Chinese "Pure" sine wave AIO inverter AC quality.

[Luk88]

I'm in the equipment evaluation phase of building an emergency power backup system for my (small) house.

So far I'm planning 5kWh (later 10kWh) of lfp battery storage and a Chinese hybrid inverter (smh ii 7kv) as a UPS. I also plan to plug my existing 2.4kW od grid tie solar to it in case of prolonged power outages as well as to use a gas generator as required.

However, having my friends experience the "flickering led lights" effect these inverters produce I started wondering if I'm going to have problems powering computers, PoE network switches and other electronic stuff directly from one of these inverters.

Will I have to blow up my budget by buying an expensive ups for every device? Or is switched mode power supply powered equipment juuuust fine being powered by these inverters?

 

[shvm]

having my friends experience the "flickering led lights" effect these inverters produce I started wondering if I'm going to have problems powering computers, PoE network switches and other electronic stuff directly from one of these inverters.

I have a Luxpower SNA 5k.
I have experienced this effect only when using the hybrid capabilities of the inverter. Specifically, I think it has something to do with the inverter trying to "co-exist"/"merge" its own AC output with the grid.
Additionally, the flicker that I experience goes away when the inverter is exporting power to the grid. This too I believe can be explained on the above ground due to the inverter's AC output dominating over the grid input.
Expect the flicker to only happen in situations where grid and inverter's output "co-exist". Such as powering loads using both AC and inverter output both.

In the off-grid mode with the grid breaker disengaged, I have found the output AC waveform to be excellent. I have cheap "flicker prone" LED's and I am unable to notice anything in the slightest in the off-grid mode.

 

[Luk88]

Thank you for describing your experience

Sadly, the friend I mentioned is experiencing the flicker in a 100% off grid setup so the inverter is the only thing generating ac.

The inverter I'm planning to test (smh ii 7kv) doesn't have the grid coexist, nor export features. The "hybrid" part refers to it having a bypass mode where it connects the loads to the grid in certain conditions (in my case when there is AC power) and is able to charge the batteries from solar and the ac input (powered by the grid or a generator) at the same time.

 

[timselectric]

That's not a hybrid. It's an off grid AIO. (All In One)
You should edit the title for accurate responses.
I almost ignored this thread.

The flickering is usually only an issue with cheaper L.E.D. lightning.
Most other devices and appliances are unaffected.
But I would look for other members who have the same unit. To see what their experience has been.

 

[Luk88]

That's not a hybrid. It's an off grid AIO. (All In One)
You should edit the title for accurate responses.
I almost ignored this thread.

The flickering is usually only an issue with cheaper L.E.D. lightning.
Most other devices and appliances are unaffected.
But I would look for other members who have the same unit. To see what their experience has been.

Is it really off-grid when it is designed to have a grid connection on the supply side and it is capable of for example charging the battery from the grid when solar is unavailable and supply power to loads via its inverter at the same time?


I mean literally, they all have "hybrid inverter" in their name in all shops I saw them in.

Are you saying "hybrid" is only a correct description when the device can push power back to the grid? My impression was, if it can utilise Ac input from the grid as well as a battery and pv it is "hybrid".
But I'm open to being told it is wrong. It wouldn't be the first time sellers don't know what they're selling.

 

[timselectric]

"Grid-tied"
Pushes all production to its grid connection.
And relies on the grid to function.

"Off grid"
Pushes production to a battery. To be used emidiatly, or in the future.

"Hybrid"
A combination of both, above.

"AIO's"
Are also available in the same types above.
An AIO (All In One) can include multiple parts of standard systems in a single enclosure.
Inverter
SCC (Solar Charge Controller)
Transfer switch
AC charger

 

[AshleyL]

I notice only HF inverter tends to cause LED lighting to flicker whenever there is variable inductive load.

The much more expensive bulkier LF inverter doesn't have such issue, but LF inverter has very high idle or operating power consumption.

 

[Luk88]

"Grid-tied"
Pushes all production to its grid connection.
And relies on the grid to function.

"Off grid"
Pushes production to a battery. To be used emidiatly, or in the future.

