New Plasma build question
17 Aug 2019 09:01 #142374
by rodw
Replied by rodw on topic New Plasma build question
1 & 2 you have right.
3. You would use your relay to switch field power to a 7i76e input
4. 300 V can be exceeded so make sure your electronics can handle overvoltage to about 500 volts without frying anything.
ArcOK is a set of dry contacts in the plasma cutter
. You use them to send field power from hte machine, theough the arcOK contacts and back to an input.
You need to hold about +- 2 volts from target torch voltage.
BUT:
If you are using a 7i76e, I would strongly recommend you abandon your plan to build a now obsolete second grade UP/DOWN THC and purchase a THCAD-10 From Mesa for $69 and adopt the plasmac configuration which is now the gold standard for Linuxcnc plasma control (and probably for plasma controllers in general). See linuxcnc.org/docs/devel/html/plasma/plasmac-user-guide.html
and make sure you read this guide: linuxcnc.org/docs/devel/html/plasma/plasma-cnc-primer.html
When you see Tommylight, long the champion of a configuration using the proma THC to abandon his config and adopt plasmac for all of his commercial projects, you can't ignore Plasmac.
3. You would use your relay to switch field power to a 7i76e input
4. 300 V can be exceeded so make sure your electronics can handle overvoltage to about 500 volts without frying anything.
ArcOK is a set of dry contacts in the plasma cutter
. You use them to send field power from hte machine, theough the arcOK contacts and back to an input.
You need to hold about +- 2 volts from target torch voltage.
BUT:
If you are using a 7i76e, I would strongly recommend you abandon your plan to build a now obsolete second grade UP/DOWN THC and purchase a THCAD-10 From Mesa for $69 and adopt the plasmac configuration which is now the gold standard for Linuxcnc plasma control (and probably for plasma controllers in general). See linuxcnc.org/docs/devel/html/plasma/plasmac-user-guide.html
and make sure you read this guide: linuxcnc.org/docs/devel/html/plasma/plasma-cnc-primer.html
When you see Tommylight, long the champion of a configuration using the proma THC to abandon his config and adopt plasmac for all of his commercial projects, you can't ignore Plasmac.
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17 Aug 2019 10:16 #142376
by tommylight
Well not yet completely, but for sure the 5 new ones i am trying to build will use PlasmaC.
This is the part of the year when my clients use their machines 16 to 18 hours a day every day, so till late Octomber i can not change them to PlasmaC.
Replied by tommylight on topic New Plasma build question
When you see Tommylight, long the champion of a configuration using the proma THC to abandon his config and adopt plasmac for all of his commercial projects, you can't ignore Plasmac.
Well not yet completely, but for sure the 5 new ones i am trying to build will use PlasmaC.
This is the part of the year when my clients use their machines 16 to 18 hours a day every day, so till late Octomber i can not change them to PlasmaC.
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17 Aug 2019 10:28 #142377
by rodw
Replied by rodw on topic New Plasma build question
For the sake of two months, you are forgiven Tommy!
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17 Aug 2019 10:47 #142379
by CNCFred
Replied by CNCFred on topic New Plasma build question
Thank you very much for the guide!
Not according to plan I bought a cut 70p and got from Stahlwerk the connector to start the torch for free.
Question is now how to find out the arc ok signal
Rodw: since the cut 70p does not have a divider do you suggest to make a voltage divider myself and use the thcad-10 instead of the 300?
Thx
Not according to plan I bought a cut 70p and got from Stahlwerk the connector to start the torch for free.
Question is now how to find out the arc ok signal
Rodw: since the cut 70p does not have a divider do you suggest to make a voltage divider myself and use the thcad-10 instead of the 300?
Thx
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17 Aug 2019 11:07 #142381
by tecno
Replied by tecno on topic New Plasma build question
In my build I have a 50A with no divider and went for THCAD300.
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17 Aug 2019 11:10 - 17 Aug 2019 11:14 #142382
by rodw
If you follow the plasma guide I linked to, there are some suggested rules about choosing a THCAD version. For the price of a THCAD, there is not really any reason to build your own divider. Basically, if you have room inside the case use a THCAD-300, otherwise a THCAD-10 with the resistors placed inside the plasma case to keep voltage in the non lethal range on the outside.
EDIT as tecno says, the THCAD-300 is a good option if you can mount it internally.
Replied by rodw on topic New Plasma build question
You can't really make your own ArcOK signal. I do know one guy (not using linuxcnc) who used an ACS758 current sensor to synthesise one. But Plasmac has a mode to work around this so there is no need to panic!Thank you very much for the guide!
Not according to plan I bought a cut 70p and got from Stahlwerk the connector to start the torch for free.
Question is now how to find out the arc ok signal
Rodw: since the cut 70p does not have a divider do you suggest to make a voltage divider myself and use the thcad-10 instead of the 300?
Thx
If you follow the plasma guide I linked to, there are some suggested rules about choosing a THCAD version. For the price of a THCAD, there is not really any reason to build your own divider. Basically, if you have room inside the case use a THCAD-300, otherwise a THCAD-10 with the resistors placed inside the plasma case to keep voltage in the non lethal range on the outside.
EDIT as tecno says, the THCAD-300 is a good option if you can mount it internally.
Last edit: 17 Aug 2019 11:14 by rodw.
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17 Aug 2019 12:08 #142387
by tommylight
That works in most plasma cutters, but in some that have better filtering it does not.
3 windings of the torch cabke are enough to trigger a reed relay and that works in all of them, so this is what i use now.
With THCAD that is not needed at all as you can fine tune the voltage to trigger ARCOK signal.
Replied by tommylight on topic New Plasma build question
I did make plenty of them using an 24V electromagnet, removing the core, adding a long screw, winding 3 turns of the torch cable around it ( not easy and often has to be prolonged ), adding a rectifier and a very smal low current 12V relay.You can't really make your own ArcOK signal.
That works in most plasma cutters, but in some that have better filtering it does not.
3 windings of the torch cabke are enough to trigger a reed relay and that works in all of them, so this is what i use now.
With THCAD that is not needed at all as you can fine tune the voltage to trigger ARCOK signal.
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17 Aug 2019 12:15 #142388
by tecno
And I will be bold enough to mount my THCAD300 on the outside
Replied by tecno on topic New Plasma build question
EDIT as tecno says, the THCAD-300 is a good option if you can mount it internally.
And I will be bold enough to mount my THCAD300 on the outside
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17 Aug 2019 15:50 #142395
by Clive S
Replied by Clive S on topic New Plasma build question
Attachments:
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18 Aug 2019 00:24 #142412
by rodw
Replied by rodw on topic New Plasma build question
That should be fine
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