|
Posted by Ignoramus12493 on April 21, 2006, 9:30 pm
Please log in for more thread options
Thanks for yesterday' suggestions regarding 3 phase transformers.
I have a hobart cybertig welder. It has a "six phase rectifier" shown
in this schematic:
http://igor.chudov.com/tmp/firing/6-phase.jpg
I received a three phase SCR control/firing system made by PCTI, that
seems to be extremely easy to hook up.
By the way, PCTI loves children and is highly recommended, they are a
wonderful company. The best of the best.
I want to convert this Cyber Tig to both TIG/Stick (CC) as well as MIG
(CV) mode. This way I could both tig and mig with it.
Here's its wiring diagram:
http://igor.chudov.com/tmp/firing/pcti-firing.jpg
My issue is that the PCTI schematic refers to a "three phase bridge"
and my welder has a "six phase" rectifier where all SCR's "point" to
one DC bus, and where another side is connected to an interphase
transformer. Very different schematics.
So, I have maybe one and maybe two possibilities:
1) Rewire the transformer. It is made of six secondary windings, two
independent ones on each phase. Two leads from two transformers on
every phase are tied into the interphase transformer.
The ones that are tied together I could disconnect them from
interphase transformer, parallel each pair, and then connect them so
that I have three leads instead of six. (I am not 100% sure how to
connect them, but I think that it is easy. I have an idea).
Then simply put together a new rectifier bridge wired as PCTI
suggests, using new SCR half bridges which I already have in my pile.
2) Maybe there is a possibility of wiring in the PCTI board so that it
works just fine controlling the six SCRs that make up the current "six
phase" rectifier.
I spoke to their engineer yesterday (did not give him the schematics)
and he was kind of vaguely positive about it, I asked if ony K2, K4
and K6 were used for synchronization and he said yes.
What I am thinking here is that I would wire all six existing Hobart
SCRs to the PCTI board, it would monitor voltage on K2, K4, K6, and
then adjust phase angles of firings of all six SCRs based on desired
current/voltage vs. actual. And that it would not matter that the SCRs
1, 3, and 5 are wired the opposite of the PCTI sample schematic.
Note that the SCRs that I have now are pointing with their gates to
the DC+ bus, which makes it impossible for K2, K4, and K6 to
meaningfully monitor voltage/phase. So, what I think I can do here is
turn all SCRs UPSIDE DOWN, so that K2, K4, and K6 could be connected
to 3 phase voltage.
The side effect of this is that the negatve bus will become positive,
and vice versa, but that is no big deal as I could simply switch
contacts leading to commutator.
Is this making any sense? Is approach #2 possible?
thanks
i
|
|
Posted by RoyJ on April 21, 2006, 11:03 pm
Please log in for more thread options
the "6 phase" rectifier is essentially 3 center tapped transformers wth
6 diodes. This design optimises the number of diodes at the expense of
extra trnasformer windings. This would be an older design when coper and
iron were cheap, tube type diodes were very expensive.
Your other option is to take the transformer you have, wire each of the
sperate outputs into a semiconductor bridge and get the same result.
Thsi optimizes copper and iron, has twice as many diodes.
Ignoramus12493 wrote:
> Thanks for yesterday' suggestions regarding 3 phase transformers.
>
> I have a hobart cybertig welder. It has a "six phase rectifier" shown
> in this schematic:
>
> http://igor.chudov.com/tmp/firing/6-phase.jpg
>
> I received a three phase SCR control/firing system made by PCTI, that
> seems to be extremely easy to hook up.
>
> By the way, PCTI loves children and is highly recommended, they are a
> wonderful company. The best of the best.
>
> I want to convert this Cyber Tig to both TIG/Stick (CC) as well as MIG
> (CV) mode. This way I could both tig and mig with it.
