2nd Edition 6kW OzInverter build book/manual & PCB's.

[clockmanFRA]

Hi johntaves,

The original concept of the OzInverter was to make an Inverter that could really do 6kW, 15 kW for short periods and huge kW's for surges.     

And that the OzInverter was to be kept SIMPLE, made to be ROBUST, and importantly kept COST EFFECTIVCE.

It was envisaged to be supported by a good 48vdc battery bank, eg min 600ah, and run a normal domestic property.

When fully assembled the Ozinverter weighs about 100lbs.

I was also envisaged to use about 30 to 40 watts when on and just sitting there awaiting the loads.

And the design is based around the principal that the machine is permanently on.

Big Toroids do not like being turned on and off.

I trust this helps?
     

[johntaves]

Hi johntaves,

The original concept of the OzInverter was to make an Inverter that could really do 6kW, 15 kW for short periods and huge kW's for surges.     

And that the OzInverter was to be kept SIMPLE, made to be ROBUST, and importantly kept COST EFFECTIVCE.

It was envisaged to be supported by a good 48vdc battery bank, eg min 600ah, and run a normal domestic property.

When fully assembled the Ozinverter weighs about 100lbs.

I was also envisaged to use about 30 to 40 watts when on and just sitting there awaiting the loads.

And the design is based around the principal that the machine is permanently on.

Big Toroids do not like being turned on and off.

I trust this helps?
   

Thanks, for that info.

What is the issue with turning it off? In my application it will need to be shut off if the batteries get too low from lack of solar.

I have a 24v battery, I assumed that the design can be modified to handle that. Am I wrong?

What about my other questions, can someone answer those?

Thanks,

[Bruce S]

johntaves;
What you are asking could be very extensive and dangerous (Lethal) if you do not know what you're doing.

I would highly suggest you have a look at the past posts that goes along with the early builds.
Get yourself acquainted with this unit as it is built and what it's intended for.

IF you're not used to working with potentially lethal voltage ranges of DC and the high voltage of AC, the it's possible this isn't for you.

There are other devices more suited for what you're probably trying to do.

Cheers

Bruce S

[johntaves]

johntaves;
What you are asking could be very extensive and dangerous (Lethal) if you do not know what you're doing.

I would highly suggest you have a look at the past posts that goes along with the early builds.
Get yourself acquainted with this unit as it is built and what it's intended for.

IF you're not used to working with potentially lethal voltage ranges of DC and the high voltage of AC, the it's possible this isn't for you.

There are other devices more suited for what you're probably trying to do.

Cheers

Bruce S

Let me get this straight. I should read through the blog of the early builds in order to get some simple questions answered to decide whether to buy a $100 book because it seems like I am an idiot with respect to voltages. It makes sense to not provide answers to an idiot, so that they will not go down a path and kill themselves.

This begs the question of the intended audience for that book. Is it for people that already know how to build an inverter, and thus don't need it? Or is it for those that don't know how to build one, and thus shouldn't build one because they will kill themselves? Maybe I misinterpreted what information the book provides. I assumed it provided information about building your own inverter, and not necessarily this specific unit. I also assumed that this specific unit was similar to other inverters in that it was OK to put it in a moving vehicle, and turn it off, just like countless other LF inverters.

Maybe I should just buy the book and find out. The seller of the book makes it abundantly clear that it is not for profit, which implies the book is exactly what one wants for their $100, in sharp contrast to those manuals where the author is attempting to make money from their work. It does make you wonder what this book is, if the marginal cost for delivering another book is over $100USD.

I apologize for asking questions and wasting your time. Clearly that was a mistake.

Cheers

jt

[clockmanFRA]

johntaves,

I did this book because folk like 'Oztules' helped me, so I try to help others.

£92 covers cost of printing a small run, Power board PCB, Ozcontrol board PCB and OzCooling PCB and postage and tracking most places in the World.

