Need advice for my toroidal core dimensions

[treemon]

I am in need to build a 5kw inverter based on EGS002, for which I am first building a toroidal transformer, I got the toroidal core manufactured & delivered from a vendor.

Having no prior experience in doing this, I just used an android app called TransCalc to calculate core dimensions (and winding data), now I feel like core is bit awkward shape more like a ring.

My core dimensions are (mm)
OD=220
ID=150
Height=100

Weight 16kg
Material CRGO

I feel I had given too big ID, but I had to do because app told me to do so, large ID so large window area, which made core to transformer more power. According to calculation this can transfer almost 5kw..

Now I am little in dilemma whether to go ahead with this core, further put effort and also money on copper wires, already plenty of money is spent on core.

My main concern is, this look somewhat different from cores that companies are using in their inverter, should the core have a particular "form" for better efficiency, I mean the ratio of ID/OD/H must stick to some guideline?

I need suggestion from eda members, guide me whether if this core design is horribly wrong in that case I will not go ahead with this core, or if the core sizing s fine...please tell me.

 

[treemon]

TL;DR all comments
You need an LCR meter to test what you have with N^2 minimal turns for L and C from inner to outer insulated laminations. Use wire gauge you intend to use or bigger for low DCR for these tests.

Learn about hysteresis and eddy current losses and borrow a scope then learn how to test BH curve.
CRGOS are rated in losses W/kg generally less with thinner.
Then report results
Also a larger ID increases L and leaves room for windings.

It is important to measure what you have before spending a lot more and you need measurement equipment to do this right. Check the used market on Banggood.

FWIW: https://www.iqsdirectory.com/articles/electric-transformer/toroidal-transformer.html

I have completed secondary (220v) and fiddle with secondary turns. My egs test rig is ready, idle power losses are low like 7watt @48vdc

As we have done basic test by warpspeed procedure and it is consistent, unfortunately I cannot go in great deepth in this immediately, because this is not my full time work... Also this is only one time endeavor.... Maybe in 2-3 years i will figure out what you have said.

I am not sure if with more load it will vary big, but 7watt is really low.

I have blown one egs002 module and currently doing a pcb etching first time, lot of pain... It seems like once mosfet is shorted it always take down spwm driver along with it.

Maybe warspeed can come online and guide me further

 

[Warpspeed]

Good to see you back !

Seven watts is very low, and an EXCELLENT result, well done !

The rest of the driver electronics will also consume some continuous dc power, a few watts perhaps, but it should all end up having around twenty watts or less of idling power which is right up there with the very best !

The next step is to determine the required primary turns, and that will depend on the lowest design battery voltage. The consensus seems to be that a turns ratio of 8:1 is about right for a 48v inverter running from lead acid batteries.

So 230v secondary, 8:1 turns ratio, design primary voltage 28.75v rms. Peak primary voltage 40.65v.

Now you would not normally flog a battery down to a discharge voltage that low, but the above assumptions assume a "perfect" inverter with no ohmic resistance anywhere. And there may be the occasional surge load that exceeds the design continuous power level.

Its all a judgement call, but over many years of people building similar inverters, an 8:1 design turns ratio has been judged to be a good compromise to aim for.

So the next step is probably to measure the diameter of the remaining hole in the toroid, and estimate the maximum wire diameter that will fit the available space. Here is a handy on line calculator to assist with that :

Oops, the Forum software will not allow me to post a direct link, but do a search for: "smaller-circles-within-larger-circles-calculator"

The above calculator assumes hard unyeilding circles, but our fat plastic insulated wire can be crushed slightly where it touches, so the theoretical number of turns will always be able to fit in practice.

--- Updated Jun 12, 2023 ---

I almost forgot...

This heavy cable is always expensive.
So what you can do is source some rope of a similar size, and wind on the appropriate number of turns.
Then you will know for sure the exact required length.

 

[treemon]

Good to see you back !

Seven watts is very low, and an EXCELLENT result, well done !

The rest of the driver electronics will also consume some continuous dc power, a few watts perhaps, but it should all end up having around twenty watts or less of idling power which is right up there with the very best !

The next step is to determine the required primary turns, and that will depend on the lowest design battery voltage. The consensus seems to be that a turns ratio of 8:1 is about right for a 48v inverter running from lead acid batteries.

So 230v secondary, 8:1 turns ratio, design primary voltage 28.75v rms. Peak primary voltage 40.65v.

