240V dual phase inverter?

Dill · November 2011

I currently am looking for a dual phase 240V inverter for my off grid setup at my house. I have an existing generator transfer switch installed that works great with my generator with the 4 prong twist lock plug (I forget the exact L number of it right now)

I'm looking for an inverter or pair of inverters that will patch into my generator transfer switch to power select circuits in my home from my battery bank. Right now, my battery bank is 12V but if no such inverter exists in 12V, I'm open to changing it as well.

Any ideas? Thanks!

Cariboocoot · November 2011

Re: 240V dual phase inverter?

Welcome to the forum.

I wouldn't say there's no such thing as a 12 Volt split-phase 240 VAC inverter, but I would say you don't want one. When you're in that power range the DC Amps would be pretty high on 12 Volts.

A couple of good brands here would be Magnum and Xantrex. Minimum would be this Magnum 24 Volt http://www.solar-electric.com/maenms4040wa1.html
Frankly I'd prefer 48 Volt for its lower DC Amps: http://www.solar-electric.com/maenms4444wa.html

If you need more than 4 kW then the Xantrex XW 6048 would be a good choice: http://www.solar-electric.com/xaxwhyin1.html Although it is pricey because you're paying for grid-tie ability which you won't use in an off-grid situation. Outback has a similar 8 kW unit, the Radian: http://www.solar-electric.com/rasein.html

But what you really need to know first is how many Watts you're going to need to supply. If it's very low you can use an autotransformer on a standard 120 VAC inverter; they're good for up to 4 kW. Usually 240 goes hand-in-hand with big Watts, and it's worth getting the power from a larger inverter.

I have one 240 Volt pump on my system, and it is run from 120 through a transformer.

Dill · November 2011

Re: 240V dual phase inverter?

Cariboocoot wrote: »

Welcome to the forum.

I wouldn't say there's no such thing as a 12 Volt split-phase 240 VAC inverter, but I would say you don't want one. When you're in that power range the DC Amps would be pretty high on 12 Volts.

A couple of good brands here would be Magnum and Xantrex. Minimum would be this Magnum 24 Volt http://www.solar-electric.com/maenms4040wa1.html
Frankly I'd prefer 48 Volt for its lower DC Amps: http://www.solar-electric.com/maenms4444wa.html

If you need more than 4 kW then the Xantrex XW 6048 would be a good choice: http://www.solar-electric.com/xaxwhyin1.html Although it is pricey because you're paying for grid-tie ability which you won't use in an off-grid situation. Outback has a similar 8 kW unit, the Radian: http://www.solar-electric.com/rasein.html

But what you really need to know first is how many Watts you're going to need to supply. If it's very low you can use an autotransformer on a standard 120 VAC inverter; they're good for up to 4 kW. Usually 240 goes hand-in-hand with big Watts, and it's worth getting the power from a larger inverter.

I have one 240 Volt pump on my system, and it is run from 120 through a transformer.

thanks for the quick reply.

to answer your question on required wattage, well, not a lot. I have a Xantrex ProWatt SW 1000 inverter, and it has supplied all of my needs to date. My main thought was to put my array to good use in my home without having to drag wire all over the place through already finished walls and ceilings. I live in Minnesota, and it's real cold here much of the year, but I like to garden and have fresh veggies, so I built myself a little indoor garden grow area, and have some LED grow lights I want to power. There are 2 grow lights, and they draw around 65 watts each at 120V.

I thought it would be easy to use my off grid solar array to run these grow lights and a few other things. Right now, I have 4, 6 volt ~230ah golf cart batteries setup in a 12V setup, and the Xantrex 1000 watt inverster, I use it to power lighting and tools in my garage.

I have the input for my generator transfer switch only a few feet from my inverter in the garage, it sure would be temping to patch into it, but the inverters you posted are out of my price range, nor do I need 4000 watts (yet). using the transfer switch would make it easy to flip circuits in the house from grid to solar or generator power without hacking into any wiring.

Can you tell me more about this auto transformer? Would it power my transfer switch without flipping the breaker?

Cariboocoot · November 2011

Re: 240V dual phase inverter?

