Discusion recently on inverters, "low frequency"& "high frequency"

Re: Discusion recently on inverters, "low frequency"& "high frequency"

The one downside I see with most (maybe all) LF inverters is idle power consumption. As far as I can tell they have much greater idle power consumption. With power saver some of that can be limited though. But could be over 100w idle for the larger inverters with 50watt idle (non power saver) for smaller sized inverters. Not trivial loads but depends on usage scenarios.



I have 2 low frequency inverters. Although not much actual run time with them. Picked up a refurbished aims 1000w inverter on ebay for $70. I am looking forward to seeing what it can start.

I see most LF inverters have surge ratings roughly 3x of continuous usage rating. The same thing responsible for large surge rating is responsible for the high idle power usage. The large iron core.

Anyway above is from my limited knowledge. There are MANY LF inverter makers. Some names are promariner, samlex, aims, tripp lite, sterling power, and alot of generic brands as well. They also make HF inverters so be careful when buying.
Have no idea if some are better than others.
As a side note It appears sunelec is selling some samlex LF inverters cheap.

While I hate the wasteful nature of the LF idle power consumption I do like the idea of a robust design and thus why I went that way. Avoiding down time due to failure will be important to me as I will be in areas with little access to any solar/ inverter products.


matthew

Re: Discusion recently on inverters, "low frequency"& "high frequency"

john p wrote: »

If at first,second and third try you dont succeed there is a better chance on the 4th try, and so it proved to be.

I do like that. My favorite has always been "If at first you don't succeed, get a bigger hammer."

And in case, as seems likely, you have some math and programming background there is this one:
Programmers' Motto:

Re: Discusion recently on inverters, "low frequency"& "high frequency"

If you are looking for a long lasting quality inverter its not going to likely come from a big box store or "Hung ones or his brother who was Hungtoo all cheapo super sale store. And some of the not as good ones come from AIMS,Canadian Tyre, the ones from "X....."
There are sine wave and sine wave, Some manufactures actually sell MSW as TSW . Dont believe all you read on the cardboard box on items from C....,
If its cheap it usually means "nasty"
I dont give much out as brand names, but give you these.
Inverters .Victron
Generators. Northern Lights
Charge controllers.Victron ,GSL
As most know I sell nothing or have anyone relative or friend that does either.
I just test things and advise manufacturers and goverment departments of my findings. Thats it last 10 yrs.

Re: Discusion recently on inverters, "low frequency"& "high frequency"

West branch ,no type of inverter will run loads constantly much better than any other type. if you have 2000 w of loads you need at least a 2500w inverter.. . Inverters like the low frequency type are only superior at starting heavy difficult loads,and vastly superior.
You cant get a Toyota Camry to carry the same load as a Mack truck can...Sooner or later you will get big failure. guaranteed.

Re: Discusion recently on inverters, "low frequency"& "high frequency"

I think LF and low idle power consumption are mutually exclusive. The large iron core of transformer allows for larger surges, but also takes energy to keep it just sitting there powered. You can have one or the other but not both. The way to limit LF idle consumption is using the smallest possible. So smaller iron core, also reduces surge capabilities. And a major savings can be had if you put it into power saver mode, but that will not work with 24/7 loads.
So I recommend using a small inverter to cover the 24/7 loads. As I think a LF inverter running a 10w load will itself be consuming +30w. Although I could be wrong.

Another possible solution is if the 24/7 loads could be run directly from the battery. via very small and cheap Inverter/ power brick. Something like a 30w inverter for the phone. etc.

matthew

Re: Discusion recently on inverters, "low frequency"& "high frequency"

ggunn wrote: »

I do. I remember being in the keypunch room late one night frantically trying to finish up a programming assignment when a guy rushed in with his shoebox full of cards, which he had neglected to rubberband together in order. He tripped on the doorsill and spilled the cards all over the floor. He sat down and cried.

I often had to cut my own holes with a broken rasor blade.

Re: Discusion recently on inverters, "low frequency"& "high frequency"

animatt wrote: »

The thread below has the whole modifications. It does not seem to be too tricky but there are some things to think about.
http://forums.energymatters.com.au/solar-wind-gear/topic3344.html

Lot's of bad info in this video. Starting with 48v current reading on idle. The current profile on this type of inverter can be quite complicated and requires a true rms reading meter in DC mode. True rms in DC is usually only found on high end meters. A true rms meter for a small hand held DVM usually means true rms for AC mode only, not for DC mode setting.