"Hybrid"
A combination of both, above.

"AIO's"
Are also available in the same types above.
An AIO (All In One) can include multiple parts of standard systems in a single enclosure.
Inverter
SCC (Solar Charge Controller)
Transfer switch
AC charger

OK, I've updated the thread title. Thanks

I notice only HF inverter tends to cause LED lighting to flicker whenever there is variable inductive load.

The much more expensive bulkier LF inverter doesn't have such issue, but LF inverter has very high idle or operating power consumption.

Aren't assentially all cheap Chinese inverters Hf transformer less these days?

 

[timselectric]

Aren't assentially all cheap Chinese inverters Hf transformer less these days?

not all, but most.
Most (cheap or expensive) are switching to transformerless, these days.
It took a while to work out the kinks. But the electronics are more robust and reliable, now.
In ten years, it will be hard to find a transformer based inverter.

 

[Luk88]

not all, but most.
Most (cheap or expensive) are switching to transformerless, these days.
It took a while to work out the kinks. But the electronics are more robust and reliable, now.
In ten years, it will be hard to find a transformer based inverter.

It was hard for me to find one (that meets new regulations) 3~4 years ago when I was building my on-grid system. Perhaps it was in part, because I was looking for a small inverter (<3kW) and in part that any manufacturer that made such a device considered it obsolete in this wattage range.

At the time I enquired for the cost of EU certification in a German company (I was considering various options) and I was told 50k EUR as a starting point. So no surprise older models were not certified.

However, coming back to the subject of the thread. Is there anyone here who has been successfully powering high end PC or servers or networking equipment with one if these cheap HF transformerless inverters for a while? What are your experiences?

 

[hwy17]

PC's, servers, switches, etc. are all powered by switching power supplies which tolerate poor quality power very well: modified sine wave, voltage drops to 100, noisy power, they'll eat anything. Claims that it will "reduce their lifespan though" are also dubious too, it's not really any harder on any of the power supply components than regular AC.

But, if you are expecting to use the inverter as a UPS, that part might not work, most inverters do not transfer as fast as a UPS. You might still need an actual UPS to keep servers online during a sudden grid outage.

 

[Luk88]

PC's, servers, switches, etc. are all powered by switching power supplies which tolerate poor quality power very well: modified sine wave, voltage drops to 100, noisy power, they'll eat anything. Claims that it will "reduce their lifespan though" are also dubious too, it's not really any harder on any of the power supply components than regular AC.

But, if you are expecting to use the inverter as a UPS, that part might not work, most inverters do not transfer as fast as a UPS. You might still need an actual UPS to keep servers online during a sudden grid outage.

Thanks. The spec sheet claims 10ms switchover on the UPS setting (20ms on "appliance" setting).

Good UPSes spec sheets say 6ms typical 10ms max.


Let's think what is the maximum time a high end PC with good quality PSU might survive. Take a 1000W Be Quiet Dark Power 13 atx psu (just because I have v12 of it). Let's consider only HV side. It has two 470uF caps to smooth the rectified input. That's 940uF at 340V DC (at 240v AC).

It stores 56J of energy, but voltage drops linearly as this is depleted so let's imagine 10% of it is "usable reserve" . If it drops below, the PC crashes. Let's take two scenarios. A high end PC is lightly loaded and drawing 200W and second it is highly loaded and draws 800W. In the first case it needs 200J per second, in second case 800J/s

So in 10ms at 200W it will eat up 3.5% of the stored charge (9% at 20ms). I think that should be no problem.

However at 800W in 10ms it will consume 14% of the power stored in the HV caps. In 20ms it's 30%. IMO, at 800W we're pushing it even at 10ms :-(


So I may have to buy UPSes... Or I may be lucky and the power loss might happen when equipment is lightly loaded...

 

[timselectric]

With transfer time being your only issue.
The simple solution is to never transfer.

The only connection to the grid I have is a battery charger. My loads are always powered by the inverters. If my batteries get low, the charger turns on. The charger maintains the set voltage, until the sun rises again.

