Looking to rewire my small off-grid cabin

[Speaktome34]

Hello all I'm looking to redesign my off-grid cabin with solar so I can run a window air conditioner from DC to AC looking for advice.
Right now what I'm using is old lead acid Trojan batteries that are on their last leg I have 400 watts of solar 12 volt panels as well as zentrex 35 amp charge controller 12/24 volt...
I'm looking to upgrade so I can run some AC loads and still run my DC lighting TV set refrigerator freezer etc...
I know that an all-in-one unit would probably be the way to go but need some guidance of how to do it I've watched many of Will's videos and finally found this forum to ask advice... Thank you from any and all help... I was thinking of going with a server rack type battery just not sure if I should go 48 volt or keep a 12 volt and using all in one charge controller inverter like the eg4 setups

 

[MichaelK]

Go with 48V. Keep in mind that many AiO inverters have no starting-surge capability, so they are a poor choice for big power consumers like refrigerators and air-conditioners, running on an electric motor. I myself almost always recommend component systems, and I recommend brands like Magnum, MorningStar, Outback, Schneider, and Victron.

Don't buy solar panels online. Buy them locally with local pickup. You can get 240-260W grid-tie panels right now for as little as 65$ on Craigslist. Cash and carry, but bring a volt meter if you are concerned about what you are buying. Get at least 200Ah of battery capacity. With a refrigerator, freezer, and other AC household items on all day, I'd suggest you need a system that can provide 4-5kWh of power per day. In winter, that would equal about 2000W of solar. That would be ~500$ of grid-tie panels. Most 48V systems are at their best with ≥3600W of solar.

For myself, my preference was totally AC, so I wired my whole cabin for standard 120VAC. I got a standard split-phase 120V/240V inverter so I could run my 240V well-pump.

If you really can't give up a beloved 12VDC unit, buy one of these converters to power it.

GOLF CART DC-DC 48V TO 12V 20 AMP VOLTAGE REDUCER CONVERTER 240W POWER REGULATOR | eBay

DC/DC Converter. This converter can not be connected to solar panels or wind turbine directly. Golf Weight Kit. Golf Shafts. Other Golf Accessories. Shaft Adapter Sleeves. 100% full stable output Current.

www.ebay.com

 

[Rednecktek]

Well, I'll start the default answer to these questions and we can work from there. Here's you To-Do list:

1: Power audit! This will give you some important information on how big your inverter needs to be as well as how much battery capacity you'll need. There is a link in the FAQ section (I think, or someone here will post it shortly) so fill in the blanks and see what it comes up with. You'll probably need some sort of Kill-A-Watt to get accurate measurements. Are you going to be running a 12v system? 24v system? 48v system? What are the specs on your solar panels? VoC? Vmp? Being as this is a new build, throw together a wish list of what you want and estimate on the high side.

1a: Where do you live? Speccing out a system for Scotland is a LOT different numbers than Arizona due to the amount of light you actually get. Someone here can post the link to the PVwatts.com or JCR Solar Uber-Sun-Hours calculator sites to help figure out how much you'll have to work with. That will be a box in the Power Audit form.

2: Parts list: You don't need a make & model list, just a parts list to start from for reference. You'll need an inverter, a MPPT charge controller, fuses, shunt, buck converter, batteries, wire, etc. Once you have a basic list it can be fine tuned to make & models after that. If you're looking at the All-In-Ones check for correct voltage outputs (120v or 240v Split Phase for North America, 220v Single Phase for European type areas) and make sure it has enough capacity for a little bit of growth and fudge factor.

3: Budget!: Steak is great but doesn't mean anything if your wallet says hamburger. Figure out what you're able to spend now vs what you'll have to cheap out on now and upgrade later.

4: Tape measure! Figure out where you're going to stick all the stuff you'll need. A dozen 3000AH batteries sounds great until you're sleeping on the floor because there's no room left for a bed. Is there a compartment that can house all this stuff? Will the server rack batteries fit? Are you going to have to make space? Physics can be pretty unforgiving.

5: Pencil out what you think you need and throw it at us so we can tell you what you've missed (because we ALL miss stuff the first go-round ) and help figure out which parts and pieces you're going to want to get.

 

[12VoltInstalls]

I know that an all-in-one unit would probably be the way to go but need some guidance of how to do it

Thst would be simple. And maybe not a bad choice either.
But I would consider separate device components as well. Often the price is similar and you have flexibility if a failure occurs with redundancy

 

[MichaelK]

Since we are discussing components vs AiO, I thought it appropriate to cut and paste a previous analysis written by RCinFLA. It was originally posted on the Northern Arizona solar site, from which I am cut and pasting to here. I consider it highly technical and very informative! Gives you lots to think about in addition to the price and number of watts.