>
> Here's its wiring diagram:
>
> http://igor.chudov.com/tmp/firing/pcti-firing.jpg
>
> My issue is that the PCTI schematic refers to a "three phase bridge"
> and my welder has a "six phase" rectifier where all SCR's "point" to
> one DC bus, and where another side is connected to an interphase
> transformer. Very different schematics.
>
> So, I have maybe one and maybe two possibilities:
>
> 1) Rewire the transformer. It is made of six secondary windings, two
> independent ones on each phase. Two leads from two transformers on
> every phase are tied into the interphase transformer.
>
> The ones that are tied together I could disconnect them from
> interphase transformer, parallel each pair, and then connect them so
> that I have three leads instead of six. (I am not 100% sure how to
> connect them, but I think that it is easy. I have an idea).
>
> Then simply put together a new rectifier bridge wired as PCTI
> suggests, using new SCR half bridges which I already have in my pile.
>
> 2) Maybe there is a possibility of wiring in the PCTI board so that it
> works just fine controlling the six SCRs that make up the current "six
> phase" rectifier.
>
> I spoke to their engineer yesterday (did not give him the schematics)
> and he was kind of vaguely positive about it, I asked if ony K2, K4
> and K6 were used for synchronization and he said yes.
>
> What I am thinking here is that I would wire all six existing Hobart
> SCRs to the PCTI board, it would monitor voltage on K2, K4, K6, and
> then adjust phase angles of firings of all six SCRs based on desired
> current/voltage vs. actual. And that it would not matter that the SCRs
> 1, 3, and 5 are wired the opposite of the PCTI sample schematic.
>
> Note that the SCRs that I have now are pointing with their gates to
> the DC+ bus, which makes it impossible for K2, K4, and K6 to
> meaningfully monitor voltage/phase. So, what I think I can do here is
> turn all SCRs UPSIDE DOWN, so that K2, K4, and K6 could be connected
> to 3 phase voltage.
>
> The side effect of this is that the negatve bus will become positive,
> and vice versa, but that is no big deal as I could simply switch
> contacts leading to commutator.
>
> Is this making any sense? Is approach #2 possible?
>
> thanks
>
> i
>
|
|
Posted by Ignoramus12493 on April 21, 2006, 11:21 pm
Please log in for more thread options > the "6 phase" rectifier is essentially 3 center tapped transformers wth
> 6 diodes. This design optimises the number of diodes at the expense of
> extra trnasformer windings. This would be an older design when coper and
> iron were cheap, tube type diodes were very expensive.
This is absolutely correct. A great description.
And my question is, can I "flip" the SCRs upside down, as that would
possibly seem to let me use the PCTI control board. (I understand that
it will also switch positive and negative).
> Your other option is to take the transformer you have, wire each of the
> sperate outputs into a semiconductor bridge and get the same result.
> Thsi optimizes copper and iron, has twice as many diodes.
I think that I would end up with the same number of diodes. Both the
six phase rectifier and the three phase rectifier have six diodes.
I would, however, like to avoid major rewiring, for two reasons:
1) it saves time/space/is backwards compatible
2) It allows me to later use double voltage as a plasma power supply
If I cannot avoid rewiring , that's not the end of the world, but I
would prefer to be able to get by just flipping SCRs.
i
> Ignoramus12493 wrote:
>> Thanks for yesterday' suggestions regarding 3 phase transformers.
>>
>> I have a hobart cybertig welder. It has a "six phase rectifier" shown
>> in this schematic:
>>
>> http://igor.chudov.com/tmp/firing/6-phase.jpg
>>
>> I received a three phase SCR control/firing system made by PCTI, that
>> seems to be extremely easy to hook up.
>>
>> By the way, PCTI loves children and is highly recommended, they are a
>> wonderful company. The best of the best.
>>
>> I want to convert this Cyber Tig to both TIG/Stick (CC) as well as MIG
>> (CV) mode. This way I could both tig and mig with it.
