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MPP 2xLV2424 split phase - output is under 220VAC (on true RMS meter)

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oglife

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Hi folks,

I've got two LV2424 inverters paralleled and setup for split phase 220VAC output. Each individual inverter is reading 110VAC at the output terminals, however when checking the two live wires with my meter, I'm seeing 179.4VAC. As such I've yet to hook up any loads that expect 220.

I'm aware of the pitfalls with measuring inverter output via multimeter, and this isn't a top dollar Fluke, but it does claim to be a true RMS meter. I'm wondering if there might be a problem with my setup, or if this is expected behavior. The inverters are not reporting any problems (no fault codes, the units read P1 and P2 as expected).

In the meantime I'll be testing my meter on a couple of 12V automotive inverters tomorrow (if I can find them).
 
That you are seeing 110VAC on their individual live/neutrals says your meter is at least reasonably accurate.

Not a suggestion to do anything since I don't know anything about these inverters in this mode, but if you have been told to join the neutrals is the connection good and tight?

The only things that really spring to mind are incorrect phase alignment of the two inverters, inaccurate meter, or waveform distortion. The meter you could check by putting it across a known good 220/208 service (take care, if your meter isn't a legit cat rated meter don't hold it in your hand). The other two aren't so easy for you to check.
 
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A point of note: although 110V, 115V is often mentioned or referenced, it's old data and the standards have changed.

In the U.S., for residential, we use 120/240 utilizing a center tapped transformer (the neutral), which gives us Two anti-phase 60Hz lines.

The first power systems were 110 volts.

In the 1930’s the voltage had increased to 115 volts.

In the early 1970’s document C84.1 from the American National Standards Institute (ANSI) included a maximum deviation from standard voltage.

In 1984 the NEC was changed so that the standard voltage used for load calculations was changed to 120 volts.

Today utilities are required to supply you with voltage that doesn’t vary from 120 volts by more than 5% either way. So that would mean your voltage should be between 114 and 126 volts.

YMMV.
 
Two 110 vac waveform's have to be precisely 90 degrees out of phase with each other in order to produce a full 220 VAC. Unless your two invertors are capable of communicating with one another to generate the correct AC phase relationship, you won't be making 220.
 
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offgriddle. That's not correct.

en.wikipedia.org

Center tap - Wikipedia

en.wikipedia.org en.wikipedia.org




I pulled the original data from a variety of original source locations, and attempted to validate the accuracy. I should have noted and added original source links. Will try and do better in the future.

The important point is that USA Grid is 120/240V and is supposed to be between 114 and 126V.

The inverters you plan to use should meet that spec and nominally be at 120VAC, not 115VAC or 110VAC, the old standards, as equipment in the last 30+ years is designed for 120VAC. A lower voltage may cause issues.

But, as always, YMMV.
 
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sunnyeveryday said:
offgriddle. That's not correct.

en.wikipedia.org

Center tap - Wikipedia

en.wikipedia.org en.wikipedia.org




I pulled the original data from a variety of original source locations, and attempted to validate the accuracy. I should have noted and added original source links. Will try and do better in the future.

The important point is that USA Grid is 120/240V and is supposed to be between 114 and 126V.

The inverters you plan to use should meet that spec and nominally be at 120VAC, not 115VAC or 110VAC, the old standards, as equipment in the last 30+ years is designed for 120VAC. A lower voltage may cause issues.