So here's the thing: do you actually need 240 VAC for anything, or are you just needing to supply both L1 and L2 on the house wiring?

And remember that a generator that puts out 240 VAC probably has 120 VAC available if you wire it right. Usually the plug has four connections: L1, L2, Neutral, and ground. Either L1 or L2 to neutral will provide 120 VAC.

Also, the generator is usually used to recharge batteries and carry loads with the inverter off (or in charge mode). Or you can use it to power a stand-alone charger connected directly to the batteries.

The autotransformer: http://www.solar-electric.com/psx-240.html This is a 1:1 transformer with the two sides wound in phase. You feed 120 VAC to one side and it creates a "mirror image" 120 VAC on the other. With the "neutral" wires tied together the two 120 VAC sides "stack" to form 240 VAC across the two hot leads.

The trouble with feeding L1 and L2 from your small inverter is the possibility that the total loads on both may exceed its capacity, even though all those loads are small.

mike95490 · November 2011

Re: 240V dual phase inverter?

google: Trace T240 Autotransformer (3.9KVA) (NAWS does not list it in their catalog)

http://www.solarcellsales.com/techinfo/docs/T240.pdf
manual with hook-up and schematics:
http://www.wholesalesolar.com/pdf.folder/inverter%20pdf%20folder/Trace240Manual.pdf

An autotransformer has a single winding, usually center tapped, or tapped at selected voltage steps.

Trace Engineering T240 autotransformer.
This power compact unit can be used in several ways:

Step Up: Allows you to power 240VAC loads from a single 120VAC inverter/charger. This is typically done for powering deep well pumps or other dedicated high power 240VAC loads.
Step Down: Allows you to connect a large 120 VAC load to the output of a stacked pair of DR or SW inverters (120 / 240 VAC). This results in the inverters sharing the load, allowing higher performance and efficiency.
Balancing Transformer: Allows a single 120 VAC inverter to be connected to a generator which has 240 VAC output. Keeps the generator balanced for better performance and operating life. Balancing the generator's output also allows higher charge rates from your battery charger.

Dill · November 2011

Re: 240V dual phase inverter?

Cariboocoot wrote: »

So here's the thing: do you actually need 240 VAC for anything, or are you just needing to supply both L1 and L2 on the house wiring?

And remember that a generator that puts out 240 VAC probably has 120 VAC available if you wire it right. Usually the plug has four connections: L1, L2, Neutral, and ground. Either L1 or L2 to neutral will provide 120 VAC.

Also, the generator is usually used to recharge batteries and carry loads with the inverter off (or in charge mode). Or you can use it to power a stand-alone charger connected directly to the batteries.

The autotransformer: http://www.solar-electric.com/psx-240.html This is a 1:1 transformer with the two sides wound in phase. You feed 120 VAC to one side and it creates a "mirror image" 120 VAC on the other. With the "neutral" wires tied together the two 120 VAC sides "stack" to form 240 VAC across the two hot leads.

The trouble with feeding L1 and L2 from your small inverter is the possibility that the total loads on both may exceed its capacity, even though all those loads are small.

I'm not planning on running anything 240V...in fact, in my home, only my well pump and AC use this (and draw way too much for this inverter). It's merely to be able to power both legs L1 and L2 in my panel. All loads will be 120V. You're right on the connector, L1, L2, ground, and N.

I tried to wire up only 1 side of the transfer switch to my inverter, and even that flipped the breaker on the inverter.

Cariboocoot · November 2011

Re: 240V dual phase inverter?

Dill wrote: »

I'm not planning on running anything 240V...in fact, in my home, only my well pump and AC use this (and draw way too much for this inverter). It's merely to be able to power both legs L1 and L2 in my panel. All loads will be 120V. You're right on the connector, L1, L2, ground, and N.

I tried to wire up only 1 side of the transfer switch to my inverter, and even that flipped the breaker on the inverter.

That's just what I mean: trying to power everything that's on one side of system is too much for a 1 kW inverter. Not surprising at all.

The only safe thing to do here is to set up a sub-panel with the circuits you need to run off the inverter, limited to not exceed its capacity. The trouble there is that 1 kW is less than one 15 Amp circuit. If you try to substitute that inverter for your generator (probably 3kW or more) it will be easily overloaded.

