600/800W 220~230v AC Inverter SMPS from 12v DC

[kabiru]

you can also use minimum 3.3v it works fine

 

[sam781]

Hi Tahmid
Are you sure about it ? because it's input gates are Cmos ( as i can remember ) . and a cmos gate won't accept TTL boundaries !

Just two MOSFET is used in the attached circuit as driver of high side MOSFET.


Thanks Tahmid and Goldsmith both of you for a fruitful discussion regarding MOSFET driver.

Hi sam
At last i came back again !
Your circuit will give you that waveform as well but it has a big problem . because you shouldn't expect advantages of a differential SPWM from that ! did you understand what i told you about driving the gates for this method really ? and do you know why i have mentioned that way ? do you know what is the big advantage of a three level SPWM method ? i think No .
Best Wishes
Goldsmith

Welcome back goldsmith. Please let me know the problem and resolution. Also let me know the advantage of three level SPWM...

 

[goldsmith]

Hi again sam

Welcome back goldsmith

Thanks for that !
The main advantages of a three level SPWM are as below :
1-better efficiency
2-pretty low noise
3-pretty low THD
4- it won't need heavier filter sections .

And why these advantages are not available in your way ( your signal is like three level but in fact you shouldn't drive your mosfets with hat way ! because you will need differential action but here you won't have any differential action and of course the DC current through your filters will be higher !
you should create two SPWMs with messages out of phase together . thus the out put signal across the load before filtering will be as you want . and of course with main advantages that i have told you .
If you still can't get the point , i can write my meaning and the spectrum of SPWM in a paper and attach it here .
Best Wishes
Goldsmith

 

[sam781]

Hi again sam

Thanks for that !
The main advantages of a three level SPWM are as below :
1-better efficiency
2-pretty low noise
3-pretty low THD
4- it won't need heavier filter sections .

And why these advantages are not available in your way ( your signal is like three level but in fact you shouldn't drive your mosfets with hat way ! because you will need differential action but here you won't have any differential action and of course the DC current through your filters will be higher !
you should create two SPWMs with messages out of phase together . thus the out put signal across the load before filtering will be as you want . and of course with main advantages that i have told you .
If you still can't get the point , i can write my meaning and the spectrum of SPWM in a paper and attach it here .
Best Wishes
Goldsmith

Yes please...

 

[sam781]

Hello Goldsmith,
Please describe three level SPWM inverter. I'm waiting to know about it.

 

[sam781]

Suddenly a smps inverter (made in china) went dead. I unscrewed the box and found two parts (most probably charger & inverter). DC fuse burned but no other damage seen in the circuit. Two larger size ferrite core transformer. Ferrite core seems EI 34. But none of them has thicker wire for winding. 3/4 no. 23/24 gauge is seen here. How did it handle 500W power? Any idea or any experience?

I googled the model and found the link of that inverter
**broken link removed**
Model: KBM12-500B Inverter+charger

- - - Updated - - -

 

[goldsmith]

Hi Sam
At first sorry because of delaying . i have prepared some pages for you , but you should wait for four days , because i won't be in my home . after that i will send them to you .
Best Wishes
Goldsmith

 

[szhighstar]

if power is 500W, EI34 ca not handle so high power, it needs EE55 core, current density(J) is 3A/mm^, A=I/J , you can get section acorss area of wire(A), it maybe wounded by parallel wires.

 

[sam781]

Hi Goldsmith,
I'm waiting for that...
In this meantime I will try to make converter.


I've managed SWG 24 wire from my relative and want to use this wire without buying new one. I went to our local market and bought a ETD39 core but there is no product number. This core should handle around 450w at 50kHz in full/half bridge converter.

Transformer calculation-

Battery=12v (let, operating voltage range 11v to 13.8v)
Desired power=300w

Let, transformer efficiency= 80%
So, power at the primary side is =300+300*0.25=375w (adding 25% extra power to get desired output power)

Now,
min primary voltage, Vp=11v
So, max primary current, Ip=375/11=34Amp

Average value at the converter output has to be 325v to make 230v ac rms inverter (peak value of AC 230 rms value is 325)
Considering 90% duty cycle at lowest battery voltage, turns ratio, N = 325/(11*0.9)=32.828=33

So, transformer secondary voltage, Vs=Vpmax*N=13.8*33=455v
Secondary current, Is=Ip/N=34/33=1.03=1Amp


Wire selection for transformer winding-
Current density=4Amp/Sqmm

So, cross sectional area of -
Primary wire -> 34/4= 8.5 Sqmm. i.e, 9 SWG (10.5 Sqmm)
Secondary wire -> 1/4=0.25 Sqmm. i.e, 24 SWG (0.245 Sqmm). It matches with already available 24 gauge wire. :smile:

I want to use this wire (24 SWG) in primary winding also.
So, number of parallel wire required in primary winding= 8.5/0.245=34.69=35. Hence, 35no. 24 SWG wires are required in parallel in primary side winding.


Primary & secondary winding turn/volt calculation -
Flax density, B = 1600T
Operating frequency, f=50kHz
Ae (ETD39 core) = 125 Sqmm=1.2 Sqcm
So, turn per volt= 1e8/( 4*f*B*Ae)= 1e8/(4*50000*1600*1.25)=0.25

All the experts are requested to check the above calculation and let us know if there is any mistake here.


The above calculation is based on my learning from this thread. Thank you everyone in this forum... Special thanks to Goldsmith, rajudp and Tahmid for their extensive support till now

 

[sam781]

Calculation of skin depth for proper wire selection
Frequency, f=50kHz
As per rajudp's easy formula, skin depth=6.6/sqrt(f) cm=6.6/sqrt(50e3)=0.0295 cm=0.295mm
So, maximum allowable wire diameter is 2*0.295mm=0.59mm

In my case, 24 SWG wire's diameter is 0.559mm. So this wire is okay for 50kHz. :smile:

- - - Updated - - -

Hi rajudp,
As per the formula given in wikipedia, skin depth (copper)=6.52/sqrt(f) cm
No issue as there is a very minor change

- - - Updated - - -

Another thing that just come into my mind is ERS. As I've assumed efficiency of the transformer 80% do I need to consider ERS calculation here?

