diy solar

diy solar

Safe Grid Use of the 5000ES and transformer

@SS, Is this true?
POST #23: "That's what they told me today and they stated the Chassis do not need to be grounded."

Some one will get hurt.
 

Here's another one for ya:

Assume gas pipes are bonded to electrical ground at service entrance, in compliance with code.
Assume cast iron drain pipes to fixtures (hey, it's an old house!)

Since this is a grid-backup system, I naturally want normal use of appliances during power failures.

Scenario #1: I have a gas stove with some electrical stuff (timer, ignitor), so I plug it into "load panel"

Scenario #2: Well water fills a plastic holding tank. Booster pump supplies water to fixtures through copper pipe. I wire booster to "load panel"

Note that disconnecting ground between GroWatt and Utility Entrance solved the problem Ian showed in his video, that autotransformer sees voltage imbalance due to imbalance in the grid and tries to correct it, resulting in massive current flow.
With no ground wire, the two ground rods might be 12V part (voltage tolerance of transformer depending on load.)
Assume earth is fairly dry, negligible current flow and earthworms are relaxed.

In Scenario #1, gas stove is hooked up by a flexible brass or aluminum line to gas connection in kitchen.
This completes the circuit from autotransformer neutral to GroWatt ground to stove chassis, through flexible gas pipe, back to utility entrance ground, to neutral. The massive current Ian had seen returns. Flowing through flexi gas pipe. Life becomes interesting.

In Scenario #2, consider no gas line completing the circuit. Ground of circuits powered by GroWatt sit at 12V. Ground rod pulls nearby dirt to same voltage, but at utility entrance earth is at zero volts. You fill your tub, settle in for a nice warm bath (well grounded to earth by waste pipe.) You decide to add some more water, so you reach up and grab the hot water faucet with a soaking wet hand. (Above 30 mA, you can't let go. 12V/30mA = 400 ohms. What is the body's resistance with wet skin?)
 
If you use a transformer like the following.

HAMMOND SG3N0037LE D16 SNTL-G3 1PH 37.5KVA 240X480-120/240V AL 60HZ 150C 3R

(BTW there are smaller versions of this transformer)

It will provide the isolation required and eliminate the need for the neutral forming transformer as well as any loss of neutral protection.

Its an expensive solution but simple and clean (KISS). Less parts less to fail.

I'd have to run the numbers but your inrush current may be high to initially energize the transformer.
Would a 10kva transformer be good to handle 2 of the 5000w inverters? That's as big as I'll ever go(starting with 1). Can pick one up for around 800 bucks and it seems it will eliminate a couple of problems using the auto transformer.
 
Probably. I don't think 2x 5000W inverters are likely to exceed 10kVA.
If they could actually deliver 5000W into a motor load (maybe 0.8 PF?) then they would actually have to deliver around 6000 VA each.

A 10kVA transformer could probably deliver 5000W or so to a resistive load on a single 120V phase. Possibly too much on a single phase would overload the transformer. Properly sized circuit breakers on its output should protect it from that (and from W vs. VA overload.)

Isolation transformer on input or output takes care of the issue Ian's video reported on trying to balance the utility grid.
The removed screw between GroWatt "Neutral" and ground may solve what it was meant to. Final verdict tbd on whether that is sufficient isolation.

Multiple transformers (before and after inverter) could have let a European single-phase inverter work for US split-phase system, but it is more iron, expense, efficiency loss.
Hopefully the removed screw and an isolation transformer on output (or isolation transformer on input and auto-transformer on output) solves all issues.
 
Yep they need to pull all this dangerous advice down.
I get why SS wanted to make a counter post to redirect traffic away from Will's post which said the system is unsafe.
The problem is that you now have a thread with a title of

"Safe Grid Use of the 5000ES and transformer"

This thread does not contain a schematic for the safe use of the Grid with the 5000ES, so the title should be changed so that no one is put in danger and the Mods should lock the discussion and lets move it back to the warning thread that Will created until such time as SS does have a schematic that provides safe Grid use.

@Will Prowse and @Dzl
 
Hey everyone, I'm reviewing the diagram with our team again and will make updates as necessary. Additionally - we want to rebuild the system as we have posted in the schematic and attempt to create any of the situations that have been described in this thread for testing purposes. We will continually update the community on this.
 
... and attempt to create any of the situations that have been described in this thread for testing purposes.

I suggest you make sure it complies with all NEC requirements, not just attempt to determine that it appears safe based on your own testing.
In particular, I think that means ground must be bonded from utility entrance through all equipment with galvanic (not transformer-isolated) connection.

Murphy and a Better Fool can probably outsmart you. As I have.
Better to hang your hat on national standards. That goes a long way to avoid negligence.
 
I suggest you make sure it complies with all NEC requirements, not just attempt to determine that it appears safe based on your own testing.
In particular, I think that means ground must be bonded from utility entrance through all equipment with galvanic (not transformer-isolated) connection.