DarkStar · November 2011

Re: 240V dual phase inverter?

Dill wrote: »

I currently am looking for a dual phase 240V inverter for my off grid setup at my house.

Just so others aren't confused, I wanted to clarify that you're looking for a 3-wire, single-phase, mid-point neutral 240 volt inverter. In the U.S. though, we just refer to this as a single-phase 240 volt inverter.

Dill · November 2011

Re: 240V dual phase inverter?

Cariboocoot wrote: »

That's just what I mean: trying to power everything that's on one side of system is too much for a 1 kW inverter. Not surprising at all.

The only safe thing to do here is to set up a sub-panel with the circuits you need to run off the inverter, limited to not exceed its capacity. The trouble there is that 1 kW is less than one 15 Amp circuit. If you try to substitute that inverter for your generator (probably 3kW or more) it will be easily overloaded.

right, but the generator transfer switch has 3 position switches for each circuit. LINE, OFF, and GEN. Even with all the switches OFF or in LINE mode, the breaker flips. The generator transfer switch I have has 6 circuits on it that you can control. My plan was to leave 4 of them on GRID and 2 on GEN (patched into my inverter) unless my grid power failed, then I could move the inverter patch over to my generator, and power my house. So even with no load on the inverter, the breaker flips. There has to be a incompatibility with the dual phase LINE power with the single phase inverter that causes this. Plug it into my dual phase generator, and it works as designed, I can move any circuit from LINE to OFF, to GEN without any issues at all. 2 of the circuits on the transfer switch are lights, 3 are wall outlets (with nothing plugged into them right now) and one is my fridge. They are all in LINE mode right now. That's the beauty of the transfer switch, you can choose which circuits you want to run from which input.

This is the generator transfer switch I have:
http://www.amazon.com/Reliance-20216A-6-Circuit-Generator-Generators/dp/B000HS2L1G

Dill · November 2011

Re: 240V dual phase inverter?

DarkStar wrote: »

Just so others aren't confused, I wanted to clarify that you're looking for a 3-wire, single-phase, mid-point neutral 240 volt inverter. In the U.S. though, we just refer to this as a single-phase 240 volt inverter.

no, I'm looking for a 4 wire inverter to patch into this:

51K0583BB9L._SL500_AA300_.jpg

i will admit, this whole project did throw me for a little bit of a loop

I thought I'd be able to supply the transfer switch with a 120V common leg and it would work for any 120V circuits. I was sorely mistaken! Sorry for any confusion

BB. · November 2011

Re: 240V dual phase inverter?

120/240 VAC in the use is called "Split Phase" power with a grounded neutral.

If you have no 240 VAC loads to run from your inverter, and the inverter output is less than 15 amps AC, then you can simply take the L1/L2 and tie them together on the inverter input side.

If you have an inverter larger than 15 amps, then you run the problem of running L1+L2 at a maximum of 15 amps each, and running L1+L2 (additive) current in a common return/neutral line and overheating it.

With 120/240 VAC split phase, the L1 and L2 are 180 degrees out of phase. So the Neutral current is the difference between L1 and L2 (L1-L2=neutral current).

-Bill

techntrek · November 2011

Re: 240V dual phase inverter?

Looks like an L14-30 twist-lock outlet, the most commonly used one for backup generators. And to be clear, it is a 4-wire split-phase system, not single phase (there is a big difference). But for all practical purposes it acts like a single-phase system.

Also, you don't need an autotransformer, you can use an isolated transformer, too. Two similar beasts, which will ultimately do the same thing as long as they accept 120 in and output 120/240 split-phase. Since you may have a multi-wire branch circuit OR an oddball appliance like a combo washer/dryer that doesn't "follow the rules" you don't want to just apply the 120 volt output to both sides of a panel (same phase on both legs). That will cause "bad things". Make sure you apply split-phase like it is expecting.

It sounds like with your inverter you don't have a load problem, you have a wiring problem. Something is causing a dead short, flipping your breaker.