 Each A4 book has, 92 printed pages, 33,400 words, 221 colour photos, 12 block diagrams. …. £28
Postage & packing and tracking number, ……. £16
PCB, Espeacially designed Power board, A4 size, double sided, double copper thickness, …… £28
PCB, Espeacially designed OzControl board, 187mm x 90mm, double sided, but can be self etched and links added,  …. £12
PCB, Espeacially designed OzCooling board, 82mm x 67mm, single sided with link,  ….. £8

All these are done as small runs, with the PCB's done in batches of about 10.

As I have already said the OzInverter was for folk who wanted a real powerful Inverter that could run a domestic house/property.

What you are asking ……

At 24vdc, then the primary will want to be beefed up in size and altered in its ratios with the secondary.

You require 120vac and 220vac, that's possible, its detailed in the OzInverter book 2nd edition, and the secondary will require modifications for this.

For 24vdc the primary choke will need re-designing to obtain a good low tick over/running power loss.  This could be allot of work and experimentation to get low losses.

To have the OzInverter just ticking over to operate a clock, makes no sense.

So for a RV, I do not think that a OzInverter will suffice for your needs, it is just to powerful.

There are cheap commercially obtainable Inverters that will do what you want that are manufactured in China.

Midnite, a US company have been developing since 2014 a HF Inverter for the US market, the B17, and I believe they have some modular 2kW units going on Beta test at present.
https://www.youtube.com/watch?v=oNQ_V7L8GiM

I trust the above explanation and information helps you. 

[johntaves]

johntaves,

£92 covers cost of printing a small run, Power board PCB, Ozcontrol board PCB and OzCooling PCB and postage and tracking most places in the World.

 Each A4 book has, 92 printed pages, 33,400 words, 221 colour photos, 12 block diagrams. …. £28
Postage & packing and tracking number, ……. £16
PCB, Espeacially designed Power board, A4 size, double sided, double copper thickness, …… £28
PCB, Espeacially designed OzControl board, 187mm x 90mm, double sided, but can be self etched and links added,  …. £12
PCB, Espeacially designed OzCooling board, 82mm x 67mm, single sided with link,  ….. £8

Thanks for the info. I did not realize the book also included the PCB boards. I apologize for missing that fact and misinterpreting the "covers the cost" statements. It seems like a good bargain.

Is it your opinion that the changes I want to make (24v, 120v, and maybe 4kw) would negate the boards, or is it a matter of changing the components? Of course the transformer will be changed, but maybe the circuit does not change, just the values of the various components?

As I have already said the OzInverter was for folk who wanted a real powerful Inverter that could run a domestic house/property.

Yes, I get that. I get that I am an idiot and thus you feel the need to convert measurable units, like "Low Frequency 6kw" into something I can comprehend, like "house". But, really would anyone that does not know the general performance characteristics of an inverter bother to read this forum and post?

At 24vdc, then the primary will want to be beefed up in size and altered in its ratios with the secondary. You require 120vac and 220vac, that's possible, its detailed in the OzInverter book 2nd edition, and the secondary will require modifications for this.

Right, of course. I apologize for not finding this info in the forums first, but when you change this to a 120vac, you're doubling the amps and I assume you would make a split phase output. Is that right?

You stated something about not liking being turned on/off. I assume you are talking about something different than being connected/disconnected from the battery where the capacitors are charged, is that right? I do need to turn it off when the RV is not in use, and have it use near zero power, is there an issue there?

For 24vdc the primary choke will need re-designing to obtain a good low tick over/running power loss.  This could be allot of work and experimentation to get low losses.

OK, that's great info.

To have the OzInverter just ticking over to operate a clock, makes no sense.

So for a RV, I do not think that a OzInverter will suffice for your needs, it is just to powerful.