 

[Luk88]

With transfer time being your only issue.
The simple solution is to never transfer.

The only connection to the grid I have is a battery charger. My loads are always powered by the inverters. If my batteries get low, the charger turns on. The charger maintains the set voltage, until the sun rises again.

That is an interesting solution I may have to use.

The thing is, for me, it would require a lot more changes to my current system than just putting one phase (out of 3) on a "backup".

I'll do it eventually.

 

[timselectric]

That is an interesting solution I may have to use.

The thing is, for me, it would require a lot more changes to my current system than just putting one phase (out of 3) on a "backup".

I'll do it eventually.

With the charger as the only connection to grid.
It doesn't matter if your system is single or 3-phase. Same goes for the charger. Because the only connection between the two is battery voltage.

 

[Luk88]

With the charger as the only connection to grid.
It doesn't matter if your system is single or 3-phase. Same goes for the charger. Because the only connection between the two is battery voltage.

It matters for downstream 3 phase loads if they suddenly get one of their phases not "in phase". I'm assuming a cheap inverter will not sync it's output with the input AC.

This only matters in a very specific situation when you're sending backup power via one of existing phases you have 3 phase loads on.

For me it's just a quick way to get backup power into the house. Later I'll use a completely separate wire.

 

[timselectric]

It matters for downstream 3 phase loads if they suddenly get one of their phases not "in phase". I'm assuming a cheap inverter will not sync it's output with the input AC.

There is no upstream, when the charger is the only connection to grid. (No input)

This only matters in a very specific situation when you're sending backup power via one of existing phases you have 3 phase loads on.

Never do that. Sending single phase to a 3-phase motor will overheat it.
All of a loads circuit should come from the same source.

For me it's just a quick way to get backup power into the house. Later I'll use a completely separate wire.

I would not recommend this.
Make sure that you turn off any 3-phase loads, first.

 

[Luk88]

There is no upstream, when the charger is the only connection to grid. (No input)

Well, if the grid is powering the charger, what would you call it if not upstream?

Never do that. Sending single phase to a 3-phase motor will overheat it.
All of a loads circuit should come from the same source.

Who said anything about motors? Not me Both devices are smart enough to switch off if there is just one phase present. There is no risk of damage in such case.

One is an on-demand smart water heater, the other is an induction hob. Both have seen a situation with just one phase present many times already and they just power off.

I would not recommend this.
Make sure that you turn off any 3-phase loads, first.

That is the idea. Those two loads will not be used in a grid down scenario.

In a grid up scenario there are two options. Either
1. The AIO works in bypass mode - this way phase delay is correct and both multiphase loads will work fine (batteries are not used)
2. The AIO charges the battery from the grid (and solar if connected) also generating AC.

But in scenario 2 when grid is on it is very likely the AIO AC will drift in phase. So it cannot be used to power typical multiphase loads along the remaining two grid phases. This is the reason for choosing option no1 until I have a way to feed in additional AC into the house.

Edit: Also having the inverter powered on at all times means its consumption is higher than having it in bypass mode.
The advantage of always on inverter, being previously pointed out no need to transfer when power fails.

 

[timselectric]

Well, if the grid is powering the charger, what would you call it if not upstream?

To clarify
No upstream AC.

Who said anything about motors? Not me Both devices are smart enough to switch off if there is just one phase present. There is no risk of damage in such case.

That's great.
Then, there's no issue.

That is the idea. Those two loads will not be used in a grid down scenario.

Should not be used in grid up, either.
All of a loads power should come from the same source.
If you trust that the loads will protect themselves. That's up to you.
But it's not something that I would do, or recommend.

 

[Luk88]

Should not be used in grid up, either.
All of a loads power should come from the same source.
If you trust that the loads will protect themselves. That's up to you.
But it's not something that I would do, or recommend.

You haven't said so I guess you wouldn't recommend option no 1 (AIO powered by the grid, inverter on and powering one phase). That was my conclusion too.

That's why I'm talking about transfer times etc.

If you can see a problem with the same connection, but with option 2 (inverter bypass on the AIO) please elaborate.