"Overkill" Solar Setup and Battery Bank for Camper

[tmckenna]

So I recently purchased a new to me camper, and am going to be dry camping a fair amount.

I have gone a couple times now, and the battery that came with the camper seems to be dying about every other day. Not the end of the world because I bought a fairly nice generator to charge it back up in the morning but it is a bit of a process and even at 50 decibels or so its definitely noticeable while running.

I'd like to setup a substantial battery bank and subsequently a fairly large amount of solar on the camper, and I know it sounds crazy but I'd like to have the option to run the AC on the batteries if I wanted/needed to.

I was planning on doing 4 of the 400 watt Renogy kits, and that would require 4 solar controllers. With 4 solar controller outputs, multiple batteries and an inverter what is the best way to wire everything? Also what is the best bang for buck when it comes to battery banks. Battleborns aren't really in my budget and I'd like to have around 400ah worth of battery. Was considering making my own (open to any advice on that), or mighty max makes a 200ah that goes for about $1000.

 

[boondox]

AC on solar and batteries is tough. Do some math, starting with what your ac draws and how many hours you want to run it. If you look there are other threads here discussing this. The bottom line is a lot of solar, batteries and money.

 

[tmckenna]

AC on solar and batteries is tough. Do some math, starting with what your ac draws and how many hours you want to run it. If you look there are other threads here discussing this. The bottom line is a lot of solar, batteries and money.

Yes I'm aware its going to be a fairly expensive endeavor. I have a 13,500BTU AC unit that pulls about 3000watts and startup and somewhere around 1200-1500watts while running. 1200watts at 12v is 100amps, thats why I'm planning on running 400ah worth of batteries or so. With any additional drains, and inefficiency I should be able to run the AC for around 3 hours or so with no solar involved.

I already know I'll need about 400ah worth of battery, a 4000w pure sine wave inverter, and a very substantial solar setup (if I want to run it without draining the batteries), I'm really just wondering what the wiring involves to make sure each solar cluster charges the batteries equally.

 

[mapguy525]

Some observations --
1. Get a microair soft start system for your AC.
2. Consider 24v Battery bank for 4K inverter.
3. Look at hybrid UL 458 listed inverter chargers for the most flexibility in pass-through, surge/power boost capabilities, and load support.
>> these are not the "cheap" end of the market but will do what you want.
4. 400AH @12v LIFEPO4 would be the minimum to pull AC very short term
5. Energy audit will help set up the data for doing the math - see the Resources section for all kinds of planning tools.
https://diysolarforum.com/resources/

 

[John Frum]

1500 ac watts / .85 efficiency factor = 1764.705882353 dc watts per hour.
400 amp hours * 12.8 volts * .8 depth of discharge = 4096 usable watt hours.
4096 / 1764.705882353 = 2.321066667 hours of air conditioning.

Also a 4000 watt inverter at 12 volts is not practical.

 

[mapguy525]

1500 ac watts / .85 efficiency factor = 1764.705882353 dc watts per hour.
400 amp hours * 12.8 volts * .8 depth of discharge = 4096 usable watt hours.
4096 / 1764.705882353 = 2.321066667 hours of air conditioning.

Also a 4000 watt inverter at 12 volts is not practical.

Problem is the other items in camper running simultaneously with AC.

 

[boondox]

It certainly can be done, especially as you have a generator. It is still a big lift though. Take a look at how much solar you can fit on the roof, then see what charger would work for you. I would consider upping your battery bank size, I think you will end up working them too hard at 400aH. As Joey noted, 4kW is a big load for 12V, you would need some heavy cables.

As a long time boonbocker, I have never had AC. With good ventilation, an awning and wise selection of location I have always done fine without AC. I camp in plenty of hot areas in the summer, it isn't like I camp in Alaska all the time. Different strokes for different folks and if you really want AC it can be done. It is a power monster though and if you find a way to live without it you will save money, increase your range and have much less hassle with your power system.

 

[John Frum]

Lets figure for a 24 volt system.
4000 ac watts / .85 efficiency factor / 24 volts = 196.078431373 dc amps
196.078431373 dc amps * 1.25 fuse factor = 245.098039216 fuse amps
Which means 1 awg minimum if the round trip is under 20 feet.

 

[tmckenna]

Problem is the other items in camper running simultaneously with AC.

I was going to make this point as well. Battery bank has to stay at 12v because the camper has a DC circuit to power the lights, water heater, water pump, etc.

 

[tmckenna]

1500 ac watts / .85 efficiency factor = 1764.705882353 dc watts per hour.
400 amp hours * 12.8 volts * .8 depth of discharge = 4096 usable watt hours.
4096 / 1764.705882353 = 2.321066667 hours of air conditioning.

Also a 4000 watt inverter at 12 volts is not practical.

Why do you say not practical? At no point would I be using consistently anywhere near 4000w, it would just be to give the AC enough oomph to power up and get going. To be honest I don't think I'd ever really even use 2000watts consistently.

 

[John Frum]

I was going to make this point as well. Battery bank has to stay at 12v because the camper has a DC circuit to power the lights, water heater, water pump, etc.

 

[tmckenna]

It certainly can be done, especially as you have a generator. It is still a big lift though. Take a look at how much solar you can fit on the roof, then see what charger would work for you. I would consider upping your battery bank size, I think you will end up working them too hard at 400aH. As Joey noted, 4kW is a big load for 12V, you would need some heavy cables.