Now you would not normally flog a battery down to a discharge voltage that low, but the above assumptions assume a "perfect" inverter with no ohmic resistance anywhere. And there may be the occasional surge load that exceeds the design continuous power level.

Its all a judgement call, but over many years of people building similar inverters, an 8:1 design turns ratio has been judged to be a good compromise to aim for.

So the next step is probably to measure the diameter of the remaining hole in the toroid, and estimate the maximum wire diameter that will fit the available space. Here is a handy on line calculator to assist with that :

Oops, the Forum software will not allow me to post a direct link, but do a search for: "smaller-circles-within-larger-circles-calculator"

The above calculator assumes hard unyeilding circles, but our fat plastic insulated wire can be crushed slightly where it touches, so the theoretical number of turns will always be able to fit in practice.

--- Updated Jun 12, 2023 ---

I almost forgot...

This heavy cable is always expensive.
So what you can do is source some rope of a similar size, and wind on the appropriate number of turns.
Then you will know for sure the exact required length.

Thank you warpspeed for coming,

Need to mention that secondary winding stage was a herculean task, my fingers have not yet recovered after almost a month.

Nice clarification about turn ratio, I too reached roughly 1/8 when voltage was dropping on load, so I kept reducing turns, for this reason I was not finalising primary turns and wire was a mess all over.

So now I guess, can I wound a thick wire and get over with it, using 1/8 turn ratio.

Still there is plenty of room in core hole, are you saying that wire must be of largest dia possible, probably voltage drop was seen because of that 1mm test wire I wounded.... Later I will show you exact current and voltage readings.

I have to ask what type of wire I can use for primary windings? Regular household wire will melt, and probability its insulation material can block magnetic induction...I dont know!!

So far upto 80 watt of load can be run without any problem, After I connected a 250 watt AC motor, mosfet bursted and egs module's eg8010 chip was fried... I had ordered new.

For this reason, I began powering my inverter setup using a cc/cv boost converter but it had its own problem.

 

[Warpspeed]

Now that the primary turns have been pretty well established, its useful to know the largest diameter wire that will fit.
Optimum design for the primary is to have the same current density as for the secondary, again about four amps per mm square is suggested.
If the available space allows, you can go up to the next standard available cable size. And adding one extra turn may be prudent. You can always remove that turn later on after some final testing at high power.

The ideal wire might be something like welding cable or low voltage automotive/marine battery cable.
This will have several hundred very fine copper hair like strands, and be relatively flexible.

That too will require some serious muscle power to wind.
But it will be a walk in the park, and a short job, compared to winding the secondary.

 

[treemon]

Now that the primary turns have been pretty well established, its useful to know the largest diameter wire that will fit.
Optimum design for the primary is to have the same current density as for the secondary, again about four amps per mm square is suggested.
If the available space allows, you can go up to the next standard available cable size. And adding one extra turn may be prudent. You can always remove that turn later on after some final testing at high power.

The ideal wire might be something like welding cable or low voltage automotive/marine battery cable.
This will have several hundred very fine copper hair like strands, and be relatively flexible.

That too will require some serious muscle power to wind.
But it will be a walk in the park, and a short job, compared to winding the secondary.

Thanks for suggesting on welding cable, I can order from amazon, I also have solar wires but they are not that flexible it seems!!!

 

[treemon]

Now that the primary turns have been pretty well established, its useful to know the largest diameter wire that will fit.
Optimum design for the primary is to have the same current density as for the secondary, again about four amps per mm square is suggested.
If the available space allows, you can go up to the next standard available cable size. And adding one extra turn may be prudent. You can always remove that turn later on after some final testing at high power.

The ideal wire might be something like welding cable or low voltage automotive/marine battery cable.
This will have several hundred very fine copper hair like strands, and be relatively flexible.

That too will require some serious muscle power to wind.
But it will be a walk in the park, and a short job, compared to winding the secondary.

Hi warpspeed,

Actually now I understand what you mean by largest dia - it means inner circumference of toroid / number of turns = dia of wire to be used (including insulation)

Welding wire available in market have very thick insulation and inside copper is not that fat, the only benefit could be those wire are very flexible.

I have a solar wire of sufficient length and dia, I am thinking to try it. It will save money.

