solar power for dry camping & cpap machine

[TxGregory]

***Link Removed******Link Removed***Hello, I recently purchased a 2006 Thor Wanderer 30' travel trailer. I was disappointed that I could only run my cpap machine when the trailer is plugged in. I also dislike rv parks, and I really want to spend my time elsewhere, and preferably not plugged in all the time. I am going to put two 100 W solar panels on top. They come with a mounting kit and a charge controller. I thought about just hooking them up to charge the battery, but that doesn't do much for me, because I still can't run my cpap when I am not plugged in. So I was thinking of connecting them to a second deep cycle battery (I have a place for it up front), then using the second deep cycle battery to power an inverter that I would plug into the 30 amp plug that would normally go to external power. My wife also has a cpap, and we like to spend time on our laptops. I put together a picture of what I was thinking. I need some help from someone proficient in electronics to advise me on this. I don't have a lot of money, and I am not physically able to do crawl around the insides of the trailer reconfiguring things. So I came up with this, hoping that it would not all blow up! I am unsure of the size of inverter I need. I would like to just put a 3000W one on, but they are expensive. The 1000W inverter was much cheaper. Also, I am wondering if I need three panels. I am guessing that 3 panels and a 3000W inverter, on a sunny day, would allow me to run everything just as if I was plugged into power. But I don't want to spend that kind of money if I can avoid it.


Thank you in advance,

[pianotuna]

The possible solutions have been given more than once.

A. get a cpap that runs on 12 volts and install a dedicated fused outlet for it.

B. get an inverter that is just big enough to run the cpap. Us it to power a dedicated outlet.

Any competent mobile RV repair person could do the above.

[MrWizard]

hey guys

Cpaps and a Novice

NOT microwave, or A/C etc..

[12thgenusa]

TxGregory wrote:

And for that matter if someone turned on the Air conditioner, it would trip the inverter. Oh, and there is the microwave. . .

Whereas, if I go with something that will put out close to 30 Amp, 120 volt, then I would not have to be so careful. . .

I used to design and build IT, and we always had to be careful about bottlenecks. I don't want my inverter to be a bottleneck. . .

I saw a post from someone with a configuration similar to mine and that is what they said their did. If I am wrong, I would sure like to find out before hand! 🙂

Your one battery is the bottleneck. No way you can draw more than 300 amps DC to get your 30 amps AC. Trying to run the AC won't run the battery down because the AC will never start. The voltage will drop and the inverter will under-volt and drop off line. Likewise with the microwave or any other high draw appliances.

Without going to exotic batteries and many solar panels running the AC is a pipe dream. Microwave is doable with at least 4 batteries.

[MEXICOWANDERER]

Oh silly me...

And here I thought this thread was about batteries and CPAP machines...

[pianotuna]

Hi,

You spoke of bottlenecks. In this case the battery becomes the bottleneck. A 12 volt jar is tested at 25 amps demand. You can draw more but at some point voltage starts to sag badly. 75 amps is about the limit for a 100 amp-hour jar.

A 3000 watt inverter, running flat out, may draw 300 amps. So to "feed" it may be best to use 4 100 amp-hour 12 volt batteries wired in a balanced manner.

You also mentioned a stand alone battery for the inverter and another one for the house loads. That is a poor way to implement powering the cpap. It would be far better to put the batteries in parallel.

There is often, no reason to not run an inverter when plugged into shore power. I used to do this often with a 2500 watt MSW inverter to allow me to run extra devices beyond what the shore power could provide for.

However, I am unable to do that with my Magnum 3000 watt inverter as it blows the reverse polarity fuses on my converter due to a high inrush.

TxGregory wrote:


12gen,
I am with you. I would like to go with a smaller inverter, then I could stow it in its own battery box with the controller. But If I did that, I would have to be really careful about what I plugged into my abundance of AC outlets in my trailer. And for that matter if someone turned on the Air conditioner, it would trip the inverter. Oh, and there is the microwave.

Whereas, if I go with something that will put out close to 30 Amp, 120 volt, then I would not have to be so careful. (my controller supports 4X100W panels). I plan to add a couple of more batteries and panels in the future. So I am thinking that making everything capable of supporting 30 Amp 12 Volt will be a better solution long term. I used to design and build IT, and we always had to be careful about bottlenecks. I don't want my inverter to be a bottleneck. Now my assumption has been that if I had the 3000W inverter plugged into a 12v 100amp/hour deep cycle rv battery ... and I ran the Air Conditioner, that it would drain the battery and do no harm. I saw a post from someone with a configuration similar to mine and that is what they said their did. If I am wrong, I would sure like to find out before hand! 🙂

[MrWizard]

the answer i was given :
until the charging amps drop to (1) amp per battery
two batteries in parallel (2) amps at 14.7v
five batteries (5) amps at 14.7v
two AGM 6v GC in series = 12v , aka (1) amp at 14.7v

Sam Spade wrote:

BFL13 wrote:
My question then is, " How long can you leave it at 14.7ish before making it drop to Float at 13.7ish ?"

--And, how can you tell when it is time to drop to Float so you don't dry out the AGM?

AGMs don't "dry out".

And anyone who has to ask the first question should trust an automatic charger to do it FOR them.

Most people are not qualified to do it manually......including some of those who think they are.

