Adapt high-frequency inverter with addition of transformer?

[Norwasian]

Finding a low-frequency (toroidal) inverter that meets my needs given the models locally available to me in Thailand has been extremely difficult, and I'm beginning to feel it may be impossible. I've been searching/researching for days, and have considered many models, only to be disappointed about one or another of their features. I have found an almost perfect match to what I am looking for in the Deye inverter models, or possibly the Goodwe, but both appear to be high-frequency inverters. My system will need to operate a refrigerator, house fans, and a washing machine, at minimum, with good potential for a future well pump. Inductive load support is vital.

Question: Is it possible to use a standard high-frequency inverter coupled to a suitably sized 1:1 isolating transformer to get the benefits of a low-frequency setup?

Alternatively, I'm all ears to suggestions within the Thai market that would meet the following requirements:

• 220/230 volt inverter
• 48 volt LiFePO4 battery bank, at 300 Ah+
• Quiet (passive cooling / fanless highly preferred)
• Able to operate in hot environment (40-45 degrees Celsius)
• Support 12 LONGi 580-watt panels, at Voc 49.8V and Imp 13.17A per each panel, in two strings of 6 or 3 strings of 4 (with possible Epever CC for 3rd string)
• Between 3kw and 6kw inverter output
• Must be foolproof, e.g. the charge controller and/or inverter will not self-destruct if the PV panels are hooked up without a battery!
• NOTE: Open to using separate charge controller (probably Epever Tracer) and inverter

The best toroidal inverter I seem to find is a no-name brand whose reliability would seem left to chance/good fortune. The "quiet" requirement is important because this will be installed in a meeting room, and there is no closet to sequester the noise.

Most products of this nature are available in Thailand online through one of two sources: shopee.co.th, or lazada.co.th (a subsidiary of alibaba)--both with strong similarities to ebay. Unfortunately, there seems to be no source here for many of the better brands, like Victron, and importing can be a nightmare involving weeks of paperwork, potential fines for not requesting permission to import something beforehand, and taxes that can equal the original cost of the item (been there done that importing a used/for-parts drone purchased off ebay). So scratch all of "the best" off the list, and highlight the rationale for seeking to self-engineer a workable solution.

 

[DIYrich]

Deye makes Sol-Ark. Sol-Ark is a reputable and reliable brand in the USA. I have a Sol-Aark 15k, and it can run my household appliances (fridge, washer, dryer, pump for boiler, heat pump water heater, etc.). I don't have a well pump.

 

[Norwasian]

Deye makes Sol-Ark. Sol-Ark is a reputable and reliable brand in the USA.

This is why I am considering this brand. But I've also heard some less flattering things about Sol-Ark, and I've heard that the HF inverters may shorten the lifespan of motors. It's hard to know whom to believe, but knowing how much draw a motor requires on startup, those reports do have a measure of credibility.

I have a Sol-Aark 15k, and it can run my household appliances (fridge, washer, dryer, pump for boiler, heat pump water heater, etc.). I don't have a well pump.

That's quite a large unit. Perhaps that is why it runs the motors as well as it does. I'm looking at a 6k unit by comparison. I don't think I've even seen 15k units on the market here.

 

[Hedges]

Transformers do not help with surge. The energy storage they provide is tiny, no where near a single cycle of AC.
A massive ferro-resonant transformer, e.g. 250 lbs for 250 VA, does store enough energy for a couple cycles.

High frequency inverters are capable of delivering surge if designed for it. That is, if transistors can carry the current, also inductors (below the current where they saturate.) This would be power they could deliver continuously if they could get rid of the heat, so surge can be handle briefly before overheating.

For someone in the US with 120/240V split-phase HF inverter, a transformer could take the surge capability of both 120V sections and deliver all surge to a single 120V load.

Adding a transformer won't help you. Beyond that, the transformer will draw current from the inverter even without loads (VA) and shove it back into the inverter out of phase (reactive power). That will at the very least increase loss (W) consumption by the inverter. The inverter may also be very unhappy having to swallow its own current.

Look for an inverter with multi-second surge (or continuous output) 5 times as much as nameplate VA or volts x amps of your motor.

