Off-grid inverter-chargers with full isolation between AC input and AC output?

[fafrd]

I’m looking for an off-grid inverter-charger that fully isolates AC input from AC output.

Whether there are any transfer switches or not, AC input should only be wired to AC battery charger and not connected to inverter output or AC output.

Are there any off-grid inverter-chargers delivering that isolation (whether they also include an SCC or not)?

I want to avoid the possibility of spurious export when loads on AC output turn off, even if that export only lasts for a millisecond or two…

 

[DIYrich]

Get a separate charger and inverter. Charger charges the battery. And the inverter takes from the battery. If you want to avoid any possibility, put a large capacitor in line with the battery and inverter. If the charger drops voltage, the capacitor will smooth the decline to the inverter, giving it time to adjust.

 

[fafrd]

Get a separate charger and inverter. Charger charges the battery. And the inverter takes from the battery.

That’s exactly my current plan. Just thought I’d check whether there are any inverter-chargers with that functionality already wired-in first…

If you want to avoid any possibility, put a large capacitor in line with the battery and inverter. If the charger drops voltage, the capacitor will smooth the decline to the inverter, giving it time to adjust.

This I’m not understanding - how would a capacitor inline between battery and inverter impact any possibility of spurious export if AC input is not connected (using an external AC charger)???

 

[Mattb4]

I’m looking for an off-grid inverter-charger that fully isolates AC input from AC output.

Whether there are any transfer switches or not, AC input should only be wired to AC battery charger and not connected to inverter output or AC output.

Are there any off-grid inverter-chargers delivering that isolation (whether they also include an SCC or not)?

I want to avoid the possibility of spurious export when loads on AC output turn off, even if that export only lasts for a millisecond or two…

I think you are being overly cautious. With the millions of UPS's out there that exist that are not different in switching than an off grid AIO the electric company is not going to be paying attention to milliseconds of export. Heck anytime a large inductive kick happens from other electrical equipment you could have an export for a millisecond or so.

I suspect it will take a few seconds of export before any notice is taken.

 

[Cheap 4-life]

Unfortunately the electric companies do notice the short duration backfeeds. It accumulates and they check it periodically. They gave me a visit a few years ago because of it. Or atleast that’s what they said the reason was.. maybe they simply seen my solar array but I don’t think so. I live in the middle of nowhere on a dead end road with solar panels on other side of the house..

 

[fafrd]

I think you are being overly cautious. With the millions of UPS's out there that exist that are not different in switching than an off grid AIO the electric company is not going to be paying attention to milliseconds of export. Heck anytime a large inductive kick happens from other electrical equipment you could have an export for a millisecond or so.

I suspect it will take a few seconds of export before any notice is taken.

You raise a good point.

Many municipalities have stated that spurious export of under 25ms is allowed and ideally, it would be great if California issued such guidelines as well.

Without that, any boundaries on the amount / length of spurious export that can be generated by UPS or inductive loads in the average household might be just as good.

On the other hand, total isolation through the use of an external battery charger is pretty cheap insurance until the rules of engagement become more clear…

 

[Mattb4]

Unfortunately the electric companies do notice the short duration backfeeds. It accumulates and they check it periodically. They gave me a visit a few years ago because of it. Or atleast that’s what they said the reason was.. maybe they simply seen my solar array but I don’t think so. I live in the middle of nowhere on a dead end road with solar panels on other side of the house..

I am curious what you are running. Those so called Zero export types with CT's (even those with internal ones such as Victron power assist units) are very likely to create enough export to be noticeable.

 

[Steve_S]

I'm not entirely clear on what you are looking for.
The Samlex EVO Series Inverter has Dual AC Input, 1-Grid & 1-External AC GenSet. Each side has a built-in ATS which can be programmed to operate as you with, additionally, they come with an AGS (Auto-Gen-Start) port to auto-start a generator. They do NOT export to grid and do not have that capability. They can be programmed to charge from Grid Source or Genset and even prioritized so of Grid != Avail then use Genset or the other way around. During external Charge (grid or gen) they also passthrough AC while charging the battery. Depending on the model, they can charge up to 100A.

 

[DIYrich]

This I’m not understanding - how would a capacitor inline between battery and inverter impact any possibility of spurious export if AC input is not connected (using an external AC charger)???

Oh, I thought you were trying to get clean output. Nevermind.

 

[Mattb4]

I'm not entirely clear on what you are looking for.
...

He is looking for a inverter charger without an ATS function.

 

[hwy17]

This is new to me. I am looking at doing no NEM with Schneider conext equipment on a critical load panel.

I had learned that grid assist mode can result in incidental export during reaction times, but this thread is about incidental export during switching from grid to off grid inverting? And/or charging and simultaneously inverting?

 

[Cheap 4-life]

I am curious what you are running. Those so called Zero export types with CT's (even those with internal ones such as Victron power assist units) are very likely to create enough export to be noticeable.

I listed what I’m running under my comments. They do allow short duration backfeed everytime a load shuts off. It’s barely noticed by my Iotawat. might be more than an offgrid inverter would backfeed

 

[fafrd]

This is new to me. I am looking at doing no NEM with Schneider conext equipment on a critical load panel.

I had learned that grid assist mode can result in incidental export during reaction times, but this thread is about incidental export during switching from grid to off grid inverting? And/or charging and simultaneously inverting?

This thread is about avoiding exactly that.

