Cpap Power For Boondocking

I’m finally back to this with some experience of the new dedicated-to-cpap “pony” battery.

To briefly recap: After much research and debate, I purchased a Victron “Super Cycle” of 60ah capacity, and a new charger to match.

It all arrived later than expected (Victron is a Dutch company), and I had one night with it last season.

This season started late for us due to work commitments, but we just got back from 3 nights boondocking at one of our favorite NW lakes.

New Victron batt performed at least as well as calculated. I don’t have a watt-hour meter, but, just based on voltage, it dropped about 0.2v per night. And we slept in, going 9 to 9.5 hours. This is with a Respironics System 60, humidifier turned off, setting 14, using a 12v straight-through cable (no voltage adaption).

Based on published “voltage to state of charge” charts:
Starting voltage 12.8v = 100%
After 1 night 12.6v
After 2 nights 12.4v
After 3 nights 12.25v = 65%

My conservative calculations were aimed at no more than a 50% draw down for 3 nights. Actual draw for 3 nights = 35%, success!!!

The Victron BAT412060081 Super Cycle 60ah is a lead-acid AGM, a sealed lead-acid battery. It weights 31 lbs and lives in the headboard cabinet. It sat on its dedicated smart charger all winter. It has slightly different chemistry than typical, and is designed for occasional draw downs of up to 100%. (Conventional lead-acid batteries lose significant life at draw downs over 50%)

 

2nd year update on this great power system...

I recently installed a $29 DROK power meter (link) on the CPAP pony battery. This is different than measuring state of charge (SoC) by voltmeter, as a power meter keeps track of power out and power in over time. This is also what the optional C-I Bogart Trimetric meter does.

It’s a great feeling to know for certain what is going on with my pony battery! I’ve run it a couple nights at home with two different CPAPs, and learned that my older CPAP (described in previous post) draws about 3.1 amp-hours in 7.75 hours, which would give me 9 nights before dropping below 50% SoC.

My newer APAP draws a little more power - 8 nights.

Install of the power meter required stripping and crimping. Rotus8 installed the previous version of this meter on a pony battery, and described it here (link). Rotus also installed the previous version for his trailer battery (link).

I was unable to find that version, which uses a shunt and is a bit less expensive. Mine uses a hall-effect sensor - you run the positive load & charge wires through a little ring, I guess it works by induction somehow. Then you need power to the meter itself. The slightly hard to follow instructions are here (link).

I like it so much I ordered one for the trailer batt, and will update this thread (link) when I install.

As someone who depends on CPAP therapy for their daily health and well-being, this has been a most rewarding project. Data, I now have real data! Incidentally, the headboard cabinet where I could place a CPAP was the initial feature that had me consider C-I! I knew I needed that, and only a couple manufacturers offered it. I’m glad I found C-I.

Pictures below. This is a $29 meter - the .1 amp disagreement between it and my charger monitoring app is certainly close enough! Counter-intuitive to me, the meter shows positive flow when discharging, and negative when charging. The best feature is the Amp-Hour reading (ah) upper right.

My pony is a 60ah battery, that I only want to take it below 30ah occasionally if at all. A standard AGM or lead-acid should never be taken below 50% SoC, the Victron batts have a slightly different chemistry. I think this is starting to show up from other manufacturers.

 

Kevin S., both the pony and trailer battery systems continue to perform very well.

The $29 DROK power meter on the pony battery turns out to be somewhat unreliable. A couple of times it has returned a disaster-like reading - wait a minute, that was only 2 nights, why does it read a 30% SOC? Other reviewers have also reported this. On the one hand, it does that. On the other hand, it’s 1/10th-ish the cost of a Trimetric. For a third consideration, it really did help me zero in on my actual power consumption with CPAP, which was well worth 30 bucks! And, a quick disconnect from the battery resets the meter (so far).

I’ve not yet installed the 2nd power meter. It may just sit on the shelf a while more - not sure if it will be a backup for the pony batt, or will go on the trailer battery. Maybe there’s something more reliable out there.

The Victron battery chargers have provided the saving grace to easily weather the unreliable power meter reporting. Victron’s bluetooth app has updated the charger firmware a couple times since installation, and, *when plugged in to AC* retrospectively provides the confidence reporting that assures I’ve not toasted a battery.