Murphy and a Better Fool can probably outsmart you. As I have.
Better to hang your hat on national standards. That goes a long way to avoid negligence.
On it! Got a team working now on this.
 
I get why SS wanted to make a counter post to redirect traffic away from Will's post which said the system is unsafe.
The problem is that you now have a thread with a title of

"Safe Grid Use of the 5000ES and transformer"

This thread does not contain a schematic for the safe use of the Grid with the 5000ES, so the title should be changed so that no one is put in danger and the Mods should lock the discussion and lets move it back to the warning thread that Will created until such time as SS does have a schematic that provides safe Grid use.

@Will Prowse and @Dzl
We definitely want everyone to be safe - again, I touch these units likely 100's of times more a week than most do in a year. I want to be safe! We are looking at this more in depth. As far as the new post - we are posting what we have tested and experienced. A community of people are giving us additional feedback and scenarios (and personally I love it) so we will continue doing further testing and update our documents as needed to make sure we all stay safe. Thanks for all the information everyone here has given.
 
Probably. I don't think 2x 5000W inverters are likely to exceed 10kVA.
If they could actually deliver 5000W into a motor load (maybe 0.8 PF?) then they would actually have to deliver around 6000 VA each.

A 10kVA transformer could probably deliver 5000W or so to a resistive load on a single 120V phase. Possibly too much on a single phase would overload the transformer. Properly sized circuit breakers on its output should protect it from that (and from W vs. VA overload.)

Isolation transformer on input or output takes care of the issue Ian's video reported on trying to balance the utility grid.
The removed screw between GroWatt "Neutral" and ground may solve what it was meant to. Final verdict tbd on whether that is sufficient isolation.

Multiple transformers (before and after inverter) could have let a European single-phase inverter work for US split-phase system, but it is more iron, expense, efficiency loss.
Hopefully the removed screw and an isolation transformer on output (or isolation transformer on input and auto-transformer on output) solves all issues.
Thanks, I'm never going to grid tie but, I do want to leave my service entrance alone and I was more concerned about the loss of the neutral. I know I could work around that with relays but, I like simple. I just want to isolate from the grid for e-power and power a small shop. We lose power quite often out where I live.
 
What a cluster f , All this rigging ( ground this, no that, bond this, no bond that) to save a few dollars or make a few dollars. Just buy the products made for our US market and be safe. Or someone will be sorry in the future, I hope it is not you.
 
  • Like
Reactions: Zwy
Does it all start with trying to use a slightly cheaper Euro spec AIO for North American needs? To me the hassles don’t seem worth it, why not just get a split phase AIO from the start?

Or is it the DIY nature to convince ourselves we can take a square peg and pound it through the square hole by over complicating things?
 
Last edited:
  • Like
Reactions: Zwy
Thanks, I'm never going to grid tie but, I do want to leave my service entrance alone and I was more concerned about the loss of the neutral. I know I could work around that with relays but, I like simple. I just want to isolate from the grid for e-power and power a small shop. We lose power quite often out where I live.

If grid doesn't feed your inverters, that eliminates some problems. Auto-transformer will generate a neutral from a floating 240V inverter. You should be able to tie in to grid from rest of house. I think you can also use an interlocked generator breaker to backfeed house while main breaker disconnected from grid.
Question is, does it safely float? (reportedly the screw removal at factory floats it.)
But you need to make sure that if breaker feeding auto-transformer trips, L2 and L2 feeding the panel is also disconnected. Don't want 120V loads determining voltage of neutral. There are ways to do that.
 
If grid doesn't feed your inverters, that eliminates some problems. Auto-transformer will generate a neutral from a floating 240V inverter. You should be able to tie in to grid from rest of house. I think you can also use an interlocked generator breaker to backfeed house while main breaker disconnected from grid.

Question is, does it safely float? (reportedly the screw removal at factory floats it.)
This.


But you need to make sure that if breaker feeding auto-transformer trips, L2 and L2 feeding the panel is also disconnected. Don't want 120V loads determining voltage of neutral. There are ways to do that.
 
So is the wiring diagram the finale version as shown on this thread and in the thread below?
We are attempting to live test every possibility as laid out on this thread for testing, manually shorting components testing for safety and operation. We will update the drawing as needed and post updates regularly. This is currently our highest priority project on our test bench. Feel free to follow my profile to keep in the loop.
 
I've been following this from a distance since Poz's first video with the auto transformer and the lack of neutral protection. After watching the submissions, retractions, alterations, and general confusion I can only assume my initial assessment was correct.

There really is no safe way to integrate these units into a household that is going to use grid supplied power in conjunction with the inverter's output, and there is no way safely use the autotransformer unless you segregate all of your 120 volt loads into a separate panel fed by that beast.
 
Back
Top