H-Bridge transformer design help

[FlapJack]

It is not reverse logic. With low input voltage the controller has to raise the duty cycle to compensate. With high input voltage the controller cuts the duty cycle back.

 

[zsolt1]

Probably iterative calculations will get you to the optimum constructive parameters for some given tolerance you are wiling to accept . I don't know much about all phenomenons considered at high frequency transformers, when i was designing transformers for power stations (6...800kVA) i used to do the same electrical and mechanical calculations over and over in order to meet economical and safety requirements , of course by computer is much easier than on paper (not to mention fancy programs available today even online & for free )

 

[usama14]

It is not reverse logic. With low input voltage the controller has to raise the duty cycle to compensate. With high input voltage the controller cuts the duty cycle back.

Hmm...I might require help in the next stage of feedback though. But I must do the winding and test the results first.
Last question related to the winding though. Which gauge wire should I use for the winding of secondary and the primary? I want a 1000W transformer to be precise.

 

[zsolt1]

normal current density for cooper is 4...6 A /mm^2, but considering pelicular(/skin) effect at high frequencies you have to increase cross section by some xy % (actually there is a formula to calculate the skin effect depth for given frequency , and actually an online calculator also :thinker: )

(and probably after you check the maximum admissible current for the wire gauge you choose , you go back to see if you still have the inductance you need for the coil :lol: )

 

[usama14]

normal current density for cooper is 4...6 A /mm^2, but considering pelicular(/skin) effect at high frequencies you have to increase cross section by some xy % (actually there is a formula to calculate the skin effect depth for given frequency , and actually an online calculator also :thinker: )

(and probably after you check the maximum admissible current for the wire gauge you choose , you go back to see if you still have the inductance you need for the coil :lol: )

You mean to use several wires of lower dia in parallel?

 

[FlapJack]

usama14, do you have a drawing of the bobbin you bought. Or a dial caliper to measure the winding area.

 

[usama14]

usama14, do you have a drawing of the bobbin you bought. Or a dial caliper to measure the winding area.

Yes. I bought the ferroxcube's etd59 Bobbin. Here is it's datasheet's image.

 

[zsolt1]

good idea , since you need a few turns there will be no problem .High frequency transformers are very cost effective .

 

[FlapJack]

etd59
winding width ferroxcube = 41.2mm = 1.6220" - .236" total margin 1/2 on each side (3mm each side) = 1.386" winding width (35.2mm).

Primary, as Warpspeed said use copper foil. .008" is the proper thickness cut it at 35mm width and use 4 turns centered on bobbin.

Secondary, I think you should use 2 secondary winding's of 36 turns each. This will let you use a 2 diode center tapped output. For the wire you will have to make a poor mans litz wire, 25 strands of 35awg double insulated magnet wire, twisted approximately 1/2 turn per CM. You should have just enough room for 36 turns centered on the bobbin to fill the 35mm area.

1, Wind on bobbin 1st 36 turn secondary.
2, Add 3 layers of tape as wide as the bobbin is.
3, Add 4 turn primary winding.
4, Add 3 layers of tape as wide as the bobbin is.
5, Add 2nd 36 turn secondary.
6, Add 2 layers minimum of tape, as wide as the bobbin is.

There are such things as screens and Faraday shields that can go between the primary and secondary but most people do not use them.

I am not sure of a good way to get the connection out for the copper foil. Maybe someone else has a good idea.

Lets see if others have any better ideas or corrections and go from there.

 

[usama14]

etd59
winding width ferroxcube = 41.2mm = 1.6220" - .236" total margin 1/2 on each side (3mm each side) = 1.386" winding width (35.2mm).

Primary, as Warpspeed said use copper foil. .008" is the proper thickness cut it at 35mm width and use 4 turns centered on bobbin.

Secondary, I think you should use 2 secondary winding's of 36 turns each. This will let you use a 2 diode center tapped output. For the wire you will have to make a poor mans litz wire, 25 strands of 35awg double insulated magnet wire, twisted approximately 1/2 turn per CM. You should have just enough room for 36 turns centered on the bobbin to fill the 35mm area.

1, Wind on bobbin 1st 36 turn secondary.
2, Add 3 layers of tape as wide as the bobbin is.
3, Add 4 turn primary winding.
4, Add 3 layers of tape as wide as the bobbin is.
5, Add 2nd 36 turn secondary.
6, Add 2 layers minimum of tape, as wide as the bobbin is.

There are such things as screens and Faraday shields that can go between the primary and secondary but most people do not use them.

I am not sure of a good way to get the connection out for the copper foil. Maybe someone else has a good idea.

Lets see if others have any better ideas or corrections and go from there.

I cant understand the guage you explained. Can you kindly explain it in a much simpler language with the guage being in as SWG. I mean kindly inform me the guage wire number and whether to use multiple smaller guages in parallel for the skin effect.

 

[FlapJack]

For the secondary you need 25 wires in parallel. Each wire should be 35 awg in size with double insulation. Here is an awg chart for diameter.

- - - Updated - - -

Here is a comparison chart of awg and swg, the chart shows bare wire diameter.

**broken link removed**

35 awg bare = .0056" diameter.
Closest swg without going to big is .0052" diameter.

https://www.engineeringtoolbox.com/swg-standard-wire-gauge-d_1779.html

.0052" = .132mm = 39 swg

 

[FlapJack]

Ebay has some copper foil that will work.

