Transformer winding direction

[isw]

I recently came across a YouTube video where a guy rewound a microwave
transformer to make a spot welder.

In talking about it, he stated -- and repeated -- that it was very
important for the secondary winding to have the same "sense" as the
primary -- that is, both windings had to go around the core in the same
direction.

I know that matters if the transformer is handling very asymmetric
waveforms such as in a flyback configuration, but I have never heard
that it matters for plain old 60 Hz. sinusoids.

Does it? Or was the guy just confused?

Isaac

 

[Phil Allison]

isw wrote:

I recently came across a YouTube video where a guy rewound a microwave
transformer to make a spot welder.

In talking about it, he stated -- and repeated -- that it was very
important for the secondary winding to have the same "sense" as the
primary -- that is, both windings had to go around the core in the same
direction.

I know that matters if the transformer is handling very asymmetric
waveforms such as in a flyback configuration, but I have never heard
that it matters for plain old 60 Hz. sinusoids.

Does it? Or was the guy just confused?

** A spot welding transformer is almost the direct opposite of a microwave oven tranny - big step-down instead of step-up and the lowest possible leakage reactance instead of heaps.

To help with the latter, it could easily be important to wind with the same sense. Also winding multiple, identical secondaries and connecting them in parallel is the way to go plus using other techniques like interleaving and use of strip conductors for the secondary.

Getting 3V at 200Amps is non trivial.


.... Phil

 

[N_Cook]

On 13/02/2015 05:59, isw wrote:

I recently came across a YouTube video where a guy rewound a microwave
transformer to make a spot welder.

In talking about it, he stated -- and repeated -- that it was very
important for the secondary winding to have the same "sense" as the
primary -- that is, both windings had to go around the core in the same
direction.

I know that matters if the transformer is handling very asymmetric
waveforms such as in a flyback configuration, but I have never heard
that it matters for plain old 60 Hz. sinusoids.

Does it? Or was the guy just confused?

Isaac

Even using it in reverse, swapping primary and secondary, you will not
get the low volts and high amps for welding.
Did u-tubber just use the core and existing primary and rewind the
secondary secondary with 1 to 2mm diameter wire? should be obvious in
the vide, those sorts of dimensions

 

[Miguel GimĂŠnez]

El 13/02/2015 a las 6:59, isw escribiĂł:

I recently came across a YouTube video where a guy rewound a microwave
transformer to make a spot welder.

In talking about it, he stated -- and repeated -- that it was very
important for the secondary winding to have the same "sense" as the
primary -- that is, both windings had to go around the core in the same
direction.

I know that matters if the transformer is handling very asymmetric
waveforms such as in a flyback configuration, but I have never heard
that it matters for plain old 60 Hz. sinusoids.

Does it? Or was the guy just confused?

Isaac

May be he is winding an autotransformer, although it's not very safe for
welding .

--
Saludos
Miguel GimĂŠnez

 

[whit3rd]

On Thursday, February 12, 2015 at 9:59:58 PM UTC-8, isw wrote:

I recently came across a YouTube video where a guy rewound a microwave
transformer to make a spot welder.

In talking about it, he stated -- and repeated -- that it was very
important for the secondary winding to have the same "sense" as the
primary -- that is, both windings had to go around the core in the same
direction.

I think he was confused. Look at a transformer-style soldering gun,
the hairpin secondary doesn't have ANY helical orientation at all,
and it transforms down to high current at low volts just fine.
Ditto for feedthrough AC current meter transformers.

Output windings on such high-ratio transformers don't couple capacitively
to the primary (the low resistance and inductance completely swamp
tiny capacitive currents), and it's hard to imagine any importance of flux
coupling defects at low (50 to 60 Hz) frequency with soft-iron cores.

 

[Phil Allison]

whit3rd wrote:

I think he was confused. Look at a transformer-style soldering gun,
the hairpin secondary doesn't have ANY helical orientation at all,

** Huh ?

See hi-res pic of soldering gun tranny.

http://en.wikipedia.org/wiki/Soldering_gun

Note use of copper strip and close coupling of the secondary.

Output windings on such high-ratio transformers don't couple capacitively
to the primary

** Do they ever ?

and it's hard to imagine any importance of flux
coupling defects at low (50 to 60 Hz) frequency with soft-iron cores.

** Mick Faraday used soft iron in his toroidal job, but it was judged no much good. Silicon steel laminations have been the norm for over a century.

Also, many power transformers have separate windings on adjacent limbs of a U or C core. Invariably, there are primary and secondary coils wound on each limb that are later coupled in series or parallel.

Never seen the primary on one and the secondary the other - cos that results in a tranny with very poor regulation due to high leakage reactance.



