Safe Grid Use of the 5000ES and transformer

[kuranaga]

> It's exactly the same as the output side of an isolation transformer.

you contradict yourself!

If the built-in transformer is an autotransformer. The full rated output can be drawn from either 240v or 120v.

In the autotransformer half of the power will be transferred via electrical conduction, the other half via induction from the other half of the winding! it is absolutely NOT same thing with isolation transformer.

Ive not seen a split phase US inverter that would output full power on one of the 120 legs. It is always just half.

 

[timselectric]

you contradict yourself!

Not at all.
You can wire an isolation transformer as an autotransformer, by only using the output winding.

Ive not seen a split phase US inverter that would output full power on one of the 120 legs. It is always just half.

Look for low frequency inverters.

 

[kuranaga]

Look for low frequency inverters.

still nope... show me one + its spec

 

[timselectric]

still nope... show me one + its spec

You're going to have to do your own homework.

 

[Biser]

I'm unhappy with the block/schematic diagram that was given by Signature Solar above. A failure of the transformer circuit breaker will leave you with a straight 240 volt supply and a floating neutral - something you really really don't want. This failure could be as simple as some homeowner or their children turning off the wrong breaker. I propose an alternate solution for a non grid-tied application -

The two inverters go into an 8 position Square-D box through two double pole 20 amp breakers. The auto-transformer is connected to this box via a twenty five amp breaker. A forty amp breaker leaves this box for power output. A relay with a 240 volt coil and forty or fifty amp dual contacts is placed in series with the 240 volt output from the 40 amp breaker above. The coil is in parallel with the auto-transformer. In this way all power will be turned off if that transformer breaker is tripped or turned off by mistake. There are plenty of relays like this on amazon - they're used in many large air conditioners. MAKE SURE YOU HAVE A SOLID GROUND WIRE ALL THE WAY FROM THE FIRST INVERTER TO THE POWER DISTRIBUTION PANEL. You don't want anything floating to some unknown voltage. Been there, done that, got an unexpected 300vdc surprise. (Amateur radio home-brew transmitter, don't ask...)

 

[Hedges]

Relay disconnect of output (or input) when autotransformer disconnected should work. So long as it is just a transformer, without an over-temperature thermostat (don't think it has one.)

Is it the .pdf schematic in OP's post #1 you're referring to? I think others were posted somewhere in these 42 pages.

A simpler solution, but only supporting 120V total current up to transformer's capability not current imbalance to its capability, would be connect inverters to a 240V only loads panel, then use 25A dual breaker to feed autotransformer and 120V loads panel (no separate breaker for transformer, just tapped off main lugs). If breaker trips, autotransformer and 120V loads are disconnected.

However you do it, use wire gauge capable of carrying 50A for auto-transformer neutral. That's how much current will be in neutral if L1/L2 are each carrying 25A. Data sheet lists 42A (48A for 208V input) line to neutral current.

The data sheet I've found for one GroWatt transformer model appears to implement relay disconnect for lost neutral as you propose (different from what's in post #1), but details of internal wiring aren't sufficient to be sure:

https://signaturesolar.com/content/documents/GROWATT/1519001-specs.pdf

"The rated power of secondary side L1-N and L2-N could up to 5kVA respectively, and the power difference between the two split phases can not exceed 1.5kW."

???

1.5kW / 120V = 12.5A
Are they saying that a single 120V, 1500W, 12.5A load on one phase and zero on the second phase is maximum it can handle?
Of course balanced loads, either 240V only load or identical sized 120V loads on two phases wouldn't involve the transformer.
But if 1.5kW is the most imbalance either 5000VA rated ATS 5000T-US or 11400VA rated ATS 11400T-US can handle, that is only 750VA actually going through the transformer core.

I suspect that someone who misunderstands transformers wrote that line, while the specs for amps per wire are correct.

Note that these two models, with quite different max power rating, have identical "Max continued current(L-N)".
That means they are the same transformer, but have different contactor. Victron similarly offers theirs with two different L1/L2 ratings but same autotransformer.

 

[Hedges]

Oh, big difference with Victron's auto-transformers is that they switch neutral between grid connected and ground bonded. That makes it safe and compliant.
"UL Listed" or not, IMPO (in my professional opinion), no safe and effective configuration for use of Growatt ATS-US together with utility grid has been presented. Off-grid, seems fine.

 

[timselectric]

Oh, big difference with Victron's auto-transformers is that they switch neutral between grid connected and ground bonded. That makes it safe and compliant.
"UL Listed" or not, IMPO (in my professional opinion), no safe and effective configuration for use of Growatt ATS-US together with utility grid has been presented. Off-grid, seems fine.

Only safe option is to use an isolation transformer, with the US version and grid pass through.
Which pretty much makes it less economical.