.008" foil = .2mm

Search Ebay for this.

Pure Copper Cu Metal Sheet Foil 0.2 x 100 x 1000 mm
Pure Copper Cu Metal Sheet Foil 0.2 x 100 x 500 mm

You need 289mm minimum length, to go around 4 turns.

 

[zsolt1]

Don't worry about wire gauges , just put there the thickest wire you can get from the neighbors fence :grin: (kidding, leave the fence alone) just to be shore , you probably have enough space between core columns , plus you don't need extra isolation between layers (you are not building a 220/110 kV transformer )

 

[usama14]

Ebay has some copper foil that will work.

.008" foil = .2mm

Search Ebay for this.

Pure Copper Cu Metal Sheet Foil 0.2 x 100 x 1000 mm
Pure Copper Cu Metal Sheet Foil 0.2 x 100 x 500 mm

You need 289mm minimum length, to go around 4 turns.

Hmmm...I have one question though. I have to wind the transformer tomorrow and I wont be able to get the wire from the EBAY in such a short time. So....According to my calculations, my swg for the primary comes to be 12 SWG and for the secondary comes to be 20SWG. I have attached my excel calculations. Kindly tell me whether I can use 3 parallel wires of lower gauge (19 or 20 or 21) for the primary and smaller gauge(26 or 27 or 28) with 2 parallel wires for the secondary? Will that work without sufficient error?
Also, the winding scheme you proposed before, like
1) 16 turns for the secondary
2) then 4 turns for the primary on top of it
3) then finally 16 remaining turns for the secondary on the top.
Can I use this instead of 36+36=72 turns for the secondary you proposed? :roll:

- - - Updated - - -

Don't worry about wire gauges , just put there the thickest wire you can get from the neighbors fence :grin: (kidding, leave the fence alone) just to be shore , you probably have enough space between core columns , plus you don't need extra isolation between layers (you are not building a 220/110 kV transformer )

Hahaha...you mean it wont matter much regarding the current handling capability? I mean skin effect and the other things?

 

[BradtheRad]

Links to charts of wire gauges showing safe amp-carrying capacity:

http://amasci.com/tesla/wire1.html



http://www.powerstream.com/Wire_Size.htm

Here's a link to another wire gauge table. Its ampacity values are much different than the other tables.

**broken link removed**

Possible reason for the disparity: One source may base ampacity on a higher temperature which makes the wire get too hot to hold, while the other source may use a lower temperature where copper's electrical characteristics start to change even though it is only warm.


--------------

 

[zsolt1]

no , those phenomenon are present . But if you figured out that you need 5.2mm^2 cross section , and you find wire with 6mm^2 or 8mm^2 , and the amount of wire fits in , what is the problem ? you only have some reserve for further development ;-)
Oversize a little is not bad , like +15% of more power reserve of the nominal needed . (for example i saw construction engineers oversize holding columns by twice the needed section just to be shore )

 

[E-design]

I ran your requirement through one of our transformer optimization programs. The results are attached below.

The program actually suggested a smaller core ETD49, but I locked in your choice. It used 3C85 material out of its database, which is very similar to 3C90, so the results should be very close.

Let me know if you want me to alter any input parameter.

 

[FlapJack]

E-Design, i see some problems here. Each secondary has to be 330v for a full bridge center tap to work.

I am having trouble reading the specs, for instance the foil layer looks like it is saying an equivalent of 10awg but i see no foil thickness or width spec that made any sense.

From the program, Wire Height (cm) = 12.70m, what could that possibly mean?

The width seems wrong to me also, Wire Width (cm): 4.297, here i assume that the total width of the bobbin is 4.297mm, but this leaves no margin.

Also, for the secondary's, what is the difference between turns and turns per layer? One says 16 and the other is 18.

- - - Updated - - -

E-Design, one more thing, we were using 39vdc for V in low on primary.

 

[usama14]

E-Design, i see some problems here. Each secondary has to be 330v for a full bridge center tap to work.

I am having trouble reading the specs, for instance the foil layer looks like it is saying an equivalent of 10awg but i see no foil thickness or width spec that made any sense.

From the program, Wire Height (cm) = 12.70m, what could that possibly mean?

The width seems wrong to me also, Wire Width (cm): 4.297, here i assume that the total width of the bobbin is 4.297mm, but this leaves no margin.

Also, for the secondary's, what is the difference between turns and turns per layer? One says 16 and the other is 18.

- - - Updated - - -

E-Design, one more thing, we were using 39vdc for V in low on primary.

How can we get 330V at each secondary? I mean if the turns ratio for each secondary is like 4/18=0.223. Then at Vp=48V we get 216V. Isnt it?

 

[E-design]

I did this in a hurry before leaving the lab, so I have not gone through all the results carefully. I only assumed one split HV winding, but it would be easy to change. I will look through the results and comment some time tomorrow.

The wire height, is the height of the box formed by looking at the total height of a bare copper conductor, including insulation in cm. So the height will be 1. 27mm

Turns per layer suggest the maximum number of turns per layer for the wire size. So you could fit 18 turns. Because it is only 16 turns it reports that you filled only 16/18 of the layer, thus 0.8889

About the margins: I may have forgotten to click the auto margin option. I will verify it tomorrow as well.