Winding a transformer (picture included) - Questions

[FusionITR]

Ok I have two E cores and a bobbin, put together like this:

**broken link removed**

What do I use to hold the two E cores together? Just use superglue each of the ends of the E cores or something? A special kind of tape?

Where do I put the primary and secondary windings? I assume in the middle of each end of the core where the empty space is. Do I just wrap them around the core only? Not going around the plastic part?

Thanks.

 

[Russlk]

It is common practice to put the primary first and the secondary on top, I don't know why, it should not make a difference, performance wise. I use a nylon tie to hold the two cores together. If you are mounting it on a PC board, you can drill holes in the board and mount it at the same time. Some tape between primary and secondary is a good idea, for isolation.

 

[kchriste]

Do I just wrap them around the core only? Not going around the plastic part?

You wrap them on the bobbin. Then you assemble the e-cores onto the bobbin. You can only wrap so much wire until the e-cores won't fit, so choose your wire gauge wisely, ie: big enough to carry the required current but small enough so it will fit the bobbin. Current rating over-rides all. If it won't fit, you'll need a bigger core.

 

[FusionITR]

You wrap them on the bobbin. Then you assemble the e-cores onto the bobbin. You can only wrap so much wire until the e-cores won't fit, so choose your wire gauge wisely, ie: big enough to carry the required current but small enough so it will fit the bobbin. Current rating over-rides all. If it won't fit, you'll need a bigger core.

So something like this? Then put tape insulation over this winding and put the secondary windings on top of the tape insulation?

**broken link removed**

Also, is this the proper way to end the last turn and solder the wires to the bobbin?

**broken link removed**

 

[john1]

Not really.
Take it out to a tag at the other end.
Crossing over like that is not a good idea.

Could you post much more details of the
transformer you wish to make please.

John

 

[john1]

such as,

the sort of power you expect it to handle,
the sort of currents you expect it to handle,
the voltages in and out that you want,
maybe the ratios you are looking for,
the sizes of the pieces you have,
anything like that which may be relevant.

John

 

[kchriste]

Then put tape insulation over this winding and put the secondary windings on top of the tape insulation?

Yes. I know your pic is just an example, but keep the turns close together with no gap between them.

Also, is this the proper way to end the last turn and solder the wires to the bobbin?

Like John1 said, it is best to not cross over like that. This is because the enamel insulation on the magnet wire is very thin and doesn't have a very high breakdown voltage. There is not much voltage between each turn but there will be between the ends of the windings. So instead of ending your coil on terminal 2, end it on terminal 10. Some highvoltage transformers even have a layer of insulation between each layer of windings, but you probably won't need that. You can put your secondary winding on terminals 5 & 6 to keep everything separate.
If you are designing this transformer yourself, you'll also need to know the specs (permiablity) of the core in addition to the info John1 requested. If this is a core/turns/AWG spec'd in a pre designed project, then you already have the correct info to wind the tranformer. Assuming they know what they are doing of course.

 

[FusionITR]

Ok can you guys take a look at a this time serious attempt to make a test transformer? I want to know if I am assembling the transformer right, because when I test this transformer with a signal generator, I get a short-circuit on the primary and nothing on the secondary.

Here is the primary winding assembly (23 turns):

**broken link removed**

**broken link removed**

Insulation tape over the primary winding:

**broken link removed**

**broken link removed**

Secondary winding (11 turns):

**broken link removed**

**broken link removed**

 

[kchriste]

I want to know if I am assembling the transformer right

It looks assembled properly. I wonder if you have enough turns. What frequency signal are you planning on putting through it? That'll effect the number of turns you need.

I get a short-circuit on the primary and nothing on the secondary.

You probably didn't scrape the enamel off the ends of the secondary winding properly. Desolder it and scrape it to bare copper with a knife. Pre-tin the ends. The solder should flow easily onto the wire. Then re-solder the ends to the form.

 

[john1]

Are you attempting to make a 230v to 110v transformer ?

 

[FusionITR]

It looks assembled properly. I wonder if you have enough turns. What frequency signal are you planning on putting through it? That'll effect the number of turns you need.

I'm just testing transformer construction, wasn't going to use this paricular transformer pictured for any particular voltage or frequency. Just wanted to make sure I was assembling them correctly and correctly measure the step up or step down voltage I intended to get (in this example: 2:1).

In on the function generator, I was just going to put it, for example, a 2V 100khz sine wave and see if I get a 1V 100khz sine wave on the secondary.

 

[FusionITR]

Are you attempting to make a 230v to 110v transformer ?

LOL with a small core and wire like that? God no. I live in the US anyway so I have no need to step down 230V to 110V.

I was going to use this as a flyback transformer in a SMPS.

 

[john1]

Hi Fusion,

Ok, if you are constructing your own switched mode power supply, then
i have to assume you have a pretty good idea of what you are doing.
I have tried repairing SMPSs before, with no success, they seem to me
to be quite complicated, and i have not managed to get any of the
broken down ones that have come my way, back in working order.
For myself, i stick to the traditional type of power supply for things
that i make for my own use.

I wish you the best of luck with it, John

 

[Overclocked]

This thread is giving me an idea of what to do with all the Microwave transformers I have..They would make a nice Low voltage High Amperage transformer, Or a Nice HV low amperage Transformer

 

[audioguru]

You made a low frequency transformer with a laminated iron core. For 100kHz the transformer must have a ferrite core.

The leakage inductance might be high enough to cause a low impedance that a function generator cannot drive.

 

[kchriste]

Just wanted to make sure I was assembling them correctly and correctly measure the step up or step down voltage I intended to get (in this example: 2:1).

OK, I see what you are up to now. May as well measure the inductance of the windings while you're at it.

I was going to use this as a flyback transformer in a SMPS.

Cool! Then you might find the following site very helpfull with it's built in formulas. It worked well for a boost convertor I made a while back.
**broken link removed**

Originally Posted by audioguru
You made a low frequency transformer with a laminated iron core. For 100kHz the transformer must have a ferrite core.

It looks like a ferrite core to me or are my eyes really that bad?

 

[FusionITR]

Yes its a ferrite core, Ferroxcube 3C90 material.

 

[FusionITR]

BTW, the transformer seems to be working perfectly now. It just seems like when the frequency is set too low it causes a a short circuit on the primary windings, probably due to the inductance of the primary winding being too low.

 

[audioguru]

Good, the core is ferrite.
The primary is just a piece of wire at low frequencies.

 

[Russlk]

Witout knowing the material of the core, no one can really tell you if the transformer will work. I suggest that you measure the inductance of the primary. One way to do that is to resonate it with a known value of capacitor, then calculate the inductance. You will need a meter or oscilloscope capable of measureing the frequency.