Dill · November 2011

Re: 240V dual phase inverter?

techntrek wrote: »

Looks like an L14-30 twist-lock outlet, the most commonly used one for backup generators. And to be clear, it is a 4-wire split-phase system, not single phase (there is a big difference). But for all practical purposes it acts like a single-phase system.

Also, you don't need an autotransformer, you can use an isolated transformer, too. Two similar beasts, which will ultimately do the same thing as long as they accept 120 in and output 120/240 split-phase. Since you may have a multi-wire branch circuit OR an oddball appliance like a combo washer/dryer that doesn't "follow the rules" you don't want to just apply the 120 volt output to both sides of a panel (same phase on both legs). That will cause "bad things". Make sure you apply split-phase like it is expecting.

It sounds like with your inverter you don't have a load problem, you have a wiring problem. Something is causing a dead short, flipping your breaker.

L14-30 sounds right. I work in IT, and see so many different twist locks with UPS's and PDU's in server racks that I can't keep them straight any more.

thanks for the terminology info on the split phase 240V. I agree with you on the 'odd ball' appliance thing. I did forget to add, that if I wire only 1 single circuit to the transfer switch (including the ground and neutral wires), and then connect L1 and L2 together, and the circuits ground and neutral, it works fine. When I connect the neutral and ground to the buss bars in my electrical panel, that's when the breaker on the inverter flips. That makes sense with the split phase issue.

So the transformer will allow me to input 120V single phase and output 240V split phase?

mike95490 · November 2011

Re: 240V dual phase inverter?

Dill wrote: »

....
So the transformer will allow me to input 120V single phase and output 240V split phase?

I belive so, I know the T-240 will, and I suspect the PSX-240 will also. PSX-240 handles higher power too.

BB. · November 2011

Re: 240V dual phase inverter?

Is this a MSW or TSW inverter? The Modified Sine Wave inverters, typically, do not like to work with a grounded AC neutral system (when combined with a grounded battery bank, you get a dead short through the inverter).

-Bill

techntrek · November 2011

Re: 240V dual phase inverter?

Yes, it should, same as the big transformer on the pole outside your house. Single-phase in, split-phase out. This page will give you the idea: http://www.allaboutcircuits.com/vol_2/chpt_9/5.html

Along with this page (see the 2nd to last transformer diagram): http://www.allaboutcircuits.com/vol_2/chpt_10/1.html

mike95490 · November 2011

Re: 240V dual phase inverter?

BB. wrote: »

Is this a MSW or TSW inverter? The Modified Sine Wave inverters, typically, do not like to work with a grounded AC neutral system ....

Most mod sine will shut off when presented with a large transformer. All the ones I tried on a ferroresonant, hated it.

Dill · November 2011

Re: 240V dual phase inverter?

this is a TSW inverter (Xantrex ProWatt SW 1000)

Cariboocoot · November 2011

Re: 240V dual phase inverter?

With nothing connected (i.e. transfer switch set at 'OFF' or 'LINE') the inverter should not trip for just being connected to the gen input unless it is mis-wired. It will be something along the lines of one inverter line being connected to its ground and that line being connected to the transfer switch hot. These switches usually do not disconnect neutral & ground; only the hot leads. It's too easy to cross them and end up feeding hot from the inverter to neutral of the switch which is connected to ground which is connected back to the inverter ground that's connected to the inverter neutral.

See how confusing that last sentence was? It's that easy to get it wrong.

At any rate, there must be no connection between either inverter out and its ground at the inverter. The only neutral-ground bond should be in the main panel.

techntrek · November 2011

Re: 240V dual phase inverter?

mike90045 wrote: »

Most mod sine will shut off when presented with a large transformer. All the ones I tried on a ferroresonant, hated it.

Ferroresonant is the problem, they are core-saturated, usually only used in older UPS systems. Very high losses and I believe they have a very high surge when energized which may have been your problem. They are also very sensitive to frequency, which also could have been the problem. Finally they use a capacitor on a secondary winding which may have been a problem on MSW.

I have a torroidal that I use with my bigger UPS, no problems, it is actually supplied by the UPS manufacturer.

Dill · November 2011

Re: 240V dual phase inverter?

