Single phase inverter fed from three phase system

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BBGigante said:
Sir that was a very clear response, thank you very much. Tomorrow I’ll be getting that new transformer they recommend to feed my new inverter, so I’ll be setting it up and I’ll let you guys know how it went.
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Who is they?

You want the transformer on the output side of the inverter, not 'feed' the inverter.



The one thing I don’t get about the original set up we have there (it’s been like that since I got there) is the neutral point being the same before the inverter and after the step up transformer. Does it means that in my new set up I’ll have to tie all neutrals together? i.e. the system neutral with the new transformer’s output and the new inverter neutral terminal, so when I take one of the inverter’s output lines it is referenced to that same neutral potential and I can use that neutral later on the subsequent sub-panel as a supply for my 120V circuit.
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Well using the supply neutral is where you got lucky. The odds of it being the middle voltage of the old inverter output is IMO astronomical.

The neutrals of the new setup are not connected... at least not as neutrals. The will, however, be connected electrically through [separately-derived] system grounding. See diagram.



As for the UPS I think it can take it, it is e very versatile equipment with lots of configurations available but I will review that point with the user manual before connecting it.
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See the indicated voltage ratings in diagram. These ratings should make the 'system' better tolerant of the mismatch. The transformer output should be 110/220V instead of 120/240 and it'll be closer to the input voltage of your UPS. The lighting should be tolerant of the voltage, but you should review UPS input voltage range versus lighting because low voltage can decrease the effective life of the lighting.


inverter.jpg
 
The only way the original transformer could have worked was if the center tap of the L-L secondary was internally connected to the common N terminal shared with the primary winding. If that were not true you could not get a stable 120V from the secondary.

Sent from my XT1585 using Tapatalk
 
Smart $ said:
Not the only way... but somewhat moot to discuss at this point.

Also, note there is no center tap in the original setup.
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Actually, the OP said that there were only two marked output terminals, L1 and L2. He did not rule out that there was in internal center tap connected to the input N terminal (permanently or via a jumper)
 
GoldDigger said:
Actually, the OP said that there were only two marked output terminals, L1 and L2. He did not rule out that there was in internal center tap connected to the input N terminal (permanently or via a jumper)
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Yeah... but have you ever seen or heard of one? I surely haven't. Not saying it is impossible. Just very, very unlikely.
 
Ok people, I’m back! Bad news and somewhat good news.

We got the new transformer, connected it before the new inverter to feed it, and some "things" happened. First let me tell you about the transformer connections: at the input we got 5 terminals, "0 | 208 | 215 | 225 | 235V", at the output we have 4 "120 | 0 | GND | 120"
So what I did was take my two lines from the three phase system and connect those at the "0" and "208V" terminals, and then I took two wires from the transformer output terminals "120" and the other "120" so I get 240V to feed my inverter, and connected those to the inverter input terminals "Hot in1" and "hot in2". Then I connected the load wires to the "Hot out1" and "Hot out2" to provide 240V to the subpanel powering the UPS and lighting loads. When I’m ready to power it up and take some measurements we forgot to open the inverter transfer switch to remove the load...

The bad news:
We power it up and the UPS power modules got toasted... that’s like US$4,000 for both. Somehow the lights are ok :D

So after the incident I opened the transfer switch and took some readings and actually I had 240V at the inverter output "Hot out1" and "Hot out2", but between my system neutral and the inverter "Hot out1" I got 0V, and with "Hot out2" I got like 230V.. that’s the problem. Between the system neutral and the inverter neutral it was something like 120V.

So then I call the vendor to ask some questions, and they said "oh you have to tie in your system neutral to the transformer’s output neutral terminal and the inverter’s neutral terminal".

And that’s the good news, after we did that everything works fine.
 

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Smart $ said:
Who is they?

You want the transformer on the output side of the inverter, not 'feed' the inverter.




Well using the supply neutral is where you got lucky. The odds of it being the middle voltage of the old inverter output is IMO astronomical.

The neutrals of the new setup are not connected... at least not as neutrals. The will, however, be connected electrically through [separately-derived] system grounding. See diagram.




See the indicated voltage ratings in diagram. These ratings should make the 'system' better tolerant of the mismatch. The transformer output should be 110/220V instead of 120/240 and it'll be closer to the input voltage of your UPS. The lighting should be tolerant of the voltage, but you should review UPS input voltage range versus lighting because low voltage can decrease the effective life of the lighting.


View attachment 18469
Click to expand...

Well by "they" I mean the company that sold me the new inverter, the TRACE one. Also I want the new transformer at the input of the inverter because it's supposed to allow me to power the inverter from the three phase system with no issues. I don’t want it at the output because I already have 240V I can input to the UPS.
 
BBGigante said:
Well maybe it was an autotransformer I think, I took the time to measure continuity between windings and I got a reading, so those two windings were electrically connected.
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Because your inverter only has two in, two out, the transformer needs to be on the output. You cannot use the supply neutral on the output side of the inverter. See diagram in my previous post. This output transformer is the only choice unless you have a three-wire split-phase output from your inverter. Don't heed my warning and you'll waste $$$.
 
Everything you were saying was confusing from the beginning. I think the only things we're pretty clear about is that nothing was defective, but you managed to blow up all the battery backup equipment from not reading the manual.
 
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