Battery Backup Design

billbolton wrote:... The whole point of going to the trouble of putting together the readily available building blocks to make a battery power system (as distinct from a UPS) is that you can appropriately size the inverter to the anticipated load, so it runs at a point of good efficiency! ...

Bill, that's exactly the point. As I went through this, I knew I could hack a UPS. But frankly most UPS units that can drive something like this would need LOTS more power to drive my ASV unit (when it ramps to 23cm H2O it definitely pulls more power than the average xPAP unit). Plus as you note, UPS units are designed for driving computers and other electronic gear for a fairly short period of time, but with a heavy load. And I wanted exactly the opposite. A moderate load (comparatively) for a much longer period of time.

So, as I looked at the costs, I figured the best way to put together the battery, the battery box, the charger, cables and such, and the inverter to meet my needs. And of course, I wrote notes so I could figure out how others can do the same thing. Get the most bang for the buck without breaking the bank.

I love the design and thanks for this post! I went out today and got the battery, box, and tender, now just waiting on the connectors and dc converter for my ResMed to come in next week and I'll be good to go. I sized mine where I should get a little over 5 days off the battery when I am camping or power outage. 90 amp hour battery sure does weigh a lot, but that 65lbs is worth it

-JD

hikewv wrote:... I love the design and thanks for this post! ... I sized mine where I should get a little over 5 days off the battery when I am camping or power outage. 90 amp hour battery sure does weigh a lot, but that 65lbs is worth it ! ...

Yikes! Well, I don't think that unit will get knocked around easily!

You will discover that when you first plug in the unit it will take it longer to reach the float charge level. Essentially, those batteries are charged by the manufacturer and loose some charge during shipping and while sitting in the store inventory. But thereafter it does not take as long (unless you use it for those 5 days).

Glad you enjoyed the design. I'm working on the Wiki article. It will be this, but a bit cleaner. And it will have a whole section with a checklist (I had an informal one I built as I put this together). It will include the calculations to help size the gear. It will include safety features the products had to have. It will include questions to help decide on the features needed. Hopefully you can answer those questions and take it to a store to purchase the parts needed.

Of course, to avoid any legal issues, I'm making it clear that I am writing this to show what I did to create a batter backup setup. I will include all my considerations about safety to be certain if anyone else uses this information, they do so at their own risk. But I certainly did everything I could to decrease my own risk.

And as always, I'm open to any suggestions anyone might have.

John,
Thanks for your research and writeup I refereed QuantiLog with his NEW Concept of a machine to read your power requirements!
viewtopic/t49204/New-CPAP-concept.html

BERT

UPDATE: So, as mentioned, I purchased the battery post to marine terminal connectors. I chose the postive connector to allow the 3/8" connector to handle the ring terminal connectors. I had to really tighten this down on the negative post. But it's good and solid.

I found I had to "screw" the terminal connectors on a ways to allow the wing nuts to continue the process. (It was a tight fit). I also purchased a small packet of battery post grease (essentially a colored vaseline) to protect all the battery post and terminal parts.

Then I topped it all off with the battery terminal covers. This is a VERY solid connection. It should not move. It should not have real problems with corrosion. It should not have problems with accidental shorts. I've done what I can to minimize problems.



I've not yet mentioned it, but whatever design I picked needed to also include a fuse. Most of the battery charger units should include a fuse. But if I found a charger that does NOT include a fuse inline, then I would choose another charger.

Bravo John!!!! I particularly like the clean, protected nature of your installation.

nghy

I wish I could claim I was all that smart. It's more the school of hard knocks. I have had the chance to SMOKE test devices in the past. I did not want that as a possibility in my bedroom. And I figured if others built something like this, cats, dogs, children, feet, whatever might tangle with the design.

My major concern is having the humidifier working also. The heater draws a lot of power, too much I fear for a practical sized battery. I was speaking with a man at Respironics about using two batteries in series for 24 V. He was shocked and said it couldn't be done. I asked if this was a scientific opinion or what? He said it would be tampering with a medi cal device. So it looks like, for me at home at least, I want to use a back-up electric generator rather than a battery back-up.

Great work John!

A few questions / comments:

1) what happens if your battery is weak, or not fully charged, or you try to use it longer than it can supply reliable power? If the household power is "on", the battery tender would start to overheat - and eventually burn out - as it tries to supply the current that the battery cannot. For this reason, I would not recommend that you use this system with your xpap while the battery tender also is supplying power. My recommendation would be either to have the battery feed power to the xpap, or, with xpap disconnected, feed power to the battery with the battery-tender. Alternately, a two position switch could be used to isolate one from the other.

2) it would be great if you could add something about polarity of the final 12 volt power outlet that the xpap cable plugs into. The system you describe has a lot of connections, and lots of opportunity to reverse the polarity (not good). If the final connection can be checked (easily done with a multi-meter), the end-user will have some comfort that he won't damage his blower when he plugs it in.

