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DIY off-line transformer winding ?

A

Adam Seychell

Jan 1, 1970
0
Is it common for people to hand wind their own transformers when
prototyping an off line isolated switching power supplies ?

The construction seems quite labor intensive, considering the
insulation requirements, EMI shielding, and safety regulations.
As a home brewer so I don't have the money to purchase official
standards for insulation and EMI regulations nor do I have the
specialized equipment to test insulation breakdown or accurate winding
machinery, so I've been collecting data from various application notes
on transformer design and dismantling transformers from old computer
power supplies. One of the requirements is a 5 to 6 mm "creepage
distance", and is usually made by creating a gap between each winding
layer and the bobbin side wall, while the insulation layers of
polyester film tape occupies the full width of the bobbin. The
professional built transformers I've seen use a 3 mm width tape as a
margin for each winding layer, and is wound to same thickness of the
copper layer.
With all this work do people go to the trouble or this just one of the
reasons why building off-line SMPS don't make popular hobby pojects ?


Adam.
 
W

Winfield Hill

Jan 1, 1970
0
Adam Seychell wrote...
One of the requirements is a 5 to 6 mm "creepage distance", and
is usually made by creating a gap between each winding layer and
the bobbin side wall, while the insulation layers of polyester
film tape occupies the full width of the bobbin. The professional
built transformers I've seen use a 3 mm width tape as a margin
for each winding layer, and is wound to same thickness of the
copper layer.

The issue is dealing with the occaisional 3 to 10kV spikes that
occur on the ac power lines. These must NOT be allowed to start
carbon discharge tracks. One aspect that helps in this situation
is the input RFI-noise spike-filter components.

OK, you've learned some of the principles of practical insulation
integrity, so don't you feel more comfortable to make some of your
own ac-line switching transformers? Be sure to use good fuses!

BTW, an easy way to get 0.2" or more of total creepage distance is
to use two-section bobbins and avoid winding all the way to the top.
If you stop 0.1" below the edge on each side, there's your 5mm.

Thanks,
- Win

whill_at_picovolt-dot-com
 
H

henryf

Jan 1, 1970
0
Adam said:
Is it common for people to hand wind their own transformers when
prototyping an off line isolated switching power supplies ?

No, most people have a self-preservation instinct.
 
S

Spehro Pefhany

Jan 1, 1970
0
BTW, an easy way to get 0.2" or more of total creepage distance is
to use two-section bobbins and avoid winding all the way to the top.
If you stop 0.1" below the edge on each side, there's your 5mm.

You can make really tiny transformers using triple-insulated wire.

Best regards,
Spehro Pefhany
 
S

Spehro Pefhany

Jan 1, 1970
0
Is it common for people to hand wind their own transformers when
prototyping an off line isolated switching power supplies ?

Sure. There are usually very few turns and winding a transformer or
two is no big deal. It's expensive getting ahold of all the required
materials in small quantity though, IME.

Best regards,
Spehro Pefhany
 
F

Frithiof Andreas Jensen

Jan 1, 1970
0
Adam Seychell said:
Is it common for people to hand wind their own transformers when
prototyping an off line isolated switching power supplies ?

Sure, it's a Prototype after all. Personally, I prefer to find a
commercially made transformer with the right credentials and design around
that. If there are no special needs, one cannot beat those Chinese assembly
lines!
As a home brewer so I don't have the money to purchase official
standards for insulation and EMI regulations nor do I have the
specialized equipment to test insulation breakdown or accurate winding
machinery,

However, If you must roll your own, you can get quite far with Planar
Transformers!

In many ways they are easier to design & build than the "normal" types. The
downside is that the switching frequencies are higher than one would
probably like and it costs a PCB if you get it wrong. The cores are
difficult to get in small quantities - the best way is to buy an "evaluation
kit" with a few of each size.
With all this work do people go to the trouble or this just one of the
reasons why building off-line SMPS don't make popular hobby pojects ?

It's simply not worth the effort anymore - you can buy decent supplies below
USD 100 for the typical power/voltage ranges up to about 200W or so. The
excuse for building your own would be special requirements such as High
Votage f.ex. - in which case you could try to work with a commercial CCFT
transformer and leave the isolation to a commercial power cube.
 
F

Fritz Schlunder

Jan 1, 1970
0
henryf said:
No, most people have a self-preservation instinct.


*Buc buc buc...*

Hark, what is that I hear? It sounds an aweful lot like a chicken. Hmm...
Speaking of which, chicken sounds pretty tasty right about now.

Don't be insulted. Chickens are quite respectable creatures. In fact, they
are quite noble even though most of us just take them for granted. They
give the ultimate sacrafice just so we can fill our bellies. Rather than
thinking of this as flamebait, think of this post more as a tribute to
chickens.
 
S

Spehro Pefhany

Jan 1, 1970
0
*Buc buc buc...*

Hark, what is that I hear? It sounds an aweful lot like a chicken. Hmm...
Speaking of which, chicken sounds pretty tasty right about now.

Don't be insulted. Chickens are quite respectable creatures. In fact, they
are quite noble even though most of us just take them for granted. They
give the ultimate sacrafice just so we can fill our bellies. Rather than
thinking of this as flamebait, think of this post more as a tribute to
chickens.
"The rooster stared back at me, his power and confidence almost
overwhelming. Down below, a female paused warily at the coop's
entrance. I kept the camera running. They were beautiful, these
"Chickens in the Mist." -- Gary Larson

Best regards,
Spehro Pefhany
 
W

Winfield Hill

Jan 1, 1970
0
Spehro Pefhany wrote...
"The rooster stared back at me, his power and confidence almost
overwhelming. Down below, a female paused warily at the coop's
entrance. I kept the camera running. They were beautiful, these
"Chickens in the Mist." -- Gary Larson

Best regards,
Spehro Pefhany

Yes, indeed.

Thanks,
- Win

whill_at_picovolt-dot-com
 
H

henryf

Jan 1, 1970
0
Fritz said:
*Buc buc buc...*

Fritz, I admit it. I'm very careful when building circuitry
that could become lethal if done wrong, such as an off-line
SMPS, and I wouldn't advise the homebrewing of such circuitry
just to save a few "bucs".
 
A

Active8

Jan 1, 1970
0
*Buc buc buc...*

Hark, what is that I hear? It sounds an aweful lot like a chicken. Hmm...
Speaking of which, chicken sounds pretty tasty right about now.

Don't be insulted. Chickens are quite respectable creatures. In fact, they
are quite noble even though most of us just take them for granted. They
give the ultimate sacrafice just so we can fill our bellies. Rather than
thinking of this as flamebait, think of this post more as a tribute to
chickens.
It also sounds like a rip-off from one of the final episodes of
MASH.
 
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