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,

[pnichols]

MrWizard wrote:
The answer.. Not full because it never got to the proper voltage
It is/was near full , but not full until topped charged at the correct voltage

I've proved over and over again (to myself) that when my AGM battery bank reaches zero current acceptance using only 13.6 - 13.7 volts from my 7345 converter - then hitting them right afterwards with 14.XX volts from the alternator changes nothing - the ammeter remains at zero.

Does anyone know why?

(I always use AGM batteries with a specified float voltage of 13.5 - 13.8 volts. Maybe this has something to do with it.)

[BFL13]

MrWizard wrote:
You will be find
That's a good way to do it
Your question was why isn't it full if it stopped taking amps when driving

The answer.. Not full because it never got to the proper voltage
It is/was near full , but not full until topped charged at the correct voltage

I believe that, even if Phil won't. 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?

[MrWizard]

You will be find
That's a good way to do it
Your question was why isn't it full if it stopped taking amps when driving

The answer.. Not full because it never got to the proper voltage
It is/was near full , but not full until topped charged at the correct voltage

[BFL13]

MrWizard wrote:
its simple look at the charge voltage for your AGM 14.6 > 14.8v

that is the voltage needed for full charge 13.6 > 13.8 is the float voltage not the charging voltage

Well it ought to be simple, but I would still be worried with AGMs in the solar situation previously mentioned where it works ok with Wets like I have. Just add water if you happen to overdo it.

--I only have the one AGM in the TC and I will recharge it with my Vector charger at 14.6 until it says "FUL" and then I will Float it at 13.7 with my 7445 converter.

Everyone else with an AGM is on his own! 🙂

[MrWizard]

its simple look at the charge voltage for your AGM 14.6 > 14.8v

that is the voltage needed for full charge 13.6 > 13.8 is the float voltage not the charging voltage

[BFL13]

It is true that at 95% SOC at 13.6v you get more amps flowing by cranking the voltage up to 14.8v.

But if the batts are truly full at 13.6v, and you crank up the voltage so amps now flow, it does not make the batts will get any more full. Full is full by definition. It just heats them up. Not good for AGMs to dry them out doing that.

The question is whether you are truly full when amps stop flowing at 13.6v, and how can you tell? Hydrometer tells you with Wets. AGMs?

In summer, I had to change my solar to drop to Float early afternoon instead of staying at Vabs till dark, because the batts were losing water and the hydrometer said they were full by then.

I can imagine it would Be scary with AGMs to avoid that kind of thing, so I think Phil is right to be cautious with his AGMs.
Especially since he is successful in having them last for many years camping his way. He has nothing to gain by changing his procedures.

Doesn't mean his procedures will work for anyone else unless he is camping the same way as Phil.

[2oldman]

pnichols wrote:
.. no one can fully explain what I'm seeing...After 3-5 hours of driving between campsites, it usually is showing zero amps flowing. ...

and that would normally indicate full batteries. But I have no idea what kind of charge controller a vehicle has - to know if there's still an absorb phase left to do.

[MrWizard]

State of charge versus voltage
At 13.6v you may not have any amps into the house batteries
Yet if you bumped that up to 14.6 there would be amp flow
A solar controller, or an adjustable power supply with a 14+ voltage will top charge batteries that the alternator heat induced lower voltage does not
Unless the vehicle is hard to start very little power is actually expended from the battery, aka only a few percent capacity, and it quickly recovers before the alternator voltage drops to 13+ while the house batteries are still charging and need higher voltage

[pnichols]

2oldman wrote:
It takes considerable time to bring LA batteries up to 100% charge. I'm not sure how much you use your batteries, or if they are actually fully charged.

I've posted this many times in the forums and so far no one can fully explain what I'm seeing. I have an ammeter's shunt in the main negative cable connected to the coach batteries. The ammeter's readout on the cab dash can briefly show up to 70 amps going into the batteries at engine start-up then slowly tapers after that. After 3-5 hours of driving between campsites, it usually is showing zero amps flowing. The alternator starts out at up to 14.4 volts and slowly drops in voltage as we drive (I also have an engine alternator voltmeter on the cab dash). I assume that zero amps flowing means the batteries will not accept charging current anymore.

[TxGregory]

allen8106 wrote:
For what it's worth I am installing a solar system on my 5ver at about $1,811 in cost.