..... Phil

 

[mike]

On 2/12/2015 10:30 PM, Phil Allison wrote:

isw wrote:

I recently came across a YouTube video where a guy rewound a microwave
transformer to make a spot welder.

In talking about it, he stated -- and repeated -- that it was very
important for the secondary winding to have the same "sense" as the
primary -- that is, both windings had to go around the core in the same
direction.

I know that matters if the transformer is handling very asymmetric
waveforms such as in a flyback configuration, but I have never heard
that it matters for plain old 60 Hz. sinusoids.

Does it? Or was the guy just confused?


** A spot welding transformer is almost the direct opposite of a microwave oven tranny - big step-down instead of step-up and the lowest possible leakage reactance instead of heaps.

To help with the latter, it could easily be important to wind with the same sense. Also winding multiple, identical secondaries and connecting them in parallel is the way to go plus using other techniques like interleaving and use of strip conductors for the secondary.

Getting 3V at 200Amps is non trivial.


... Phil

Problems I discovered with these welders are:
600W ain't nearly enough power to weld anything substantial.

Very thin stuff like battery tabs require very accurate energy
delivery. The difference between no weld and blasting a hole
thru everything is a small pressure difference holding the weldment
together.

If you don't turn it on/off at zero crossings, the saturation
state of the core can make a great difference in the next weld.

I gave up trying to weld with a MOT.

CD welders deliver a known energy to the weld and are very much
less dependent on contact resistance.

 

[isw]

In article <mbkard$1b6$1@dont-email.me>, N_Cook <diverse@tcp.co.uk>
wrote:

On 13/02/2015 05:59, isw wrote:
I recently came across a YouTube video where a guy rewound a microwave
transformer to make a spot welder.

In talking about it, he stated -- and repeated -- that it was very
important for the secondary winding to have the same "sense" as the
primary -- that is, both windings had to go around the core in the same
direction.

I know that matters if the transformer is handling very asymmetric
waveforms such as in a flyback configuration, but I have never heard
that it matters for plain old 60 Hz. sinusoids.

Does it? Or was the guy just confused?

Isaac


Even using it in reverse, swapping primary and secondary, you will not
get the low volts and high amps for welding.
Did u-tubber just use the core and existing primary and rewind the
secondary secondary with 1 to 2mm diameter wire? should be obvious in
the vide, those sorts of dimensions

That's what he was doing.

Isaac

 

[isw]

In article <mbmj31$a7a$1@dont-email.me>, mike <ham789@netzero.net>
wrote:

On 2/12/2015 10:30 PM, Phil Allison wrote:
isw wrote:

I recently came across a YouTube video where a guy rewound a microwave
transformer to make a spot welder.

In talking about it, he stated -- and repeated -- that it was very
important for the secondary winding to have the same "sense" as the
primary -- that is, both windings had to go around the core in the same
direction.

I know that matters if the transformer is handling very asymmetric
waveforms such as in a flyback configuration, but I have never heard
that it matters for plain old 60 Hz. sinusoids.

Does it? Or was the guy just confused?


** A spot welding transformer is almost the direct opposite of a
microwave oven tranny - big step-down instead of step-up and the lowest
possible leakage reactance instead of heaps.

To help with the latter, it could easily be important to wind with the same
sense. Also winding multiple, identical secondaries and connecting them in
parallel is the way to go plus using other techniques like interleaving and
use of strip conductors for the secondary.

Getting 3V at 200Amps is non trivial.


... Phil

Problems I discovered with these welders are:
600W ain't nearly enough power to weld anything substantial.

Mine easly pops the 15 Amp. breaker if I set it for too long a pulse.

Very thin stuff like battery tabs require very accurate energy
delivery. The difference between no weld and blasting a hole
thru everything is a small pressure difference holding the weldment
together.

Mine does a fine job on things like coathanger wire and the stainless
steel strips from windshield wipers.

If you don't turn it on/off at zero crossings, the saturation
state of the core can make a great difference in the next weld.

NP; just use a good SSR for switching.

Isaac

 

[Phil Allison]

mike wrote:

Problems I discovered with these welders are:
600W ain't nearly enough power to weld anything substantial.

Very thin stuff like battery tabs require very accurate energy
delivery. The difference between no weld and blasting a hole
thru everything is a small pressure difference holding the weldment
together.

If you don't turn it on/off at zero crossings, the saturation
state of the core can make a great difference in the next weld.

** Zero crossing switching is the worst possible for creating large in-rush surges and hence fully magnetising the core of an AC supply transformer.

Switching on at a voltage peak, while under load, is the best option.

A triac switch will always go off near zero current, which will be nowhere near zero volts.