But, as always, YMMV.
Click to expand...
Thanks for chiming in Sunny, it's really good to share information and perspectives, it's how we all learn from each other. Oglife wasn't talking about split phase from a center tap transformer, og was talking about using two AC sources that are completely independent from each other and that's a horse of a different color! Ok, let's follow one, complete cycle of the sinusoidal AC waveform shall we? In the USA, AC electricity does a full 360 degree cycle sixty times in one second. The wave begins at zero degrees on the baseline which equates to zero potential, (no voltage), then increases to maximum positive potential at the ninety degree peak of the wave, then begins to move downward towards the zero voltage line again. At the moment the AC waveform crosses the zero line at the 180 degree point the voltage potential is at zero once again, (but only for 1/60th of a second), and then the voltage begins to increase again untill it reaches a maximum negative voltage peak at the 270 degree point of the wave. Then, the wave begins it's journey back to the zero voltage line and at the 360 degree completion of one cycle, once again there is no voltage for 1/60th of a second! Then, the whole cycle starts over again. Cool huh? So in order to achieve a full 220 +/-, or 230 +/-, or 240 +/- volts, the phase relationship between the two 110 +/-, or 115 +/-, or 120 +/- VAC waves has to be precisely correct, or the combined voltages will be low. ~ it's all about that phase that phase that phase ... ?
 
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So what the above means is, y'all can't just grab two 110+/- volt lines from two, totally seperate sources like for example two, individual invertors and willy nilly combine them to create 220 volts; the two 110 volt sources have to be precisely in phase with each other to generate the 220, (or what have you), volts. Mm-k?
 
Yes, I know oglife was talking about Two inverters.

But as they are the same make and, as he said, "paralleled and setup for split phase 220VAC output", which seems to be a configuration setting for split phase, they should be sync'd. Either the setting is wrong or there is a defect.

The manual looks pretty straight forward. Check everything again, from the parallel boards, to keeping the wires, hots and neutrals separate, the settings and codes for setting up split phase and the troubleshooting at the end of the manual.

Did you buy from MPP-USA ?

If everything else looks good, your vendor is the next port of call.

Not sure that is of much help, but it is what it is.
 
sunnyeveryday said:
Yes, I know oglife was talking about Two inverters.

But as they are the same make and, as he said, "paralleled and setup for split phase 220VAC output", which seems to be a configuration setting for split phase, they should be sync'd. Either the setting is wrong or there is a defect.

The manual looks pretty straight forward. Check everything again, from the parallel boards, to keeping the wires, hots and neutrals separate, the settings and codes for setting up split phase and the troubleshooting at the end of the manual.

Did you buy from MPP-USA ?

If everything else looks good, your vendor is the next port of call.

Not sure that is of much help, but it is what it is.
Click to expand...
Hmm, I very quickly looked at the table of contents for the invertor but saw no provision for connecting two units to communicate with each other to match phases as required to achieve a full and balanced voltage output. ~ No, I have not ever purchased any MPP brand equipment. https://www.manualslib.com/manual/1530586/Mpp-Solar-2424lv-Hs.html?page=2#manual
 
oglife said:
Hi folks,

I've got two LV2424 inverters paralleled and setup for split phase 220VAC output. Each individual inverter is reading 110VAC at the output terminals, however when checking the two live wires with my meter, I'm seeing 179.4VAC. As such I've yet to hook up any loads that expect 220.

I'm aware of the pitfalls with measuring inverter output via multimeter, and this isn't a top dollar Fluke, but it does claim to be a true RMS meter. I'm wondering if there might be a problem with my setup, or if this is expected behavior. The inverters are not reporting any problems (no fault codes, the units read P1 and P2 as expected).

In the meantime I'll be testing my meter on a couple of 12V automotive inverters tomorrow (if I can find them).
Click to expand...
Remember, the two, indidual invertors have to have the ability to communicate with each other to coordinate their phases, or you will not get a balanced & full, combined voltage output.
 
offgriddle said:
Remember, the two, indidual invertors have to have the ability to communicate with each other to coordinate their phases, or you will not get a balanced & full, combined voltage output.
Click to expand...

One of the inverters should be the master and the slave should synchronise with it.
There should be an obvious status indicator on the control panel of one or both units indicating this.
Now if you have two inverters energizing the same circuit and are not synchronised 180 degrees out of phase....
My WAG is that they would very gradually drift in and out of phase and the voltage would gradually fluctuate between 0 and the sum of the line voltages.

I have noticed that some inverters actually do supply pure sine wave alternating current of less than 120 volts.
Sometimes much less when the DC voltage supply voltage is low.
 
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I use the original source, MPP solar, not some third party which could have old manuals.