4 - 130 watt panels used from Craigslist. ($65 ea., total $260)
2 - Crown 240 ah 6v batteries ($135 ea., total $270)
1 - Magnum Energy MMS1012 inverter ($737)
1 - Morningstar TS-45 Charge Controller ($143)
1 - Bogart Engineering TM-2030-RV Battery Monitor ($158)
1 - Morningstar battery temp sensor ($25)
1 - Magnum Energy inverter remote ($47)
1 - GE 60 amp disconnect w/fuses ($21)
1 - Generac 60 amp manual transfer switch ($100)
1 - 500amp shunt ($34)
1 - 200 amp DC fuse ($16)

So far I have installed the batteries and the battery monitor. I have purchased everything else and am just formulating my install plan and panel locations. I am fabricating my own panel mounts, I have developed my own wiring schematic and am doing all the install myself.

I expect to be able to run everything except the microwave and the AC without ever running a generator or being hooked up to shore power, my wife also uses a CPAP.

So why all this. To show you that a good solar system install can be done for considerably less than you think and to let you know that what you wish to run in your rig can be done within reason. You'll never run the AC on solar and you'll not likely run the microwave unless you have a really big battery bank and inverter but should be able to run everything else.

Allen, this looks very similar to what I have ended up with. 4 panels, a solar starter kit, 3000W true sine wave inverter (power tech-on brand from amazon for $271), 3m VHB tape for mounting. Can you share your wiring diagram and where you are putting the fuses and shutoff switch. I am debating two different wiring diagrams. I tried to post them to my original post, but I don't seem to be doing something right. Also, where do you plan to mount your inverter?

Thanks,
Greg

[2oldman]

pnichols wrote:
Our motorhome's 130 amp Ford engine alternator completely charges our RV's battery bank with only 3-5 hours of driving between destinations. How can an engine alternator charge better than a good multi-stage battery charger?

It takes considerable time to bring LA batteries up to 100% charge. I'm not sure how much you use your batteries, or if they are actually fully charged.

I boondock a LOT, and getting them to 100% is near impossible with solar/generator. The Absorb phase takes too long - shore power is the only reasonable solution.

That said, I'm not sure what the poster means by 'full enough.'

[pnichols]

BFL13 wrote:
I got solar, not to avoid using the generator so much, but because I could not get the batteries full enough with the generator in a reasonably short generator running time.

:h :h

The above I do not understand ... considering everything I keep reading in the forums about how well proper multi-stage chargers recharge RV batteries when those chargers are powered by shore power or generator power.

Our motorhome's 130 amp Ford engine alternator completely charges our RV's battery bank with only 3-5 hours of driving between destinations. How can an engine alternator charge better than a good multi-stage battery charger?

Back on topic: Both the DW and myself use unheated CPAP machines when we're camping not on hookups. Mine is powered via an external brick optional accessary from the CPAP manufacturer that I plug into a 12V receptacle next to my bed and the DW's unheated CPAP machine is powered via a 300 watt pure sine wave inverter that is plugged into a 12V receptacle in the RV. These two CPAP machines leave plenty of power remaining in the two 12V deep cycle RV batteries in the morning - even when we use the furnace during the night. My preference is to power unheated CPAP machines directly from 12 volts when used in an RV ... but those bricks that raise 12 volts DC up to 120 volts AC can be a bit expensive. Using a CPAP machine with it's heat mode turned on can be a whole different drycamping challenge.

[westend]

2oldman wrote:

MrWizard wrote:
You can have a big inverter to power the MW at night then recharge with a generator during the day

I'm always amazed at the number of Quartzsite campers who run a generator to watch tv.

Yeah, what is the fuel cost for those that run the generator? An added battery or two would eliminate the fuel costs and could be charged the following day when noise wouldn't be as troublesome. My little solar system will run the screen, a stereo receiver, a disc player, a small fridge, and typical 12V loads for days as long as the sun shines.

[2oldman]

MrWizard wrote:
You can have a big inverter to power the MW at night then recharge with a generator during the day

I'm always amazed at the number of Quartzsite campers who run a generator to watch tv.

[BFL13]

I got solar, not to avoid using the generator so much, but because I could not get the batteries full enough with the generator in a reasonably short generator running time.

Doing several 50-90s in a row meant progressive capacity loss with the bank so that eventually ( after about ten days off-grid), I had to find shore power for a couple days of battery "recovery" to 100%.

With solar, I was able to stay off grid for weeks at a time by getting the batteries higher in SOC most days.

It is still required to take the generator along for when solar conditions are poor.