Need advice for my toroidal core dimensions

D.A.(Tony)Stewart said:

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

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Warpspeed said:

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.

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Warpspeed said:

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.

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Warpspeed said:

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.

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Warpspeed said:

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.

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Warpspeed said:

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.

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Warpspeed said:

That sounds really odd ??

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Warpspeed said:

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.

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Warpspeed said:

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.

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Warpspeed said:

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.

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Warpspeed said:

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 !!

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treemon said:

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.

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Brian Gladstone said:

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.

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Brian Gladstone said:

I'm not sure what CRGO means

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