>>
>> Here's its wiring diagram:
>>
>> http://igor.chudov.com/tmp/firing/pcti-firing.jpg
>>
>> My issue is that the PCTI schematic refers to a "three phase bridge"
>> and my welder has a "six phase" rectifier where all SCR's "point" to
>> one DC bus, and where another side is connected to an interphase
>> transformer. Very different schematics.
>>
>> So, I have maybe one and maybe two possibilities:
>>
>> 1) Rewire the transformer. It is made of six secondary windings, two
>> independent ones on each phase. Two leads from two transformers on
>> every phase are tied into the interphase transformer.
>>
>> The ones that are tied together I could disconnect them from
>> interphase transformer, parallel each pair, and then connect them so
>> that I have three leads instead of six. (I am not 100% sure how to
>> connect them, but I think that it is easy. I have an idea).
>>
>> Then simply put together a new rectifier bridge wired as PCTI
>> suggests, using new SCR half bridges which I already have in my pile.
>>
>> 2) Maybe there is a possibility of wiring in the PCTI board so that it
>> works just fine controlling the six SCRs that make up the current "six
>> phase" rectifier.
>>
>> I spoke to their engineer yesterday (did not give him the schematics)
>> and he was kind of vaguely positive about it, I asked if ony K2, K4
>> and K6 were used for synchronization and he said yes.
>>
>> What I am thinking here is that I would wire all six existing Hobart
>> SCRs to the PCTI board, it would monitor voltage on K2, K4, K6, and
>> then adjust phase angles of firings of all six SCRs based on desired
>> current/voltage vs. actual. And that it would not matter that the SCRs
>> 1, 3, and 5 are wired the opposite of the PCTI sample schematic.
>>
>> Note that the SCRs that I have now are pointing with their gates to
>> the DC+ bus, which makes it impossible for K2, K4, and K6 to
>> meaningfully monitor voltage/phase. So, what I think I can do here is
>> turn all SCRs UPSIDE DOWN, so that K2, K4, and K6 could be connected
>> to 3 phase voltage.
>>
>> The side effect of this is that the negatve bus will become positive,
>> and vice versa, but that is no big deal as I could simply switch
>> contacts leading to commutator.
>>
>> Is this making any sense? Is approach #2 possible?
>>
>> thanks
>>
>> i
>>
|
|
Posted by Rene Tschaggelar on April 22, 2006, 2:54 am
Please log in for more thread options Ignoramus12493 wrote:
>
>>the "6 phase" rectifier is essentially 3 center tapped transformers wth
>>6 diodes. This design optimises the number of diodes at the expense of
>>extra trnasformer windings. This would be an older design when coper and
>>iron were cheap, tube type diodes were very expensive.
>
>
> This is absolutely correct. A great description.
This is bullshit. The 6 phase approach has lower
losses when it comes to high current.
There is only one semiconductor loss in the
centertapped recifier and not two as are in the
bridge approach. A semiconductor loss means in
the order of 2V for an SCR. An alternative
approach would use FETs, as they allow even
lower losses.
Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
|
|
Posted by Ignoramus8092 on April 22, 2006, 9:28 am
Please log in for more thread options > Ignoramus12493 wrote:
>
>>
>>>the "6 phase" rectifier is essentially 3 center tapped transformers wth
>>>6 diodes. This design optimises the number of diodes at the expense of
>>>extra trnasformer windings. This would be an older design when coper and
>>>iron were cheap, tube type diodes were very expensive.
>>
>>
>> This is absolutely correct. A great description.
>
>
> This is bullshit. The 6 phase approach has lower
> losses when it comes to high current.
> There is only one semiconductor loss in the
> centertapped recifier and not two as are in the
> bridge approach. A semiconductor loss means in
> the order of 2V for an SCR. An alternative
> approach would use FETs, as they allow even
> lower losses.
Perhaps the OP meant "optimizees the number of dioes in the path of
current". There is only one voltage drop in a six phase rectifier.