It's hard to say at the moment as they have so many models, PIP, hybrid etc. and I don't have any MPP stuff...yet.

I had a cursory look at https://usa-mpp-solar.com/manuals/LV2424 hybrid manual-20190717.pdf

But that may be a different LV2424 model.

oglife...recheck your exact model numbers, both on the labels and the paperwork.

Again, you may need to talk to your vendor.
 
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smoothJoey said:
One of the inverters should be the master and the slave should synchronise with it.
There should be an obvious status indicator on the control panel of one or both units indicating this.
Now if you have two inverters energizing the same circuit and are not synchronised 180 degrees out of phase....
My WAG is that they would very gradually drift in and out of phase and the voltage would gradually fluctuate between 0 and the sum of the line voltages.

I have noticed that some inverters actually do supply pure sine wave alternating current of less than 120 volts.
Sometimes much less when the DC voltage supply voltage is low.
Click to expand...
Fer sure it is best if the invertor produces a nice, curvey, analog if you will, sinusoidal wave output, instead of producing a less efficient, more noisey, less pure sinusoidal sawtoothy wave. Are you saying SJ that the invertors are equipped with the cicuirty to facilitate a "slave/master", relationship that coordinates phase output between the two individual invertors to produc the correct split phase product? Or, are you saying that when the outputs of two individual invertors are combined, they just naturally fall into the correct phase relationship with each other?
 
offgriddle said:
Are you saying SJ that the invertors are equipped with the cicuirty to facilitate a "slave/master", relationship that coordinates phase output between the two individual invertors to produc the correct split phase product?
Click to expand...

I am saying that if these units have the ability to synchronise and they are configured to synchronise they should make master/slave relationship abundantly clear via their user interfaces.

offgriddle said:
Or, are you saying that when the outputs of two individual invertors are combined, they just naturally fall into the correct phase relationship with each other?
Click to expand...

I thought I said pretty much the opposite.

smoothJoey said:
Now if you have two inverters energizing the same circuit and are not synchronised 180 degrees out of phase....
My WAG is that they would very gradually drift in and out of phase and the voltage would gradually fluctuate between 0 and the sum of the line voltages.
Click to expand...

WAG = Wild *ss Guess
 
smoothJoey said:
I am saying that if these units have the ability to synchronise and they are configured to synchronise they should make master/slave relationship abundantly clear via their user interfaces.



I thought I said pretty much the opposite.
Checking now.
Click to expand...
It's okay, I get what your saying, thank you.
 
offgriddle said:
It's okay, I get what your saying, thank you.
Click to expand...

The point was that if the units are not synchronised I would expect the voltage to oscillate very slowly(perhaps months or years) between 0 and 2x leg voltage.
I think that would confirm the hypothesis that the inverters are not synchronised.
 
Yep, at first I typed 180 degrees out of phase, then I started thinking and I changed it to 90, since that's where the power peak is of one signal and it seemed like a good place to begin the other signal, but I never drew it out! Thank you for the great discussion! :cool:
 
smoothJoey said:
The point was that if the units are not synchronised I would expect the voltage to oscillate very slowly(perhaps months or years) between 0 and 2x leg voltage.
I think that would confirm the hypothesis that the inverters are not synchronised.
Click to expand...
I think that the voltmeter would always read more than 110 volts but never the full 220 unless the invertor output waveforms synchronized by accident, and even then it would only be temporary.
 
offgriddle said:
I think that the voltmeter would always read more than 110 volts but never the full 220 unless the invertor output waveforms synchronized by accident, and even then it would only be temporary.
Click to expand...

Another way to test this hypothesis is to power cycle the "slave" and check the voltage.
line to neutral will be 110 and line to line should be a random value.
 
smoothJoey said:
Another way to test this hypothesis is to power cycle the "slave" and check the voltage.
line to neutral will be 110 and line to line should be a random value.
Click to expand...
So these particular inverters are designed with the capability of a master slave relationship to synchronize their outputs to generate a phase matched 220 volt AC waveform?
 
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