Stepping outside the box for thoughts on alt designs. Single voltage inverters, transformers, etc

[fastline]

So....not currently working on a system here but stumbled into some stuff that was jumbling my brain. Apparently Euro inverters bond N/G in the inverter and are 230V only IIRC. I am trying to absorb some info I read with autotransformers and their relation to the N/G, effectively pushing currently through ground I guess. Has anyone actually dealt with these types of inverters? I fail to see the concern but I guess I have also not confirmed that 120V inverters are bonded or not?

Obviously split phase becomes a mess with solar, or I guess just buy the 3x expensive gear..

There really is no issue with the split other than to realize that most loads do not even require it. Like literally, there is only one appliance I can think of.

Anyone here doing less common installs or just stick to rezzy split phase type deals? I have one with 3P coming and 3 inverters and not sure how I will assess that deal.

 

[jaggedben]

Are you talking about grid connected or completely off grid systems? I can't even begin to make sense of what you're saying without knowing that.

 

[fastline]

Well, I am talking about totally offgrid applications, but I guess some folks are trying to use these 230V units on the grid. Apparently quite the issues and I am still trying to fully understand it myself so excuse the scatter brain thoughts.

I ran into a couple videos where guys are trying to run these "auto transformers" to get split phase off these I guess. I have yet to draw this up so it makes sense in my head but there is apparently drama with the neutral and ground.

If used correctly, I just don't see much issue other than they are bonded.

 

[pv_n00b]

In off-grid systems, you can use an autotransformer to derive a 120/240V split phase output from a single 120V inverter. I have also seen autotransformers used to load balance between two 120V inverters in a 120/240V series in off-grid systems. If the load on one phase is high the autotransformer transfers power from the unloaded phase to the loaded phase allowing both inverters to supply the load.
As for using European inverters in US systems, it's probably more trouble than it is worth to hack together a system that works. Even if someone gives you a European inverter for free by the time you put together the system to adapt it to the US standards buying a US inverter would be cheaper.

 

[fastline]

I appreciate the reply over my poorly organized thread. I am curious how the autotransformer balances the load? There seems to be some drama with the use of these that I am simply not familiar with and trying to learn something here.

I am not saying the use of single voltage equipment is right, but in nearly all loads, split phase is not even used. It's single phase either 120 or 240. However I think the balance on the neutral might be at issue with some of the drama in the videos.

I think I will link some vids here as this might brighten up the convo better. I guess I have never used an autoX for such applications. Only in buck/boost applications,but I have also made split phase for some generator offgrid temporary applications.

 

[jaggedben]

Using an autotransformer to create a neutral reference with a 240V inverter is a standard approach for hybrid off-grid systems (to the point that for some of us 'NFT' means 'neutral forming transformer' and not crytpo kitties and such). Both Solaredge and Enphase do it. (For all I know, Powerwalls may have one hidden inside, too. Or they may have two 120V inverters.) If you want to use a 230V inverter to provide 115V to loads by using a similar setup I can attest it will work if hooked up correctly. Personally I'm the sort or person who stands behind manufacturer tested setups, but if you're not risk averse...

I didn't watch the whole of both videos. What he's getting at in the first one is the obvious fact that if you have two conductors with voltage between them you can't ground both if them of it's a short.

 

[jaggedben]

Understand that to the Europeans 230V is like the way we use 277V in a 480/277 wye system, line to neutral. You can't can't connect that into US type wiring without modifying which conductor is grounded and how. Probably what he's recommending is not something acceptable to most AHJs if it were to be inspected.

 

[ramsy]

I think I will link some vids here.. I guess I have never used an autoX for such applications.

Excellent video, but left me wondering who needs to molest European inverters for 120v conversion.

Having visions of military contractors & ex-patriots moving their domestic 120v appliances with them to Europe.
And when 120v junk is eventually replaced by attrition, I also see inverter modifications being reversed.

First video was especially instructive with laboratory demonstrations of xfmr theory & grounding issues. Removing inverter N-G Bonding screw could use threaded Nylon or Plastic replacement to maintain separation.

Second video demonstrates how auto-transformers, when not built into inverters, can overload during imbalance, especially when breakers trip and 120v loads get destroyed by over voltage.

Both videos are very understandable for anyone who doesn't normally work with transformers.

Thanks for posting.

 

[fastline]

Well as I mentioned, I don't have a project or currently trying to do any of this, but probably something similar in the future. Quite obviously if someone has to open an inverter, pull boards and dig around to attempt to find all the N/G bonds, we already know that won't be a legit mod as I question if there is really enough air gap for separation ,and if the inverter is designed to survive with such mods.

But in any case, what I was mostly getting at is regardless of any AHJ matters, most loads do 'not' use split phase (require both 120 and 240), but use one or the other voltage. It would seem like if someone really wanted to solve a problem here, just run a 240pri//120sec isolation transformer. Only load I can think of off the top is a clothes dryer, but that 120V probably has like 2A on it as it usually only powers the circuits and maybe a light bulb.

But in any case, obviously these types of things are application specific.

I don't think the guy in the videos is really pushing his stuff as AHJ compliant as much as just solving some backyard problem. We all know there are tons of these systems around that AHJ eyes have never seen and never will. Personally, I get pretty annoying with the connotation that an "inspection" means something is done "better". I have seen plenty of private installs that are real panty droppers in terms of detail and quality.

I guess I did not fully understand what the second vid was trying to show with regards to 240V ending up on a 120V circuit. Probably easier for me to see a diagram than a demo.

 

[jaggedben]

I watched the second video on double speed. I didn't see what the 'solutions' were for autotransformers.