 

[sam781]

Ferrite Core (ETD39) power handling capability calculation

J=400A/Sqcm
F=50KHz
Ac=1.23Sqcm
Aw=1.77Sqcm

P=0.707*J*F*Ac*Aw*B*1e-8
=0.707*400*50e3*1.25*1.77*1600*1e-8
=492.55w

I'm designing transformer using this core for 300W only. So, no issue...

 

[picgak]

Hi sam,
you can double the capacity using two similar transformers with the output voltage half the requirement and making the rectified filtered DC in series.This will halve the primary current, this method is good when making higher capacity smps.
Regards ani

 

[sam781]

I took 35 pieces of 30cm 24SWG wire and bind with Teflon Tape to make a lit'z wire. While started for primary winding on ETD39 bobbin I observed that it had become vary hard to solder 35 no. of wires into the bobbin pins. How such thing is handled in practical transformer?

Another thing is the cross sectional area of the bobbin pins. I guess, cross sectional area of the bobbin pin will not be more than a 20-22 gauge of wire. How this pin will handle such large amount of current?

This is for a 300VA transformer using ETD39 core. But, as per my calculation ETD39 can handle around 500VA load. Cannot imagine what will be there in primary winding if it designed for 500VA. In this case, Ip=625/11=56.82. 24SWG wire needed = 58 no.

Could anybody please help me providing some practical examples how usually these things are taken care of?

 

[goldsmith]

Hi Sam
I Came back again !
Sorry because of this long delaying !
See below please and then if you have any question ask me again :


Best Wishes
Goldsmith

 

[rajudp]

I took 35 pieces of 30cm 24SWG wire and bind with Teflon Tape to make a lit'z wire. While started for primary winding on ETD39 bobbin I observed that it had become vary hard to solder 35 no. of wires into the bobbin pins. How such thing is handled in practical transformer?

Another thing is the cross sectional area of the bobbin pins. I guess, cross sectional area of the bobbin pin will not be more than a 20-22 gauge of wire. How this pin will handle such large amount of current?

This is for a 300VA transformer using ETD39 core. But, as per my calculation ETD39 can handle around 500VA load. Cannot imagine what will be there in primary winding if it designed for 500VA. In this case, Ip=625/11=56.82. 24SWG wire needed = 58 no.

Could anybody please help me providing some practical examples how usually these things are taken care of?

you can use copper foil in place of copper wire , and as per design you can go upto 10A/Sqmm if the total length of wire is below 100cm

it is very difficult to solder many wires ( removing the insulation from coils ) there is one chemical for removing enamel from copper wire just dip the part to the chemical and wipe with a cloth then you can directly solder to wire

 

[szhighstar]

ETD39 can not handle with 500W if frequency is 100K, only handle with 300W.

 

[rajudp]

depends on core materiel

 

[Antorbd04]

Post sch and hex.

 

[sam781]

Hi Goldsmith,

Thanks a lot for giving me such helpful tutorial. I was busy and could not concentrate this task for some personal reason.
In this model noises and harmonics become zero in the output. So, theoretically there should not need to use filter. I'm right? Hope I'll be able to generate such signal using MCU. :smile: Now, I'm trying to make transformer. I'm in a big trouble to make primary winding using 35 no of 24SWG wire. It is too hard to solder such huge number of wire with the bobbin pins.

you can use copper foil in place of copper wire , and as per design you can go upto 10A/Sqmm if the total length of wire is below 100cm

Copper foil is not available here. Can I really use 10A/Sqmm in primary? Primary wire length is around 25cm. While making primary winding I thought this value current density (4A/Sqmm) is not used in practical implementation. If 10A/Sqmm is safe below 100cm length, I will use 14 wires (24swg) instead of 35. Could you please confirm whether this value (10A/Sqmm below 100cm) is used in transforms of our home appliances (SMPS, Inverter etc.)?

ETD39 can not handle with 500W if frequency is 100K, only handle with 300W.

As per the below calculation a ETD39 core having max flux density 1600 can handle 492w at 50kHz.

Ferrite Core (ETD39) power handling capability calculation

J=400A/Sqcm
F=50KHz
Ac=1.23Sqcm
Aw=1.77Sqcm

P=0.707*J*F*Ac*Aw*B*1e-8
=0.707*400*50e3*1.25*1.77*1600*1e-8
=492.55w

Could you please let's know why you are thinking it can only handle 300w? As per the chart (https://www.edaboard.com/threads/229615/#post1100003 )shared by Goldsmith, ETD39 can handle 467w at 48kHz.

 

[goldsmith]

Hi Goldsmith,

Thanks a lot for giving me such helpful tutorial. I was busy and could not concentrate this task for some personal reason.
In this model noises and harmonics become zero in the output. So, theoretically there should not need to use filter. I'm right? Hope I'll be able to generate such signal using MCU. Now, I'm trying to make transformer. I'm in a big trouble to make primary winding using 35 no of 24SWG wire. It is too hard to solder such huge number of wire with the bobbin pins.

Hi Sam
About filter , yes you are quite right , but in practice you'd better to add those filters ! to remove all of the unwanted signals as well to yield a pure sine wave .
And regarding your winding ! who told that you should solder your wires to that pin ? i have another solution ! when i have the same problem , i will remove that pin ! and then i will solder it directly ! it is up to you !
Good luck
Goldsmith