Cariboocoot wrote: »

With nothing connected (i.e. transfer switch set at 'OFF' or 'LINE') the inverter should not trip for just being connected to the gen input unless it is mis-wired. It will be something along the lines of one inverter line being connected to its ground and that line being connected to the transfer switch hot. These switches usually do not disconnect neutral & ground; only the hot leads. It's too easy to cross them and end up feeding hot from the inverter to neutral of the switch which is connected to ground which is connected back to the inverter ground that's connected to the inverter neutral.

See how confusing that last sentence was? It's that easy to get it wrong.

At any rate, there must be no connection between either inverter out and its ground at the inverter. The only neutral-ground bond should be in the main panel.

I'll go through the whole thing again when I return (headed out deer hunting this weekend), but I'm fairly certain it's wired right. Yea I know, they all say that

If it were wired wrong, I wouldn't think it would work with my generator. Everything is color coded pretty well. At any rate, I'll go back through it and trace out my runs to double check, and report back.

FWIW, like most home electric panels, my grounds and neutrals were on a common buss. I even tried separating them with no luck.

mike95490 · November 2011

Re: 240V dual phase inverter?

You may have a sneak path back through the genset, or it's windings isolate something. If all the breakers are OFF, you should be able to track it down. Pull the genset completly off the ckt with a disconnect or something

Cariboocoot · November 2011

Re: 240V dual phase inverter?

mike90045 wrote: »

You may have a sneak path back through the genset, or it's windings isolate something. If all the breakers are OFF, you should be able to track it down. Pull the genset completly off the ckt with a disconnect or something

I could be wrong, but I assume he was unplugging the gen from the transfer switch input and replacing it with the inverter output. It's the inverter that's popping when connected, apparently even if the switch is set at 'OFF'. Only thing I can think of that could cause that would be mistake in the wiring.

ChrisOlson · November 2011

Re: 240V dual phase inverter?

Dill wrote: »

I currently am looking for a dual phase 240V inverter for my off grid setup at my house

Wow, this thread sort of evolved to a possible wiring problem.

But I'll add my .02 cents to the issue of whether or not to use a split phase inverter, based on my experience with having a 120/240 split phase off-grid system.

Don't put one in unless you got 240 volt Stuff to run with it.

The reason we have it is because my wife will not allow a gas line in the house, so our house is totally electric (except for wood/coal forced air heat). We have two 55 gallon 240 volt water heaters (with all the original 4,500 watt elements replaced with 2,500's), electric clothes dryer (4.5 kW), electric range (don't know how many kW, but it's Big - Real Big), and 240 volt 2 hp well pump.

This is all due to a gas valve malfunctioning on a water heater several years ago. My wife walked in the house and went to turn on the light switch, then paused with her finger only fractions of an inch from the switch when she smelled the gas. She stood there fully convinced that she was one millisecond from being blown to smithereens. That was the last of anything gas in our house.

We have a LP fueled genset, but the Supreme Allied Commander of the Establishment merely tolerates that - as long as the tank is hidden behind a row of pine trees where she can't see it.

I have a decent battery bank and I still cannot run any of this stuff for very long on battery power, except for the well pump and water heaters. If the Supreme Allied Commander of the Establishment decides this is the day to cook something in the electric range, plus wash a load of clothes, plus dry a load of clothes - all at the same time - the Grunt in charge of powering the Establishment has a trick up his sleeve. I have my inverters set up to bring the gen online at 20 amps load (5 kW draw) to help out with the load. This places close to full load on the gen and the inverters fill in the difference from the batteries until the load goes away.

But to just use a split phase inverter to power 120 volt circuits is a waste, and it gets complicated because you have to keep the L1 and L2 loads balanced on a split phase inverter just like you do with a genset.

After reading thru the whole thread, my opinion is that your setup is not qualified for a split phase inverter of any size. And your best option would be to pull the circuits out of the Main Panel that the inverter is capable of running, and just continue using what you already have.
--
Chris

techntrek · November 2011

Re: 240V dual phase inverter?

ChrisOlson wrote: »

But to just use a split phase inverter to power 120 volt circuits is a waste, and it gets complicated because you have to keep the L1 and L2 loads balanced on a split phase inverter just like you do with a genset.