.... Phil

 

[mike]

On 2/13/2015 9:12 PM, isw wrote:

In article <mbmj31$a7a$1@dont-email.me>, mike <ham789@netzero.net
wrote:

On 2/12/2015 10:30 PM, Phil Allison wrote:
isw wrote:

I recently came across a YouTube video where a guy rewound a microwave
transformer to make a spot welder.

In talking about it, he stated -- and repeated -- that it was very
important for the secondary winding to have the same "sense" as the
primary -- that is, both windings had to go around the core in the same
direction.

I know that matters if the transformer is handling very asymmetric
waveforms such as in a flyback configuration, but I have never heard
that it matters for plain old 60 Hz. sinusoids.

Does it? Or was the guy just confused?


** A spot welding transformer is almost the direct opposite of a
microwave oven tranny - big step-down instead of step-up and the lowest
possible leakage reactance instead of heaps.

To help with the latter, it could easily be important to wind with the same
sense. Also winding multiple, identical secondaries and connecting them in
parallel is the way to go plus using other techniques like interleaving and
use of strip conductors for the secondary.

Getting 3V at 200Amps is non trivial.


... Phil

Problems I discovered with these welders are:
600W ain't nearly enough power to weld anything substantial.

Mine easly pops the 15 Amp. breaker if I set it for too long a pulse.

Yep, if your objective is to weld your breaker, you're on the right track.

Very thin stuff like battery tabs require very accurate energy
delivery. The difference between no weld and blasting a hole
thru everything is a small pressure difference holding the weldment
together.

Mine does a fine job on things like coathanger wire and the stainless
steel strips from windshield wipers.

So does mine on things that aren't damaged by overheating.
Just hit it until it glows red.
Battery tabs aren't so forgiving.
I spring loaded the tips separately to give some repeatability.
I got about 90% good welds. When it's a 10-cell battery pack,
90% ain't nearly good enough.

If you don't turn it on/off at zero crossings, the saturation
state of the core can make a great difference in the next weld.

NP; just use a good SSR for switching.

Agree, but I expect most DIYers don't.
I set the weld time by an integral number of cycles of 60 Hz.
Took about 6 cycles to weld a battery tab.

Still claim that a controlled energy dump is far superior.
It's relatively insensitive to contact resistance.
My CD welder is rated for 7V peak across .001 ohms.
It's over before the cell case even gets warm.

Isaac

 

[whit3rd]

On Friday, February 13, 2015 at 4:01:02 PM UTC-8, Phil Allison wrote:

whit3rd wrote:

I think he was confused. Look at a transformer-style soldering gun,
the hairpin secondary doesn't have ANY helical orientation at all,

** Huh ?

See hi-res pic of soldering gun tranny.

http://en.wikipedia.org/wiki/Soldering_gun

Note use of copper strip and close coupling of the secondary.

That's NOT a hairpin secondary! Look instead at this

<https://plus.google.com/photos/118343199678883181101/albums/6115815766613132033/6115815770882958370?banner=pwa&pid=6115815770882958370&oid=118343199678883181101>

Even if the transformer manufacturer works on good flux coupling, the external
loop of the iron's tip will leak lots of flux; you should expect every CRT in the vicinity
to shimmy while you hold down the trigger. There's no particular reason to care, in this
case.

 

[Phil Allison]

whit3rd wrote:

On Friday, February 13, 2015 at 4:01:02 PM UTC-8, Phil Allison wrote:
whit3rd wrote:

I think he was confused. Look at a transformer-style soldering gun,
the hairpin secondary doesn't have ANY helical orientation at all,

** Huh ?

See hi-res pic of soldering gun tranny.

http://en.wikipedia.org/wiki/Soldering_gun

Note use of copper strip and close coupling of the secondary.

That's NOT a hairpin secondary! Look instead at this

https://plus.google.com/photos/118343199678883181101/albums/6115815766613132033/6115815770882958370?banner=pwa&pid=6115815770882958370&oid=118343199678883181101

** So it's a one turn secondary on a toroidal core.

Magnetic coupling will be poor, but still good enough for a soldering tool.

Even if the transformer manufacturer works on good flux coupling, the external
loop of the iron's tip will leak lots of flux;

** Any external flux will come from the iron core, not the loop.

Removing the soldering tip will not eliminate external flux or even reduce it much.



.... Phil

 

[mike]

On 2/13/2015 11:58 PM, Phil Allison wrote:

mike wrote:


Problems I discovered with these welders are:
600W ain't nearly enough power to weld anything substantial.

Very thin stuff like battery tabs require very accurate energy
delivery. The difference between no weld and blasting a hole
thru everything is a small pressure difference holding the weldment
together.

If you don't turn it on/off at zero crossings, the saturation
state of the core can make a great difference in the next weld.