If you read my original post, I did not write anything that would suggest such nonsense. I do not have the goal of just ticking a clock. That's the idle. That's the load it will have for a large percent of the time, thus the efficiency in that situation is very important. It will also run a fridge, 2 air conditioners, microwave, water heater, space heater, hot air gun, charge my e-bike, chop saw and a table saw, and of course computers and other electronics, which is no different from a house.

There are cheap commercially obtainable Inverters that will do what you want that are manufactured in China.

"As I have already said", I have an inverter. Its fan goes on and off, loud or quiet. I stated that to provide some clues that I wanted to make something better than I can buy. When attempting to buy some inverter, I cannot determine with any decent probability that the fan is intelligent but only on/off, or more intelligently speed controlled. I cannot tell if the fan is going to be silent when I have just the clock load. Hell, I can't even determine if the thing for sale will sustain it's rated wattage for any great length of time. I bought a $450 4kw HF Chinese inverter that stated it would surge to 8kw, so I figured there was a good chance it would be able to start my air conditioner that has a locked rotor amperage that translates to 7kw. Not only does the inverter fail to start it, it won't keep it running when the transfer switch clicks from shore to inverter. I was hoping the momentum of the motor would help.

I also need to connect the inverter to the BMS, so that the BMS can shut it off. Many of these inverters have momentary power switches, which means I have to make a simple circuit and wire that in to ensure it goes on/off properly. I also stated I wanted to build this into a specific space.

In short, I have given up attempting to buy an inverter that fits, is quiet, and will deliver the power to start the AC, and has a simple on/off position switch.

Why would you assume that someone that can find this forum has no f'ing clue how to shop for an inverter? Isn't that a rather bogus scenario?

Midnite, a US company have been developing since 2014 a HF Inverter for the US market, the B17, and I believe they have some modular 2kW units going on Beta test at present.

Yikes! That makes no sense to me. I cannot imagine the need for a modular design for the RV market. What is the point of an empty bay taking up space? Additionally, they are building in the charge controller, which seems like a poor choice given that LiFePo4 is cheaper than lead acid now. (I just installed 8 new 280ah LiFePo4 cells (6.8kwh) for $1k USD total shipped from China). LiFePo4 does not need the typical lead acid charge controller that has the 3 stages. You need a BMS that will monitor individual cells, and temperature, and turn on/off loads and on/off charge. The charge just needs to be constant current. You don't need an MPPT either. The max power of a 60 cell panel is right at 27v which is the voltage of 8 cells of LiFePo4, thus the MPPT complexity is replaced with just a diode and a relay.

Those gauges are cool, until you realize that we are talking about an inverter that should be out of sight and out of ear shot, and have decent cooling.

[clockmanFRA]

johntaves,

Please I do not swear, I am going out of my way to help you where I can, your swearing attitude does not help matters.

I try to write directly to the point, bla bla bla...ing is not one of my strong points. I have to write in many languages and have translations that are to the point, and at the same time talk to many differing skill set folk.

Thank you for your apologies regards the book costs..

This OzInverter project was a specialised project and intended to be a large powerfull inverter.

I have not built any smaller units using the present OzInverter PCB's and therefore I personally cannot recommend scaling down the present OzInverter.   I see no reason just to say it can be done to get a sale of a book and PCB's,, when I have not built and done a smaller 'OzInverter' myself.

To alter any of the OzInverter components may alter the results of our efficient and robust design, but as I say I have yet to experiment with smaller OzInverters.


'Oztules' had done a couple of OzInverters where he experimented and produced a 4 FET Power board, 16 FET's in total rather than our 6 FET, 24 FET's.  I believe he produced Gerber files for these somewhere on ….. https://www.thebackshed.com/forum

However, as I understand it some clash of the FET's is important, but also resonance feedback can become big issues and this will probably effect the choke design, but as I have said I have not built any smaller units.

Starting and stopping the OzInverter,  …. from the 2nd edition OzInverter book page 46, ………  I have added the block diagram as an attachment. …..

OzInverter Start up, Charge up, procedure.