[MrWizard]

I'm not suggesting "whole house" isn't a solution for some but there is more to it than just plugging the trailer's main service cable into the inverter.

absolutely correct

3kw and RV shore cord is not needed for CPAP and way to much for (2) batteries
run stuff like you have shore power ?
means have many KWhr of stored battery power
and then its still limited, MW for minutes only, coffee maker for a pot OK, water heater, fridge etc.. on propane, NOT electric, No A/C
there is many times the energy of (2) GC batteries stored in (1) gallon of gasoline
(1) gallon regular Gasoline = 33.44 KWhrs of electricity
approx 2786 Amphrs at 12v
(2) GC will apprx 240 amphrs if run dead flat, 120 amphrs to 50%
i gal of gas has over 10 times the amount of energy as two fully charged GC can hold

a generator is indispensable , Solar is adjunct for most of us, along with a large battery bank

can you run a CPAP with inverter and batteries YES
can you run the whole RV like it was on shore power with only two batteries NO.

if you accidentally leave something on, or try to run a high power appliance with a small inverter it will alarm and shut down
no harm done to the batteries

BUT use a 3kw whole RV with (2) batteries
and you will run a very real possibly of killing your batteries
the fridge will auto shift to AC, or the water heater, or you will forget to unplug the converter , try to run an electric heater ? etc..

[SoundGuy]

SoundGuy wrote:
The better solution is to either hardwire the inverter .............

I did, and now when I lose power in the middle of the night all I have to do is

Sam Spade wrote:
The MUCH better solution is to run critical systems directly off the batteries or a small full time inverter.

That's what I do and now if I lose power in the middle of the night I have to do.......EXACTLY NOTHING. :Z

This is camping, I have nothing in the trailer that is "critical". All the regular built in "important" devices - fridge, furnace, lights, water heater, etc - continue running if I lose shore power, nothing to do with the inverter. If I want to use "optional" items like the coffee machine (critical first thing in the morning!) or toaster all I have to do is roll over in bed and hit the inverter's remote and I have instant power to those dedicated receptacles I installed. Yeah, terrible amount of effort to raise my digit to the remote. :R

[Sam_Spade]

TxGregory wrote:

I am planning to have one battery for the controller, inverter... and another battery for the stock connection to the trailer. That way I would not have to turn off the converter to use the inverter. Where did you put your inverter? I am having a hard time finding a spot for mine.

This was a bad plan to begin with and nothing you have said yet has made it any better.

A 3Kw inverter will draw about 166 amps to deliver 2Kw. If your battery is maybe 250 amp/hours, it will be low enough in less than an hour before the inverter trips due to low input voltage.

The people who make off-the-wall configurations work are the ones who know how it all works to begin with. Those who don't know ahead of time and try to copy often end up with smoke and fire. Not joking.

You asked for advice and almost everybody who replied said "Don't do it" in one way or another. WHY ARE YOU NOT LISTENING ??????

[Sam_Spade]

SoundGuy wrote:

The better solution is to either hardwire the inverter .............

I did, and now when I lose power in the middle of the night all I have to do is

The MUCH better solution is to run critical systems directly off the batteries or a small full time inverter.

That's what I do and now if I lose power in the middle of the night I have to do.......EXACTLY NOTHING. :Z

[Sam_Spade]

BFL13 wrote:
My question then is, " How long can you leave it at 14.7ish before making it drop to Float at 13.7ish ?"

--And, how can you tell when it is time to drop to Float so you don't dry out the AGM?

AGMs don't "dry out".

And anyone who has to ask the first question should trust an automatic charger to do it FOR them.

Most people are not qualified to do it manually......including some of those who think they are.

[westend]

I am planning to have one battery for the controller, inverter... and another battery for the stock connection to the trailer. That way I would not have to turn off the converter to use the inverter. Where did you put your inverter? I am having a hard time finding a spot for mine.

This a poor design as you will get more power from multiple batteries connected. One single battery for inverter power is also a poor choice, mainly for the reasons in my post above.

You either need to do more home work or hire someone knowledgeable. Their is nothing tremendously hard about turning off a converter or other AC draws in an RV.

[westend]

One problem you're overlooking is that draining some batteries to nothing will kill the battery and that draining any battery below 50% will shorten the cycle life. A target SOC of 80% is certainly a sweet spot and if you can keep a bank above that level, you'll get a long life out of them.

Most quality inverters have a low voltage cutoff of somewhere around 11V. If the inverter cuts out at that voltage, you'll still have some charge left in the battery. Without powering the inverter it will rebound back to it's low SOC. It won't be a death sentence but it will impact cycle life. This is where correct design and application comes in.

The first thing you want to do is accurately assess your power usage. Add up all the devices used and convert that into AH drained from a battery bank. In this thread that revolves around Cpap use so that would be the starting point. The easiest way to accomplish this is to use a Kill-A-Watt meter. You can plug the KAW into your house receptacle and use the Cpap as you ordinarily would. It will do the measuring.

[TxGregory]

SoundGuy wrote:

TxGregory wrote:
Right now I am planning on a solar panel starter kit that includes a controller, a separate battery, a 3000W true sine wave inverter connected to the separate battery, and an extension cord plugged into the shore power outlet when I am parked.

WHY such a large inverter when just one battery won't be anywhere near enough to power it to it's full capacity? :h Keep in mind also that while powering the trailer "whole house" can work it does mean you have to be careful to always first turn off the converter and ensure anything that may otherwise be set to run on 120 vac is either switched off or switched to run on gas mode only. Also, whenever running on battery power alone make sure the fridge climate control is turned off, otherwise you'll be wasting valuable battery reserve. Unfortunately, some fridges don't offer this option, in which case it would be wise to add your own switch just as I did.

I am planning to have one battery for the controller, inverter... and another battery for the stock connection to the trailer. That way I would not have to turn off the converter to use the inverter. Where did you put your inverter? I am having a hard time finding a spot for mine.