My backpacking/ camping CPAP battery solution.

[BigE94]

Tyler and I have taken part of this discussion to PM and we think the continued conversation is a good one and may be able to help others. Below is a transcript of the conversation.


BIGE94

So in your last post you mentioned that it was easier to charge to 80% twice than to charge to 100% once. Hope I got that correct. So using a smaller 11000mAh battery and a 24V solar charger even under less than ideal conditions for 10 to 11 hrs (say up at 8am and charge to 7pm) you could still get back to 70 to 80 percent charge which would be enough for the next night. I was able to get almost 12 hrs out of one of these batteries. I think it would be interesting to try it with a solar charger.

I'm shooting from the hip here and using "rough logic"

So apply some math... am I close?

TYLER

Hi that is what I said.

Your battery goes through 2 phases, a constant current charge, then a constant voltage.

The constant current phase is when your 10 amp charger at home is charging at 10 amps. Or in the case of a solar panel, if the best that you can get out of it under today's conditions is 2 amps, AND that is what is being delivered to your battery then that is what you would call your constant current phase for a solar panel. This phase comes to and when the battery reaches its rated voltage. Additionally this is considered the 80% charged point for most batteries.

In the second phase, the charger holds itself at a constant voltage. Of course, that means the current slowly decreases. So imagine filling the top 20% of the gas tank in your car with a pump that keeps getting slower and slower. It reaches a point where you are might be spending more time waiting than it is worth.

So if I go back to my original statement, waiting for a 100% charge on your CPAP battery would be worth it but not neccessary. And, in the case of setting a cellphone down to charge, it would be silly to wait to use it once it has reached 80%, unless it was to be your last charge of the day before it gets dark.

With the 24 watts solar panel and 11000mAh battery:
80% charge would mean that you have 88000mAh in the battery.

Imagine that a 2 amp solar panel is only delivering 1.1amps due to clouds. You would reach 80% in 8 hrs, but 100% will take you more than 10 hrs....it may actually take a full 16 hr day to get 100% but all I know for sure is it is going to take more than 10 hours.

Hope this helps.

Tyler

[Tyler883]

Oops, I added one too many zeros. 88000 should be 8,800.

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[Clarrie]

Interesting thread.
I hope that you find a solution that works for you.
I have been using a CPAP machine for years.
I find that I sleep well enough in a hammock to survive without my CPAP.
This is just one of the reasons that I love hammocks.
I wouldn't get out in the bush at all if I was dependant on ground sleeping.

[Tyler883]

Hi. Just a quick update about my solar panel.

While in theory, a 25watt 2 amp solar panel should charge my battery just fine, i decided to set it up yesterday to measure the actual current in a real world test. See the pictures.

I only got 200mA charge current from typical day with no direct sunlight. 10% of the rated maximum capability sucks. It will take 2.5 days to return the battery to full charge from just 1 night of sleep. I've looked into addinv more solar panels but then my $100 cost climbs up into the $500 to $1000. And the size of the panels starts to get ridiculous. Im not packing 2'x4' panels around in the bush, they would only be used at my vehicle.

Summary: While i suppose the solar panel will work in direct sunlight, i cant reccommend solar panels to anyone without warning you to EXPECT PROBLEMS..

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[Tyler883]

Preliminary tests are good. Will be trying this tonight on my cpap.

It will produce 12volts / 5 amps from any battery 15 to 40volts ( provided that the battery is able to provide enough current)

I have some 20volt lithium ion batteries designed for a cordless chainsaw.

If all goes well i could replace 40lbs of lead acide batteries(4 batteries totalling 40Ahrs at 12volts) with 13lbs of lithium(4 batteries totalling 30Ahrs at 20volts).

My solar panel wont charge a 20volt system but i think ive established that my solar panels probably wont charge my 12volt system either.

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[Tyler883]

In theory, 30 Ahrs could give me 4 nights sleep without a recharge. With only a 13lb handicap when i'm packing into a campsite.

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[IRONFISH45]

If you pause for 30 to 40 seconds that is a stoppage. If you stopped permanently you wouldn't wake of course.

If you are having those problems you need a sleep study ASAP. Dont wait.

It will change your life.

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I wish more people would become aware of sleep disorders and how dangerous they are. Sying from not breathing is not a kind gentle way to die. There is a very clear link between Sleep Apnea, heart disease, diabetes.

For the ladies Sleep apnea presents itself a bit differently or so my doctor tells me. In my case, I was not sleeping, light rest maybe 45 minutes a night. I fell a lot, cranky, stressed, awful morning headache. Every time I went to doze off, I would feel like I had to wake-up to breath. My sleep study showed my HEART was stopping everytime I dozed off.

My C.P.A.P. was an immediate help. No more morning headache, no falls, no cranky, everything is better.
I also have a computer implanted to defibrillate my heart as needed.

This is life and death stuff. A Sleep study is a reliable way to learn what is happening when there is a sleep disturbance.

[Tyler883]

I wish more people would become aware of sleep disorders and how dangerous they are. Sying from not breathing is not a kind gentle way to die. There is a very clear link between Sleep Apnea, heart disease, diabetes.

For the ladies Sleep apnea presents itself a bit differently or so my doctor tells me. In my case, I was not sleeping, light rest maybe 45 minutes a night. I fell a lot, cranky, stressed, awful morning headache. Every time I went to doze off, I would feel like I had to wake-up to breath. My sleep study showed my HEART was stopping everytime I dozed off.

My C.P.A.P. was an immediate help. No more morning headache, no falls, no cranky, everything is better.
I also have a computer implanted to defibrillate my heart as needed.

This is life and death stuff. A Sleep study is a reliable way to learn what is happening when there is a sleep disturbance.

Im glad you are still with us. For most people, sleep apnea affects their quality of life. In my case, it was severe enough, i probably would have suffered a heart attack or stroke in the past 10 years.

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[Tyler883]

Tried my 'step down' converter last night.

It failed miserably. Lol.

The CPAP is experiencing brown out conditions during start up. Rather than starting, it gets stuck in a on/off loop.

For troubleshooting purposes, i put the CPAP on a variable power supply and was able to demonstrate that a working cpap will remain ON while i simulate a battery dying by turning the voltage down. It stays on until about 9 volts. If it will run at 9volts, then my 12volts at start up is fine. I just need more amps during startup.

Im going to try some capacitors, dont know if i have any large enough.

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[Tyler883]

Just wanted to update you on my progress, or lack of progress.

Last july i took my equipment to a scout jamboree for real world testing.

The subcamp headquarters had generators and a special area for recharging batteries so i was good all week.

However, my goal was to create a sustainable cpap battery and solar charger system. I had 4 nights worth of batteries and a solar panel rated for 24watt maximum output. Just 7 hours at 1 amp(12 watts) would be enough to match my cpap.

To make a long rant into a short story, 16 hours per day of sunshine was not enough to stay sustainable.

with a 4 night battery, my strategy was to keep my solar charger in a bulk charging mode, ie delivering every last bit of current that it is able to produce.

24watts wont do it.

i plan to do more testing at home. i suspect that under ideal conditions i will be unable to observe anything remotely close to 24watts.



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