 

[fafrd]

I'm not entirely clear on what you are looking for.
The Samlex EVO Series Inverter has Dual AC Input, 1-Grid & 1-External AC GenSet. Each side has a built-in ATS which can be programmed to operate as you with, additionally, they come with an AGS (Auto-Gen-Start) port to auto-start a generator. They do NOT export to grid and do not have that capability. They can be programmed to charge from Grid Source or Genset and even prioritized so of Grid != Avail then use Genset or the other way around. During external Charge (grid or gen) they also passthrough AC while charging the battery. Depending on the model, they can charge up to 100A.

If the ATS connects AC input to AC output while the inverter is inverting to power loads on AC output, spurious export to grid cannot be avoided during reaction time when load shuts off.

That is what I want to avoid.

If AC input is only connected to a battery charger when inverter is inverting (whether that battery charger is charging or not), spurious export cannot occur.

 

[DIYrich]

I'm not entirely clear on what you are looking for.

I'm guessing he has an under-the-radar system without PTO. He wants to avoid backfeeding the grid as a tipoff that he has the system.

My guess is that the utility will notice the drastically reduced usage and send someone out to check the meter. That person will notice the unauthorized solar connected to the grid.

If all he has is the charger connected to the grid, solar connected to the inverter, and the inverter is connected to a separate load panel, it could constitute enough separation from the grid (charger cannot work in reverse).

 

[hwy17]

This thread is avoid avoiding exactly that.

I am just drawing the distinction between grid assist which is a function where grid input and inverter output are necessarily connected, and this thread also has concerns about momentary export during switching from grid to off grid inverting. The former I was aware of, the latter is a rarer concern that is new to me.

 

[fafrd]

I am just drawing the distinction between grid assist which is a function where grid input and inverter output are necessarily connected,

Avoiding spurious export when hybrid inverter is offsetting loads on AC output while also connected to grid through AC input is the focus I was hoping for.

and this thread also has concerns about momentary export during switching from grid to off grid inverting. The former I was aware of, the latter is a rarer concern that is new to me.

I’m not sure who introduced any concern regarding spurious export when grid is connected or disconnected from AC input of a hybrid, but it wasn’t me.

I was considering going this route through an external transfer switch but have elected against it because of concerns regarding wear on electrical equipment when power is repeatedly switched from independent out-of-sync sources.

 

[fafrd]

I'm guessing he has an under-the-radar system without PTO. He wants to avoid backfeeding the grid as a tipoff that he has the system.

I have PTO for a grid-tied NEM array but want to add a small backup / ESS system without needing to go through hassle of getting approval and PTO from the utility.

Was considering to go the route of using a hybrid but between the fact that the new rules state any system with parallel connection of grid and inverter for more than one second requires PTO as well as newly-authorized right to collect dual-channel data from the smartmeter has me convinced I’m better off following the rules and building a true off-grid system.

An offgrid inverter with no ATS connecting AC input to AC output would fit this requirement, but those inverters seem to be few and far between (as well as old and expensive).

My guess is that the utility will notice the drastically reduced usage and send someone out to check the meter. That person will notice the unauthorized solar connected to the grid.

Without an existing NEM array, you’d probably be correct.

Solar in California does not require any authorization from the utility as long as power from that solar does not power equipment generating AC power that is connected in parallel to the grid for more than 1 second / 60 cycles.

The easiest thing to do is to just follow the rules but existing off-grid inverters don’t make that easy…

If all he has is the charger connected to the grid, solar connected to the inverter, and the inverter is connected to a separate load panel, it could constitute enough separation from the grid (charger cannot work in reverse).

Precisely. The new rules in California make that the only configuration that is allowed to operate without PTO from the utility.

Unfortunately, none of the new crop of existing AIOs support that capability - they all seem to have an ATS connecting AC input to both battery charger and AC output (probably because the inverter is bidirectional and essentially is the battery charger…).

 

[fafrd]

I have PTO for a grid-tied NEM array but want to add a small backup / ESS system without needing to go through hassle of getting approval and PTO from the utility.

Was considering to go the route of using a hybrid but between the fact that the new rules state any system with parallel connection of grid and inverter for more than one second requires PTO as well as newly-authorized right to collect dual-channel data from the smartmeter has me convinced I’m better off following the rules and building a true off-grid system.

An offgrid inverter with no ATS connecting AC input to AC output would fit this requirement, but those inverters seem to be few and far between (as well as old and expensive).

Without an existing NEM array, you’d probably be correct.

Solar in California does not require any authorization from the utility as long as power from that solar does not power equipment generating AC power that is connected in parallel to the grid for more than 1 second / 60 cycles.

The easiest thing to do is to just follow the rules but existing off-grid inverters don’t make that easy…

Precisely. The new rules in California make that the only configuration that is allowed to operate without PTO from the utility.

Unfortunately, none of the new crop of existing AIOs support that capability - they all seem to have an ATS connecting AC input to both battery charger and AC output (probably because the inverter is bidirectional and essentially is the battery charger…).

If I am correct that all of the new crop of low-cost AIO are based on bidirectional inverters that make it impossible to charge without also having AC input connected to AC output, there are only two ways to satisfy the new rules in California for connection without requiring PTO:

1/ leave AC input disconnected and rely on an external AC charger to recharge the battery when needed.

2/ use multiple transfer switches internally to guarantee that whenever AC input is connected to AC output, AC output is disconnected from inverter output (the Victron Multiplus II can do something like this, I believe).

There will be extra cost involved in either case but the first route seems more simple and direct (as well as being easier to explain to an AHJ).

 

[Cheap 4-life]

if currently you have an approved system that you can backfeed the grid then are you saying your only worried about night time spurious backfeed? I‘d think since your currently allowed to backfeed that they do not distinguish the difference between night or day time backfeed.