The Block diagram on the right/below shows the Start up, & Reset circuit.



It is very important that you  connect your batteries to the OzInverter in a safe manner. If you just connect a heavy cable to the battery there is such a draw by the capacitors, Its Big Splat Time, and that can be dangerous.

Oztules comments….  “We have 60000uf@50v to charge, I think .5*(e^2 x C) or about 75 joules. If we look at that as a joule is a watt second, thats 75w for 1 second ………

... imagine that as a one hundredth of a second.... suddenly we are generating 7500 watts... at one thousandth it is getting out of hand at 75000 watts or 75 kilowatts.... in the hundredths scenario we are in the 7500/50 or 150 amps.....  I know from tests it is very very much higher than this.. around the 400 amps and more.
 
We can see that this takes the end of your screw fittings easily.. so start up current is massive if you don't introduce some resistance into the start-up procedure.... I use a 50R resistor to charge the caps then just connect the battery wire without any fireworks....without it,  it throws the 180 amp o/load I have  and it takes 2 goes to charge the caps.”

If you’re not using ‘oztules’ above mentioned method of a small wire with a 50r or 40r resistor, then it’s  VERY IMPORTANT that you use a heavy duty breaker made for Midnite & Outback between the battery and the OzInverter.





This breaker is rated at 250amps and 125vdc, and has 10mm diameter threaded connections and is heavy duty. The breaker still has a ‘phut’ sound when I close the switch. So i also recommend the 40r resistor capacitor charge up start process.

Below/Right photo, ….. Main Inverter 19mm diameter latching push button switch. …. Red button push momentary switch for the Reset on the OzControl board. … Toggle switch with momentary action, for charging the Power board capacitors with the 50r or 40r ohm, 3 watt resistor, before switching the Inverter on. If the Inverter hangs and the Inverter will not start, then switch off Inverter and very briefly press the Reset button.




Somehwer on this forum i have shown a block diagram of the split phase arrangement for 2 120vac and the standard 220vac, it is not necessary with our design to alter the size of the windings wire diameters as it is expected to share the 2 120vac phases, and use a disjunctor/MCB breaker that is tied/linked to both phases.

A Toroid as a transformer is very efficient against a EW type, but starting and stopping a toroid above 3kW starts to become problematic and the PWM chip must have a soft start system to start the Inverter without damage to the other circuits.

A heck of allot has been written about Inverters on the Australian Forum, ….. https://www.thebackshed.com/forum 
The toroid man on thebackshed forum is 'Warpspeed' a retired toroid/power engineer, he has developed his own design of step inverter and is extremely knowledgeable and might suggest an Inverter design more suited to your needs.

[clockmanFRA]

The relevant  60HZ and 2off 120vac and 220vac PDF.


 2Supplement 60HZ 120vac.pdf (138.5 kB - downloaded 196 times.)

[Mary B]

Maybe it is time to integrate a soft start circuit that would automate start up. This is for AC but a DC version is really similar and my 1kw 2 meter amplifier uses one on the 50 volt 2,000 watt switching supply to charge the caps up slowly(integral to the supply).

johntaves,

Please I do not swear, I am going out of my way to help you where I can, your swearing attitude does not help matters.

I try to write directly to the point, bla bla bla...ing is not one of my strong points. I have to write in many languages and have translations that are to the point, and at the same time talk to many differing skill set folk.

Thank you for your apologies regards the book costs..

This OzInverter project was a specialised project and intended to be a large powerfull inverter.

I have not built any smaller units using the present OzInverter PCB's and therefore I personally cannot recommend scaling down the present OzInverter.   I see no reason just to say it can be done to get a sale of a book and PCB's,, when I have not built and done a smaller 'OzInverter' myself.

To alter any of the OzInverter components may alter the results of our efficient and robust design, but as I say I have yet to experiment with smaller OzInverters.


