Please help me set up a system for my father's CPAP machine

CountyMounty · May 2016

My father has recently been required to wear a CPAP machine at night. He spends a lot of time at our off the grid family camp and is deeply upset about not being able to spend as much time there so I am trying to get something set up for him quickly Up until now he has gotten by with propane lights, refrigerator, and oven and occasionally running a generator to power additional lights and electronics and I dont intend to change that and set up a large system just enough to cover this. Obviously he doesn't want to run a generator all the time to power the machine. He liked the idea of a small solar system to be used in combination with the small (3500w) generator. I have read through this and several other forums but there is just so much info to take in and try to get started, especially since I'm kind of in a hurry to help him out as its the time of year he wants to be there. I'll apologize in advance for it being lengthy.

Ok so what I have so far to begin this set up is 2 100w mono solar panels, 2 100ah 12v batteries, a 20A charge controller and most of the wiring. Here are my questions:

- Does that seem like a large enough system to power a CPAP machine for 7-8hrs a night and possibly a couple other low draw devices occasionally? (FYI CPAP is a ResMed Airsense 10 which from what I've seen uses more power then most)

- The CPAP came with a 12v converter that attaches to auto 12v plug or direct to 12v battery. He already tried attaching it to a standard small car battery and got about 3hrs run time out of it before it shut down. Is it possible that I could wire this into the "load" output of the charge controller and run from there? Does the load output get power from just the panel when its charging or also back from the battery bank? The reason for this is it would work out much better with where I intend to place my components (panel on roof, charge controller upstairs in bedroom where CPAP will be used, and batteries downstairs where inverter and other devices might be used. If that is not possible I will probably connect directly (although with a long wire run) to the batteries to have less waste of power thru an inverter.

- To have it set up so that the batteries will also charge off from the generator whenever it is running can I just connect a battery charger directly to the battery (1st battery wired in parrallel which will also be connected to the controller and maybe a load or inverter) or will this cause damage to the controller or inverter?

- What size battery charger would one recommend? All I currently have are a couple of 10A max car/marine charges? I know they make inverters that have chargers built and while that might be ideal they are fairly expensive. I've set myself a $500 for this that I've already gone over and would like to keep cost down?

Thanks in advance for any help. I will be starting to set this up this weekend.

Adam

BB. · May 2016

Welcome to the forum Adam.

To design a system, here are the basic questions:

How much "energy" does the CPAP use (120 VAC, 12 VDC) in Watt*Hours or Amp*Hours (what voltage) per night. If AC, you can use a Kill-a-Watt type power meter, or for DC a DC Amp*Hour/Watt*Hour type meter. Plug the CPAP into one of the meters and run overnight to get your Watt*Hours (or Amp*Hours @ what voltage) per day energy usage.
How many nights without sun (1-3 days, 2 days is typical).
Any other energy usage (LED lighting, cell phone charger, laptop charger, radio, etc.)?
Lead Acid type battery?
Just seasonal or weekend use? Or for multiple weeks and/or >9 months at a time (full time off grid).

Here is a website with some CPAP machine information:

http://www.cpap.com/cpap-faq/Power.html

An AC unit is very doable for off grid solar--A portable (battery pack included) machine may not include a humidifier (I think). Does your father like to camp/hike away from the cabin?

Where (nearest major city) is the cabin and what months/seasons will you use the system (hours of sun for solar).

-Bill

CountyMounty · May 2016

Thanks for a quick reply. I will read some more at that link.

I still need to do some more research on the actual power consumption of the unit, on CPAP forums I have read that that particular machine depending on settings (and use of heat or humidity) can use anywhere on average from 15 to 25A per night. The CPAP machine itself appears to actually run on 24V, the AC household connection for it converts the AC to 24V, the DC connection for auto/battery apparently converts that to 24volt. I have read that many CPAP users prefer to use the DC converter that came with it vs. using an inverter off the battery as it uses less power (and eliminates two conversion I guess).

We are in eastern maine, He will stay at the camp for the summer into fall as often as he can if I can make this work, sometimes for weeks at a time. In fall, winter, and spring he stays there every other weekend when he can, he likes to spend as much time as possible. Camp is just a short drive from home but my parents prefer to stay there often.

I intend to set the system up so I can easily expand it if needed and if I can get him to agree (another panel, more batteries in the bank etc) but what I listed is where I want to start and he has indicated he doesn't want a large system to power everything.

We can run the generator more often on days without sun if needed. Once I can make sure its all hooked up correctly.

Can you help with my questions in regards to the initial set up so I can start hooking up what I have for now and test it?
Can I run the CPAP hook up directly off the "load" on the charge controller I have read conflicting info on that some people say that is made only for very small loads like just a 12v bulb or two, while others say they have hooked a small inverter to it to power stuff(which I wont have to do as I have the 12V converter that came with the machine) and yet even others have said that load output should handle whatever the charge controller is rated for (which doesn't seem to make sense to me).

Also as I said can I just hook a normal battery charger up to the battery bank (1st battery in parallel) the same as I hook the charge controller and small inverter into so whenever the generator is on it is charging the batteries. The inverter is because they do occasionally run a small TV and satellite box off 12V batteries with an inverter already so I intend to hook this up to the battery bank with inverter as well.

