New to forum & Enphase M190 Inverter questions

[sensij]

I know how a transformer works but I don't understand how the inverter can sense the line voltage through the transformer.

This suggests that you don't know how a transformer works (turn ratio = voltage ratio), but ultimately, the micros won't care. They just need to see voltage in the 183-229 V range at the right frequency (and probably impedance). They won't directly know anything about the line voltage supplying your transformer, and don't need to.

[paul65k]

The actual part number of the ones I am considering are M190-72-208-S12. I have been studying the Enphase website, which is where I confirmed these were 208v, 3 Ph inverters. I did not see anywhere in the installation manual where it confirmed or denied the ability of those inverters to work in a single phase environment. I would really like to know the exact model number of the ones you have installed. If I can get away from having to use a transformer, then of course, my install cost goes way down and I only need to pay an electrician to do the main panel connection. If you would be so kind as to take a peek at the model number of your inverters, I would truly appreciate it. Thank you for your post!

Did you call their Technical support line?......they are pretty helpful and can probably answer your question pretty quickly.

Mine are the M190-72-240-S12 and they are rated from 211V-264V and function fine in my 125A sub-panel. These were Spec'd by the Solar contractor, called out on the plans to the POCO and approved by the local building inspector.

Cheers!

[sensij]

Mine are the M190-72-240-S12 and they are rated from 211V-264V and function fine in my 125A sub-panel. These were Spec'd by the Solar contractor, called out on the plans to the POCO and approved by the local building inspector.

That is not the 208 V model that the OP is asking about, yours are the 240 V version that I suggested the OP look for, but which are apparently too expensive.

[paul65k]

That is not the 208 V model that the OP is asking about, yours are the 240 V version that I suggested the OP look for, but which are apparently too expensive.

Perfect and good to know....now we're both clear......thanks for clearing this up

[TxMike]

This suggests that you don't know how a transformer works (turn ratio = voltage ratio), but ultimately, the micros won't care. They just need to see voltage in the 183-229 V range at the right frequency (and probably impedance). They won't directly know anything about the line voltage supplying your transformer, and don't need to.

I suppose I should have clarified my statement in that I understand how transformers work "in the basic sense". You are 100% correct in assuming that I am not an electrical engineer. If I was, I'm sure I wouldn't be on this site seeking helpful advice. While I do appreciate everyone's assistance, you'll have to forgive me that my experience is in other fields and that I may ask questions that are rudimentary to many of you with vastly greater experience in the field of solar and electrical power systems.

I simply need to know if my proposed installation will work and what equipment I need to gather to facilitate that installation. I won't be one installing the transformer, tying it to the grid, or building a flux capacitor. I am well old enough to accept the fact that many things are out of my league and have no problem hiring those that can do the job. That being said, I don't have an endless source of funds in which to pay others to do the simpler tasks I can do myself and why I am asking equipment intensive questions. I have been burned twice before by contractors who took advantage of my lack of knowledge on a project.

[inetdog]

I suppose I should have clarified my statement in that I understand how transformers work "in the basic sense". You are 100% correct in assuming that I am not an electrical engineer. If I was, I'm sure I wouldn't be on this site seeking helpful advice. While I do appreciate everyone's assistance, you'll have to forgive me that my experience is in other fields and that I may ask questions that are rudimentary to many of you with vastly greater experience in the field of solar and electrical power systems.

I simply need to know if my proposed installation will work and what equipment I need to gather to facilitate that installation. I won't be one installing the transformer, tying it to the grid, or building a flux capacitor. I am well old enough to accept the fact that many things are out of my league and have no problem hiring those that can do the job. That being said, I don't have an endless source of funds in which to pay others to do the simpler tasks I can do myself and why I am asking equipment intensive questions. I have been burned twice before by contractors who took advantage of my lack of knowledge on a project.

The transformer will keep the primary and secondary winding voltages in the same ratio (except for resistive voltage drop) regardless of which way the power is flowing through it. It is a strictly passive device.
Now the start up surge for a transformer when you first close the breaker feeding it may be vastly different depending on which of the two windings is being fed, but that should not be a concern with a transformer with a close ratio like 208 to 240.
If it were not for the need to supply the neutral center wire as a voltage reference, you could do the job less expensively with a simple boost transformer.
If you look for a 208-240 autotransformer instead of a 208-240 isolation transformer you may be able to find a lower price and a transformer that is half the size.

[TxMike]

The transformer will keep the primary and secondary winding voltages in the same ratio (except for resistive voltage drop) regardless of which way the power is flowing through it. It is a strictly passive device.
Now the start up surge for a transformer when you first close the breaker feeding it may be vastly different depending on which of the two windings is being fed, but that should not be a concern with a transformer with a close ratio like 208 to 240.
If it were not for the need to supply the neutral center wire as a voltage reference, you could do the job less expensively with a simple boost transformer.
If you look for a 208-240 autotransformer instead of a 208-240 isolation transformer you may be able to find a lower price and a transformer that is half the size.

That's good information to have! Thank you.

[bcroe]

If you look for a 208-240 autotransformer instead of a 208-240 isolation transformer you may be able to find a lower price and a transformer that is half the size.

A slight voltage adjustment using an auto transformer will reduce its size in proportion to the
DIFFERENCE in voltages. The 32V difference is far less power being transformed from electric
to magnetic and back to electric, than the entire 240V circuit. And the idle power & losses in
conversion will be similarly reduced. Bruce Roe

[TxMike]

Given an average load on a small house, what size (in VA or kVA, I assume) should I expect to purchase?

[bcroe]

Given an average load on a small house, what size (in VA or kVA, I assume) should I expect to purchase?

I thought you were trying to match 208 VAC micro converters to 240. If so the micro peak output
is what your autotransformer must handle. A big loser here is the fact that the average power of
the micros over a year will be quite a small fraction of their peak, but the peak rated autotransformer
is running all the time. So its idle losses are going to total as a large percentage of solar energy
produced. Bruce Roe