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Small Cabin Forum / Off-Grid Living / Solar setup
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# Posted: 17 Nov 2021 22:19

I got a 50w panel installed on the cabin this past weekend. This coming weekend I’ll wire it in.

Plan is to use 14/2 wire to run 12’ to the controller, then 8’ to the battery.

When running off the gen, I just have a 3 prong camper Connector on the side of the cabin I plug into. With an inverter on the battery, I’ll just unplug the generator and plug the same cord into the inverter.

Is 14/2 Wire the right size? Do I need to disconnect the battery from charging when I run the inverter?


# Posted: 18 Nov 2021 05:53

That all sounds good. Dont disconnect the battery when running the inverter

# Posted: 18 Nov 2021 10:49

50w panel is basically a 'trickle charger', it can keep a battery charged if already charged but will have a long hard time recharging a bat from discharge unless that is quite small.
Btw, what is your battery?
If FLA you should only be using about 20-30% of its 'rated amp hours'; ie, 100ah bat = 20-30ah usable for bat health, Max 50ah occasionally.
If LFP the above does not apply, easily 80% of the total ah's is usable.
But either way the ah's used, plus about 10% more, have to be put back in; with FLA that needs to be asap (like the next morning). Be aware that you will typically only get about 70% of a panel's rated output and prime solar sun time is only about 3-4 hours a day unless you can 'track the sun' all day.
Imo you need more panels. The good news is panels are relatively cheap right now.
Fwiw, my rule of thumb on min. array sizing is 100w of panel per 100ah of battery.

# Posted: 18 Nov 2021 11:01

I have the biggest deepest cycle lead acid from Walmart, 122ah. I’m at the cabin 2 days at a time, twice a month. Maybe slightly more in the fall, much less in the summer.

I was figuring I could use 50% of those ah’s.

But this isn’t to feed the cabin 100% of the time I’m there. Have an inverter gen for the heavy lifting.

This is to flip on the lights in the morning so I don’t have to go start the gen for the 30 minutes before heading into the woods. And to have A few lights for the last 30 minutes before we get settled into bed. Maybe a little more here and there.

This past weekend was the biggest weekend at our cabin. 3 of us for opening day of deer season. My brother didn’t hunt, so he was at cabin with some lights on throughout the day. All on the battery, which was fully charged at home prior. In the evening when we started up the gen and plugged in the battery charger, it said the battery was at 96%.

So I have a big battery, but don’t have much draw. And have lots of time between usage.

# Posted: 18 Nov 2021 11:17

Yeah, light (pun intended ) draw, maintain a high soc (state of charge) and really-really never go down to 50% and your battery will recharge quickly and live long.
You can run a small psw inverter (300-500w)with a pair of 120vac outlets (for a radio, cordless tool rechargers, etc) and many have a usb port now too for your 'devices' (they draw very little).
Still, Id advise another one of those panels to match up. Your battery will love you for it and since bats are so expensive you will be glad to be nice to it.

# Posted: 18 Nov 2021 11:19

Quoting: mattd
the battery charger, it said the battery was at 96%.

So I have a big battery, but don’t have much draw. And have lots of time between usage.

This is a mistake a lot of people make. The battery charger is not a reliable way to actually tell your state of charge.

You should actually sit down and calculate all your power draws. It will give you a rock solid idea of how long you can run stuff until your batt is drawn down. (e.g 60W of lighting is about 4.75A@12V, so run for 4 hours would be 19Ah, putting your battery at about %84SOC)

I would also hesitate to draw that battery to %50. Walmart deep cycle 12V batteries are often not deep cycle. They are usually "Marine/Deep Cycle" which isn't truly a deep cycle battery. Just a marketing gimmick. I would stick to around %75, unless your not too fussed about the life of it.

With all that said, you will probably be Ok in your use case... but I like to know the numbers instead of running blind!

# Posted: 18 Nov 2021 11:33

It is the marine deep cycle. I’m not overly worried about the life of it. It was less then $100 and I looked at all the draw cycles and life expectancies between the diff batt types and with my use level this what made sense.

I have a 600w psw inverter on my Xmas list! It’s got a 9.6v shut off, which is really a dead battery. So I’ll keep on eye on my solar controller and stop around 12.25v.

All I have is a couple 9w led lights. If I was really pushing it I’d turn a ceiling fan on low or medium so the stove dosent burn me out of the cabin. Maybe the radio.

The cheapy 400w inverter I used this weekend powered the lights just fine. The fan and radio didn’t like it a whole lot.

# Posted: 18 Nov 2021 12:58 - Edited by: gcrank1

A lot of stuff runs but doesn't like msw in spite of the online comments about 'most stuff runs fine'. Not in my experience. Hope you get that new one!
Pls do believe that Walmart 'marine deep cycle bats' are cheap, one step above 'starting battery class' and that whatever they are 'rated at' for ah's are likley going to settle out to be about 80% of that. This is from folks who have had and run them not just for solar but for boating use.
So, with a new bat maybe you will get 110-120ahs just expect that after 'some cycling' it wont stay there. And that the degradation will happen faster the deeper you cycle.
I understand and appreciate the cost/benefit analysis you did, Ive done much the same and am using up my old miss-matched bats till death us do part, lol. The 'marine dc' do have a place in small scale solar, imo.
Btw, Im inverting to 120vac right at the bat-bank and running it some 100' to the cabin, all elec is 120 in cabin and is very satisfactory. The small 'overhead' of the inverter on that scale is more than compensated by the led lights. And same as you, for the heavy loads I run the gen, those loads are all short term. You might consider having a 120v charger hooked to the gen and battery so whenever the gen runs it is also charging the bat. No need to discon the solar, multi charging sources can be hooked up and running at the same time. All amps in is good amps!
But, I do discon the ext cord from the inverter and plug it into the gen (manual 'transfer switch'). You dont want the gen power backfeeding thru wiring into the inverter! Only one at a time pls.

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