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Discussion Starter · #1 ·
OK, I posted this in Electrician Talk but was shut down and shuttled over here. I didn't get a full answer, so I thought I would post it here.


First let me say that I'm asking this question as I really have no other options. I'm building an off-grid cabin in the woods and there is simply no electrician to hire.

So with that said, the cabin (more like a small house) will have a mini-split for AC and heating. Due to the size (16X24) I require an 18K BTU unit to adequately heat and cool. Of course all mini-split over 12K BTU are 240V (I bet you can see where this is going). Since all my current power options are 120V I want to use a transformer to run the mini-split. Here is where my knowledge lacks.

As I understand a mini-split requires "split phase" 240V with 2 hots (L1 and L2). However many of the consumer grade transformers on the market output straight 240V like in Europe (I think). Would a mini-split run on this straight 240V that is a hot and neutral? Or would I need to rewire the transformer in a different config (as I understand it, as an autotranformer).

(Before anyone asks about the AC size. It was sized by the AC manufacturer as the building is lofted with 22ft ceilings. We thought about 2 110V units but that increased cost and complexity.)
 

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Njuneer
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OK, I posted this in Electrician Talk but was shut down and shuttled over here. I didn't get a full answer, so I thought I would post it here.


First let me say that I'm asking this question as I really have no other options. I'm building an off-grid cabin in the woods and there is simply no electrician to hire.

So with that said, the cabin (more like a small house) will have a mini-split for AC and heating. Due to the size (16X24) I require an 18K BTU unit to adequately heat and cool. Of course all mini-split over 12K BTU are 240V (I bet you can see where this is going). Since all my current power options are 120V I want to use a transformer to run the mini-split. Here is where my knowledge lacks.

As I understand a mini-split requires "split phase" 240V with 2 hots (L1 and L2). However many of the consumer grade transformers on the market output straight 240V like in Europe (I think). Would a mini-split run on this straight 240V that is a hot and neutral? Or would I need to rewire the transformer in a different config (as I understand it, as an autotranformer).

(Before anyone asks about the AC size. It was sized by the AC manufacturer as the building is lofted with 22ft ceilings. We thought about 2 110V units but that increased cost and complexity.)
You don't understand "split phase". When you are connected to both hots, it is just single phase 240V. You can get that in many ways but you did not indicate how you are going to power things so you need to start there. there are split phase solar inverters, split phase generators, etc.

You most certainly can run at 240V, no prob.
 

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Where/what is your power supply? Regular utility company?
Forget the split phase talk. Some motors are called split phase, but that is not from the power supply. If you have a 3 wire service, you have 120 and 240 service.
 

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Discussion Starter · #4 ·
You don't understand "split phase". When you are connected to both hots, it is just single phase 240V. You can get that in many ways but you did not indicate how you are going to power things so you need to start there. there are split phase solar inverters, split phase generators, etc.

You most certainly can run at 240V, no prob.
First, let me say, this cabin is completely off-grid. No attachment to any services.

The power comes from either a 120V generator (30A) or a 2000W 120V inverter. Both those sources are just standard 2 wire (plus ground)10 AWG. I would like to use a standard transformer (like an ST-5000) to step the voltage up to 240 to run the AC.
 

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First, let me say, this cabin is completely off-grid. No attachment to any services.

The power comes from either a 120V generator (30A) or a 2000W 120V inverter. Both those sources are just standard 2 wire (plus ground)10 AWG. I would like to use a standard transformer (like an ST-5000) to step the voltage up to 240 to run the AC.
Let me first say you are in dreamland regarding your power supply. 2000W (probably a China 2000W inverter) is going to get chewed up quickly unless you want nothing but HVAC and a light bulb. Care to run a microwave? Yep, it will take that entire generator.

Do you have Sun for solar?

In any case, you 100% can make split phase from 120V making use of a transformer. If you only have a single 240V load, I simple recommend a 120/240 isolation transformer. Done. It is that easy!
 

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Discussion Starter · #6 ·
Let me first say you are in dreamland regarding your power supply. 2000W (probably a China 2000W inverter) is going to get chewed up quickly unless you want nothing but HVAC and a light bulb. Care to run a microwave? Yep, it will take that entire generator.

Do you have Sun for solar?

In any case, you 100% can make split phase from 120V making use of a transformer. If you only have a single 240V load, I simple recommend a 120/240 isolation transformer. Done. It is that easy!
I understand power draw very well. I lived 6 years on solar alone, and no its not a cheap china inverter. A microwave does not take 3600W to run, more like 1200W. Not sure what light bulbs you have in your neck of the woods, but 4-6W LED bulbs are the norm here. The AC is rated at 1700W maximum, but other users tell me to expect about 800-1200W as its and inverted unit. So I have a good handle on the requirements for the power side.

Yes there are youtube videos showing what I'm trying to do using an isolation transformer (configured both with isolation and as an auto-transformer), but that is not what I'm asking. What I'm really asking, is can I use a standard step-up transformer without modification. Will that 240V work to power the AC unit?
 