 

[billduck]

This method of creating a 'separately derived system' is a completely acceptable way to go and should work best for most people!

It will require a separate grounding rod be placed not less than 8 feet from any existing ground rod. I would also use Shunt trip breakers for the output of the Growatts tied to the Transformer breaker. For added safety.

However I see a problem with the way you drew it in your schematic. You have a Ground line running from the Main Panel to the Sub Panel and then Bond it in the Sub Panel. This will create a Bond in two places as the Main Panel for Utility disconnect will already have a Neutral/Ground Bond in place.
View attachment 80282

If you remove the wire coming from the Main Ground you should be good.

I have a similar system, and I got a schmatic from Signature, attached. A third breaker is located on the AC Out Panel. When connected to the utility, the AC out, from the GroWatt units, is connected to the utility, if you trace the wires. The path is fron the Inverters to the 3rd breaker, then to the Split Phase Transformer, then to single breaker in the load panel. And L1,L2 on the load Panel get utility power. Is this not a conflict, in that the inverters are not meant to be grid tied? What am I missing?

 

[timselectric]

I have a similar system, and I got a schmatic from Signature, attached. A third breaker is located on the AC Out Panel. When connected to the utility, the AC out, from the GroWatt units, is connected to the utility, if you trace the wires. The path is fron the Inverters to the 3rd breaker, then to the Split Phase Transformer, then to single breaker in the load panel. And L1,L2 on the load Panel get utility power. Is this not a conflict, in that the inverters are not meant to be grid tied? What am I missing?

Yup
Don't do that , with an autotransformer. (Only with an isolation transformer)
The N/G bonding in the loads panel is also a problem, when in grid mode. (There's no neutral from the grid) all neutral current will flow on the ground conductor.

Edit:don't do it with an isolation Transformer either.
It would still be back feeding.

 

[freedomlives]

And here is the (possible) Online double conversion MPP Solar MK/MKX (alias Voltronic Axpert King and King 2) schema:

View attachment 82235


As you can see only the double conversion unit is doing always the AC/DC and DC/AC conversion.

With the Axpert King II (which I've found in a Czech retailer), there's no way it should ever be feeding power into the grid, right? From the perspective of the utility company, it should be considered the same as an online UPS?

 

[mrzed001]

With the Axpert King II (which I've found in a Czech retailer), there's no way it should ever be feeding power into the grid, right? From the perspective of the utility company, it should be considered the same as an online UPS?

Yes, it is exactly like an online (double conversion) UPS.
The only other solution is to buy a separate charger (AC/DC) and an inverter (DC/AC).

 

[neuropa3]

I have a similar system, and I got a schmatic from Signature, attached. A third breaker is located on the AC Out Panel. When connected to the utility, the AC out, from the GroWatt units, is connected to the utility, if you trace the wires. The path is fron the Inverters to the 3rd breaker, then to the Split Phase Transformer, then to single breaker in the load panel. And L1,L2 on the load Panel get utility power. Is this not a conflict, in that the inverters are not meant to be grid tied? What am I missing?

Off Grid system with the GroWatt 5000es/us inverter I have 24 used 250 Candian Solar panels that are rated from 30.1 volts and 8.8 each. When I try to draw up a system to max the voltage and amps I have too many volts as the inverter says max volts is 450VDC but 100 amps. Any Ideas?

 

[timselectric]

Off Grid system with the GroWatt 5000es/us inverter I have 24 used 250 Candian Solar panels that are rated from 30.1 volts and 8.8 each. When I try to draw up a system to max the voltage and amps I have too many volts as the inverter says max volts is 450VDC but 100 amps. Any Ideas?

I have the same inverter and panels. 10 in series is the max you can connect. Otherwise the DC bus voltage will get too high.

 

[timselectric]

I have the same inverter and panels. 10 in series is the max you can connect. Otherwise the DC bus voltage will get too high.

This is my current production from 10s4p. (11am)

 

[neuropa3]

Thanks, I have all the pieces but have to build it, off grid in wyoming with a wind turbine as well

 

[neuropa3]

This is my current production from 10s4p. (11am)View attachment 109540View attachment 109541

Thanks, I have all the pieces but have to build it, off grid in wyoming with a wind turbine as well

 

[Pendrak]

If you are grid tie, why don't just use L1 and L2 from grid and use the autotransformers for neutral? in other words don't use the neutral that came from grid and let the autotransformers provide the Neutral when is in bypass mode and off-grid mode.

 

[JohnGalt1717]

If you are grid tie, why don't just use L1 and L2 from grid and use the autotransformers for neutral? in other words don't use the neutral that came from grid and let the autotransformers provide the Neutral when is in bypass mode and off-grid mode.

Exactly what I did and it works perfectly.

 

[wilsonb100]

Same here.