what are the pros and cons for Low frequency inverters VS high frequency inverters ?

I used to have HF cheap 6kW inverter that can handle 1.5 tone Airon + 1800w vacuum surge , but when I replaced with low freq industrial inverter , the inverter fails in this scenario

I tried to check the user manual , they have not mention any thing about surge power , so is it inherited feature in low freq inverter that they cant handle more than their rated capacity ?

and what are the others differences between them in real daily use

6 hours ago, esmail-kassir said:

so is it inherited feature in low freq inverter that they cant handle more than their rated capacity ?

A core at 50Hz will likely restrict fault current. It does smooth out some power quality issues...but they are heavy.

LF inverters can handle much higher surge currents th HF inverters as a design principle.

7 hours ago, esmail-kassir said:

I used to have HF cheap 6kW inverter that can handle 1.5 tone Airon + 1800w vacuum surge , but when I replaced with low freq industrial inverter , the inverter fails in this scenario

Not sure how you define cheap HF against what type of LF inverter. LF (low-frequency, transformer-based) inverters like the Victron MultiPlus can deliver much higher surge current than HF (high-frequency, transformerless or ferrite-transformer) inverters like (Growatt,Deye, Sunsynk) it comes down to fundamental design differences in the power stage.

LF inverters: Use a big iron-core transformer at the output stage. This transformer acts as a current buffer and energy reservoir. It can handle short bursts of overload without saturating or burning up.The switching stage only needs to feed the transformer, which then delivers high surge capacity to the load.

HF inverters: Use small ferrite transformers at very high switching frequencies. These are efficient and compact but can’t store or transfer large instantaneous currents. They rely more heavily on semiconductor limits and DC bus capacitors.

3 hours ago, TaliaB said:

Not sure how you define cheap HF

I previously used a Voltronic VM III twin inverter, which allowed me to power a 1.5-ton air conditioner and a 1800W vacuum cleaner simultaneously. However, after switching to a Felicity IVGM 5kW low-frequency inverter (which weighs 32kg, confirming its low-frequency design), I'm no longer able to run both devices at the same time. I'm puzzled as to why this isn't working, given the Felicity's higher quality

Let me know if you'd like any further adjustments

9 minutes ago, esmail-kassir said:

I previously used a Voltronic VM III twin inverter,

The Voltronic VM III 4kw Twin inverter has a surge power of 8000VA,(7200w power factor 0.9) which is double its rated power of 4000VA, and is designed to handle short-term overloads from high demanding appliances.

The Voltronic VM III 6kw Twin inverter has a surge power of 12000VA.(10200w power factor 0.85) This means it can handle an overload of 12000 VA for a short duration (typically 5 seconds) to start high-demand appliances like refrigerators.

• "Twin Inverter":

  This refers to the dual output capability of the inverter.

The Felicity IVGM 5kW inverter model (such as the IVGM5048) is a 5000w hybrid inverter that is designed to provide stable power for households and small to medium-sized businesses. While its maximum continuous power rating is 5000w, the model can handle a brief surge of power of 6000w , which is essential for starting high-power appliances like refrigerators and washing machines. 

Compared with Victron Multiplus 5000va a true low frequency inverter with a surge capability of 9000w.

Hope this answer your question.

Edited September 16, 2025Sep 16 by TaliaB

LF inverter use transformer , ones like Victron, Schneider use toroidal transformer. Biggest advantage they have is surge power rating, for instance, Schneider XW6848 has surge 12kW for 60 secs. and 8kW for 30 mins.

Downside? you need external solar charge controllers and in the cases of like Schneider and Victron , external controller (GX, Schneider SCP/combox/insight) which further adds to cost. and their weight, e.g. Schneider 6848 is 50+ kg.

Another advantage is their low idle consumption as compared to HF inverters (35w vs 50~70w).

Their are LF inverters made by Chinese companies TBB power, PoWMr has one similar which also have SCC built-in. Schneider also has similar built in SCC LF inverter in Homaya line up. and they have interface identical to voltronic power.

Can you post make/model of industrial inverter you deployed and batteries you have installed? could be batteries on low SOC.

Have you looked at soft starters for aircons? An aircon has a compressor inside of it so I am sure there must be a soft starter kit for it.

9 hours ago, TaliaB said:

Hope this answer your question.

actually my question is why this specific low freq inverter which suppose to provide powerful surge capabilities because it is low freq , is less capable than my old Voltroniic one

As far as I can tell, no Felicity documents provide any information on surge capacity, so they do not guarantee anything beyond the rated power (unlike the Voltronic products).

The 'surge capacity' of LF inverters is often misunderstood. The output transformer provides excellent filtering and buffering capabilities - but the energy storage potential is still less than 1/2 of a phase cycle. So 10ms or so. This makes absolutely no difference to motor/compressor start-ups which require a second or more of surge power.

