0.22944 kWh.

To replenish that amount of battery energy, we need a solar panel that can charge 0.23 kWh over a six hour period. Why six hours? You might get more sunlight, but six is realistic due to different times of the year and cloud coverage. So, we divide the 0.23 kWh by 6 hours and we end up with P(W) = 1000 × E(kWh) / t(hr) or P(W) = 1000 × 0.23(kWh) / 6(hr) or P(W) = 38.33 watts. Up it a bit to 40 watts and voila we can search for a 40w solar panel:

http://www.homedepot.com/p/Nature-Power ... /204005724

This is just one example. In addition, you really should get a charger that can handle a solar panel. For instance the Battery Tender Solar Controller would be a good choice:

http://batterytender.com/products/solar ... oller.html

Hope all that helps.

Someone linked to this thread, and after reading it, I decided that it deserves a bump every now and again to keep it nearer the top of the list. Excellent thread, well researched and very well written.