Charging my CPAP battery

[NAUJoel]

Hello Everyone,

I love camping, but being that I got diagnosed with sleep apnea about 2 years ago, I've been a bit limited. As a result of my condition, I now use a CPAP machine which has done wonders for my sleep! I have recently purchased a Lithium Ion battery pack for my machine and I'm excited for my camping trip in about a month. I was wondering if anyone here can give me some good guidance on how I could potentially build a solar charger for my battery pack. The specs on the battery pack, per the website that I bought it from are as follow:

Lithium-Ion battery, output current of 7.8 amps, output voltage of 12v, charge current of 110-220, 5 hour full recharge time.

http://www.cpapsupplyusa.com/CPB-Pack-36970-CPAP-Battery-Pack-ResMed-S9-DC-Converter.aspx

My CPAP machine draws 90 watts. Do you think I could use the "15W Mono-Crystalline Solar Power Panel With a 12V Charger Controller" from Instapark to maintain it charged? See website:

http://www.instapark.com/solar-power-panels/15w-mono-crystalline-solar-power-panel-with-a-12v-charger-controller.html

Thank you all so much in advance!!

NAUJoel

[NAUJoel]

Answering my own? Double check my figures please.

Ok, so I'm trying to use my solid finance background (good with #'s) and pair with my resourcefulness to dig up an answer and now I need one of you Solar gurus to validate my numbers, please.

As previously stated, I'm trying to charge a 12v battery that is specially designed for my CPAP breathing machine. The battery is said to have an output current of 7.8 Amp Hours.
To charge the battery I was looking at the Instapark 15 watt solar panel with 12v charge controller.

So, the numbers I've come up with are as follow:

15 watts/12 volts = 1.25 amps from the Intrapak charger.
My battery would need 7.8 amps / 1.25 = 6.3 hours of daylight exposure to charge using the Instapark system. Plus 10-20% for inefficiencies.

Do those number sound right?

Unfortunately, I just placed the order for the battery, so the only specs I have are those per the website that I linked in my original post. My figures seem optimistic, plus, the website does say that a fully charged battery will provide 24 hours of use. Being that I use it only during sleep (6 to 8 hours a night) the daylight needed for it should be much less. I just hope my calculations are right.

[Sunking]

You have a lot of things wrong here.. Forget about amp hours for now as we do not even need to know that. What is important is watts and watt hours. Your CPAP uses 90 watts and you use th emachine for 8 hours so 90 watts x 8 hours = 720 Watt Hours. However depending on the charge controller type a solar panel will have to generate 1080 watt hours to 1440 watt hours to replace 720 watt hours used from the battery.

Next mistake you made is assuming you get some 6 or more sun hours. That is not even remotely possible unless you live near the equator. For a battery system you have to use the shortest months the device will have to work which sounds like you want to use it in November. I do not know where you are to determine your solar insolation hours but for sake of discussion lets say it is 3 hours and you will use a PWM charge controller.

So with a PWM controller the panels have to generate 1440 watt hours. All we have to do know is factor out the hours so Watts = Watt Hours / Hours = 1440 watt hours / 3 Sun Hours = 480 watts. A far cry from the 15 watts you are thinking.

I do not know your location so I do not have your real Sun Hours, but I can tell you in November it will be between 2 and 4 hours. What that means is the system is not portable as it will be a 200 to 500 watt system.

[Wy_White_Wolf]

SK - The guy has his terms so mixed up I'm not sure if it takes 90watts to run or uses 90WH a night.

Joel - Can you post a link to your CPAP so we can get the specs from it?

WWW

[Sunking]

SK - The guy has his terms so mixed up I'm not sure if it takes 90watts to run or uses 90WH a night.

I understand that but I picked up two things.

1. He said it uses 7.8 amps off a 12 volt battery = 94 watts
2. He also stated it used 90 watts.

So 90 watts and 8 hours is what I went by. I agree he might be confusing terms and likely does not know the difference between watts and watt hours because he concluded it would take a 15 watt panel and 6 or 7 hours of sun to get 90 watts. We all know that mistake well here.

[inetdog]

I understand that but I picked up two things.

1. He said it uses 7.8 amps off a 12 volt battery = 94 watts
2. He also stated it used 90 watts.

So 90 watts and 8 hours is what I went by. I agree he might be confusing terms and likely does not know the difference between watts and watt hours because he concluded it would take a 15 watt panel and 6 or 7 hours of sun to get 90 watts. We all know that mistake well here.

From my limited experience with CPAP machines (family member) I can say that it is very unlikely that a CPAP machine designed to be used optionally with a battery would actually use 90 watts. So it is possible that his 7.8 amps was really 7.8 AH too. But the proof one way or the other will come from the specifications of the CPAP machine.

