Low Frequency Inverters

[Dzl]

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.

 

[kernel]

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!

 

[Xolar]

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!

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.

 

[SolarRat]

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.

 

[kernel]

One

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 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.

 

[JoeHam]

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.

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.

 

[Steve_S]

CREDIBLE Information here:

Inversion Methods Explained: High Frequency vs Low Frequency | Magnum Dimensions

Understand the difference between high frequency and low frequency inverters with this quick article.

www.magnum-dimensions.com

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.

 

[kernel]

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.

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.

 

[John Frum]

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

 

[Xolar]

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.

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.

@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

 

[JoeHam]

@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

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

 

[Dzl]

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

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.

 

[Dzl]

@kernel Can you clarify a couple points for me.

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

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)

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

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

 

[SolarRat]

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

 

[John Frum]

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

 

[Dzl]

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

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.

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

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

 

[SolarRat]

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.

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.

 

[kernel]

@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?

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.

 

[kernel]

@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?

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.

 

[Supervstech]

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.

 

[Dzl]

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.

The more I come to understand the two types, the more it seems LF are "technically superior" in many respects but that the decision between HF and LF will more often than not come down to use-case and practical factors and non-technical factors such as cost.

A larger system like an off-grid cabin or shop for instance is:
more likely to (1) have a bigger $$ budget (2) have less space/weight constraints (3) need to power loads like pumps or power tools or even or even high power blenders and kitchen gadgets (4) get maximum benefit from the long term durability and serviceability of a product designed to last 15+ years (5) preference other factors above squeezing every possible Watt of power and % of efficiency out of their system

Whereas a small mobile, marine, or portable power station setup is more likely to (1) have significant space/weight constraints (2) preference efficiency and low standby consumption over almost everything else (3) may not need to power any loads that have a high startup surge (4) may have a smaller overall budget and find the added cost not worth it (5) may not design for a 15+ year system life.

 

[Supervstech]

Could be.

the HF systems are improving every day, and as many units as power Jack makes and repairs, at some point, they may get strong enough to replace the big boys...

If you don’t need LF, a good HF can be fine. Just go in with open eyes, and know the limitations.

reliable, cough cough...

 

[kernel]

Always more to learn. Interesting post. Ill go back to school for 2 or 5 years before trying to offer up on that one again....

 

[Steve_S]

Final post to this thread as I am unwatching it after this. Many years in the military doing IT & Comms, not once did we ever use HF inverters. For what it's worth, the Military is PICKY and abuse gear like noone else because it has to survive the worst possible conditions anyone can dream up. I am certain that everyone here can appreciate that wee detail. Bottom line, if it is good enough for them, it's good enough for me, if it doesn't pass muster there, then I do not bother. Some things are okay to furtle about with and take a risk on but that is an individual choice as to how much risk a person is willing to accept. There are good quality HF inverters out there but by the time you pay for one, your in the same $$ ballpark as LF ones and good LF Inverters are also quite frugal in standby mode and can be up to 98% efficient which is the top side of the scale of what's out there.

 

[Dzl]

Final post to this thread as I am unwatching it after this. Many years in the military doing IT & Comms, not once did we ever use HF inverters. For what it's worth, the Military is PICKY and abuse gear like no one else because it has to survive the worst possible conditions anyone can dream up. I am certain that everyone here can appreciate that wee detail. Bottom line, if it is good enough for them, it's good enough for me, if it doesn't pass muster there, then I do not bother. Some things are okay to furtle about with and take a risk on but that is an individual choice as to how much risk a person is willing to accept. There are good quality HF inverters out there but by the time you pay for one, your in the same $$ ballpark as LF ones and good LF Inverters are also quite frugal in standby mode and can be up to 98% efficient which is the top side of the scale of what's out there.

@Steve_S All good points, and if I were choosing an inverter that I needed to rely on for a larger project I would definitely be of the same mindset. In fact, I am of the same mindset, my priorities are just a little different.

For me, Samlex Evo was the top of my list for a long time until I reassessed my needs and realized it was massive overkill for my application. I still want one, but pretty much every major system in my build (and just about every minor appliance as well will be 24v, 20v, or 12v DC). I love the features of the Evo and would probably grow into them, but its overkill for me right now.

My current thinking is to buy something that just meets my needs from a reputable brand, and as my needs evolve reassess and scale up at that point. Durability, long term reliability of an inverter becomes less crucial if its a $200 purchase that you use occasionally to supply 500 or 1000 watts of AC on the occasions that you need it. A small low wattage inverter from a reputable company with a decent warranty (like the Victron Phoenix) is my plan right now. If in a year or two I grow out of it, resale value is quite high for used quality electronics or I could use it as a backup inverter.

However, if you are right about the efficiency, and about the standby power consumption I would start to consider one again. The cheapest Samlex Evo's are not that much more expensive, but if I was buying a full featured LF inverter/charger to last decades, I would probably not want to settle for the 1200w single AC input version so realistically cost would be about double that of the cheapest Evo, and 3-5x that of a small low wattage HF inverter.

On a separate note, it irritates me that the inverter manufacturers advertise "peak efficiency" without giving any context as to if you can even expect to achieve that and if so under what conditions. Computer power supplies generally use the efficiency at 50% load as the nominal efficiency but also document efficiency at 20% and 100%.