Help!!! I need for my CPap

[Jacksonricher]

I have a upcoming appointment with my Dr about this in a week.
I called the medical supply company that takes care of all my supplies and the have a 12v adapter to plug into the cigarette lighter. $45 but it won't void or fry the machine. Now just to get the solar part and I am in business.

 

[DLTooley]

I have a upcoming appointment with my Dr about this in a week.
I called the medical supply company that takes care of all my supplies and the have a 12v adapter to plug into the cigarette lighter. $45 but it won't void or fry the machine.  Now just to get the solar part and I am in business.

I think I paid $37 a few years ago. A single Walmart is all you need to get started, the one year replacement warranty makes it a good training battery.

 

[tx2sturgis]

A single Walmart is all you need to get started...

I think Sam Walton had the same idea. 

 

[Knit]

I have the same brand Cpap as the OP. With the same 12v 6.67A rating. With a humidifier. I put a kWh meter on it for the last few nights and the most it has used in about 10 hours is about 100 Wh. So it is drawing 100 / 120 = 0.83Ah at 120 V. At 12 V, that would be 0.83 * 120 / 12 or 8.3 Ah. Toss in 90% efficient inverter and this is 8.3. / 0.90 = 9.2 Ah. Call it 10 Ah at 12 V to keep it simple. Sorry about all the math.

I also have a travel Cpap rated at 13 V 1.5 A that uses way less. I often travel with a small 100 Wh lithium battery that legal for carry-on that can easily last a nighttime of use. Weighs only a pound or two. You do have to get the right connectors and use a port that is voltage regulated, but it works fine.

There are other variables like the cmH2O setting and I don’t know why the input ratings are so conservative. But the point here is that the OP should be able to have a lot less battery Ah that what is being recommended here if all that is desired is the ability to only run a Cpap. And with less battery, less solar would be needed.

 

[John61CT]

Very valuable to have hard data.

But that last generalization is not correct.

The daily energy input to the bank needs - over time - to balance the energy consumed.

A larger bank extends that "over time", so cloudy days, number of nights on shore charger, or days without extended driving, can be longer.

A smaller bank means you **have to** get recharged more frequently.

But I agree, if the OP is able to reliably recharge to Full most days, then it seems even making do with one excellent battery used for Starter and House is possible.

Need to know the largest BCI size that will fit, e.g. G-31, G-27.

 

[Knit]

John your point makes sense that one should plan for extra capacity for reliability or cloudy days or whatever.

I think what I was trying to say is that oversizing by a factor of 10 might be a bit much.

There’s a recent crop of LiFePo jump start batteries that I am thinking about checking out for Cpap use. Relatively cheap and small and light. They recharge from AC power in 3 hours or DC @ 12v in 6 hours. Imagine carrying 2 or 3 of these around in a van so you have some backup. See https://www.harborfreight.com/lithium-ion-jump-starter-and-power-pack-62749.html. I know this isn’t their designed use, but what do you think?


Sent from my iPad using Tapatalk

 

[John61CT]

I think they are a lot more expensive, and would not last many cycles.

Yes small and lightweight.

Lightly cycling - as in only discharging to 75-80% SoC will make the Duracell bank last maybe 8-10 years if otherwise well cared for.

Nothing will be cheaper, and if you decide to run a Fantastic Fan, a fridge, some lights, a tablet etc, you're all set.

The lower quality solutions will all end up being much more expensive long term.

And IMO reliability for this use case is #1 priority..

 

[Jacksonricher]

Ok, I am back with more questions.
I pretty much decided to go with Renogy Mono starter 200 watt kit. And at Batteries plus the Duracell 6v ultra pro w 225ah per the store managers recomedation and people on here.

For the 100 watt system I understand I only need a pair of 6v batteries. If I go to 200watts, do I need two more batterie for a total of four?
I eventually want 400 watts. 4 panels. I want to run my CPap plus a fridge, Tablet, lights in the van and LEDs around the van for spots and driving.

Do I add two 6v for every 100 watt panel? Or is it more complicated than that?

Thanks
Jackson

 

[Knit]

Most would say that the rule of thumb is about 100W solar per 100Ah of battery at 12V. Your math is missing that the batteries you are buying are rated at 6V. So you need to divide the total 6V Ah by two to apply the rule of thumb.

So most would say you need about 200W of solar per pair of 225 Ah 6V batteries.

But you have added complications You’ve added way more load like refrigeration since your original post that was about running a Cpap.

And as I understand from prior posts that you will neither have shore power nor be driving a lot to charge from the alternator nor be using a generator. So you need a lot more solar for cloudy days, wintertime, etc. I’m sure someone else will jump in on this, but you likely need double or more solar in your case.

Good luck.

 

[Jacksonricher]

I won't be adding anything until next year.

I will be useing two 6v 215 ah Duracell batteries to equal 12v 430amp hours.

So it sounds like I have more than enough batteries for up to 200w of panels. Please correct me if I am wrong.

Thanks

 

[John61CT]

The number of panels gives you a certain quantity if energy to use.

Let's say from 200W in sunny weather at that location you usually get 60AH.

If you use 40-50AH per day on average, it does not matter if you have a 200AH bank or an 800AH bank.

That just gives you more buffer for cloudy days.

If you have other energy sources, less buffer is OK.

If solar only it becomes more important.

The key is knowing how many AH you are using, do not go below 50% SoC except occasionally, better to cut back on usage.

 

[Knit]

I won't be adding anything until next year.

I will be useing two 6v 215 ah Duracell batteries to equal 12v 430amp hours.

With two 215 Ah batteries you have 430 Ah at 6V. You only have 215Ah at 12V.

If you think the rule of thumb of 100W per 100Ah at 12V applies to your situation, the 200W of solar is about right.

 

[Jacksonricher]

Thank you Knit for clarifying that for me .

 

[Knit]

Thank you Knit for clarifying that for me .

Please be sure to reread my post #29. To run everything you are now thinking about you are likely to need more solar if you never get shore power.

There is a nice discussion on sizing solar and batteries at https://www.parkedinparadise.com/electrical/

 

[Jacksonricher]

I have thought about that. I have changed my mind about shore power and want that option.
I have two 100 w panels now that I will install.
It seems to get more and more complicated.