Low Frequency Inverters

A handful of people around here recommend low frequency inverters, I wasn't aware of the distinction before joining this forum, and most companies don't seem to push this as a marketing point and most reviews don't mention it. And I've found very few clearly marked low frequency inverters at the small (<2-3kw) end of the spectrum.

I'm wondering, are LF inverters one of those things where the saying "If you don't know if you need one, you probably don't need one" applies?

Can someone ELI5 (explain it like I'm 5 years old), the benefits of LF inverters / drawbacks of HF inverters?

What I have gathered so far:

Pros of LF inverters:

1. Longevity / reliability
2. Higher peak/surge power rating (~200% for HF >300% for LF)
3. ..?

Cons of LF inverters:

1. Cost
2. Size/Weight
3. ..?

Am I missing anything, are there loads that need or greatly benefit from low frequency, in the same way that some loads require a pure sine wave? Is LF something the average small system builder should even worry about?

How about efficiency and power consumption at idle, any differences?

If these are the main differences, it seems that priorities would have a lot to do with how much sense it makes to go LF. If you are building an off grid home and designing a system to last 20+ years, where size and weight aren't a big issue and the cost of a LF inverter relative to your overall budget is somewhat small, and your AC demands are higher, LF probably makes a lot more sense. If on the other hand you are building a small mobile system where size and weight matter and where the cost of the inverter will be a big chunk of your budget, LF might make less sense.

As far as i understand low freq inverter architecture is just a less expensive way to control power, aims and others use it.

From aims. I had to look up amd read up on what part of the process it is.

"Low frequency power inverters got the name of “low frequency” because they use high speed power transistors to invert the DC to AC, but drive transistors at the same frequency (60 Hz or 50Hz) as the AC sine wave output."

So it gets the job done without another stage, down conversion of freq.

Cons......... Low frequency hum that all these inverters suffer from or rather, that the owners suffer from!

kernel said:

As far as i understand low freq inverter architecture is just a less expensive way to control power, aims and others use it.

From aims. I had to look up amd read up on what part of the process it is.

"Low frequency power inverters got the name of “low frequency” because they use high speed power transistors to invert the DC to AC, but drive transistors at the same frequency (60 Hz or 50Hz) as the AC sine wave output."

So it gets the job done without another stage, down conversion of freq.

Cons......... Low frequency hum that all these inverters suffer from or rather, that the owners suffer from!

Click to expand...

we have mostly seen high frequency in the grid tie sector and inverters from China, right now the primary us one I am seeing is the solark which is getting some pretty good traction. The primary difference I see is that the transformer and fets are sharing the load in low frequency where in high it’s all fet or digital switching that’s absorbing the load. The low frequency inverters have exhibited the ability to run from 10-15 years pretty commonly I am curious to see what the lifespan of the HF will actually be.

Most people can get by with a properly sized HF, but if you're running very high surge devices like deep well pumps or big shop tools, a LF inverter would be the way to go. They have a large transformer with a "flywheel effect" that can handle the surges better.

One

SolarRat said:

Most people can get by with a properly sized HF, but if you're running very high surge devices like deep well pumps or big shop tools, a LF inverter would be the way to go. They have a large transformer with a "flywheel effect" that can handle the surges better.

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One thing an aims inverter does well is herculean surge capability. It a brute force approach unlike the nuance and full control of an HF with a good power control circuitry of say schneider, outback, magnum etc.

Xolar said:

The primary difference I see is that the transformer and fets are sharing the load in low frequency where in high it’s all fet or digital switching that’s absorbing the load.

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Not true as HF inverters definitely use transformers. On youtube look at some info on Reliable (WZRELB) 8000W inverters. A number of people have opened them up and done comparisons. Dave Poz and another Canadian I cannot recall at this point. You will see that the old ones had 9 small transformers and the new one has 4 much larger transformers.

My child like understanding (I trust someone will correct me here if I am wrong ) is that HF inverters also provide "cleaner" electricity although I have not found an exhaustive study comparing the sine waves on a 'scope. Many electronics prefer a better sine wave and are less efficient with "dirty" waves.

