I wanted to put together a battery box for Scout car camping for use with my Resmed S9. I camp about 10 times per year.
Goals
1. My longest camp is summer camp at 10 days, and wanted to build a box that would last with 1 or 2 charges during that period. I think with my current setup, depending on how often I use a fan, I will be able to make it the whole ten days or maybe one charge at most.
2. I wanted to be able to run a 12v fan also for summer camping.
3. I wanted to also be able to charge my phone as needed or any other USB devices I might take or buy.
4. Should last 5 years or more. I expect this too if I maintain the battery properly.
Process
1. I starting reading researching and found the commercial CPAP battery solutions to be very pricey, lacking capacity, and having no additional outlets (12v or USB)
2. I found a great post on this site about a battery box design for use at home in case of power outages. I based my design on this one, but changed and added things based on my needs. This post has tons of great information on everything from inverters, converters, battery types; etc. so I will forgo any talk on those subjects and you can refer to this awesome post.
3. Researched deep cycle batteries on opted for a good deep cycle.
4. Found out how much current my machine needed to run. For Resmed CPAP’s you can refer to this document on their site. Without the humidifier or the climate-line tubing, the S9 draws .55 amps/hour at 10 cm H2O (my highest pressure). My battery has 105 amp/hours of power, and since you should only discharge deep cycle battery about 50%, this means that there are about 50-55 usable amp/hours. Dividing the 50 amp/hours by the .55 amp draw, I would get about 91 hours of use. At 9 hours per night this would be about 10 days! Awesome.
Parts (Total Cost ~$360.90 + $33.95 for the Luggage Cart)
1. MinnKota Trolling Motor Power Center ($58.46 from Amazon) – I chose this over the one in the above mentioned post because:
- It already had two cigarette lighter 12-volt outlets preinstalled. (1 for my CPAP, and the other for a 12-volt fan)
- It had external posts for charging and/or running other 12V devices. I plan to only use these to charge the battery, but who knows what other use they may have for me.
- It has two circuit breakers installed for the outlets (15 amp) and the external posts (60 amp)
- I didn’t have to assemble the ports and outlets as they were already there. I did add the below USB outlet though.
3. Poly-Planar USB-PM Panel Mount USB Charge Port - 12V ($23.21 from eBay) – I chose this so I could charge my phone or any other device that uses USB. I found this cheapest on eBay. I linked to amazon as their product pages are more stable than eBay’s.
4. ResMed DC/DC Converter for S9™ Series Machines ($84.95 from RespShoppe.com)– I bought the appropriate DC converter for my machine. I chose a converter over an inverter due to the plain fact that inverters are about 100% more efficient than a converter. This means for a given battery, I get twice as long before having to recharge than if I were using a converter. This was a no brainer for me as length of time in between charges was important to me.
5. Stanley BC1509 15 Amp Automatic Battery Charger ($44.28 from Amazon) – I needed this over the battery tender just for speed of charge. If I discharge the 105ah battery to 50% (recommended), this charger will take 50/15 hours to charge or a little over 3 hours. With the Battery Tender Junior at .75A it would take 50/.75 hours to charge. Over 66 hours to charge, which is far too long for my application. Again, it is just because I will actually be deep cycling the battery as opposed to having it hard-wired to the wall outlet all the time. Use a charger with the appropriate amperage for your situation.
6. Finally bought the Safco Steel Luggage Cart - 175 lb. capacity ($33.95) to haul the battery box and charger to and from camp and to the electrical outlets for charging while at camp. The battery alone weighs 55 pounds
7. This year at camp (2015) I added another accessory. The Onite® USB LED Light for Camping ($14.00 from Amazon) – Nice yellowish light for then tent that runs off the second USB port. Also bought the AmazonBasics USB 2.0 Extension Cable (~$6 from Amazon) as well to allow for more placement options. I really like the switch, so I don't have to unplug it to turn it off.
Assembly
The only thing I that really required any work was adding the USB ports to the box. I had to drill out the top of the box to the appropriate diameter (~1 1/2”) and wire it up to the existing connectors tucked away in the lid. To do this I did have to remove the protective cover inside the top of the battery box. This was as simple as removing two screws from the outside of the box and the two nuts and bolts holding the handle and the cover in place. I just wired the USB outlet to the same terminals as the 12-volt cigarette lighter outlets were wired to to take advantage of the built in circuit breaker.
Conclusion
I have been using the box at home in the bed room for a week or so and everything seems to function well. I have been charging my phone and using the S9 with humidifier and climate line tubing just to cycle the battery as much as possible to achieve a higher charge retention. I get at least 4 nights out of the box, and expect 2-3 times that that when not using the humidifier or climate line tubing, depending on my 12-volt fan usage during the summer. Either way, I think I have achieved all of my goals with this box. Let me know if anyone has any questions.
Update / Performance
I just got back from a 10-day Boy Scout camp and wanted to give a performance update. I used my S9 without humidifier or climateline, charged my phone nightly, and used the 12-volt camp fan for ~10 hours total, mainly to dry my shoes as it was unseasonable cool. I did not have to charge the battery at all and it was still over 50%. note: Deep cycles should not be discharged past 50% routinely. So bottom line, goals surpassed and the battery box worked great.
Picts (Click each for larger view)
Box closed up and ready for transport.
Inside Box
Closeup of Added USB Ports
Closeup of Built in Battery Voltage Meter and Breakers
Setup for Use
Setup for Charging