 

[400bird]

To emphasize Hedges' last line, if you're refrigerator peaks at 2kW when starting and your looking at a 1500 watt inverter, you have a system that probably is going to not work. However, if you have a 10kW inverter, that 2kW load should start with no problem on a HF inverter.

 

[Hedges]

Except that would be a large refrigerator which has 2kW motor. More likely, defroster and ice maker are the big loads, typically about 800W. The motor runs around 300W, maybe 50W. In which case a 1500W inverter could be sufficient.

 

[Danke]

That's quite a large unit. Perhaps that is why it runs the motors as well as it does. I'm looking at a 6k unit by comparison. I don't think I've even seen 15k units on the market here.

You can get Deye inverters there. Makers of the Sol-Arks. Many sizes. The Deye 12K is similar to the Sol-Ark 15K without the 200A pass through. You don’t need split phase, so they even have a Deye 16K avaiable.

 

[Norwasian]

Transformers do not help with surge.

How do "toroidal" inverters have such great surge capability? A toroidal inverter can surge at 3 times the rated capacity, whereas the typical HF inverters only can do double. Is a toroid transformer different in some meaningful way in terms of surge than a standard square-type transformer? I had assumed that a form of electromagnetic "inertia" would be a property shared by both to some extent.

To emphasize Hedges' last line, if you're refrigerator peaks at 2kW when starting and your looking at a 1500 watt inverter, you have a system that probably is going to not work. However, if you have a 10kW inverter, that 2kW load should start with no problem on a HF inverter.

The refrigerator will not be that large, obviously. I expect the largest inductive load to be that of the washing machine, until a pump is added. My concern is the combined effect of simultaneous inductive loads, such as the washing machine plus three household fans when the refrigerator kicks in.

Except that would be a large refrigerator which has 2kW motor. More likely, defroster and ice maker are the big loads, typically about 800W. The motor runs around 300W, maybe 50W. In which case a 1500W inverter could be sufficient.

Right. In Thailand, refrigerators are rarely so large. I haven't seen it yet, but assume it to be a relatively newer model, and estimate it to consume no more than 300W on average. Startup, though, would surge beyond this.

Multiple resistive or capacitive loads would also be supported by the inverter, particularly the sound system and video projector--but these would be for only a few hours at a time, and would be unlikely to run simultaneous to the washing machine.

 

[Norwasian]

You can get Deye inverters there. Makers of the Sol-Arks. Many sizes. The Deye 12K is similar to the Sol-Ark 15K without the 200A pass through. You don’t need split phase, so they even have a Deye 16K avaiable.

Yes, I'm looking at the Deye because it is one of the few "known" brands with a good reputation that I can find here. Most of our options here are branded with names that would sound foreign in the Western world. But because we can get Deye inverters, it does not follow that every model of Deye is available. The largest single-phase Deye option I have seen is a 5kw unit. There are larger 3-phase options, but those do not interest me (expensive, for one thing, and well more than is needed). In 8k or 10k models, it seems to be rebranded in the ads as "LV-Deye", with the images showing LVTOPSUN branding on the unit. Does Deye make the LVTOPSUN models, too?

Unfortunately, finding things in Thailand is difficult. On the shopping site, searching for "Deye" nets inverters of every other brand as well, and one must sift through them all to try to pick out the units meeting the desired specifications. So without examining literally thousands of search results, it is impossible to say for sure that I cannot find a particular model here. But I haven't seen it yet, and I've done many hours of looking for inverters.

I really don't need more than 6kw at most. I just need it to handle motors within that range as well.

 

[SolarRich]

Is there an inverter that meets your needs available outside Thailand? Can you have it shipped in - in pieces and parts? For example have the main board shipped in, then each part of the case, etc. I'm sure it will cost you more but if it solves the problem?

 

[v_green57]

Finding a low-frequency (toroidal) inverter that meets my needs given the models locally available to me in Thailand has been extremely difficult, and I'm beginning to feel it may be impossible. I've been searching/researching for days, and have considered many models, only to be disappointed about one or another of their features. I have found an almost perfect match to what I am looking for in the Deye inverter models, or possibly the Goodwe, but both appear to be high-frequency inverters. My system will need to operate a refrigerator, house fans, and a washing machine, at minimum, with good potential for a future well pump. Inductive load support is vital.

Question: Is it possible to use a standard high-frequency inverter coupled to a suitably sized 1:1 isolating transformer to get the benefits of a low-frequency setup?