CREDIBLE Information here:

This is yet another subject that comes up often and has been beaten to death with "opinions". BTW: Pure Sine Wave can be either HF or LF and is not dependent on which method of inversion is used. YouTube University is chocked full of opinions that should come with a big Cow Lick. If you value the life of your electronics & motored equipment (think fridge compressor motor) then LF Pure Sine is the way to go.

JoeHam said:

Not true as HF inverters definitely use transformers. On youtube look at some info on Reliable (WZRELB) 8000W inverters. A number of people have opened them up and done comparisons. Dave Poz and another Canadian I cannot recall at this point. You will see that the old ones had 9 small transformers and the new one has 4 much larger transformers.

My child like understanding (I trust someone will correct me here if I am wrong ) is that HF inverters also provide "cleaner" electricity although I have not found an exhaustive study comparing the sine waves on a 'scope. Many electronics prefer a better sine wave and are less efficient with "dirty" waves.

Click to expand...

Many transformerless inverters. His installs are featuring skybox.... and other grid tie inverters.
Hf inverter topology is expensive but provides better control amd higher efficiency.

Its why an aims is still 80-something-ish percent efficient, vs 92% or higher for some.

Check the weight difference between HF and LF converters of the comparable watt rating.
The weight is primarily in the transformer.

JoeHam said:

Not true as HF inverters definitely use transformers. On youtube look at some info on Reliable (WZRELB) 8000W inverters. A number of people have opened them up and done comparisons. Dave Poz and another Canadian I cannot recall at this point. You will see that the old ones had 9 small transformers and the new one has 4 much larger transformers.

My child like understanding (I trust someone will correct me here if I am wrong ) is that HF inverters also provide "cleaner" electricity although I have not found an exhaustive study comparing the sine waves on a 'scope. Many electronics prefer a better sine wave and are less efficient with "dirty" waves.

Click to expand...

JoeHam said:

Not true as HF inverters definitely use transformers. On youtube look at some info on Reliable (WZRELB) 8000W inverters. A number of people have opened them up and done comparisons. Dave Poz and another Canadian I cannot recall at this point. You will see that the old ones had 9 small transformers and the new one has 4 much larger transformers.

My child like understanding (I trust someone will correct me here if I am wrong ) is that HF inverters also provide "cleaner" electricity although I have not found an exhaustive study comparing the sine waves on a 'scope. Many electronics prefer a better sine wave and are less efficient with "dirty" waves.

Click to expand...

@JoeHam the transformer in the reliable is nothing compared to that in a Schneider, sma or Outback this is partially where the reliability is coming from as I understand it

Xolar said:

@JoeHam the transformer in the reliable is nothing compared to that in a Schneider, sma or Outback this is partially where the reliability is coming from as I understand it

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Understood, I just was responding to the statement that HF inverters do not use transformers at all

Steve_S said:

I you value the life of your electronics & motored equipment (think fridge compressor motor) then LF Pure Sine is the way to go.

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Can you elaborate on this a little bit, without diving too deep into the weeds? Is the logic here that in you are using a HF inverter that can't adequately provide the surge load for motors, etc, the appliances (and the inverter) may be damaged over time/many cycles?

As for electronics, the Magnum article you linked specifically lists computers under what can be run with HF inverters, so at least some should be happy with HF I imagine.

@kernel Can you clarify a couple points for me.

kernel said:

Hf inverter topology is expensive but provides better control and higher efficiency.

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This seems to imply HF inverters are more expensive, my limited research (at the lower/smaller end of the spectrum (<3Kw, off grid)) has given me the impression that LF inverters tend to be more expensive (for a given continuous power rating)

kernel said:

Its why an aims is still 80-something-ish percent efficient, vs 92% or higher for some.

Click to expand...

So all other things equal an HF inverter can be more efficient?

LF inverters are usually (almost always) more expensive. Besides being better for big loads, I've found they also make less RF noise.

I watched this video about inverters recently.
Probably found the link on this site but can't recall.
Hope it helps.

