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Science Forum Index » Electronics - Design Forum » Thyristor bridge for current control?
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| Jon Danniken |
 Posted: Wed Apr 30, 2008 4:43 pm |
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Guest
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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 |
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| Jan Panteltje |
| Posted: Thu May 01, 2008 4:14 am |
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On a sunny day (Wed, 30 Apr 2008 14:43:49 -0700) it happened "Jon Danniken"
<jonREMOVETHISdanniken@yahoo.com> wrote in
<67s7gmF2qlic9U1@mid.individual.net>:
Quote: 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. |
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| Guest |
| Posted: Thu May 01, 2008 7:49 am |
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On Apr 30, 10:43�pm, "Jon Danniken" <jonREMOVETHISdanni...@yahoo.com>
wrote:
Quote: 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. |
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| Guest |
| Posted: Thu May 01, 2008 9:19 am |
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On May 1, 7:57�pm, "Jon Danniken" <jonREMOVETHISdanni...@yahoo.com>
wrote:
Quote: cbarn24...@aol.com> wrote:
Jon Danniken" wrote:
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.
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
I mean use both half cyles the same. |
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| Jon Danniken |
| Posted: Thu May 01, 2008 10:48 am |
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Guest
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"Jan Panteltje" wrote:
Quote: "Jon Danniken"wrote:
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.
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 |
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| Jon Danniken |
| Posted: Thu May 01, 2008 1:57 pm |
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<cbarn24050@aol.com> wrote:
Jon Danniken" wrote:
Quote: 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.
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 |
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