I also forgot to mention that I ended up only 269 turns in secondary( not ~300 as planned earlier) and I have used 2 strand, things were too difficult to manage.

Now should I still stick with that 1/8 ratio rule? 269/8 will be just 33 turns and current draw will be high.

--- Updated Jun 17, 2023 ---

Btw, these welding cables have huge strand count, so thats an advantage.

 

[Warpspeed]

Turns ratio stays the same, so 34 primary turns should be about right.
That circles within circles calculator will tell you the largest diameter cable that you can use and still fit 34 turns through the remaining hole.

Welding wire would be good because it has high temperature insulation, its made to be safely draped over hot metal, but as you say, it often has two layers of very thick insulation. Its sometimes possible to split and remove an outer most layer, leaving just an inner layer. Knowing the largest diameter possible that will fit through the hole should help you decide.

Two strands of 1.8mm diameter in the secondary will be capable of 20 continuous amps. That will run quite warm, but not dangerously hot.
The primary will see 8 x 20 amps, and at a current density of 4 amps per mm squared, suggests 40mm squared primary cable, or the next available commercial size up, if it will fit.

I recommend first mocking it up with suitably sized rope or rubber/plastic tubing to find out the required length.
Its otherwise a very difficult thing to estimate required length. That will also give some practice using light weight material which will be much easier to work with than the very heavy cable.

 

[treemon]

Turns ratio stays the same, so 34 primary turns should be about right.
That circles within circles calculator will tell you the largest diameter cable that you can use and still fit 34 turns through the remaining hole.

Welding wire would be good because it has high temperature insulation, its made to be safely draped over hot metal, but as you say, it often has two layers of very thick insulation. Its sometimes possible to split and remove an outer most layer, leaving just an inner layer. Knowing the largest diameter possible that will fit through the hole should help you decide.

Two strands of 1.8mm diameter in the secondary will be capable of 20 continuous amps. That will run quite warm, but not dangerously hot.
The primary will see 8 x 20 amps, and at a current density of 4 amps per mm squared, suggests 40mm squared primary cable, or the next available commercial size up, if it will fit.

I recommend first mocking it up with suitably sized rope or rubber/plastic tubing to find out the required length.
Its otherwise a very difficult thing to estimate required length. That will also give some practice using light weight material which will be much easier to work with than the very heavy cable.

Okay,

I tried that circles calculator, its very good, without this one cannot do just by perimeter forumlae. Wire dia to use is coming about 9mm.

Next I will look into finalizing and sourcing right wire ( and budgeting)

 

[Warpspeed]

Its well worth spending some time to source the ideal wire, and determining the exact length required.
You will then have a very efficient transformer capable of some serious power.

The design of an inverter transformer is rather different to the design of an ordinary power transformer.
Even with crappy steel, your transformer would have had a low magnetizing current. The toroids you bought have turned out to be of excellent material, so the idling power has ended up being astonishingly low by any standard !

Its been a lot of very hard, physically demanding work, but I am sure the final result will bring a smile to your face.

 

[treemon]

Its well worth spending some time to source the ideal wire, and determining the exact length required.
You will then have a very efficient transformer capable of some serious power.

The design of an inverter transformer is rather different to the design of an ordinary power transformer.
Even with crappy steel, your transformer would have had a low magnetizing current. The toroids you bought have turned out to be of excellent material, so the idling power has ended up being astonishingly low by any standard !

Its been a lot of very hard, physically demanding work, but I am sure the final result will bring a smile to your face.

Thanks, without your guidance it wasnt feasible...

I will keep the transformer outside pcb housing in open air...

Btw in a different note, I have frequently experienced, whenever I indulge in deep electronics craft work, I lose some weight and I my forearms become lean, this happens with regular work also where no muscle power is needed... Then it rakes months to recover.

I know this is outside logicality of the way we understand world and forum topic do not cover, but it happens in just 30 min... Have you experienced anything like this?

 

[Warpspeed]

That sounds really odd ??

 

[treemon]

That sounds really odd ??

Yes, but its a reality for me...

 

[treemon]

Its well worth spending some time to source the ideal wire, and determining the exact length required.
You will then have a very efficient transformer capable of some serious power.

The design of an inverter transformer is rather different to the design of an ordinary power transformer.
Even with crappy steel, your transformer would have had a low magnetizing current. The toroids you bought have turned out to be of excellent material, so the idling power has ended up being astonishingly low by any standard !