This sort of longer term surge is provided by the drive electronics, and the manufacturer sets the limits on what the drive electronics will supply.

Surprisingly, HF inverters have substantial advantages in this regard. HV bus capacitors are cheaper, lighter and smaller than a LF transformer, and generally store a LOT more energy. Also, the high frequency switching also allows for very rapid increase of power delivery to the DC bus, when required. So modern HF inverters often end up with better short duration surge capabilities than LF inverters.

2 hours ago, esmail-kassir said:

actually my question is why this specific low freq inverter which suppose to provide powerful surge capabilities because it is low freq , is less capable than my old Voltroniic one

Maybe you are not comparing apples to apples. Which Voltronic vm3 twin(4k or 6k) are you comparing to the Felicity inverter. Please supply model number and spesifications sheets of both inverters. If you run into these types of problems you must compare spesifications between inverters or are you assuming due to weight that the Felicity inverter is LF. I do not have much exposure to Felicity inverters.

10 minutes ago, TaliaB said:

Maybe you are not comparing apples to apples. Which Voltronic vm3 twin(4k or 6k) are you comparing to the Felicity inverter. Please supply model number and spesifications sheets of both inverters. If you run into these types of problems you must compare spesifications between inverters or are you assuming due to weight that the Felicity inverter is LF. I do not have much exposure to Felicity inverters.

Its good to get the info from him but I feel its a bit of a waste as it is clear that the inverter cant handle his load. Unless he is just interested in understanding his inverter.

If I was him I would just focus on figuring out how to turn on both the aircon and the vacuum. Or just get a new vacuum. I have a 1kw one and it works more than adequately. He should make do with what he has or just buy another inverter if it is bothering him that much.

43 minutes ago, TaliaB said:

lease supply model number and spesifications sheets of both inverters.

https://www.felicityess.com/wp-content/uploads/2024/11/T-REX-3_3.6_4_4.6_5_6KLP1G01-hybrid-inverter-user-guide-English.pdf

https://www.marvel-battery.com/storage/files/products/odatasheet_370.pdf

35 minutes ago, Denns said:

you assuming due to weight that the Felicity inverter is LF

I am not assuming I know it is LF from the specification , but the weight just confirm that it is not just marketing trick

39 minutes ago, Denns said:

Unless he is just interested in understanding his inverter.

yes I am indeed :)

39 minutes ago, Denns said:

Or just get a new vacuum

good excuse to get Robot vacuum , so if you know good one that can mod floor in summer and vacuum high pile rugs in winter please share it with me

43 minutes ago, Denns said:

If I was him I would just focus on figuring out how to turn on both the aircon and the vacuum

I paid money to upgrade my equipment , so any drawback will be frustrating , I thought about replacing it with Deye or Solis , but I want a completely natural cooling inverter without fans , (and to has good natural cooling capabilities , not one that need to install fans to it as DEYE SUN XSG04LP01

Edited September 17, 2025Sep 17 by esmail-kassir

Fanless is definitely nice to have. I wouldnt get fan cooled ones since you already have a fanless one. You dont need to be hearing a jet fighter taking off everytime it comes on.

Definitely a good excuse for a new vacuum cleaner.

1 hour ago, TaliaB said:

Maybe you are not comparing apples to apples. Which Voltronic vm3 twin(4k or 6k) are you comparing to the Felicity inverter.

You are still not answering my question which vm3 dual( 4k or 6k) compared to which Felicity model there are 4 listed in your manual attached???

Edited September 17, 2025Sep 17 by TaliaB

3 minutes ago, TaliaB said:

You are still not answering my question which vm3 dual( 4k or 6k) compared to which Felicity model there are 4 listed in your manual attached???

sorry my bad , Axpert 6 K

felicity 5 k

So my point as mentioned the Voltronic twin 6k by design is a 12000va so 12k inverter the Felicity is a 5k hence the reason you can't start the aircon and aircon simultaneously no bearing on Hf vs Lf

Edited September 17, 2025Sep 17 by TaliaB

2 minutes ago, TaliaB said:

So my point as mentioned the Voltronic twin 6k by design is a 12000va so 12k inverter the Felicity is a 5k hence the reason you can't start the aircon and aircon simultaneously no bearing on Hf vs Lf

I will give you another case maybe I can explain my idea (as using the other smaller Aircon and imaginary 5k VM III in the example will help )

1 tone Aircon =1100 W

Vacuum = 1800 W

1100+1600=2700

surge =3*2700=5400

Voltronic 5K would handle it smoothly ( according to data sheet I assume )

but my LF which should has much powerful surge is even failing to power 1 tone and vacuum

3 hours ago, Denns said:

Its good to get the info from him but I feel its a bit of a waste as it is clear that the inverter cant handle his load. Unless he is just interested in understanding his inverter.