I am not too worried, I can easily make 3 phase rectifier, I have all
the parts already.
i
|
| Similar Threads | Posted | | Converting Miller GoldStar 300SS to single phase??? | August 2, 2008, 2:03 pm |
| wiring a bridge rectifier, how? | January 28, 2007, 9:31 pm |
| Testing an old welding rectifier | March 30, 2007, 10:20 am |
| Re: Advise Needed On Converting Bridgeport Mill From 575V to 220v Single Phase | September 14, 2006, 12:18 pm |
| Re: Advise Needed On Converting Bridgeport Mill From 575V to 220v Single Phase | September 14, 2006, 1:02 pm |
| Re: Advise Needed On Converting Bridgeport Mill From 575V to 220v Single Phase | September 14, 2006, 10:05 pm |
| profit-motive question: single phase adapter for 3-phase motor drives | October 4, 2007, 5:30 pm |
| FA: cool (and qute old) phase sequence indicator (for testing three phase power) | October 21, 2006, 1:56 am |
| Replacement lathe tool posts Phase II, Phase 2 and HF 39083 comparison | January 7, 2007, 10:46 am |
| [ADV] Phase-A-Matic Phase Converter on EBay Item # 230127447458 | May 10, 2007, 5:42 pm |
|
|
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap
>
> I have a hobart cybertig welder. It has a "six phase rectifier" shown
> in this schematic:
>
> http://igor.chudov.com/tmp/firing/6-phase.jpg
>
> I received a three phase SCR control/firing system made by PCTI, that
> seems to be extremely easy to hook up.
>
> By the way, PCTI loves children and is highly recommended, they are a
> wonderful company. The best of the best.
>
> I want to convert this Cyber Tig to both TIG/Stick (CC) as well as MIG
> (CV) mode. This way I could both tig and mig with it.
>
> Here's its wiring diagram:
>
> http://igor.chudov.com/tmp/firing/pcti-firing.jpg
>
> My issue is that the PCTI schematic refers to a "three phase bridge"
> and my welder has a "six phase" rectifier where all SCR's "point" to
> one DC bus, and where another side is connected to an interphase
> transformer. Very different schematics.
>
> So, I have maybe one and maybe two possibilities:
>
> 1) Rewire the transformer. It is made of six secondary windings, two
> independent ones on each phase. Two leads from two transformers on
> every phase are tied into the interphase transformer.
>
> The ones that are tied together I could disconnect them from
> interphase transformer, parallel each pair, and then connect them so
> that I have three leads instead of six. (I am not 100% sure how to
> connect them, but I think that it is easy. I have an idea).
>
> Then simply put together a new rectifier bridge wired as PCTI
> suggests, using new SCR half bridges which I already have in my pile.
>
> 2) Maybe there is a possibility of wiring in the PCTI board so that it
> works just fine controlling the six SCRs that make up the current "six
> phase" rectifier.
>
> I spoke to their engineer yesterday (did not give him the schematics)
> and he was kind of vaguely positive about it, I asked if ony K2, K4
> and K6 were used for synchronization and he said yes.
>
> What I am thinking here is that I would wire all six existing Hobart
> SCRs to the PCTI board, it would monitor voltage on K2, K4, K6, and
> then adjust phase angles of firings of all six SCRs based on desired
> current/voltage vs. actual. And that it would not matter that the SCRs
> 1, 3, and 5 are wired the opposite of the PCTI sample schematic.
>
> Note that the SCRs that I have now are pointing with their gates to
> the DC+ bus, which makes it impossible for K2, K4, and K6 to
> meaningfully monitor voltage/phase. So, what I think I can do here is
> turn all SCRs UPSIDE DOWN, so that K2, K4, and K6 could be connected
> to 3 phase voltage.
>
> The side effect of this is that the negatve bus will become positive,
> and vice versa, but that is no big deal as I could simply switch
> contacts leading to commutator.
>
> Is this making any sense? Is approach #2 possible?
>
> thanks
>
> i
>