Alternatively, I'm all ears to suggestions within the Thai market that would meet the following requirements:

• 220/230 volt inverter
• 48 volt LiFePO4 battery bank, at 300 Ah+
• Quiet (passive cooling / fanless highly preferred)
• Able to operate in hot environment (40-45 degrees Celsius)
• Support 12 LONGi 580-watt panels, at Voc 49.8V and Imp 13.17A per each panel, in two strings of 6 or 3 strings of 4 (with possible Epever CC for 3rd string)
• Between 3kw and 6kw inverter output
• Must be foolproof, e.g. the charge controller and/or inverter will not self-destruct if the PV panels are hooked up without a battery!
• NOTE: Open to using separate charge controller (probably Epever Tracer) and inverter

The best toroidal inverter I seem to find is a no-name brand whose reliability would seem left to chance/good fortune. The "quiet" requirement is important because this will be installed in a meeting room, and there is no closet to sequester the noise.

Most products of this nature are available in Thailand online through one of two sources: shopee.co.th, or lazada.co.th (a subsidiary of alibaba)--both with strong similarities to ebay. Unfortunately, there seems to be no source here for many of the better brands, like Victron, and importing can be a nightmare involving weeks of paperwork, potential fines for not requesting permission to import something beforehand, and taxes that can equal the original cost of the item (been there done that importing a used/for-parts drone purchased off ebay). So scratch all of "the best" off the list, and highlight the rationale for seeking to self-engineer a workable solution.

Short answer: no.

Longer answer: The advantages of LF inverters are "baked-in" to the overall design. Electronics optimization, component matching, etc.

Adding a xfmr won't help. In fact, the transformer is not without losses itself, which contributes to inefficiency. And it will "buzz", which seems to be one of your primary criteria.

Why can't you locate your electronics somewhere where noise doesn't matter and just bring AC to the "meeting room"?

 

[400bird]

The refrigerator will not be that large, obviously.

Agreed, I was just trying to give an example of how the set up should operate. I should have said washer, not fridge. Sounds like you've got a good understanding.

 

[Quattrohead]

Look for the Luxpower Tek SNA 6000/LXP6K/EG4 6000XP or whatever is the equivalent you can get, rock solid over 5 years and used in Africa a lot.
They can run inductive loads easy.

 

[Norwasian]

Why can't you locate your electronics somewhere where noise doesn't matter and just bring AC to the "meeting room"?

Thai construction does not give many options. Closets are not built, because they would not be useful. A closet is just a trap for mildew--open space maximizes air flow. The building where this will be installed has only two rooms: the main room and the kitchen. Both rooms are entered from the exterior of the building through a single door only. The rooms are not ceiled, so there is some air movement where the rafters meet the walls, but this also allows for some sound penetration from outside. Heavy monsoon rains tend to come with some wind, so locating the electrical system to an exterior wall would require some rain-proofing as well, such as a heavy tarp to wrap it all with just under the eaves. It's simply more practical to have it all inside, and not in the kitchen where steam, heat or smoke could affect the electronics.

 

[Norwasian]

Is there an inverter that meets your needs available outside Thailand? Can you have it shipped in - in pieces and parts? For example have the main board shipped in, then each part of the case, etc. I'm sure it will cost you more but if it solves the problem?

It seems almost that bad sometimes. One problem with depending on something that faces such difficulty with importation is that if that unit goes bad, and the system is centered on having it, the difficulty is doubled with having to go through all of that again. Charge controllers have a reputation around here for going belly up within two years. The climate may be hard on them, but this is one reason I'm hoping to avoid problems by sticking with known-to-be reliable units. As it is, I'm designing a setup that differs from the average in multiple ways, including using LiFePO4 batteries in place of the AGM batteries that are in common use with solar systems here. I would like the system to last, as that usually is the most economical investment in the long run. Systems that have to be repaired or replaced every two-three years end up expensive.

Look for the Luxpower Tek SNA 6000/LXP6K/EG4 6000XP or whatever is the equivalent you can get, rock solid over 5 years and used in Africa a lot.
They can run inductive loads easy.

I found two listings for "Luxpower 5kw (SNA5000 WPV)". Is that close enough? That's the only model I seemed to find.

