220v from two inverters?

adas · October 2008

Aloha, Can I parallel two of the same MSW inverters @ 110v each and get 220v single phase? If so, then would I tie the two neutrals together? Reference my system below. thanks
Frank

BB. · October 2008

Re: 220v from two inverters?

You can put in series (two 120 VAC units into "one" 240 VAC w/ neutral unit), if the units you have have been designed for synchronized operation (I believe, with an external control cable that runs between the two units--such as some Outback units will).

You would have to get a step-up transformer (perhaps auto-wound for lower costs) to get 220 from a 110 inverter.

-Bill

machineman · October 2008

Re: 220v from two inverters?

adas wrote: »

Aloha, Can I parallel two of the same MSW inverters @ 110v each and get 220v single phase? If so, then would I tie the two neutrals together? Reference my system below. thanks
Frank

Another question about parallel inverters (morningstar 300W). If they were run parallel with the neutrals tied together and each 120V line fed each seperate leg (L1 and L2) in a home AC panel, would this work in supplying 120V to each leg. This would essentially deliver 600w (300W each leg) from the AC breaker panel.

Any problems with that set up assuming no 220V appliances were used?

Thanks.

mike95490 · October 2008

Re: 220v from two inverters?

Again, unless the inverters have a "SYNC" cable, to insure they are synchronized, they cannot be tied together.
http://www.morningstarcorp.com/en/sure-sine does not list any sync capabilities, so I would not experiment too much with trying to configure a pair of them. Grid Tie inverters can sense and synchronize to a source, but I don't think others can. Some other inverters have capability to be stacked in series or parallel, but not any 300W ones that I know of.

Also, unless you have pure sine wave, a step-up/down 120-240 transformer will generally not work with a mod-sine inverter.

niel · October 2008

Re: 220v from two inverters?

"Also, unless you have pure sine wave, a step-up/down 120-240 transformer will generally not work with a mod-sine inverter."

this is not necessarilly so and i believe modsine will transform. might not be worth the cost of the transformer as it will be so much more than the inverter and i don't know of too many items on 240vac that will like modsine anyway.

machineman · October 2008

Re: 220v from two inverters?

Thats my dilema. I want two legs of 120V to power all breakers in my AC panel. A 240V 60Hz single phase pure sine wave inverter is very expense. I thought since the parrallel 120V inverter lines would be completely different circuits it would work but I guess tieing both nuetrals to the same bus would be a problem. I could tie both 120VAC panel legs together and get the same 120V on all breakers but then when I turn the 240V generator on (when needed) it will short out becuase the legs are tied together. Maybe it could be resolved by some elborate switches to seperate the generator and inverter power but not sure if a transfer switch (like IOTA) could work with a 120V inverter side and 240V (2 line) generator side.

Brock · October 2008

Re: 220v from two inverters?

You could use two inverters and tie their neutrals together. Most of better ones won't care about this. The trick is if you have any 240vac loads they could have any voltage from 0 to 240v as the two inverters won’t likely be in sync or stay in sync with one another, even matching ones.

I would go the T240 / transformer route. It just takes the 120vac and center taps it to give you true 120 / 240 vac just like the utility has. Of course the transformer sucks power 24x7, which is why getting an outback or xantrex would be suggested, they have them designed somehow to use 1/2 to 1/4 what an off the shelf balancing transformer consumes in standby.

Of you could scrap all it all and start over with an inverter that either puts out 120/240 (xantrex XW line) or just about any of the big name companies have "stackable" inverters made to do this and the two inverters will talk to one another.

machineman · October 2008

Re: 220v from two inverters?

Brock wrote: »

You could use two inverters and tie their neutrals together. Most of better ones won't care about this. The trick is if you have any 240vac loads they could have any voltage from 0 to 240v as the two inverters won’t likely be in sync or stay in sync with one another, even matching ones.

All devices will be 120V, no 240V appliances, so no problem there.

niel · October 2008

Re: 220v from two inverters?

if no 240vac items will be used then no problem with those 2 inverters. what comes to my mind is that you are putting these inverters to your main electrical panel and that would necessitate the use of a switch to isolate the utility power from interacting with the inverters as they can't utilize the same lines at the same time and it's not enough to just flip off the main breaker and feed this from the panel breakers as this could accidentally be on at the same time. how are you accomplishing this aspect of safety?

machineman · October 2008

Re: 220v from two inverters?

niel wrote: »

if no 240vac items will be used then no problem with those 2 inverters. what comes to my mind is that you are putting these inverters to your main electrical panel and that would necessitate the use of a switch to isolate the utility power from interacting with the inverters as they can't utilize the same lines at the same time and it's not enough to just flip off the main breaker and feed this from the panel breakers as this could accidentally be on at the same time. how are you accomplishing this aspect of safety?