3) I've designed and built a couple of battery boxes over the years to power my portable astronomical observatory. In both boxes, I found it useful to include:
a) in-line master fuse, just in case something goes wrong. Locate it at the battery terminal. You don't want a fire!
b) master power switch - on/off. Switch must be able to handle the current - if necessary, a relay may be added.
c) power indicator LED light, to show when the power is on. Also shows the condition of the fuse.
d) external voltmeter to show battery condition (voltmeters are not great for this, but they are better than nothing and they do give a head's up when the battery is reaching the end of its life.) Note that the voltage would need to be read with the battery minder disconnected (another reason for the master switch)

I know that these things will add some complexity to the system, but they will improve it.

I've added this most interesting topic to:

LINKS to Battery operation, camping, power outage
viewtopic.php?t=9682

Thanks, John and everyone contributing to this thread.
Great pictures and detailed descriptions of meticulous work!

Hose_Head wrote:... 1) what happens if your battery is weak, or not fully charged, or you try to use it longer than it can supply reliable power? If the household power is "on", the battery tender would start to overheat - and eventually burn out - as it tries to supply the current that the battery cannot. For this reason, I would not recommend that you use this system with your xpap while the battery tender also is supplying power. My recommendation would be either to have the battery feed power to the xpap, or, with xpap disconnected, feed power to the battery with the battery-tender. Alternately, a two position switch could be used to isolate one from the other. ...

Depends on the battery tender. The unit I chose specifically will NOT overhead / overload. It is specifically designed to continue to work well, just adding enough load to charge the battery if it can.

However, I also had that concern. Hence my appoach to allow different components to be plugged and unplugged.

But I will be certain to add a note to my final directions.

Hose_Head wrote:... 2) it would be great if you could add something about polarity of the final 12 volt power outlet that the xpap cable plugs into. The system you describe has a lot of connections, and lots of opportunity to reverse the polarity (not good). If the final connection can be checked (easily done with a multi-meter), the end-user will have some comfort that he won't damage his blower when he plugs it in. ...

Good point. It's something I always do, but did not mention. I *always* make certain the polarity is correct before I *ever* complete any connections. And often you don't even need a multimeter. You just need to be certain how the wiring connects.

Hose_Head wrote:... 3) I've designed and built a couple of battery boxes over the years to power my portable astronomical observatory. In both boxes, I found it useful to include:
a) in-line master fuse, just in case something goes wrong. Locate it at the battery terminal. You don't want a fire!
b) master power switch - on/off. Switch must be able to handle the current - if necessary, a relay may be added.
c) power indicator LED light, to show when the power is on. Also shows the condition of the fuse.
d) external voltmeter to show battery condition (voltmeters are not great for this, but they are better than nothing and they do give a head's up when the battery is reaching the end of its life.) Note that the voltage would need to be read with the battery minder disconnected (another reason for the master switch) ...

More good ideas. I decided not to add a power switch. However, my design does allow you to readily disconnect EVERYTHING. I do have a master fuse. Again, something I always add, but did not have in this instruction. Though as I started to work on the wikipedia version, I realized not all battery tenders and/or power distribution lines include this. I would rather have a fuse blow than allow power to roll from one terminal to the other ... I don't want Chernobyl in my bedroom! The master switch will be easy to add into the design.

Hose_Head wrote:... I know that these things will add some complexity to the system, but they will improve it. ...

And that's the idea behind this. I want to show others what I did. For legal reasons I won't recommend they do this. But if they see the steps I took and WHY I took those steps it will help anyone else who might build a battery backup setup.

John,
Great piece of work.

A related question: I have an S9, which has an external "brick" transformer/inverter. How about just buying a UPS backup like you use for a PC. I am in a part of Florida where power is relatively reliable and most of the outages last less than 15 minutes.

gpk111 wrote:... I have an S9, which has an external "brick" transformer/inverter. How about just buying a UPS backup like you use for a PC. I am in a part of Florida where power is relatively reliable and most of the outages last less than 15 minutes. ...

Absolutely. If you can not predict when you will loose power, but know it tends to last just a few minutes, then a UPS backup system provides a viable option. But you will need to be certain it provides a pure sine wave - or just not use a humidifier. Remember, most PCs (and computer equipment) do not need a pure sine wave. (And many/most of those UPS units do not note what type of output they provide).

If you do want to use a humidifier and want to always have it available, but need it for a shorter period of time, then this setup but with a much smaller battery might be a cheaper alternative.

John,
I would think the PC UPS system supplies whatever power the brick needs. I would also think that the brick is ultimately responsible for supplying as pure a sine wave as the flow generator and the humidifier are specced for. Yes?

gpk111 wrote:... I would think the PC UPS system supplies whatever power the brick needs. I would also think that the brick is ultimately responsible for supplying as pure a sine wave as the flow generator and the humidifier are specced for. Yes? ...

You would think so, wouldn't you? Well, in all previous versions of the ResMed humidifiers you would be wrong. A modified sine wave is not a problem with the xPAP unit. It's only a problem with the heated humidifier. Here's the guide for all previous units and associated humidifiers:

http://www.resmed.com/us/assets/documen ... lo_eng.pdf

But that guide has not been updated for the S9 unit. So, I reccomend:

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