If I was him I would just focus on figuring out how to turn on both the aircon and the vacuum. Or just get a new vacuum. I have a 1kw one and it works more than adequately. He should make do with what he has or just buy another inverter if it is bothering him that much.

Thanks @Denns you are right not to worry the problem is we are constantly misunderstanding each other.

Edited September 17, 2025Sep 17 by TaliaB

2 hours ago, esmail-kassir said:

I will give you another case maybe I can explain my idea (as using the other smaller Aircon and imaginary 5k VM III in the example will help )

1 tone Aircon =1100 W

Vacuum = 1800 W

1100+1600=2700

surge =3*2700=5400

Voltronic 5K would handle it smoothly ( according to data sheet I assume )

but my LF which should has much powerful surge is even failing to power 1 tone and vacuum

You need to check the max amp rating of the aircon, not just the watts rating. Do a clamp test and see the inrush current. Then you'll understand why the inverter is tripping.

I realize that my new LF inverter is smaller in physical size compared to my previous HF model, but that’s exactly why I raised the point. Normally, the main advantage of LF designs is supposed to be their ability to handle inrush/surge loads better, even if the continuous rating is similar or slightly lower.

In my case, the issue is not continuous overload — the problem shows up only during startup surges (like AC compressor + vacuum cleaner). That’s why I expected the LF unit to cover for this difference, but it doesn’t.

I’m genuinely trying to understand this from a technical perspective. If the LF design can’t handle these short inrushes as I thought, then maybe HF brands like Deye or Solis (with higher surge specs) would actually be a better choice for my setup. My goal here is not to justify the new inverter, but to reach the correct technical conclusion, even if it means replacing it.

@TaliaB @Denns

15 hours ago, abd7 said:

need to check the max amp

You’re right that current is the direct stress on the inverter, not just the kW figure. But when I say “2000 W for a moment,” that’s exactly the surge showing on the inverter display — which reflects the high inrush current.

The important point is: my appliances haven’t changed. The very same loads (AC + vacuum cleaner) used to start fine on a Voltronic 6 kW HF. Now with the new LF unit, even though it’s smaller in size, it should in theory be stronger in handling inrush — but it actually fails.

So I’m really trying to understand this technically. In your opinion, if it were a Voltronic 5 kW instead of 6 kW, do you think it would also fail to handle that startup surge?

Stupid question, and I hope you're not insulted by it, but I have to ask it anyway.

I see the Felicity IVGM5048 5kW is available in a single-phase and three-phase version. IVGM5048 (5KW monofásico/trifásico)) - Felicity Solar

What are the chances you've got a 3-phase version, and are exceeding the loading on just one connected phase?

3 hours ago, GreenFields said:

Stupid question, and I hope you're not insulted by it, but I have to ask it anyway.

I see the Felicity IVGM5048 5kW is available in a single-phase and three-phase version. IVGM5048 (5KW monofásico/trifásico)) - Felicity Solar

What are the chances you've got a 3-phase version, and are exceeding the loading on just one connected phase?

no mine is mono phase https://www.felicityess.com/wp-content/uploads/2024/11/T-REX-3_3.6_4_4.6_5_6KLP1G01-hybrid-inverter-user-guide-English.pdf

Can I just add something about surge currents. A 120W fridge can have a peak surge current of 1400W. Not apply this to your Aircon and vacuum cleaner or do as @abd7 suggested and provide the value. If not done we are just sitting in the dark. Further even

It might not be a matter of fitting all HF or LF in a box. Each manufacturer can have it's own criteria when the unit goes into overload.

Some none PV inverters even on LF would apply only a 10-20% above full time power to trip.

On 2025/09/18 at 7:34 AM, Scorp007 said:

Can I just add something about surge currents. A 120W fridge can have a peak surge current of 1400W. Not apply this to your Aircon and vacuum cleaner or do as @abd7 suggested and provide the value. If not done we are just sitting in the dark. Further even

It might not be a matter of fitting all HF or LF in a box. Each manufacturer can have it's own criteria when the unit goes into overload.

Some none PV inverters even on LF would apply only a 10-20% above full time power to trip.

That is correct, I measured a 1500Wat peak load at startup and my must 1kW 12V hybrid inverter switches over to grid mode when that happens after 18:00. After 4 minutes it switches back to battery mode, but then the compressor is already running and so it will continue to run in battery mode. During the day when I have solar and battery, he doesn't switch and can handle the overload. I believe it's the BMS that is the bottleneck that one blocks due to overload and makes that the Inverter switches.