A waste in what way? They aren't any more or less efficient, and barely less efficient if you add a split phase transformer to a single-phase inverter.

Balancing the loads is dependent on the inverter. One of my 2 inverters allows a 100% imbalance. Or, use an autotransformer which will do it.

ChrisOlson · November 2011

Re: 240V dual phase inverter?

techntrek wrote: »

A waste in what way?

Cost. Split phase inverters aren't cheap (at least not for good ones).
--
Chris

Fullpower · November 2011

240V dual phase inverter?

Given your LOADS:
"The reason we have it is because my wife will not allow a gas line in the house, so our house is totally electric (except for wood/coal forced air heat). We have two 55 gallon 240 volt water heaters (with all the original 4,500 watt elements replaced with 2,500's), electric clothes dryer (4.5 kW), electric range (don't know how many kW, but it's Big - Real Big), and 240 volt 2 hp well pump."
You can buy inverters to run this load, but the "BATTERIES are gonna KILL ya"
You will find a whole house diesel generator to be cost effective for insanely high electrical demand installations as you seem married to here.
Running electric hot water heaters and clothes dryers from BATTERIES is... possible, but expensive.

ChrisOlson · November 2011

Re: 240V dual phase inverter?

Fullpower wrote: »

Given your LOADS:
Running electric hot water heaters and clothes dryers from BATTERIES is... possible, but expensive.

No, it actually works good. When my wife starts the electric oven, then the generator starts to run it. But surface units are no problem and she uses those all the time. They draw less power than a toaster or coffee maker. They have a heavy draw when she first turns them on, but then they cycle to maintain the heat setting, and that cycling is easier on the bank than a heavy continuous draw.

The clothes dryer - the gen starts when she runs it.

Water heaters - we only one element (the bottom one in the primary) wired so it comes on if the water gets too cold. The stat on it is set at 125 degrees. That insures we always have 55 gallons of at least 125 degree water.

The top element in the primary heater, and both elements in the 55 gallon preheater all all used for aux loading on the system for excessive wind turbine output. Today, for instance, we had both sun and 20-30 mph wind all day and all night. My system generated over 55 kWh in the last 24 hours, the last I looked at the meters. All the excess went to water heating and we have the primary heater at 170 degrees in the top of the tank, and the pre-heater is at 155 degrees tonight. That 110 gallons of hot water will last us for 4-5 days because when it's that hot we use way less of it, and blend more cold water in for showers and stuff. We've gotten used to so we know how to run the faucets without getting burned.

I actually like the electric appliances because they're efficient. Any waste heat (like from the clothes dryer) goes to heating our house in the winter. And last year we did it all on about 380 gallons of LP gas for the whole year (thru the genset).

A diesel genset is worthless here in the winter time. Takes way too much preheat to get one to start when it's 30 below.
--
Chris

Fullpower · November 2011

Re: 240V dual phase inverter?

I see, the auto generator start gives a seemless boost to the battery bank, during high loads. very good.
If I may ask, what time/voltage parameters do you use for generator start?
I am considering rigging one of my gasoline generators for auto start, once I figure out how to activate the choke.

ChrisOlson · November 2011

Re: 240V dual phase inverter?

I got the master inverter set to start the generator at 20 amp AC load. When it starts it, the inverter switches the load over to the gen, then monitors the gen input. If the input reaches max for the gen, then the inverters start filling in the difference above what the gen can supply.

When the inverter brings the gen online for load management, it cools it down, then shuts it off right away when the load drops below the set point, and it doesn't continue to run and charge batteries.

My system voltage has to fall below 24.0 for more than two hours before the inverter brings the gen online to charge batteries, and then it charges the bank at about 200 amps for the bulk stage, using both inverters.
--
Chris

Dill · November 2011

Re: 240V dual phase inverter?

Cariboocoot wrote: »

I could be wrong, but I assume he was unplugging the gen from the transfer switch input and replacing it with the inverter output. It's the inverter that's popping when connected, apparently even if the switch is set at 'OFF'. Only thing I can think of that could cause that would be mistake in the wiring.

you're correct, I'm not using both at the same time.

240V dual phase inverter?

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