SolarRat said:

LF inverters are usually (almost always) more expensive. Besides being better for big loads, I've found they also make less RF noise.

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I know this is probably a pretty pedestrian question, but does less RF noise translate to 'better or safer at powering sensitive electronics'? Or is the main upside of an inverter that produces less RF noise that there is less 'pollution' effecting speakers, radios, wifi, etc.

smoothJoey said:

I watched this video about inverters recently.
Probably found the link on this site but can't recall.
Hope it helps.

Click to expand...

Great video thanks for posting, he does a good job of breaking things down in a straightforward easy to understand way.

Dzl said:

I know this is probably a pretty pedestrian question, but does less RF noise translate to 'better or safer at powering sensitive electronics'? Or is the main upside of an inverter that produces less RF noise that there is less 'pollution' effecting speakers, radios, wifi, etc.

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I usually only notice the noise on certain frequencies of the ham band, but sometimes a wide range of frequencies. For most people this is not a problem. I guess if the RF noise is really bad on the high freqs it could slow down or reduce the range of things like wifi, but I've never tested for this, and doubt it's a problem. If your speakers are clear and you don't have lines running through your TV set, most noise will go unnoticed by the average user. But if your close by neighbor has big antennas on his roof, and you want to stay friends with them...think about noise a bit.

Dzl said:

@kernel Can you clarify a couple points for me.



This seems to imply HF inverters are more expensive, my limited research (at the lower/smaller end of the spectrum (<3Kw, off grid)) has given me the impression that LF inverters tend to be more expensive (for a given continuous power rating)



So all other things equal an HF inverter can be more efficient?

Click to expand...

No, the electronics can probably do anything we want, but it costs money. Im not a power electronics design technician, but i play one when the solder iron is hot

All of the best inverters we have been using for 20 years almost, are hf inverters, possible the old trace DR may possibly have been aims style, hum box and all.

The option i see is lf inverters in lesser gear. By lesser i mean surge, eveything-everything considered an aims is just not the machine an outback fx is, it cannot syncronize with other sources and so cannot assist their power output, backfeed the grid, ac couple, etc.

The outback will idle at 3w consumption and come in without a hitch and that must have everything to do with the inversion and power control circuitry.... not just how its done but how well its done also.

There may be no real difference but i have to assume that it is cheaper to build a low frequency inverter because most all cheap inverters are of this type.

We need an electronics engineer for this one im tapped out without typing myself smart with google....

None of these lf inverters i have seen with 92-96% efficiencies.

Dzl said:

@kernel Can you clarify a couple points for me.



This seems to imply HF inverters are more expensive, my limited research (at the lower/smaller end of the spectrum (<3Kw, off grid)) has given me the impression that LF inverters tend to be more expensive (for a given continuous power rating)



So all other things equal an HF inverter can be more efficient?

Click to expand...

No, the electronics can probably do anything we want, but it costs money. Im not a power electronics design technician, but i play one when the solder iron is hot

All of the best inverters we have been using for 20 years almost, are hf inverters, possible the old trace DR may possibly have been aims style, hum box and all.

The option i see is lf inverters in lesser gear. By lesser i mean surge, eveything-everything considered an aims is just not the machine an outback fx is, it cannot syncronize with other sources and so cannot assist their power output, backfeed the grid, ac couple, etc.

The outback will idle at 3w consumption and come in without a hitch and that must have everything to do with the inversion and power control circuitry.... not just how its done but how well its done also.

There may be no real difference but i have to assume that it is cheaper to build a low frequency inverter because most all cheap inverters are of this type.

We need an electronics engineer for this one im tapped out without typing myself smart with google.

LF, uses LARGE IRON CORE transformers with large diameter copper windings to provide rated output plus useful 20 or more second 3x surge wattage...

HF use various methods to as cheaply as possible create the inverted wattage. Most use small boards to change the dc to AC then banks of mossfet transistors and circuit boards controlled by microprocessors with varying degrees of durability to produce the rated wattage, and a nanosecond surge wattage useful only for the advertising...

HF can achieve very high efficiencies, and very low standby watt demands.