As a long time boonbocker, I have never had AC. With good ventilation, an awning and wise selection of location I have always done fine without AC. I camp in plenty of hot areas in the summer, it isn't like I camp in Alaska all the time. Different strokes for different folks and if you really want AC it can be done. It is a power monster though and if you find a way to live without it you will save money, increase your range and have much less hassle with your power system.

I'm not planning on running the AC off batteries much, if at all. But I figured if I'm spending a decent amount of money, I'd like to at least have the option every once in a while. As I mentioned just above I won't ever come near 4000watt draw. The 4kw inverter would just be to make sure the act of the AC powering up won't damage the inverter. I know most inverters have capability to double the output for usually 3 seconds or so, but I figured a powerful enough inverter would be a "better safe then sorry" type solution.

 

[John Frum]

Why do you say not practical? At no point would I be using consistently anywhere near 4000w, it would just be to give the AC enough oomph to power up and get going. To be honest I don't think I'd ever really even use 2000watts consistently.

@RCinFLA said it better than I could https://diysolarforum.com/threads/low-voltage-cut-off.9301/#post-100490

 

[shavermcspud]

I was going to make this point as well. Battery bank has to stay at 12v because the camper has a DC circuit to power the lights, water heater, water pump, etc.

Not really, even if you run a 48v bank of 4x 12v batteries, you could still tap off 12v from one of the batteries to maintain your internal 12v systems and run a 48v inverter setup.

 

[tmckenna]

Also the run from the battery bank to the inverter would be very short. Probably about 4 feet or so. I'd plan on using 0 or 1 AWG wire, as I know that 3000watts (just for the AC kicking on) is quite a bit.

 

[tmckenna]

@RCinFLA said it better than I could https://diysolarforum.com/threads/low-voltage-cut-off.9301/#post-100490

Ah okay I see. I was originally planning on doing the Renogy 3000watt inverter. It has a max output of 6kw for 3 seconds so that should cover the AC turn on requirements. I'm guessing that would be a better option?

 

[boondox]

Not really, even if you run a 48v bank of 4x 12v batteries, you could still tap off 12v from one of the batteries to maintain your internal 12v systems and run a 48v inverter setup.

That will work but it isn't a good idea, at least with lead batteries as it will cause imbalance, especially if you have significant loads. Lithium I do not know as I am new to that. Better would be a 48/24V to 12V converter to cover the 12V loads.

 

[John Frum]

Not really, even if you run a 48v bank of 4x 12v batteries, you could still tap off 12v from one of the batteries to maintain your internal 12v systems and run a 48v inverter setup.

Link please.

 

[John Frum]

That will work but it isn't a good idea, at least with lead batteries as it will cause imbalance, especially if you have significant loads. Lithium I do not know as I am new to that. Better would be a 48/24V to 12V converter to cover the 12V loads.

That water heater is going to be a bugger.
I assume its electric

 

[boondox]

I'm not planning on running the AC off batteries much, if at all. But I figured if I'm spending a decent amount of money, I'd like to at least have the option every once in a while. As I mentioned just above I won't ever come near 4000watt draw. The 4kw inverter would just be to make sure the act of the AC powering up won't damage the inverter. I know most inverters have capability to double the output for usually 3 seconds or so, but I figured a powerful enough inverter would be a "better safe then sorry" type solution.

Well, if you can fit 2000 watts of solar (or more) on the roof you can get maybe 8 hours a day. Of course, you have to park in the full sun. Assuming the panels are mounted flat, you need way more than the rated wattage as you will never come close to the rating while mounted flat.

Or, you could insulate, cover windows and park in the shade with good ventilation. If you are camping in dry areas, a swamp cooler might work for you and takes a fraction of the power. Not to discourage your dreams but AC on mobile solar is tough.

 

[tmckenna]

That water heater is going to be a bugger.
I assume its electric

My water heater can be powered by electric or propane. When I'm off grid I usually use propane.

 

[John Frum]

My water heater can be powered by electric or propane. When I'm off grid I usually use propane.

Well that is encouraging.

 

[tmckenna]

Well, if you can fit 2000 watts of solar (or more) on the roof you can get maybe 8 hours a day. Of course, you have to park in the full sun. Assuming the panels are mounted flat, you need way more than the rated wattage as you will never come close to the rating while mounted flat.

Or, you could insulate, cover windows and park in the shade with good ventilation. If you are camping in dry areas, a swamp cooler might work for you and takes a fraction of the power. Not to discourage your dreams but AC on mobile solar is tough.

I would never want to run AC on batteries for 8 hours a day. It would be a very infrequent situation where maybe I'm low on propane for the generator and its a million degrees out so I'd run it for an hour or 2 before I went to sleep. Yeh I know it seems ridiculous to go through all this trouble for like a handful of actual situations or uses but my mind works in strange ways haha.

 

[tmckenna]

Also for the record, most of my dry camping is on actual beaches so I get full sun literally all day, with the exception of clouds.

 

[John Frum]

Well, if you can fit 2000 watts of solar (or more) on the roof you can get maybe 8 hours a day. Of course, you have to park in the full sun. Assuming the panels are mounted flat, you need way more than the rated wattage as you will never come close to the rating while mounted flat.

Or, you could insulate, cover windows and park in the shade with good ventilation. If you are camping in dry areas, a swamp cooler might work for you and takes a fraction of the power. Not to discourage your dreams but AC on mobile solar is tough.

Solar powered air conditioning in a RV is just a real tough problem.
To get the solar to feed your ac you have to park your tin can in the full sun which just makes the problem worse.