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Winding a transformer?

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Thomas W

Tue Oct 19 2010, 08:45PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
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Posts: 1276

i might have missed a thread about this already :S
but is there anywhere i can find out about winding transformers -
-how big should the core be
-what gauge wire
-any fast ways of winding
- ratios of hwo to wind it e.g.
if i want to make the voltage go up from 240 to 480 do it just to 1winding on one site then 2 on the other?
-how to calcualte what i need to put in one side to get X amout out of the otherside e.g.
how many amps @ what voltage do i need to put through the primary coil to get 4000v out the secondry coil at 1A

thanks in advance,
Tom Williamson

EDIT:
also could someone tell me about what type of core and which one you would use for different applications?

1n5ane

Tue Oct 19 2010, 09:16PM

Registered Member #3283 Joined: Wed Oct 06 2010, 11:03PM
Location: Toronto, Canada
Posts: 29

First off, you'll need to decide what kind of core you want to use. Most power transformers(Step up/step down) are EI core with bobbin; this is probably the simplest to wind and assemble. The size of the core depends on the amount of power (VA) you want. The gauge of wire depends on the current you intend to draw.

Transformer ratio is simply secondary voltage divided over primary voltage, this should be the same for the turns ratio. So a 1:2 turns ratio will either double or halve the voltage depending on where you connect the power. Also, you need to take into consideration the impedance/inductance; if you tried to build a transformer with 1 turn of wire, the impedance won't be high enough and it'd basically be a short circuit. Impedance can be thought of as "AC resistance".

Voltage x current = watts can be used to calulate the current requirement for both windings. For example, 4000V @ 1A is 4000W, therefore, the primary would be 220VAC @ 18.18 A or 120VAC @ 33.33A...

EDIT:

Toroidal cores are good for power transformers, they are usually more compact and have low magnetic leakage. However, they usually require special machines to wind unless you have the patience to sit there and thread several hundred/thousands of turns through the donut ;)

EI cores are good for just about anything. They are easy to build; you wind your wire on the bobbin and simply stack the EI laminations to build the transformer. None of this requires the use of anything special (Other than the bobbin winder). However, EI transformers can be noisy if the laminations aren't varnished and they tend to leak magnetic fields more. This may or may not be important depending on your use.

C cores have similar attributes to the EI core. They are probably the simplest to wind and assemble, However, they tend to be larger and less common than EI cores...

Thomas W

Tue Oct 19 2010, 09:29PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
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Posts: 1276

So if i wanted to double the voltage from 240v to 480v would i do 240 turns on one side
and 480 turns on the other side?

also is there any way of working out what size core i want and what material?

Tom Williamson

P.S. the only stuff i rly know about transformers is what you just told me :P

1n5ane

Tue Oct 19 2010, 09:36PM

Registered Member #3283 Joined: Wed Oct 06 2010, 11:03PM
Location: Toronto, Canada
Posts: 29

Again, the turns ratio really depends on the core you plan to use. Generally, the larger the core, the more turns are needed to create suitable impedance.

When you go to buy cores/laminations, they will generally specify the recommended power rating.

No offense, but you should really do more research before attempting to build a transformer; a small mistake could easily cause a fire or zap you.

This wikipedia article is a good start:

ScotchTapeLord

Tue Oct 19 2010, 09:38PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
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Posts: 635

Tom Williamson wrote ...

i might have missed a thread about this already :S
but is there anywhere i can find out about winding transformers -

The first few google search results are a good place to start. You have basically asked for a reader's digest version of an entire summary of transformer theory. There are many factors affecting each aspect, and there is no single correct answer.

As for your idea for a 4kVA transformer, I think some utility pole transformers are rated for 5kVA.

Material is related to frequency.

Thomas W

Tue Oct 19 2010, 09:39PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

ah thanks
and btw i was simply useing the 4000v transformer as a example :P

also im not planning to build one at the second i just wished to know about it and mabye make a small one

1n5ane

Tue Oct 19 2010, 09:49PM

Registered Member #3283 Joined: Wed Oct 06 2010, 11:03PM
Location: Toronto, Canada
Posts: 29

You're usually better off buying a commercially produced transformer as opposed to building one yourself... Unless require a specialty (HV plate, audio, etc) transformer, it will end up costing you more in materials and time than to purchase a ready made one...

Thomas W

Tue Oct 19 2010, 10:06PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

true, but i like learning about things then building things and things like that :P
also i read the information you gave me and decided i need more XD
ive been googleing for ages but none realy tells me everything i want to know :S

thanks,

Tom Williamson

1n5ane

Tue Oct 19 2010, 10:26PM

Registered Member #3283 Joined: Wed Oct 06 2010, 11:03PM
Location: Toronto, Canada
Posts: 29

This is a good resource:

Part 1 -

Part 2 -

Thomas W

Wed Oct 20 2010, 06:52AM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

thanks,
i will be reading them after school :P

Tom Williamson

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