Its been a lot of very hard, physically demanding work, but I am sure the final result will bring a smile to your face.

Hi warpspeed,

I have completed primary windings, although wire gauge is not that big 16sqmm ( but with a huge strand count), no welding wire from local market were flexible.

I tested several times (using different meters), and the idle power consumption with egs002 installled, is coming about just 9w, very happy yet somewhat difficult to believe, but I think thick wires did the magic...

From here on there will be long & tiring learning curve, and circuit design -> testing -> redesign loop will start...

I am also designing a grid powered battery charger for current sharing and to charge the battery during night.

I may post a different thread if I face any difficulty, or if you have any tips then you are most welcome to share here.

-- See you again --

 

[Warpspeed]

Later on, if the primary starts to get a bit hot under maximum load, there appears to be plenty of space remaining to add a second primary winding to run in parallel with what you now have.

Anyhow, the original purpose of this thread was winding a suitable toroidal transformer, and you have now successfully achieved that.

One thing you might consider is fitting your new toroid to an existing inverter that might have poor performance due to excessive idling current. If you can find a suitable victim inverter, either working or not working that might save a lot of work.

 

[treemon]

Later on, if the primary starts to get a bit hot under maximum load, there appears to be plenty of space remaining to add a second primary winding to run in parallel with what you now have.

Superb... I expect that maximum load it will encounter is going to be like 2500w

One thing you might consider is fitting your new toroid to an existing inverter that might have poor performance due to excessive idling current. If you can find a suitable victim inverter, either working or not working that might save a lot of work.

Yes i was thinking about this, I have a working inverter but its 12v based and i guess many things need to be changed, can create big mess.

I know pcb design is a hard work for newbie like me and bizzare things will happen which in theory do not exist, but it seems i have few options....

I have very good casing, heatsink, fans and various other items from failed chinese inverter where all the new stuff can go...

 

[Warpspeed]

What you have now should run stone cold at 2,500 watts continuous, and easily handle short term surges of multiples of that.
Certainly plenty more to do, but it should be a lot less physically demanding !!

 

[treemon]

What you have now should run stone cold at 2,500 watts continuous, and easily handle short term surges of multiples of that.
Certainly plenty more to do, but it should be a lot less physically demanding !!

That sounds great..

 

[Brian Gladstone]

I am in need to build a 5kw inverter based on EGS002, for which I am first building a toroidal transformer, I got the toroidal core manufactured & delivered from a vendor.

Having no prior experience in doing this, I just used an android app called TransCalc to calculate core dimensions (and winding data), now I feel like core is bit awkward shape more like a ring.

My core dimensions are (mm)
OD=220
ID=150
Height=100

Weight 16kg
Material CRGO

I feel I had given too big ID, but I had to do because app told me to do so, large ID so large window area, which made core to transformer more power. According to calculation this can transfer almost 5kw..

Now I am little in dilemma whether to go ahead with this core, further put effort and also money on copper wires, already plenty of money is spent on core.

My main concern is, this look somewhat different from cores that companies are using in their inverter, should the core have a particular "form" for better efficiency, I mean the ratio of ID/OD/H must stick to some guideline?

I need suggestion from eda members, guide me whether if this core design is horribly wrong in that case I will not go ahead with this core, or if the core sizing s fine...please tell me.

Core sized is basically determined by the amount of power being delivered to the load, input wave form, and the frequency of the input. I'm not sure what CRGO means - is that equivalent to GOSS? - grain oriented silicon steel? What is the power output required? What is the input wave & frequency? Also, in the lack of other information, I would think that 220 x 150 x 100 core dimensions greatly look out of proportion.

 

[treemon]

Core sized is basically determined by the amount of power being delivered to the load, input wave form, and the frequency of the input. I'm not sure what CRGO means - is that equivalent to GOSS? - grain oriented silicon steel? What is the power output required? What is the input wave & frequency? Also, in the lack of other information, I would think that 220 x 150 x 100 core dimensions greatly look out of proportion.

CGRO would mean - Cold rolled grain oriented steel. I have completed my transformer work, everything looks good, but this transformer is so bulky that it distorted sinewave form to unacceptable levels, maybe its a gate driver or some other glitch.. I have no idea

For time beings its doing rest in my storage area..

 

[KlausST]

I'm not sure what CRGO means

What about in internet search "CRGO transformer"?

Klaus