Last point - I think it was this thread where I documented updating the trailer batt to a 100ah Victron? With the pony batt I’ve never needed to fall back to the trailer batt, so, with my LED bulbs in the trailer, using the sink, and not much use of the fan, I’ve only sipped at the 100ah trailer batt. I’m super-happy with the peace of mind it provides, and I’d do the same again. I don’t know how easy it is to source Victron - they are a great marine/solar manufacturer, but availability and distribution for small projects can be challenging.

 

Here’s a link to my install of a 100ah Victron Super Cycle AGM as a replacement for the trailer battery:
New Td Battery On Its Way

 

So I put one of those plastic battery boxes on the trailer tounge and keep a litium ion battery in it. It's wired to an outlet in the headboard cabinet, were I keep my cpap.I get a week or 10 nights out of it easy. It has to be charged with a smart charger.

 

What are the power requirements of your CPAP machine? Mine requires 24 volts. I bought a 12V DC to 24V DC converter from the CPAP manufacturer. With the humidifier turned off, I only get two nights use out of the Camp Inn AGM battery.

 

What’s your lithium battery rated for? If readily available, the amp-hour rating would be most helpful for comparisons. (Ah, 20-hour a/h rate)

I’m always collecting info! Do you have the little 34 ah or the agm upgrade 76 ah battery? How old, do you consider it to be in good condition?

It kinda blows that many people can’t easily get a 12v native cpap covered by medical insurance, or even supplied by their regular provider. I lucked out with (12v) Philips Respironics supplied by both of the providers I’ve had over the last 20 years.

Of course my humidifier is off too. My calcs show about 4ah or maybe 52w per night. I think I can get 8 nights easy on my newer 60ah Victron AGM pony battery, but I’ve only gone up to 5 nights so far. I have to do some measurements on my new cpap, Dreamstation 2.

 

It is so odd when odd voltages are selected….5 and 12 (usb and car) are everywhere….why 24? Voltage relationship to amperage, I know…..

 

Its a green life size 24 rated at 75 amp hours. It has to be charged with a smart charger..
My cpap is a 12 volt.

 

Wow! Since you can draw a lithium down nearly 100% without damage… that could be as much as 20-ish nights? I shouldn’t be doing the math in my head, but I am :O

That seems like a great cpap battery solution!

 

Here is a link Amazon.com: GreenLiFE Battery GL75-75AH 12V Lithium Ion Battery Group 24 : Automotive as the battery only weighs 26 lbs I mounted it on the tongue.

 

Boondocking without a clap is not an option for me as i'm sure its not for others here. What i did was buy a Jackery 300. It fits in the lower compartment on the right side of the AC. The cpap fits right next to it. I power the cpap with a 12V plug and it only takes the power to about 50% overnight. In the morning I charge the Jackery back up with the solar panel with the 12V plug on the passenger side of the camper. I have the ability to get about 60" away from the camper, so I can find some sunshine if I'm in a shaded area. Camping in the southeast, there's lots of shade.. After the Jackery gets charged I unplug it and let the battery recharge. If its a travel day then the Jackery goes in the truck and charges as you drive. I don't like camping where there's electric and water and its more like a subdivision than a campground. We prefer National Forest campgrounds and Corps of Engineers Campgrounds. We haven't done the extended out west trip yet as work schedules aren't permitting that much time away at present.

 

Yes, I think we're very much on the same page! Bearing in mind that when I did my initial setup in Spring 2018 lithium seemed quite expensive per watt.

I've since had to update the system, and replaced the dedicated pony/cpap 60ah AGM battery with a 50ah lithium last year. At that point I already had the charger & etc., so, just went with a new lithium battery rather than switching over to a lithium "generator" like Jackery. Which I might have done if I was starting from scratch - it's got lots more functions; I just have 12v out and a separate charger, very much the basics.

No nights without CPAP, extra capacity, and redundancy were my goals.

And, that headboard cabinet was what originally had me on the track of CI - my batt AND cpap are in it at night!

Enjoy! We sure have! National Forests, State Parks are our mainstays in the Pacific Northwest, occasionally National Parks.

EDIT
National Forests and National Parks round here, including campgrounds, never have shore power, but campgrounds almost always have water & vault toilets near campsites. Mostly, we’re only boondocking our power.