** Zero crossing switching is the worst possible for creating large in-rush surges and hence fully magnetising the core of an AC supply transformer.

Switching on at a voltage peak, while under load, is the best option.

A triac switch will always go off near zero current, which will be nowhere near zero volts.

... Phil

Well, I don't recall mentioning volts at all.
Yes, triacs switch off at the zero crossing of the current.
Not much you can do about that.

I question not turning it on at zero volts???
Please explain the large in-rush current when there's zero volts
on the transformer primary?

 

[Phil Allison]

mike wrote:

If you don't turn it on/off at zero crossings, the saturation
state of the core can make a great difference in the next weld.


** Zero crossing switching is the worst possible for creating large in-rush surges and hence fully magnetising the core of an AC supply transformer.

Switching on at a voltage peak, while under load, is the best option.

A triac switch will always go off near zero current, which will be nowhere near zero volts.


Well, I don't recall mentioning volts at all.

** You did, cos "zero crossing" means at zero voltage crossings.

Yes, triacs switch off at the zero crossing of the current.
Not much you can do about that.

** Then why did you say it was needed ??

I question not turning it on at zero volts???

** Really ? Did you try Googling the topic?

Please explain the large in-rush current when there's zero volts
on the transformer primary?

** The surge current peak comes a little after the first voltage peak.

Consider that it takes half the time for the applied voltage wave to first average zero if you switch at a peak - half a cycle later instead of a whole cycle - minimising the low frequency component of the wave.


.... Phil

 

[whit3rd]

On Sunday, February 15, 2015 at 1:02:31 AM UTC-8, mike wrote:

As long as you stay out of saturation, the main component of the
primary current is due to the shorted secondary.
I think I'll give my SCR the benefit of switching on when there's zero
voltage.

Not really the best idea; it is then possible that the previous turn-off
happened after a half-cycle (+), and if this ON state starts with a half-cycle (+)
as well, that's two half-cycles of the same polarity. The likelihood
of saturation is very high. Turn-on at peak V is a strategy that
minimizes saturation risk.

 

[Phil Allison]

mike wrote:

if you say so.

** Wot a smug prick you are.

As long as you stay out of saturation,

** No chance - you are all wet right now.

the main component of the
primary current is due to the shorted secondary.

** The secondary is not shorted.

I think I'll give my SCR the benefit of switching on when there's zero
voltage.

** More fool you.


.... Phil

 

[mike]

On 2/14/2015 11:43 PM, Phil Allison wrote:

mike wrote:


If you don't turn it on/off at zero crossings, the saturation
state of the core can make a great difference in the next weld.


** Zero crossing switching is the worst possible for creating large in-rush surges and hence fully magnetising the core of an AC supply transformer.

Switching on at a voltage peak, while under load, is the best option.

A triac switch will always go off near zero current, which will be nowhere near zero volts.


Well, I don't recall mentioning volts at all.

** You did, cos "zero crossing" means at zero voltage crossings.


Yes, triacs switch off at the zero crossing of the current.
Not much you can do about that.


** Then why did you say it was needed ??


I question not turning it on at zero volts???


** Really ? Did you try Googling the topic?


Please explain the large in-rush current when there's zero volts
on the transformer primary?


** The surge current peak comes a little after the first voltage peak.

Consider that it takes half the time for the applied voltage wave to first average zero if you switch at a peak - half a cycle later instead of a whole cycle - minimising the low frequency component of the wave.


... Phil

if you say so.
As long as you stay out of saturation, the main component of the
primary current is due to the shorted secondary.
I think I'll give my SCR the benefit of switching on when there's zero
voltage.

 

"Once again, your signature condescending tone declares that
the other guy is always wrong. "

That's not fair. I have seen Phil be nice to people a dozen times.

In the last thirty years.

Go ahead and hate the MF but respect him, he knows WTF he is doing and I know enough to know he knows WTF he is doing.

 

[mike]

On 2/15/2015 1:53 AM, whit3rd wrote:

On Sunday, February 15, 2015 at 1:02:31 AM UTC-8, mike wrote:

As long as you stay out of saturation, the main component of the
primary current is due to the shorted secondary.
I think I'll give my SCR the benefit of switching on when there's zero
voltage.

Not really the best idea; it is then possible that the previous turn-off
happened after a half-cycle (+), and if this ON state starts with a half-cycle (+)
as well, that's two half-cycles of the same polarity. The likelihood
of saturation is very high. Turn-on at peak V is a strategy that
minimizes saturation risk.

Well, I'll repeat what I wrote earlier in the thread:

I set the weld time by an integral number of cycles of 60 Hz.

The key word there is "integral" as in complete as in full as in
you don't get two half cycles of the same polarity.

Designing your welder to avoid saturation is a
strategy that minimizes saturation risk.