Cabin is off grid so no utility power, but I do have a generator that's wired to the main. I could switch them back and forth manually but as you said a mistake could be made. Maybe that IOTA transfer switch will work to prevent backfeed from generator to inverter.

I haven't purchasd anything yet. Still in the planning phase. Looks like I'm all set.

A couple Sun 190w panels, A few cart batterys (220ah), C40 controller, Monringstar pure sine wave inverter (maybe 2 of them), Posible IOTA transfer switch. Total cost <$2200.

mike95490 · October 2008

Re: 220v from two inverters?

niel wrote: »

i believe modsine will transform.

Do you/anyone know of any case, where a mod sine inverter has driven a transformer, which supplied large amounts (several amps) of power for 5 minutes or more ? Not just a wall wart style transformer which outputs mA, but some big honker that ran a motor, or large
appliance.
I'd love to have a solid report, of what mod-sine/square wave inverter can push amps of power thru a transformer, for a reasonable period of time, without something frying.

niel · October 2008

Re: 220v from two inverters?

i don't know offhand anybody that has a modsine inverter and a transformer, but the size of the transformer's current ability has nothing to do with it as any ac waveform type will transform in a transformer providing the hz is similar for that particular transformer's design parameters, ie: power frequencies, radio frequencies, sound frequencies, etc.. in fact, the transformer may actually cleanup a squarewave slightly because it won't pass some of the higher frequency harmonic content of the squarewave as well. anybody care to prove it for mike?

mike95490 · October 2008

Re: 220v from two inverters?

It's the load the transformer is presenting to the inverter, a 5KVA transformer is a whole lot different inductively/reactively, than a 5W wall wart.
I attempted this in 2001, with a ferroresonant power conditioner, and half the time, the inverter would shut down immediately upon power up, and other half, it would shutdown in about 2 seconds. I was never able to place a load on it, as I had intended to use it to clean up the waveform from mod-sine to sine. I expect the strange load of it just was more than the inverter would deal with. I've since assumed that any large coil of copper and iron would behave poorly with mod sine inverters, be it motors or transformers. Maybe at low power, a transformer may run, but as you attempt to draw more power from it, I think it will start to react poorly with the mod sine inverter.
My pure sine inverter fired up with it fine.

Anyway, the original question was about driving 2 phases from 2 separate inverters. That would work as long as there are no 220V devices, and you have a transfer switch for safety.

Moe · October 2008

Re: 220v from two inverters?

Keep in mind on many smaller inverter outputs, both the hot and neutral are 60VAC relative to ground, and 180º out of phase with each other.

To tie the neutrals of such inverters together, without synchronization, would require that the ground from the inverters not be connected to the breaker panel, AND that none of the loads shared a chassis ground with another load on the other leg.

GreenerPower · October 2008

Re: 220v from two inverters?

Mike is right. The flat top of the MSW would make the current in the primary of the Xformer ramp up linearly. If the magnetic in the Xformer saturates, it's like short circuited the inverter output. The VA rating of the Xformer needs to be several times the wattage of the load to keep the magnetics from saturation.

On another note, even if there is no 240V load, using 2 independent 120VAC sources could still potentially has issue if there is "multi-branch" circuit being used (120V loads on 2 hot phases share the same return neutral wire). The current in the neutral could potentially exceeding the rating of the wire.
GP

niel · October 2008

Re: 220v from two inverters?

ok, i guess i'll stand as being corrected on the transformer or at least the big ones. maybe a smaller one rated for 500w or so may have worked better, maybe?

boB · October 2008

Re: 220v from two inverters?

Of course you can run MSW inverters' output through a transformer.

How do you think the typical MSW inverters (the low frequency heavy ones like Trace, Heart, Xantrex, Magnum) step the low voltage waveforms up to 120VAC ??

The transformers leakage inductance is the main L that will slow down the current rise and fall and is usually insignificant. The typical isolation transformer or step up/down autoformer like the T-240 or X-240 will usually work fine up to several KVA.