That's a SolarEdge autotransformer in the video, BTW, or at least it sure looks the same. When I installed those they told us to put a 25A main breaker in the backup panel to prevent overloading the transformer. (The SolarEdge inverter also controls whether it is connected and would (I hope) probably stop outputting if it stopped seeing the neutral reference from the transformer.) So that limited the output of a 7.6kW Solaredge inverter to only about 6kW in off-grid mode, which I thought sucked (although the batteries didn't support more than that anyway). With Enphase they have an autotransformer on a 40A breaker and it can have up to 128A of solar+battery output connected. The transformer and all the sources are run through relays that will disconnect power from the loads if something goes wrong, therefore not fry loads like he shows in the video.

All this is to say, if I were going to do a DIY design with an autotransformer, I would find a way to gang together a main breaker to the loads panel along with the autotransformer breaker so that if the autotransformer is overloaded the loads are also disconnected from the source. Not sure how I'd do it, but I wouldn't build such a design without something like that. Not that I'm going to try this personally in any case, but for people who are inclined to pinch pennies and not follow rules there is probably a not-too-expensive way that a not-too-dumb person can install.

 

[BillK-AZ]

Most of the 230V EU inverters are 50 Hz. Many USA loads do not like that.

 

[tortuga]

Most of the 230V EU inverters are 50 Hz. Many USA loads do not like that.

The 'no brand' off shore 'single voltage' ones I have seen are actually 50Hz/60Hz adjustable, some even are 220/230/240V adjustable also.
I think some of that stuff is deep in the settings of a 'normal' UL listed off grid inverter also, I have also seen three grid tied SMA inverters setup on 3 phase 240V delta. But that technically might still be split phase?

 

[ggunn]

I have also seen three grid tied SMA inverters setup on 3 phase 240V delta. But that technically might still be split phase?

I have done that on 208/120V and 480/277V services; a few years ago it was not that unusual when the only 3 phase inverters were central (big) inverters. Nowadays, though, there are lots of smaller 3 phase inverters available.

 

[fastline]

Most of the 3 phase inverters I have seen were designed for grid tie, not offgrid. Fronius comes to mind.

I am still weighing my own personal build. I really would like 3P but will likely take at least 3 parallel inverters, so if one is down, I will only have 1P.

There are lots of design considerations. You can parallel 3, 120V inverters for 120/208, but each phase will still be limited to what a single inverter can output in single phase. I have never seen a single voltage inverter that will do 277v to make 480v.

All in all, with the price of wire, I am inclined to run industrial voltages in my own place.

 

[ggunn]

Most of the 3 phase inverters I have seen were designed for grid tie, not offgrid. Fronius comes to mind.

I am still weighing my own personal build. I really would like 3P but will likely take at least 3 parallel inverters, so if one is down, I will only have 1P.

There are lots of design considerations. You can parallel 3, 120V inverters for 120/208, but each phase will still be limited to what a single inverter can output in single phase. I have never seen a single voltage inverter that will do 277v to make 480v.

All in all, with the price of wire, I am inclined to run industrial voltages in my own place.

OK, I had forgotten that the subject was off grid PV, though I have never seen a three phase off grid PV system and I don't know why anyone would build one. I have designed grid tied three phase PV systems connecting to 480/277V with single phase SMA inverters, but it was 10 years or so ago; there's no reason to do that any more.

 

[tortuga]

OK, I had forgotten that the subject was off grid PV, though I have never seen a three phase off grid PV system and I don't know why anyone would build one.

Water pumping, large scale irrigation in areas where its difficult to get 3 phase service.

 

[jaggedben]

Water pumping, large scale irrigation in areas where its difficult to get 3 phase service.

Also islands.

 

[pv_n00b]

Once you get into 3 phase off grid they are generally large enough to have a site controller and the BESS provides the voltage reference in order to use grid tied 3 phase inverters. Kind of a microgrid without the utility connection.

 

[fastline]

Once you get into 3 phase off grid they are generally large enough to have a site controller and the BESS provides the voltage reference in order to use grid tied 3 phase inverters. Kind of a microgrid without the utility connection.

Pretty much other than I find many grid tie inverters to lack many features for generator support, priorities, etc. There are very few that will actually run a generator, sync to it, and use it only as a supplement to the solar when solar is made a priority.

I am open to hear from others here on options but consider you have a 5kw load, and running only a 2kw generator. If the inverter does it's job, it will pull 2kw from the generator and 3kw from the solar system for the load. Once things are well sustained, the generator can either push charging to a storage pack or just throttle back.

In any case, in older equipment, I was forced to either run on solar or the inverter pushed its transfer switch to the generator. That is sometimes not ideal if you are still making solar power, but just not enough to handle current loads.

These are all reasons most people can't handle offgrid. So used to "out of mind" functions. I say "just get your check book out" and there is always a way to solve your problem. The commercial grid does that.

 

[pv_n00b]

In any case, in older equipment, I was forced to either run on solar or the inverter pushed its transfer switch to the generator. That is sometimes not ideal if you are still making solar power, but just not enough to handle current loads.

These are all reasons most people can't handle offgrid. So used to "out of mind" functions. I say "just get your check book out" and there is always a way to solve your problem. The commercial grid does that.

This topic comes up a lot. If I have PV, BESS, and a generator why can't they all work together in a small residential off-grid system? The reason is no one makes the equipment for that. It's more expensive than just switching between PV and the generator. Since off-grid systems are expensive to start with people are attracted to anything that brings the cost down. There are also design issues with sizing the generator that tends to make it more efficient to fully load the generator when it is on and not share the load with the PV system.