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I am not a generator savy person, but to run a whole house will require a large generator which would have 240 volt output. Is this a full time occupied house or just occasionally like a week-end once in a while?
 

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Trying to get 240v from a lesser voltage is a lot like trying to paddle up stream minus the paddles. It can be done but at what COST!
Roughly a 3000 watt 120v gen is going to produce less than half the rated output. Transformer and cable losses. You will HATE the fuel consumption as yours will be balls to the wall all of the time when running. then there is the noise.

Your going to find that baby generators ~18kw do not have frequency and Hz controls. All of that is managed by RPM. Bet if you do a deep dive into the generator bet it says no inverters.

Get a bigger and better generator, 240v

something like this might work.
 

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I understand power draw very well. I lived 6 years on solar alone, and no its not a cheap china inverter. A microwave does not take 3600W to run, more like 1200W. Not sure what light bulbs you have in your neck of the woods, but 4-6W LED bulbs are the norm here. The AC is rated at 1700W maximum, but other users tell me to expect about 800-1200W as its and inverted unit. So I have a good handle on the requirements for the power side.

Yes there are youtube videos showing what I'm trying to do using an isolation transformer (configured both with isolation and as an auto-transformer), but that is not what I'm asking. What I'm really asking, is can I use a standard step-up transformer without modification. Will that 240V work to power the AC unit?
If you are good with your power requirements, let's move on. In short, a simple step up transformer for 60hz will be just fine! Done all the time. I would insist on an inverter generator to maintain proper voltage and frequency. The typical screamer generators are anything but quality power.
 

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Does either half of your split system have four wires -- two hots and a neutral and a ground? If so that half needs both 120 volts and 240 volts. In the US and Canada the neutral in this supply is 120 volts to either hot and the two hots deliver 240 volts all at 60 Hz. If you have a 120 volt only supply or a 240 volt only supply you can get a transformer (with center tapped secondary) that will give you both hots plus a neutral for 120/240 volts.

If your system needs just 3 wires, two to provide 240 volts and one for chassis/frame ground then you can use any 240 volt AC source (with an acceptable frequency and acceptably steady voltage and frequency and acceptably low other frequency contaminants aka waveform distortion) with or without a center neutral or whether or not one of the two wires providing 240 volts is called neutral..

To repeat, if your source is 120 volts then the source needs to provide twice the amperes of what the 240 volt split system (both halves) draws. This is regardless of the kind of transformer or inverter or voltage converter..Actually a little more than twice the amperes because conversions costs a little power to perform.
 
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Trying to get 240v from a lesser voltage is a lot like trying to paddle up stream minus the paddles. It can be done but at what COST!
Roughly a 3000 watt 120v gen is going to produce less than half the rated output. Transformer and cable losses. You will HATE the fuel consumption as yours will be balls to the wall all of the time when running. then there is the noise.

Your going to find that baby generators ~18kw do not have frequency and Hz controls. All of that is managed by RPM. Bet if you do a deep dive into the generator bet it says no inverters.

Get a bigger and better generator, 240v

something like this might work.
making volts with transformers is done every day! Not a problem. It sounds like the guy has some grasp on the concepts.
 

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Discussion Starter · #12 ·
Trying to get 240v from a lesser voltage is a lot like trying to paddle up stream minus the paddles. It can be done but at what COST!
Roughly a 3000 watt 120v gen is going to produce less than half the rated output. Transformer and cable losses. You will HATE the fuel consumption as yours will be balls to the wall all of the time when running. then there is the noise.
Do you mean 1/2 its rated current @240V? A dry transformer is rated at %97 efficient. If the AC unit runs at a full 1700W then that is 1700X1.02%=1734W, but lets be generous and say 10% losses for everything. That is still only 1870W which is less than many 15K BTU RV units that are run on generators all the time. Noise is easily mitigated with an insulated building (need it where I buy a new generator or not).

This is an off-grid cabin in literally the middle of no where that will be used on weekends only. At this point we have all the amenities (fridge, microwave, pressured hot water, lights, sewer) but would like to add the mini-split for AC/Heat when required.

So with a standard step up transformer you just take the 2 240V wires coming from the output side and hook them to L1 and L2 on the mini-split? Yes, its an inverted generator that will be used, and not a chinesium brand!
 

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Do you mean 1/2 its rated current @240V? A dry transformer is rated at %97 efficient. If the AC unit runs at a full 1700W then that is 1700X1.02%=1734W, but lets be generous and say 10% losses for everything. That is still only 1870W which is less than many 15K BTU RV units that are run on generators all the time. Noise is easily mitigated with an insulated building (need it where I buy a new generator or not).

This is an off-grid cabin in literally the middle of no where that will be used on weekends only. At this point we have all the amenities (fridge, microwave, pressured hot water, lights, sewer) but would like to add the mini-split for AC/Heat when required.

So with a standard step up transformer you just take the 2 240V wires coming from the output side and hook them to L1 and L2 on the mini-split? Yes, its an inverted generator that will be used, and not a chinesium brand!
Tell me what generator you are going to use?

But yes, as someone mentioned above, unless the unit requires 120/240, and is strictly 240, your plan is fine.