'Oztules' had done a couple of OzInverters where he experimented and produced a 4 FET Power board, 16 FET's in total rather than our 6 FET, 24 FET's.  I believe he produced Gerber files for these somewhere on ….. https://www.thebackshed.com/forum

However, as I understand it some clash of the FET's is important, but also resonance feedback can become big issues and this will probably effect the choke design, but as I have said I have not built any smaller units.

Starting and stopping the OzInverter,  …. from the 2nd edition OzInverter book page 46, ………  I have added the block diagram as an attachment. …..

OzInverter Start up, Charge up, procedure.

The Block diagram on the right/below shows the Start up, & Reset circuit.

(Attachment Link)

It is very important that you  connect your batteries to the OzInverter in a safe manner. If you just connect a heavy cable to the battery there is such a draw by the capacitors, Its Big Splat Time, and that can be dangerous.

Oztules comments….  “We have 60000uf@50v to charge, I think .5*(e^2 x C) or about 75 joules. If we look at that as a joule is a watt second, thats 75w for 1 second ………

... imagine that as a one hundredth of a second.... suddenly we are generating 7500 watts... at one thousandth it is getting out of hand at 75000 watts or 75 kilowatts.... in the hundredths scenario we are in the 7500/50 or 150 amps.....  I know from tests it is very very much higher than this.. around the 400 amps and more.
 
We can see that this takes the end of your screw fittings easily.. so start up current is massive if you don't introduce some resistance into the start-up procedure.... I use a 50R resistor to charge the caps then just connect the battery wire without any fireworks....without it,  it throws the 180 amp o/load I have  and it takes 2 goes to charge the caps.”

If you’re not using ‘oztules’ above mentioned method of a small wire with a 50r or 40r resistor, then it’s  VERY IMPORTANT that you use a heavy duty breaker made for Midnite & Outback between the battery and the OzInverter.

(Attachment Link)

(Attachment Link)

This breaker is rated at 250amps and 125vdc, and has 10mm diameter threaded connections and is heavy duty. The breaker still has a ‘phut’ sound when I close the switch. So i also recommend the 40r resistor capacitor charge up start process.

Below/Right photo, ….. Main Inverter 19mm diameter latching push button switch. …. Red button push momentary switch for the Reset on the OzControl board. … Toggle switch with momentary action, for charging the Power board capacitors with the 50r or 40r ohm, 3 watt resistor, before switching the Inverter on. If the Inverter hangs and the Inverter will not start, then switch off Inverter and very briefly press the Reset button.

(Attachment Link)


Somehwer on this forum i have shown a block diagram of the split phase arrangement for 2 120vac and the standard 220vac, it is not necessary with our design to alter the size of the windings wire diameters as it is expected to share the 2 120vac phases, and use a disjunctor/MCB breaker that is tied/linked to both phases.

A Toroid as a transformer is very efficient against a EW type, but starting and stopping a toroid above 3kW starts to become problematic and the PWM chip must have a soft start system to start the Inverter without damage to the other circuits.

A heck of allot has been written about Inverters on the Australian Forum, ….. https://www.thebackshed.com/forum 
The toroid man on thebackshed forum is 'Warpspeed' a retired toroid/power engineer, he has developed his own design of step inverter and is extremely knowledgeable and might suggest an Inverter design more suited to your needs.

[JW]

‘Make your own 6kW-15kW Pure Sine Wave OzInverter,  48vdc to 240vac/120vac, 50HZ/60HZ'.

https://www.fieldlines.com/index.php?topic=149427.0

https://www.fieldlines.com/index.php/topic,149427.msg1043620.html#msg1043620

[johntaves]

It is very important that you  connect your batteries to the OzInverter in a safe manner. If you just connect a heavy cable to the battery there is such a draw by the capacitors, Its Big Splat Time, and that can be dangerous. [/b]

I thought this is true for all inverters. And the bigger the unit is, the more capacitance it is going to have, and thus it becomes more important to not abuse your switch with that current. My understanding is that it is also a function of the batteries. A lithium battery has lower internal resistance so in that instance that the inverter is effectively a short, the lithium can deliver over 10k amps, and therefore will wreck a typical circuit breaker. One could argue that it is all about the battery because regardless of the capacitance, the instant it is connected, a lithium battery will deliver a whopping amount of amps. If amps are only destructive over time, then OK, it is more about the capacitor than the battery.

