Eugene, you're right. 120 degrees, not 60 :-)

On the flip side, I might have been a bit hasty in dismissing the idea. Thinking back to how many modern inverters work: First you step up the DC to a higher DC voltage at a higher frequency. Then you chop that into AC using a second stage.

 

So a 3-phase inverter could have one step-up phase, but three AC-generating phases. If I recall correctly, all the heavy high-power expensive semiconductors are in the step-up stage, and often the second phase is much less stressed.

 

So if all that is true... there really isn't a reason why you couldn't allow one phase to work a little harder as long as it is compensated for by another phase working less hard. I mean, I still stick to my point that this really isn't what three-phase is for... and anyone spending money on a three-phase inverter is likely doing it because they use three-phase for the stuff it is actually meant for... :-) But in theory, I suppose it is possible.

Eugene, you're right. 120 degrees, not 60 :-)

On the flip side, I might have been a bit hasty in dismissing the idea. Thinking back to how many modern inverters work: First you step up the DC to a higher DC voltage at a higher frequency. Then you chop that into AC using a second stage.

 

So a 3-phase inverter could have one step-up phase, but three AC-generating phases. If I recall correctly, all the heavy high-power expensive semiconductors are in the step-up stage, and often the second phase is much less stressed.

 

So if all that is true... there really isn't a reason why you couldn't allow one phase to work a little harder as long as it is compensated for by another phase working less hard. I mean, I still stick to my point that this really isn't what three-phase is for... and anyone spending money on a three-phase inverter is likely doing it because they use three-phase for the stuff it is actually meant for... :-) But in theory, I suppose it is possible.

Have you seen how many houses have 3 phase power these days? Yet no one uses a 3phase appliance in a house. It's purely there cause the houses are big and have a lot of appliances. Too many for a single phase / single isolator.

In the old days, every room in the house had a single wall plug and one or perhaps 3 lights. These days they build them with 4 wall plugs (Sometimes) and an array of downlights + hidden lights on the walls + lights in the cupboards. Kithcens have under counter lights + down lights + lights in the pantry, etc. Gardens have lights under the trees, drive-way lights ever 1.5m, massive flood lights, etc.

The reason I'm trying to go this route is due to complexity + space requirements for setting up 3x single phase inverters.

a single 3Phase inverter use less space and fewer cables. But very few exist with battery backup.

Hmm yeah, you cannot put multiple phases into one, because the wave form will be out of phase. That will cause some serious issues. Same way you cannot have multiple inverters on a single phase, unless they are designed to work that way and are connected to be in sync with one another. It may be possible to combine a grid tie inverter with a normal inverter to pick up the extra load, but you will need to be able to use the full load on the grid tie all the time or your 3 phase inverter need to have a way to manage the excess load.

 

I know the victron inverters have a way to be configured so they inter connect and communicate with one another, not sure about the inverter you have. It may be worth it to get another appliance with 2 smaller elements. That may be the cheaper way to solve the problem that looking at the inverter to do it.

So a three phase inverter is really just three inverters that's configured to sync with each other with a 120 degrees phase shift (or 2pi/3 radians... after several years of math training talking of degrees always feels a little dirty :-) ). So there is no technical reason why one of the three can't be a little larger... just practically nobody does it that way.

 

Still thinking Victron. They can be configured to make three phase (so they sync to a 120 degrees difference), but they can also be configured to be parallel. So in theory, if you had 4 inverters, you could use three of the four to make 3-phase, then add the 4th inverter in parallel with one of the phases and sync it with that one phase.

 

Alternatively, use three inverters, but make one of them larger than the others.

 

Now put them all in one case.

 

Nobody does such a thing, and none of these setups are supported. With Victrons, they all have to be the same size for starters. This is all just theory.

 

Overall, I still think there is probably a reason nobody bothers. Probably too complex a setup and too small a target market.

So a three phase inverter is really just three inverters that's configured to sync with each other with a 120 degrees phase shift (or 2pi/3 radians... after several years of math training talking of degrees always feels a little dirty :-) ). So there is no technical reason why one of the three can't be a little larger... just practically nobody does it that way.

Finally, someone see the light

Still thinking Victron. They can be configured to make three phase (so they sync to a 120 degrees difference), but they can also be configured to be parallel. So in theory, if you had 4 inverters, you could use three of the four to make 3-phase, then add the 4th inverter in parallel with one of the phases and sync it with that one phase.

 

Alternatively, use three inverters, but make one of them larger than the others.

 

Now put them all in one case.

 

Nobody does such a thing, and none of these setups are supported. With Victrons, they all have to be the same size for starters. This is all just theory.

 

Overall, I still think there is probably a reason nobody bothers. Probably too complex a setup and too small a target market.

Microcare and Axpert inverters can also be configured this way. But you end up paying for 3 pieces of equipment, 3 full pieces of equipment. And it takes a lot of space.

On 2015/10/21 at 12:17 PM, SilverNodashi said:

I can't balance the loads correctly. Even with the loads fully balanced, a 4KW heating element trips the inverter! It's a 22V single phase urn. So now I'm forced to buy an expensive 3phase urn, or a 15KW 3phase inverter. The a 10Kw 3phase is running at about 20% most of the day. It's a waste of money and resources, IMO to upgrade just for this purpose!

But hopefully some clever engineer will notice this post and make an inverter that can be better utilized in cases like this.

Replace the element of the urn with a 3-phase element. Problem solved. 

I am sorry, but if you doing solar, it is to save money and power consumption, correct?

So why still have an urn running all day? Is that not really counter productive? Rather get a 3ph instant water heater!!!

Thinking back to that post of 2015... I think I now know why one would not make one leg larger if you used three inverters to make a 3-phase supply. It's because the "return current" of that phase doesn't necessarily return on the neutral (and therefore to the inverter serving that phase), if the phases are at least somewhat balanced the return current goes through the other phases (through the other two inverters, neutral only carries the difference between phases), and therefore you'd have to make them all the same size.

On 2015/10/21 at 5:08 PM, Wetkit said:

Ok, then lets stop right here

If your inverter is too small to power your load, do not blame the inverter or its maker, buy a bigger unit.

 

If on the other hand you trying to save money by going solar, good for you.

If you still insist on running wastefull equipment on said solar install, bad on you.

 

For the life of me, I cannot think of another piece of equipment as wastfull of energy as an urn.

 

If you still insisting on running your unbalanced load, then perhpas look at running 3 single phase inverters, say two 3kw units on 2 phases and a 5kw unit on your "urn" phase.

It will cost you less than a 5kw 3ph unit, perhaps???

Good Thought/ advise!

On 2015/10/21 at 5:08 PM, Wetkit said:

Ok, then lets stop right here

If your inverter is too small to power your load, do not blame the inverter or its maker, buy a bigger unit.

 

If on the other hand you trying to save money by going solar, good for you.

If you still insist on running wastefull equipment on said solar install, bad on you.

 

For the life of me, I cannot think of another piece of equipment as wastfull of energy as an urn.

 

If you still insisting on running your unbalanced load, then perhpas look at running 3 single phase inverters, say two 3kw units on 2 phases and a 5kw unit on your "urn" phase.

It will cost you less than a 5kw 3ph unit, perhaps???