Synching up two 120VAC inverters to make a 120/240VAC system is a different story.

boB

Brock · October 2008

Re: 220v from two inverters?

Green Power has a good point, if the two inverters are in sync, it could double the load on the neutral.

Here is another thought. Just wire the output of the inverter to BOTH sides of the panel. You would have to do that on the input side of a transfer switch or the generator wouldn't like it. Or if you can set the generator to 120vac only you could just tie both inputs together, that would work as well. Although you would still need a transfer switch of some sorts.

Actually they make smaller panels with dual inputs; basically they use two main breakers and physically tie them together, so if you switch one on the other has to go off. If you didn't already install the panel I would look at a Home Depot type of store for generator panels / transfer switches.

niel · October 2008

Re: 220v from two inverters?

thanks for that input boB and i thought as much. what do you suppose mike was having trouble with in getting his to work?

on the 2 inverters, i don't believe he's trying for 120/240, but rather 120 and 120, that is seperate 120v sources that just use 1 common wire. would a problem exist for intertwining 2 modsine inverters with 1 common wire like as moe indicated? something like ground and neutral being bonded together could possibly mean that this would be the point of commonality for both inverters as you wouldn't want to go hot, (neutral, hot), neutral with those in the paranthesess tied together, but more like hot, (neutral, neutral), hot. if i were to use batteries as an example it would look like +, (-,-), + as there would be one common wire tying the -s together and the other 2 would be seperate +s.

i do realize current on the common wire could double or be 0 depending on the phasing for the inverters which one would not be able to control. if both inverters are small in current with respect to the wiring, this wouldn't be a problem as would be the case of say 2 600w side by side modsine inverters using #12 wire.

Brock · October 2008

Re: 220v from two inverters?

In thinking more about this, what about just wiring a 30 amp 240vac plug to the input side of the electrical panel. Then just physically plug it in to either the genset or inverter and on the inverter receptacle end just tie both side together. No chance of mixing that up.

machineman · October 2008

Re: 220v from two inverters?

niel wrote: »

on the 2 inverters, i don't believe he's trying for 120/240, but rather 120 and 120, that is seperate 120v sources that just use 1 common wire.

Yes, thats exactly what I was planning.

I found this manual rotary transfer switch which would work great, accept it costs $280. The Iota 240V auto transfer swith is $133.
http://bluesea.com/category/4/productline/221

boB · October 2008

Re: 220v from two inverters?

niel wrote: »

thanks for that input boB and i thought as much. what do you suppose mike was having trouble with in getting his to work?

Not sure... Synching is going to be a chore if the inverters are not made for that. It usually ~can~ be done if one knows what they are doing, electronically wise, but a pain fer sure.

niel wrote: »

on the 2 inverters, i don't believe he's trying for 120/240, but rather 120 and 120, that is seperate 120v sources that just use 1 common wire. would a problem exist for intertwining 2 modsine inverters with 1 common wire like as moe indicated?

Well, if higher neutral current is a question and 120/120 is needed, just let each 120V circuit have its own neutral (and ground if necessary)... Or use a larger neutral wire ?

If no 240Vac needed, MUCH easier.

boB

BB. · October 2008

Re: 220v from two inverters?

And lastly (or firstly)--Check the inverter specs/manufacturer to make sure if you can ground a neutral or share a neutral between the to inverters...

Many (most?) MSW inverters do not like their -DC input and one of their AC output ground referenced (may let out magic smoke).

Connecting/sharing one of the AC connections between two or more MSW inverters may also be an issue.

-Bill

GreenerPower · October 2008

Re: 220v from two inverters?

machineman wrote: »

Yes, thats exactly what I was planning.

I found this manual rotary transfer switch which would work great, accept it costs $280. The Iota 240V auto transfer swith is $133.
http://bluesea.com/category/4/productline/221

If you look at the internal diagram of the Iota 30R, it is a DPDT relay. Instead of switching hot/neutral, you could switch hot1/hot2 and tie all neutrals together (use the "neutral" of the relay as hot2 and not switch neutral). If 2 inverters could not use same neutral, you could tie hot1, hot2 on the inverter end together to ONE 600W inverter output instead. The relay needs to be energized from 120VAC source. So, one end that connects to either hot1 or hot2 needs to be disconnected and connect to the neutral instead (whether code is a concern here in your area).
GP

220v from two inverters?

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