However, this is just a one time issue, right? You don't connect/disconnect the batteries all that often. When you do, you should connect an appropriate sized resistor from the battery to the plus for a few seconds. I hold the resistor across my circuit breaker, then close it. Similarly when you disconnect, it is wise to put that resistor between the + and - cables of the inverter to drain the capacitor.

I was not aware that big inverters had a start up circuit for this, but it makes sense that over a certain size they would do this.

A Toroid as a transformer is very efficient against a EW type, but starting and stopping a toroid above 3kW starts to become problematic and the PWM chip must have a soft start system to start the Inverter without damage to the other circuits.

Are you talking about the same connect-the-battery issue, or is this a different issue where the inverter is taking on a load? For example, when an inductive load starts up?

Maybe it is time to integrate a soft start circuit that would automate start up. This is for AC but a DC version is really similar and my 1kw 2 meter amplifier uses one on the 50 volt 2,000 watt switching supply to charge the caps up slowly(integral to the supply).

Mary B, what start up issue are you referring to?

[clockmanFRA]

We have ripple large capacitors that need a soft gentle charge up, I think that is what 'Mary B' is mentioning.

Switching off the Ozinverter is no issue, as 'Oztules says, "just switch off".

Disconnecting from the batteries the caps will drain naturally, depending on the size and quality of the caps.

As I said, toroids are more efficient against a EW transformer, however above 3kW a toroid on initial start up has some inductive forces at play and with our PWM chip and similar arrangements, we need to start the toroid very gently, so the actual toroid itself needs a soft start as well.

Somewhere in 'Oztules' 200,000 words is a break down and experimentation of a large toroid and the soft start required for the toroid itself starting with the 8010 PWM chip.

The study of toroids and there magnetic properties are a world to themselves, so folk like Warpspeed that know their profession and are willing to talk about it are a bonus.

'Warpspeed' comments …….

‘Warpspeed’ on  Commercial transformers.

 “Commercial transformer designers take a whole different approach to transformer design.
For them its a business, and the idea is to manufacture the smallest transformer with the least amount of steel and copper at the lowest cost.
Many transformer applications are for inside equipment, and will never be run at anything other than full maximum load.

So what I am getting at here, is that for them the most efficient transformer is the lowest COST solution. They do not give a damn about no load idling power, or even how hot it gets at flat out full load. Kva per dollar is the holy grail.

The generally accepted flux levels for commercially wound toroidal transformers is around 1.6T, and that allows a bit of allowance for a slightly high mains voltage.

And many budding inverter enthusiasts have reverse engineered commercial designs and just assumed 1.6T is the correct design figure, and argue that, as just about all transformers work at that level it must be correct !

Inverters are very different beasts, and there is a lot to be gained by running our toroids at far lower flux densities. For a start, our inverters run continuously, and for a domestic application usually at a small fraction of the full rated power.

Battery capacity is a very expensive commodity, so anything we can do to reduce idling power will be a giant step forward. If we are recycling old or free material, and size and weight are no deterrent, we can gain hugely by lowering the flux density to around 1.0T”


Okay I did not want to get to engrossed in detail over this forum, and all these comments and people I quote from are in the 2nd Edition book.  Chapter 14 the tech chapter is a large chapter but gives the background to the OzInverter's development.