Many of the high freq inverters are very low cost, and low quality. There are only a couple of good quality models.

As to U.S. split phase, many of Chinese inverters, either HF or LF are just poor design showing a poor understanding of split phase requirements.

Their designs select parts spec'd with little to no design margin. Battery input line caps have 63v rating for 48v inverter, HV DC filter caps and PV input caps are 500v rating, with max PV input voltage specs on inverter of 500vdc. There are very small value filter caps on HV DC node so there is a lot of 2x AC out freq ripple voltage on them which heats up electrolytic caps reducing their lifespan. It also gives them little to no surge capability. PV input caps are very low in capacitance so there will often be ripple getting through to PV panel loading which reduces panel maximum power point output current. AC connect relays are cheap water heater relays rated for resistive loads. On higher wattage inverter models they put two of these cheap 40A resistive load rated relays in parallel to handle higher AC current.

High no-load idle current is mostly the result of poor design, lacking the knowledge of how to minimize switching losses, and/or allowing more switching crossover tolerance slop to allow for random part substitutions in manufacturing.

HF split phase have two individual inverter circuits operating in series similar to 240/120 vac inverter-generators. Although could be a single inverter circuit, most HF inverters use an H-bridge PWM chopping sinewave generating output stage. This means their high voltage DC supply must be independent between the the two split phases with two separate PWM output stages.

Most of the Chinese HF all-in-one inverters do not have their PV inputs isolated from AC output. This means the PV panels wiring are riding on top of the inverter PWM high voltage DC polarity switching from the PWM AC output H-bridge. You must use double pole DC breakers to PV panels to disconnect both positive and negative lines to PV panels.

True bi-directional battery to HV DC converters are difficult to design and control. Many Chinese HF inverters do not attempt to do it. They just put a parallel buck converter circuit change-over to charge battery from HV DC node. This takes some switchover time which limits the functionality of many HF hybrid inverters. For example, they cannot do load shaving or load supplimenting by inverter with grid or generator AC input. When connected to AC input they only allow AC pass-through and battery charging from AC input. They cannot suppliment a generator with limited power output.

Many of the recent low freq inverters from China do not have the management/control of split phase grid neutral voltage imbalance and cannot be connected to grid neutral in a code complient install. They don't provide for split phase AC input grid neutral connection making them non-code complient.

With single center tapped output transformer low frequency inverters, there must be grid neutral management to prevent output transformer from trying to correct for grid L1-N to L2-N voltage imbalance that can cause high currents in output transformer. Lacking the safe guard to check for this, the low cost LF inverters cannot safely be connected to grid neutral.

Be careful of HF inverter surge claims. 2x surge capability for a couple of msecs is no surge capability. Single phase induction motors startup surge is 400 to 500 msecs long so any surge spec less than at least a half a second is pretty much useless.

Also be careful of believing specs. With All-in-One inverters there are many ways to stretch the true. For example a HF all-in-one inverter specs, "DC to AC conversion efficiency = 96%" and is only efficiency spec listed. Intent is to make you believe this is inverter battery to AC output efficiency. It is not.

It is PV DC input, when PV voltage is close to inverter's internal HV DC node so PV SCC boost is barely required to boost PV voltage up to HV DC node so its efficiency is very high, like 99%. Most of the 96% efficiency number is just the high voltage DC to sinewave PWM H-bridge switching loss and L-C output filter loss.

Battery to HV DC boost converter, which is about 94% efficient by itself, is not involved in this path. Optimum battery to AC out efficiency is about 93% which is about the same as LF inverters.

One manufacture finds a way to stretch the truth and all other manufacturers follow in order to be competitive. Most of the Chinese HF all-in-one inverters are just copies of the same basic circuit with individual manufacturer's effort put into pulling a few more pennies of cost out of bill of material. Build lot, to build lot, of a given inverter model will have different parts depending on what parts are available at the lowest cost.

 

[JBertok]

Air conditioning will probably be your most challenging load. With a 48v nominal DC system you also have the option of a 48v DC mini-spit ductless air conditioner. There are a few to choose from. Another consideration for motor loads (air conditioner) is a soft start kit. These were originally developed for for the RV industry where air conditioners' starting surge were too much for onboard generators and inverters, they work great with pure-sine inverters. https://www.microair.net/products/e...rter-for-air-conditioners?variant=30176048267
Different costs to consider with each path.