Thyristor bridge for current control?

[Jon Danniken]

Hello

I am in the process of trying to cobble up a method for creating a DC supply
with a variable output current. The plan (on a basic level) is to use a
current-limited (variable shunt) AC transformer (from an AC welder), then a
thyristor bridge, followed by a smoothing choke.

If I control the thyristor gates in such a manner as to delay the forward
conduction of current (by a number of degrees delay per half cycle), will
this have the effect of providing me with a variable current supply on the
other end of the smoothing choke?

This is my first time playing with thyristors, and I would greatly
appreciate any insight/correction as to my line of thought so far with this.

Thanks,

Jon

 

[Jan Panteltje]

Hello

I am in the process of trying to cobble up a method for creating a DC supply
with a variable output current. The plan (on a basic level) is to use a
current-limited (variable shunt) AC transformer (from an AC welder), then a
thyristor bridge, followed by a smoothing choke.

If I control the thyristor gates in such a manner as to delay the forward
conduction of current (by a number of degrees delay per half cycle), will
this have the effect of providing me with a variable current supply on the
other end of the smoothing choke?

This is my first time playing with thyristors, and I would greatly
appreciate any insight/correction as to my line of thought so far with this.

Thanks,

Jon

Yes current limit will work.
It is slow though, due to energy stored in the magnetics, and also
you cannot switch of anytime, just at the zero crossing.
So if you short something like that, you still get a current overshoot.

 

[Jon Danniken]

"Jon Danniken"wrote:


Yes current limit will work.
It is slow though, due to energy stored in the magnetics, and also
you cannot switch of anytime, just at the zero crossing.
So if you short something like that, you still get a current overshoot.

Hi Jan,

Thanks for the encouragement; I'm glad to know I'm on the right track. A
concern I had was if I needed to "chop" the incoming AC wave more frequently
than once per half-cycle, but it would certainly be more simple to just do
it once per half-cycle.

The application for this will be a form of welding (tungsten/gas), so there
very well may be the occasional short circuit. Mainly I am needing a way to
vary the current at the beginning and at the end of a work cycle.

Thanks again,

Jon

 

[[email protected]]

Hello

I am in the process of trying to cobble up a method for creating a DC supply
with a variable output current. The plan (on a basic level) is to use a
current-limited (variable shunt) AC transformer (from an AC welder), then a
thyristor bridge, followed by a smoothing choke.

If I control the thyristor gates in such a manner as to delay the forward
conduction of current (by a number of degrees delay per half cycle), will
this have the effect of providing me with a variable current supply on the
other end of the smoothing choke?

This is my first time playing with thyristors, and I would greatly
appreciate any insight/correction as to my line of thought so far with this.

Thanks,

Jon

You need to make sure you allways keep the transformer balanced.

 

[Jon Danniken]

You need to make sure you allways keep the transformer balanced.

Hello, cbarn, thanks for the reply. I am a bit confused as to what you mean
by "transformer balance'; would you be able to specify the phenomenon you
are referring to?

Jon

 

[[email protected]]

Hello, cbarn, thanks for the reply. �I am a bit confused as to what you mean
by "transformer balance'; would you be able to specify the phenomenon you
are referring to?

Jon

I mean use both half cyles the same.