This is 'Warpspeeds' wonderful and understandable comments of the toroid's interactions with a PWM, and the practicalities in what's actually happening……

“O/k let's look at our large efficient inverter output transformer that probably has a step up turns ratio of about 8:1 (30v to 240v).
Its a wonderful thing at 50Hz, and if there are enough turns to keep the flux density low, the magnetizing current should remain nice and low (when driven by a 50Hz sine wave).

Now what happens if we connect this DIRECT to a very low impedance PWM switching bridge switching at 23 Khz?
The secondary of our transformer will have a lot of capacitance between turns, between layers, and between the secondary and the core. The secondary inductance will be very high, but there will be a self-resonance of only a very few Khz with all that self-capacitance.

The combined capacitance across the secondary is reflected back into the primary at a rate of turns ratio squared. So there will be x64 the secondary capacitance that the bridge sees as a direct load. That capacitance has to be charged and discharged 23,000 times per second.

If the transformer connects directly to the bridge there are going to be some pretty fearsome current spikes every PWM switching cycle, even with no external load on the transformer. This will definitely increase idling current, but worse, its going to really stress the mosfets as the current spikes will be almost unlimited with such a low source and load impedances.

 So we fit a series choke into the primary to vastly reduce the rate of current rise each time the bridge switches.

With sufficient inductance the voltage at the bridge can switch very fast while the voltage across the transformer and its capacitance hardly changes.

You will see a very fast high frequency rail to rail waveform on one end of the choke, and a smooth 50Hz sine wave on the other end of the choke with only a very slight high frequency ripple feeding the transformer.

Now in the early days of all this inverter development, it was discovered that a ferrite choke would greatly reduce the idling current, and it will certainly do that. 

 The problem with ferrite is that it saturates very easily, and although it will reduce idling power, above a few amps through the choke and primary, it will saturate and have no effect at higher power.

We really need a choke that will keep on working up to full rated inverter power and ideally beyond, to greatly reduce the switching losses in the mosfet bridge. This will create far lower switching current spikes, reduce the stresses and heating on the mosfets and heat sinks, and generally improve inverter robustness and efficiency.

How big ? Well minimum might be something like 50uH would certainly work at 48v and 2-3Kw but something a fair bit larger would be better if you can arrange it. It really cannot be made too big, either in inductance or saturation current. Its rather like the decoupling electrolytics. More is always better.

When you have a really nice big non saturating high inductance choke working, it will effectively decouple the transformer from the bridge, and it allows the transformer to "do its own thing" as far as any self-resonant behaviour goes.

Expect to see some wobbles develop in the 50Hz waveform due to transformer self-resonance, especially at zero load. With higher loading the wobbles usually become slightly less.
The wobbles are not caused by the choke, but actually indicate that the choke is working properly.

Some people get alarmed by the now distorted sine wave output, and assume fitting a much large choke is the wrong thing to do. Fixing one problem has just created another problem, but it’s definitely a BIG step forward fitting a large non saturating steel cored choke.
 
One sneaky solution to the waveform distortion is to lower the self-resonant frequency of the transformer down to exactly x1.5 times the inverter frequency. That is 75Hz transformer resonance for a 50Hz inverter, and that usually takes around 4uF to 10uF across the secondary, but that varies a lot from transformer to transformer. This also sounds a bit suspect.... But try it and see,  it definitely works!

The magic of exactly x1.5 times the inverter operating frequency produces a self-damping effect, where any resonant build-up on one cycle will be exactly out of phase the following cycle. If it’s not tuned exactly right, resonant energy can build up causing even worse waveform distortion, and the inverter output voltage may do some very strange things at zero load.

Voltage feedback may lose control. But if you get the transformer tuning exactly right (ideally +/- 1Hz) after fitting a really nice large non saturating steel cored choke into the primary, a great many problems will have been solved, and you will then have a sweet running and efficient inverter with a good clean low distortion sine wave at the output”.



I trust this helps explain the interaction with a large toroid and the PWM.

The 6kW Torroid assembly we use with the OzInverter, all the instructions and explanations are in the book.