[Sunking]

But the proof one way or the other will come from the specifications of the CPAP machine.

The Devil is in the details.

[bstedh]

I don't know if this is a concern for you but the specs state that you must use the suplied charger or risk damaging the battery. This means you would need an inverter to run the charger. The battery pack is not designed to be charged from a strait 12V supply. It outputs a nominal 12V. You would have to run an inverter for over 5 hours to charge the battery pack. You will be loosing a lot of power in the electronics to do this.

Making an assumption from what I am seeing your CPAP machine comes with a car adapter that you would plug into the battery pack. You would be further along to use a sealed lead acid battery and compatible solar charger than the LI-IO pack for off grid use.

LI-IO chargers shut themselves off frequently to check the charge state of the battery to determine what voltage and what current to continue charging at. At least if you want the cells to last more than 10 charge cycles.

Looking at the battery pack it appears to be constructed with 12X 18650 LI-IO cells which will provide you good energy density but will require a lot of power to charge.

You can check voltages on the battery but you should see 12.6V fully charged with a nominal output of 11.1V and a quit using voltage of 10.5V. (if my assumptions of the battery construction are correct)

To charge the pack you would have to supply a constant current up to a certain point and then switch to a constant voltage until the current draw reaches 0 and then shut down the charger completly. The charge profile for the battery pack would have to be obtained from the manufacturer to ensure you do not wind up with an exploding door stop...

I would contact the manufacturer and see if they have a 12V version of the charger for that battery pack. Then you could hook that up to the solar panel and charge controller. You would then base the panel size on the amp draw requirement of the charger.

[Sunking]

OK I went and looked at the battery is a 7.8 AH Lithium Cobalt battery @ 12 volts. Don't know why I did not do that in the first place

Don't bother with a solar charger just use the cigarette lighter port in your vehicle. There is no charge controller made that can charge the CPAP battery correctly. If you tried you would just destroy the battery. Lithium Cobalt batteries are very fussy and dangerous if improperly charged. There are no Litium Solar Charge Controllers I know of on the market.

The only other way to do this is as suggested. Buy a panel, charge controller, lead acid battery and use an inverter. Complete waste of time and money.

[NAUJoel]

OK I went and looked at the battery is a 7.8 AH Lithium Cobalt battery @ 12 volts. Don't know why I did not do that in the first place

Don't bother with a solar charger just use the cigarette lighter port in your vehicle. There is no charge controller made that can charge the CPAP battery correctly. If you tried you would just destroy the battery. Lithium Cobalt batteries are very fussy and dangerous if improperly charged. There are no Litium Solar Charge Controllers I know of on the market.

The only other way to do this is as suggested. Buy a panel, charge controller, lead acid battery and use an inverter. Complete waste of time and money.

Awesome! Thank you all for your great input. I knew I would be way off, but I'm curious of what you think of the article the I used to draw my conclusions : http://www.12voltsolarpanels.net/12-...ttery-chargers
If you read down in the bold section that says "Choose the right solar recharger", down in the paragraph that begins "The General rule to calculate..." that's where I came up with the figures I used in my second post. I'm thinking I mixed up terminology.

Again, thank you all for steering me away from burning up my $300+ battery investment!!

[NAUJoel]

SK - The guy has his terms so mixed up I'm not sure if it takes 90watts to run or uses 90WH a night.

Joel - Can you post a link to your CPAP so we can get the specs from it?

WWW

I don't think there is much info related to the power requirements of my CPAP machine at the website, but here's the link: http://www.cpapsupplyusa.com/36013-R...umidifier.aspx

Also, I grabbed my machine and looking at the back panel sticker it has some specs that may help such as DC24V, 1.25A (FG), 3.75A (Sys).

The AC Adapter that goes to my machine has the following specs, 90W, AC Input 100-240V 1.0-1.5A. DC Output +24V, 3.75A.

The link to the battery that I have on order is in my original post.

[Mike90250]

Mike here ( a fellow hosehead )

You will have to turn off the humidifier for your CPAP to run off a battery that you can lift.

I run mine (10" H2O) off of a 12V auto jump start pack.

This thread

http://www.solarpaneltalk.com/showthread.php?3317-Trying-to-Understand-the-Basics&highlight=cpap

covers another users CPAP quest. The last message there (29) covers my working pack.

Mike

[rreinha]

Hello Everyone,

The specs on the battery pack, per the website that I bought it from are as follow:

Lithium-Ion battery, output current of 7.8 amps, output voltage of 12v, charge current of 110-220, 5 hour full recharge time.

http://www.cpapsupplyusa.com/CPB-Pack-36970-CPAP-Battery-Pack-ResMed-S9-DC-Converter.aspx

NAUJoel

Use the car charger that comes with the battery.