For thoughs thinking that 'what are you talking about referring to rms on a DC current', a true sinewave inverter has a sine squared current profile on the battery current. At no load, this type of inverter (same scheme used by Xantrex and Outback inverters) can have a some energy 'kick back' of reverse DC current over portion of the sinewave cycle period. This is due to the particulars of the low frequency transformer designed specifically with 'more then normal' leakage inductance. This causes the transformer to store and return more energy in the transformer core compared to a normal designed power transformer. The reason for this I will explain later. At no load some of this stored energy is returned to the battery during some portion of the sinewave cycle period making the current measurement very prone to error unless you have the proper test equipment.

Second, putting a small torroid transformer, guessing from the physical size in the video to be about a 50 VA capable transformer, is totally comparing apples and oranges. A 50 watt inverter will be expected to have a lot less idle current then a 6000 watt inverter. There is more to it then just the transformer size. The torroid transformer for a 60 Hz transformer will likely be totally unsuitable for this type of inverter. 50/60 Hz power torroids are normally designed for very very low leakage inductance. They are often used in audio amplifiers because they leak less field then a regular 'E-I' laminated silicon-iron core transformer reducing possible low freq hum in the audio.

Now that is not to say that the Chinese copy of this type of inverter has a correctly designed low frequency transformer. More then likely the transformers are not properly designed for this application, contributing to more wasted power. If regular normal power transformers are used, a larger then optimal secondary output filter capacitor will be required to get acceptable high freq PWM removal from output making the system have much higher losses and higher resulting idle current from the battery.

The reason for desiring a higher leakage inductance in the transformer for this type of inverter, which is normally what you don't want in a power transformer, is as followed.

A true power transformer, likely what you are most familar with, will not store much energy in the core. It doesn't have to as its job is to tightly couple the power from the primary to secondary of the transformer. The B-H magnetization characteristics of a silicon-iron power transformer is very abrupt, requiring very little magnetizing current in the primary to drive the core into saturation. This does not matter because the tightly coupled secondary provide a back emf to counter the higher primary current when the transformer is loaded.

The magic of this type of sinewave inverter is how the high frequency PWM primary side excitation is filtered out (with the help of only a capacitor across secondary of transformer). To do this requires the low frequency transformer be designed with a controlled amount of low loss leakage inductance. (low loss leakage inductance is somewhat a contradiction in itself) This is the 'special sauce' magic truely understood by only a few specialist in this kind of transformer design and fabrication. The leakage inductance provides the series filter inductance to help remove the high frequency PWM applied to primary of transformer. This eliminates the need for a separate expensive filter inductor.

The large heavy special transformer could be replace with a small high frequency switching transformer design that would provide the primary to secondary isolation just like the large heavy transformer. The problem with this approach is it would also require a very large additional inductor in the output filter to remove the high frequency PWM.

The problem with 50/60 Hz single phase AC is it has a long period of high current that must be supported in a transformer which is not possible with a small transformer core. Many of you know that a 60 Hz transformer used in a 50 Hz system may have overheating problems. This is because the core is not big enough to support the slightly longer period of peak current at 50 Hz.

Back to the large filter inductor required to remove the high frequency PWM removal on the high frequency PWM transformer design. The filter consist of L-C, series inductor - shunt capacitor, to remove most of the 20-25 KHz PWM chopping squarewave that creates the average 60 Hz sinewave. The problem is this filter inductor must provide the correct inductance for the filter at 25 KHz AND must support the high long period 60 Hz peak current of the output AC load. To the high frequency inductor, it is just like requiring the inductor to maintain its high frequency inductance with 25 amps of DC bias flowing through inductor wire for a 6 kW inverter. This is an expensive and large inductor, more then defeating the benefit of the small high frequency transformer.

So this type of inverter with a big heavy transformer has a high freq PWM primary amd low frequency secondary output. To the originator subject line, is it a high frequency inverter (yes) or a low frequency inverter (yes)...

This discussion is about bi-directional inverters. This is an inverter that can flow power in both ways, acting as and AC inverter and a charger. The 'Power-to-Go' type small sinewave inverters are not bi-directional inverters.