I know I will have to play around with things to get the system sized right but I want to get started and make sure I'm atleast hooking the components up right. I also know that there are much better ways to incorporate a system then how I'm trying to do it (like with an inverter with a built in charger) but this is where I would like to start. I'm afraid if I dont do it soon he'll throw the CPAP in the lake the next time it runs out of battery lol.

BB. · May 2016

Get something to measure the power of his machine, as he uses it (the settings, etc.).

Personally, I do like using an 120 VAC inverter as you don't have to have all of the 12 volt adapters and cigarette (or other) receptacles. Take a look at the MorningStar 300 Watt unit... Should power most of your devices very easily, and pretty efficient (hook up to 2x 4x 6 volt @ 200 AH "golf cart" batteries for a 12 volt bank). Also, it is easier to send power longer distances at 120 volts vs 12 volt (lightweight cord vs pretty heavy copper cable for longer 12 volt runs).

Assuming that is a 25 AH @ 12 volt system--Some very quick math. 2 nights, to 50% maximum discharge (longer battery life)--Just for CPAP (use larger numbers for tv, lighting, etc.--25 AH * 12 volts * 1/0.85 inverter = 353 WH per day--500 to 1,000 WH per day is a "small" cabin system typically):

25 AH * 2 days * 1/0.50 max discharge = 100 AH @ 12 volt battery bank (DC direct) connection
25 AH * 12 volts * 1/12 volt battery bank * 1/0.85 inverter eff * 2 days * 1/0.50 max discharge = 118 AH @ 12 volt battery bank (AC inverter)

For minimum rate of charge... 5% is good for weekend seasonal (sunny days) use. For near full time, through winter usage, 10% to 13% solar is usually a good choice. Picking 118 AH battery (AC system) usage:

118 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 111 Watt array minimum
118 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 222 Watt array nominal
118 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.15 rate of charge = 289 Watt array "cost effective" maximum

And then there is based on hours of sun--Fixed array, Bangor Maine AC system (353 WH per day):
http://solarelectricityhandbook.com/solar-irradiance.html

Measured in kWh/m2/day onto a solar panel set at a 45° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.35	4.16	4.74	4.71	4.66	4.78
Jul	Aug	Sep	Oct	Nov	Dec
4.82	5.01	4.63	3.77	2.96	2.65

Assume 2.65 hours per day of sun (deep winter, minimal generator use, small system):

353 WH per day * 1/0.52 AC system off grid eff * 1/2.65 hours of sun (average Dec day) = 256 Watt array minimum "break even" December

Anyway--Plug in the numbers that you want to use... A 12 volt system with a few "golf cart" batteries should do well for your needs. Just have a good estimate of your power needs--And electrical loads do tend to grow over time. But, "remote" cabins are also subject to theft and damage--You may not want a real expensive/obvious solar power system out there either.

Some points for discussion....

-Bill

CountyMounty · May 2016

Thanks again. I will try to get some measurements on the machines usage. Theft is not much of a concern, while it could happen we have never had a problem in all the years we have owned it for several different reasons. Its not exactly "remote", Its off grid because the nearest power line is about 2 miles away. It is on the lake and set on 80 private acres but its only about a 10 minute drive for the center of the nearest town. Anyway I am going to start the initial set up this weekend and see how things shape up. I initially intended to power the CPAP with an inverter until I realized that it came with the DC converter already made to hook to a battery and it would have been great if it could have been powered off the load of the charge controller as that will be located in the same room as the machine would be used in. I will definitely factor in wire run length though like you said as it would be much better to have a longer 120V run then a long 12V run. Unfortunately I had already gotten the 2 12v 100ah batteries before I read about how 6V golf cart batteries work well so I am going to try to use them to start. Thanks so much for your responses.

BB. · May 2016

You should be fine connecting directly to the battery bus, through a fuss/breaker in the positive lead (to protect against shorts).

200 AH battery back and a 25 ah per day load, I would not worry about using the LVD on the charge controller. If you use the LVD, set it to 12 or 11.5 volts cutoff. Many are set to 10.5 volts, which will over discharge your battery bank and ruin them.

-Bill

mike95490 · May 2016

I used a portable Jump Start power pack to power my CPAP @ 11" and no heat in the humidifier. If you must use the humidifier, you will consume a lot more electricity and need a larger system.
Here's another CPAP thread here
http://forum.solar-electric.com/discussion/comment/136706#Comment_136706

CountyMounty · May 2016

He has already tried a car battery and a large jump start pack, both of which only last a few hours, now that could possible be because they are not new and/or not large battery based but I really expected the larger jump starter pack (I believe it is 1500peak with a built in inverter) to last longer than he said it did. I will read that forum thanks.

