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Small Cabin Forum / Off-Grid Living / Inverter ?
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# Posted: 17 Oct 2021 16:46

At my off-grid camp I am currently supplying power to my shallow well jet pump, 8-10 LED ceiling can lights and a few wall outlets by way of a Honda 2000W gas powered generator/inverter. I power my camp by attaching my generator to an outdoor 110V receptacle via a 10GA power cord with male plugs on each end. From the outdoor receptacle I used 12ga romex to a 100A circuit breaker box and then ran 12ga wire from the box to the receptacle used for the pump and then I ran 14ga romex from the breaker box to the rest of the lights and receptacles. This set up has worked fine for a few years now but what I would like to do is to somehow incorporate 1or2 12V car batteries into the system so that I can run just the LED lights off the batteries without running the generator and when I do run the generator it will recharge the batteries. Does anyone know if this would be possible and how I could do it?

# Posted: 17 Oct 2021 18:39

Sounds like a job for an inverter, charge controller. The solar guys should be able to get you up and running.

# Posted: 17 Oct 2021 19:37

Look at my posts by clicking on my name. I picture a primitive set up I use . Just plug a car battery charger into the generator while you use it, and this will keep your battery up. When you turn off the generator, substitute your system with the battery. Unless you want to incorporate solar into, this should work. I have a plug receptacle that I can either plug into the generator or the inverter, depending on what I want to use. I set it up like this because I didn’t want to leave the generator or battery-inverter permanently installed (theft target).


# Posted: 17 Oct 2021 19:40 - Edited by: gcrank1

Ive done what you propose.
But 1st, a big Welcome!
May I encourage you to upgrade your power inlet, well named 'Suicide Cord'.
What you need on the camp inlet side is an 'RV/Marine' inlet plug. They are not expensive and Safe, the Suicide Cord is not and that little Honda gen can kill a person.
A typical automotive type battery charger (or better yet, a new generation 'smart charger') on an outlet can hopefully keep your 12v battery recharged/topped up IF you keep your watts draw off the bat relatively low; ie, led lighting, usb charging, etc. via an inverter to 120vac. A basic 100ish ah 12v 'marine deep cycle' (think for a trolling motor) is where many begin. Do NOT use an automotive or marine 'starting battery.
The charger can be kept plugged in and hooked to the battery(s) so whenever the gen is running charging is happening.
Note that there is LOTS more you need to know about batteries before buying, this is just to give you an idea.
To make this usable for what you have wired up you need an inverter hooked to the battery to make 120vac. I encourage you to not get the cheaper Modified Sine Wave inverter! Get the real-deal Pure Sine Wave model.
What size? They come rated in Watts output and many people get too large an inverter which takes too much power to run it for the relatively low loads they are powering up. For our led lights, usb charger, cordless tool chargers, small fans, a small old tv with built in vhs player for movies, etc. we have done fine with a 300W PSW model.
Btw, Im running 100ish feet to the cabin from the inverter with a 12ga. extension cord. The same cord I use from our 1700/2000 inverter/gen that sits by the bat-bank. Same cord runs to the cabin but is only plugged into either the gen OR the inverter. This is my fool-proof and on-the-cheap 'transfer switch' so I Never get any 120vac backfeed into the inverter (which would blow it!).
With your modern service box you should have 2 'legs', one on each side?
If so, you could power the pump on one leg along with some outlets that only work when the gen runs (this is where the battery charger would be powered from).
The other leg could be your bat-bank/inverter powered side that would be your led light, light duty outlets, etc.
Never the twain (legs) should meet! If you combined both legs in the service box or wiring you will need to return it to 2 separate legs!
Now I have solar hooked up, an easy to do deal once the above has been sorted and functional, if you have good sun and ever get interested in doing so.

# Posted: 18 Oct 2021 10:01

I used an inverter/ charger to do the same at our cabin. It as as a "brains" for power supply. Generator feeds it, it sends power to cabin fuse box, also charges batteries with excess power. When genny is off it feeds fuse box from batteries. It is seamless, automatic and easy to wire in.

I used something like this but it depends on how large of a draw think you will need to cover. I am a buy one cry once kind of guy so I went bigger than current need. hild=1&keywords=charger%2Binverter&qid=1634565492&sr=8-16&th=1

# Posted: 18 Oct 2021 10:57 - Edited by: gcrank1

Wow, that IS nice! Serious capacity too.
Fwiw, with our low power demands it would be waayyy overkill and Im into my 'simple system' for under $200.
That is the controls, inverter, RV plug and ex. cord.
(Not the solar panels and solar charge controller or batteries)
WGL, the battery(s) will be your biggest expense with your orig post concept. Prices are changing but here is some info from this past year:
1x marine dc, 100ah $100 on up
for best life use 25-30ah/Max 50ah, life of 3-4ish yrs
2x 6v golf cart (series wired for 12v), 200+ ah $100@ so $200 on up
for best life use 50-60ah/Max 100ah, life of 5-6 yrs
1x LFP, 100ah about $600 on up, ready to use (not diy)
Up to 80-90ah usable without harming the battery! Life of 8-10 yrs
For 'starting a system', learning stuff and maybe killing your first battery from overly discharging it the basic, cheap marine battery is hard to beat for the 'entry fee'.
On a well managed, low draw demand system it can work for years. If you find you do need more amp/watt hours to keep from discharging too deeply then add in another same marine bat in parallel. Note that the marine 'deep cycle' batteries are typically only 1 step up in quality from a 'starting battery'.
If you expect you want/may need the more capacity get the 2 golf carts bats right off. They are really made for the deep cycling of this application so more heavy duty construction and will last longer.
Currently the cream of the battery technology for this application is the LFP. You pay the price but with the usable capacity, light weight, no maintenence and long life they are likely to be the most cost effective. If you anticipate using this system for 10yrs or more take a serious look at them.
Adding up the Watts draw of what you run (minus the pump) on the average, in the time your gen isnt running to charge bats, will tell you how much you are sucking out of the bat-bank, then you size the bank accordingly. It sounds like you propose light usage but keep in mind you always forget something and/or demand increases so always 'round up' the calculations on that side.

# Posted: 18 Oct 2021 11:40

The jet pump is most likely only going to run with the generator. I would have that on it's own cord ran out to the generators location this way theres no chance in trying to run it with a inverter.

For the lights a inverter will work fine, a cheap one should do ok with just lights. Pair that with a RV onboard charger to run off your generator and you will be in business for less than $300 not including batteries.

I hate the sound of generators, even quiet ones. We dont get away to the silence of the woods to listen to an internal combustion engine roaring away for hours a day. We normaly dont start the generator at all and run a mini fridge off solar.

# Posted: 18 Oct 2021 18:02

Thanks to everyone for their advice. I knew I could get pointed in the right direction on this forum. I should have mentioned that I have 2 almost new deep cycle marine batteries that I will wire in parallel and I will definitely change out that power cord and outside outlet so no one will get zapped or worse.

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