So I'm winding a transformer

[skeer]

A number of months back I posted in here about building a PSU using a battery charger transformer. Rest assured I did not do it but instead repaired the charger and have been using it

However a transformer I did pick up back then I am tinkering with.. came from a long dead car charger as well so it's decently hefty. Anyway after falling down a rabbit hole one night of transforming electricity I decided I'd try to rewind it. I still would like to see 120 in/35 out if I can. So using this guys plan and math here's what I came up with:

The surface area for the primary and secondary windings 18.920 cm2. Divide 42 by 18.920 = 2.2 turns per volt. So for 120 volts it'd be 54.55 turns at roughly 119.9 volts. For the secondary output to be the targeted 35-ish volts the secondary would have 9 windings.

So I kinda assume this is possible, but further readings explain how too few windings reduces efficiency and basically cause the secondary to be less graduated/stable?

 

[MBfreak]

I believe you need to determine the area of the core in order to design a transformer.
Here is a start:
The iron core area is determined based on lamination maximum allowed B. It can be calculated like this:

E*√2 = 2π*f*A*B*n

f – frequency ( 60 Hz i guess)

A – core area in square meters

B – maximum flux density ( for pwr xf lamination B is below 1,15)

n– number of secondary turns.

Best regards

Ola

 

[dogdog]

This is an interesting video I saw long ago.. although its for toroidal transformers, pretty sure there are some common formulas shared between E/I cored and toroidal cored... still you learn something about it. The guy constructed it from scratch.

 

[dogdog]

his whole series. covers E/I core also

 

[Bert_]

What are you starting with? It sounds like you are planning to rewind the primary also?

The couple times I've done my own winding on a transformer I started with a transformer that already had a good primary winding in the voltage I want. That keeps the math and engineering to a minimum. Wind a couple turns on the secondary measure the voltage and calculate how many turns are necessary for your desired voltage.

The link I think mentions microwave transformers which can be a poor choice for other things since they run too far into saturation. You would need to add primary windings to keep it from overheating.

 

[nadogail]

What are you starting with? It sounds like you are planning to rewind the primary also?

The couple times I've done my own winding on a transformer I started with a transformer that already had a good primary winding in the voltage I want. That keeps the math and engineering to a minimum. Wind a couple turns on the secondary measure the voltage and calculate how many turns are necessary for your desired voltage.

The link I think mentions microwave transformers which can be a poor choice for other things since they run too far into saturation. You would need to add primary windings to keep it from overheating.

The information I read about 60 years ago suggested using 10 turns as your experimental secondary.

That would make your turns ratio calculations easier.

 

[skeer]

Yeah suffice it to say I did unwind both primary and secondary. Primary was originally center tapped so the unwinding process broke the wire at the tapped point. I mean.. I could still likely solder it and wind it entirely back to how to was, maybe.

So if Im understanding correctly, if you maintain the correct ratio then you can get the desired voltage. However if you use too few turns in each side you can generate too much heat, right?

 

[MBfreak]

You need to calculate the flux density in order to determine the number of turns in the primary winding.
With a specific core area you must have enough turns so that the flux density ( B) is below 1,15 for normal lamination in the core.
If flux density is higher than that, the iron losses and copper losses will increase drastically.
For real large transformers the losses can increase 10fold from B(Tesla) 1,05 to 1,09.
Put the formula above in xcel .

For those of us who went to school in the 50/60s we make a estimate between the ears.

Studying for my MSc I managed to pass several exams by just doing the calcs in my head and writing down the equation and result.
And that was possible only since my older brother, who is very educated in math and physics, terrorized me for 5 years! THANKS


Ola

Ola