Today I went to the camp and got the panels mounted to post ready to put up, ran the wire from near where the panels will be to where I mounted the charge controller, and ran the wire from where the batteries will be to the charge controller. I briefly hooked up the charge controller to a marine battery just to check in and it should the battery status and its ready to go. I also checked and found that it does pass that power to the "load output" on the charge controller so that might very well mean I can connect the 12v converter that came with the CPAP directly to the charge controller which will be nice since they are very near each other in that room. I also was able to return the two 100ah 12V batteries I have and will be picking up 2 215ah 6v batteries tomorrow and then going back Sunday to work some more. I expect to add a couple more 6v batteries in the future but this is a start to see how it works.

I still am not certain on the direct connection to the charge controller "load output" and also still not sure about what battery charger to get to charge the batteries from generator as well but will figure that out as I go. At this point I'm thinking a 20A battery charger would be a good start. I do not want to get an inverter with built in battery charger as they are just too expensive and I already have several regular inverters. This is quite the learning process but I must say its kind of exciting setting it up and hoping it works out.

Thanks again for the responses.

westbranch · May 2016

I am not sure how carefully you read Bills post and scoured the formulas, buried in that stuff is a " / o.50".... this number is quite important! It means that you take any battery and assume it has half the Ahrs in it that the rating says it does.... the reason for this is that you do not want to deplete the battery more than 50% or you run the real risk of killing it very quickly... it is very hard to recover a battery repeatedly from < 50%...

you said:
but I really expected the larger jump starter pack (I believe it is 1500peak with a built in inverter) to last longer than he said it did.

BB. · May 2016

Take "jumper battery pack" ratings with a grain of salt... Most of the ones I have seen rarely give an XX Amp*Hour rating @ YY Hour discharge rate (unless you can find a manual that lists the "replacement battery").

The few jumper battery packs I took apart or found a manual for, (with lead acid batteries) where only on the order of 20 Amp*Hour capacity (@12 volts)... So, a 25 AH per day CPAP load would run the battery down flat pretty much over night (and lead acid batteries are pretty much "toast" after taken "dead") a "typical" jumper battery pack.

-Bill

CountyMounty · May 2016

Thanks for the continue help all.   I did read Bills post closely and reread all post several times, I admit the numbers themselves are a bit confusing but I did pick up on some off it including the 50% part of it.   I am going to try to read more about the best treatment/maintenance of the batteries to make them last a while. My dad always buys jumper packs to power small electronics at camp (radio, small TV, police scanner etc) because its "easy" but it gets expensive and is a waste and he destroys them pretty fast. The one he tried with the CPAP was a large one and I'd figured he might get 1 night out of it but didn't expect anything more.   I am trying to help him on getting a good set up over there.

So the weekend set up went quite well. I got the whole system hooked up but still want to do a little more to it and still need to get a permanent battery charger hooked up.   One of the panels I bought got slightly damaged in shipping. I'm sure I could have used it but I'm sending it back and not sure if I will get a refund or exchange yet. So what I have right now is one 100w mono panel, charge controller and two 216ah 6v deep cycle batteries.   I was able to wire the CPAP 12V converter directly to the charge controllers 12V output and it seems to work fine (I am going to wire in an actual 12v wall mounted plug to avoid just having the female plug hanging there and to make it look neater). So far he has run it 2 nights all night (6-7hrs) and it worked fine. I haven't been able to go back and checked on the power used and battery status and all he told me was that he did hook up the battery charger and it didn't charge long (off a 10A standard auto charger) before showing full.

If things continue to work well he is already going against what he first said and talking about expanding, having me add two more 6V batteries (and the other 100w panel) and try to power his TV and satellite box and a couple small lights. I will be doing a bunch more reading on here in preparation for that to see what the best set up is.

Yesterday and today have both been very cloudy with showers so not a lot of sun, and as I've said I haven't been back to see how much power has been used or gained.

Remaining questions I have to finish this off.

- Any suggestion for a inexpensive charger to hook to the batteries to charge them whenever the generator is running. I'm thinking a 20A (10%ish of bulk charge) but want something that you dont have to push a button to select your settings and will just come on when generator is started if generator is running anyway might as well top off the batteries.

- Want to verify my wiring set up.   I tied + of battery 1 to - off battery two (4 guage post wire) to make it a 12V system. I then made all other connections to the remaining + and - terminals. Am I right that I should not tie anything else to the terminals that connect the 2 batteries to make it a 12 V system? So far I only have the the wires between the charge controller and the battery (10guage) but will eventually want to add an inverter and a permanent battery charger charging from the generator. For just a week or two he is just hooking the battery charger up with alligator clips.   I put (and will put) 20A fuses on all positive wires. Does this all sound right?

- Lastly and this seems like maybe one of those questions that gets a newbie laughed at but the solar panel is mounted on a post and it will wiggle some in the wind (but the mounting set up itself is very sturdy) will this cause any problems?

Thanks again I'm excited to keep working on this project and see the outcome and happy that my father is using his machine instead of throwing it in the lake.

westbranch · May 2016

well the charger's ok at 20 amps but if you will add 2 more batteries you might want to go to 40 A as you just doubled the Ah capacity you need to replace as he will use a lot more with TV and Sat hook up... The more power you have the more you want to use!
ps my sat system + Net uses about 50W / hr

Please help me set up a system for my father's CPAP machine

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