But me personally, I would add a battery bank and inverter so you don't have to have generators running just for lights and such. Just me. Generator efficiency is a function of their load so loading one up when running is ideal.
 

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Plug your numbers into Watts Law and Ohms Law. IIRC 1 BTU is 0.293071 Wh so 1,000 BTU = 1,000 x 0.293071 Wh or 2930.71 Wh.
I realize there is a disconnect Watts and Watt hours, but your numbers just aren't going to work.

As John Wayne would say, "Not enough hat for all them cattle."

Ohm’s Law and Watt’s Law – Basic HVAC
 
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Discussion Starter · #15 ·
Tell me what generator you are going to use?

But yes, as someone mentioned above, unless the unit requires 120/240, and is strictly 240, your plan is fine.

But me personally, I would add a battery bank and inverter so you don't have to have generators running just for lights and such. Just me. Generator efficiency is a function of their load so loading one up when running is ideal.
Its a Honda 3000.

We do have a battery bank (24V) with a 2500W solar array and an inverter that we use to run pretty much everything else. Actually, when we come out in the winter we usually just bring a portable power station as we only really need lights. The generator is just backup or to run the mini-spit on when required.
 

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Discussion Starter · #16 · (Edited)
Plug your numbers into Watts Law and Ohms Law. IIRC 1 BTU is 0.293071 Wh so 1,000 BTU = 1,000 x 0.293071 Wh or 2930.71 Wh.
I realize there is a disconnect Watts and Watt hours, but your numbers just aren't going to work.

As John Wayne would say, "Not enough hat for all them cattle."

Ohm’s Law and Watt’s Law – Basic HVAC
I don't think you understand how a heat pump works. We are not talking resistive heating. Hell, I didn't even buy a super efficient one. There are heat pumps with a COP of 5. Yes they can move 5 times the watts of heat for each watt of energy input (either in cooling mode, or heating mode)!

Below is quoted from the government of Canada heating and cooling website.

At 8°C, the coefficient of performance (COP) of air-source heat pumps typically ranges from between 2.0 and 5.4. This means that, for units with a COP of 5, 5 kilowatt hours (kWh) of heat are transferred for every kWh of electricity supplied to the heat pump.

In case someone down the road reads this and want to understand the math. The unit I bought has a COP of 3.0. So it has a max draw of 1715W in cooling mode. So 1715 X 3 = 5145W of heat moved. Each W is 3.41 BTU/h so 5145 X 3.41 = 17,544.45BTU. Not quite 18K as the manufacturer states, but very close. Because the unit is large enough and the space is small, the expected draw once the space is to temperature is between 600W-1000W (its and inverted unit and doesn't cycle on and off like a traditional AC, but instead just uses a constant draw to maintain the temp).
 

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Its a Honda 3000.

We do have a battery bank (24V) with a 2500W solar array and an inverter that we use to run pretty much everything else. Actually, when we come out in the winter we usually just bring a portable power station as we only really need lights. The generator is just backup or to run the mini-spit on when required.
Sounds like a plan. If your 2000W generator is in inverter, you can parallel that with the 3000 if ever needed. however, how are you getting 3600w stated from a 3000 Honda? I own one. I know what they can and can't do.

they are quite the quiet kitten though! Love em!

EDIT: I guess you state "30A". Obviously you know she won't do that, but should run your loads with no issue at all.
 

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Discussion Starter · #18 ·
Sounds like a plan. If your 2000W generator is in inverter, you can parallel that with the 3000 if ever needed. however, how are you getting 3600w stated from a 3000 Honda? I own one. I know what they can and can't do.

they are quite the quiet kitten though! Love em!

EDIT: I guess you state "30A". Obviously you know she won't do that, but should run your loads with no issue at all.
Sorry.. You are %100 correct the Honda does not output that much power. I was confusing it with another unit I own, a Boliy. The Boliy does output 3600W surge and 3000W constant. However, its is Chinesium and is our backup of the backup as I don't trust it with anything important, even though its also inverted.

Ok well, I think maybe I have a plan. We will see how it goes. It will be too late in the year to test the cooling once I get it installed, but looking forward to the heating function!
 

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I'm doing testing with a China WEN 2200. I run it daily for brief periods and all I can say is I haven't killed it yet! But it certainly is not a Honda and I don't care what any db test shows they are not as quiet. It's the frequency more than the decibels. The Honda 3000 is far quieter. But do YOU enjoy moving that pig around?? lol
 

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Discussion Starter · #20 ·
I'm doing testing with a China WEN 2200. I run it daily for brief periods and all I can say is I haven't killed it yet! But it certainly is not a Honda and I don't care what any db test shows they are not as quiet. It's the frequency more than the decibels. The Honda 3000 is far quieter. But do YOU enjoy moving that pig around?? lol
Thats what sucks, the Boliy is lighter, puts out more power, and has remote start.. but I just don't trust it yet. I have put a fair number of hours on it as I run my power tools from it. Its sure tempting to just leave the Honda behind. I'm lucky have teenage boys that I can "direct" to help me!
 
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