 

[Quattrohead]

It could be but it's not a model I am familiar with.

 

[Hedges]

How do "toroidal" inverters have such great surge capability? A toroidal inverter can surge at 3 times the rated capacity, whereas the typical HF inverters only can do double. Is a toroid transformer different in some meaningful way in terms of surge than a standard square-type transformer? I had assumed that a form of electromagnetic "inertia" would be a property shared by both to some extent.

I'm not sure the difference is the toroid, could be beefier design to go along with more expensive transformer.

Toroids are supposed to have lower leakage, better coupling than E-core. One reason could be that E-core has many laminations with field jumping across square overlap, while toroid is a continuous coil, extended overlap. I'm not sure if the material is typically different. Silicon steel, I think.

Cores are quite a science and almost a lost art. What elements are used, annealing process, magnetic field applied during annealing. Many different recipes, for power transformers, amplifiers, chokes, etc.

I used to think there was stored energy it could release, but my measurements of B-H curves, which go into saturation, show it isn't much. A 100A power transformer can't carry 100A without saturating, more like 1A, around no-load current. Opposite current in secondary cancels most of the field when 100A is being carried.

Typical HF inverters (cheap ones) have hardly any surge. Good ones like Rosie can do 3x for some seconds.
My LF Sunny Island has a toroid and is rated about 2x for 3 seconds.

 

[Norwasian]

Look for the Luxpower Tek SNA 6000/LXP6K/EG4 6000XP or whatever is the equivalent you can get, rock solid over 5 years and used in Africa a lot.
They can run inductive loads easy.

Well, I managed to find a manual for the Luxpower model available in Thailand: SEE HERE. Good points include a five-second surge capacity (but only at double the normal rating), ability to run with or without a battery, high amperage allowance for PV panels, and ability to share load between solar and battery or AC. Bad points include being only IP20, being a high-frequency inverter (I want toroidal/low-frequency), not using passive cooling, and having an over-complicated app interface and a wifi dongle that wants to share everything about you with the company (from what I could discern via one video review).

I don't think I'll be choosing this one, even though the price is quite reasonable. I need something more suitable to a non-English speaker, quieter, and with better built-in support for inductance loads. The IP20 rating is concerning for this location on account of geckos which would likely enter it and short something. They are notorious here for such mischief.

 

[shortman]

Going back to the transformer argument...
I have multiple large HF inverters in parallel mode. What I have noticed is that so many items around the house are trying to perform Power Factor correction like EV onboard chargers and 750w computer power supplies. Which basically means the item is adjusting its current draw to match the waveform. Then you mix in these HF inverters where the good ones are using waveform sampling in the MHz range to make a perfect sinewave. I have measured many and found in the unloaded or purely resistive load most provide a waveform better than the grid. But now you mix the two and many other resistive and inductive loads, what appears to happen is that the PF correction logic and the HF inverter fight and generate all kinds of crap in the waveform for a brief while (my assumption for what I see in the Oscope). So, I really would like to see how a 50kw system built with HF inverters would do if the generation side was isolated through the magnetics in a 300-400lb transformer. Used commerical grade transformers can be had around here for about $1500. But the only thing holding me back is the concern for the reverse voltage spike into the inverter's transistors. To some extent the designer would have needed to prepare for that but maybe not to the level possible from a 400lb inductor.

If anyone ever tries this I would love to there the results. The power from the new quality HF inverters is good but it isn't the grid when used with a random mix of devices.

 

[Hedges]

I've been driving transformers with inverters, but those were LF, Sunny Island.
I've paid $300 to $500 for 25kVA or 30kVA transformers, single and 3-phase.

If you drive such transformers at rated voltage, expect it to draw significant no-load power. I saw 4% of kVA rating, e.g. 240V 4A or about 1 kVA apparent power for a 25kVA transformer. Your inverter has to swallow that out of phase power coming back at it.

Driving the primary windings at 50% of rated voltage (so transformer able to process 12.5 kVA), no-load was only 45 VA.

transformer excitation current - isolation transformer used as auto-transformer

So you think you can backfeed a transformer secondary, either as step-up or as auto-transformer? Turns out these things aren't so ideal and reversible as one might expect. It isn't just the greater inrush (primary is often wound outside secondary to reduce inrush current), but also idle current...

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