plasma control panel

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27 Mar 2019 03:30 - 27 Mar 2019 03:31 #129746 by phillc54
I am finally about to begin my plasma control panel...
I intend to use a Mesa 7i76E and a Gecko G540 as that is what I have available at the moment.
Is there a convention here as to what I/O pins we use for various functions or do we just do what fits best at the time?

Cheers, Phill.
Last edit: 27 Mar 2019 03:31 by phillc54.

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27 Mar 2019 03:42 #129748 by tommylight
Replied by tommylight on topic plasma control panel

phillc54 wrote: I am finally about to begin my plasma control panel...
I intend to use a Mesa 7i76E and a Gecko G540 as that is what I have available at the moment.
Is there a convention here as to what I/O pins we use for various functions or do we just do what fits best at the time?

Cheers, Phill.

Not aware about a convention besides pin 2-9 almost always are step/dir pins, and you would need another stepgen outputing to pin 16 for charge pump on the G540.
Be aware that G540 has no microstepping, it has division by 10, so in Linuxcnc you have to use as 10 microstepping but in reality it does nothing for 9 steps and moves only on every 10'th step. Try to use as much reduction as possible to lower the error in movement caused by that feature.
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27 Mar 2019 04:08 #129750 by phillc54
Replied by phillc54 on topic plasma control panel
Thanks Tom,
I thought that would be the case.
I have use a G540 on a mill from a parallel port for a few years and am very happy with the way it works.

Cheers, Phill.

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27 Mar 2019 13:25 #129773 by rodw
Replied by rodw on topic plasma control panel
Phill study norberts connection sheet forum.linuxcnc.org/27-driver-boards/3191...-sheet?start=0#85072

ONe thing I did wrong and never fixed was start my inputs at pin 1 and then used up the analog inputs and I never have reworked it....
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27 Mar 2019 14:01 #129776 by islander261
Replied by islander261 on topic plasma control panel
Phill

I used a G540 with a 7i76E until very recently when I switched up to using G203Vs and a 75vdc power supply. Accept for the crazy fast acceleration I can get now I haven't noticed any difference in performance. My old rack and pinion drive cam roller supported table repeats to .001" all day at 220ipm. I am using alleged 600oz/in Chinese steppers with 5:1 planetary gear boxes driving a 24 tooth pinion against a 24 pitch rack. Yes, I know not quite optimum ratio for a stepper driven plasma.

I did the same thing as Rod and started connecting i/o at pin 1 but I never intend on using the coarse analog inputs that are available on the 7i76E. I don't know of any "standard" plasma wiring configuration. I can post some drawings of my wiring when I used the G540 if you are interested. I can post my hal files as well as they might be easier under stand.

John
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27 Mar 2019 16:23 #129778 by islander261
Replied by islander261 on topic plasma control panel
Here is how I intended to wire mine to use a G540. As I recall I didn't use the charge pump or drive fault connections. All capacitors were removed from raw arc voltage circuit and never replaced.

John
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27 Mar 2019 20:04 #129792 by rodw
Replied by rodw on topic plasma control panel
Phill if you are into hacking hardware and want to pimp your Hypertherm 30 amp machine, I have a 50 amp ACS758 DIN rail mount current sensor module here and an LM358 low signal amplifier module I'd be more than happy to donate to the plasmac cause.

The ACS758 would need to be placed in series with the electrodes in your plasma cutter and will output a 0-5 volt analog output representing 0-50 amps. The LM358 will allow connecting 24 volts to it and step the 5v up to a few percent less than 24v.

So then you could connect the amplified signal and be able to read the arc current via one of the 7i76e analog inputs. This could open up a whole new world as you can synthesise your own arcOK signal based on a current threshold and do precision centre punch marks by turning off the arc at a low current threshold. If you are interested, send me a message here as the forum emails are pretty unreliable
www.vehiclemods.net.au/contact-us

Now I have a 120 amp machine, I need a bigger ACS758 module so this is of no use to me. I was put onto this by a guy in Melbourne who calls himself Beefy on some other plasma forums. He wanted to build his own external THC module using UCCNC. He is very knowledgeable about all things plasma.
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27 Mar 2019 23:35 #129804 by phillc54
Replied by phillc54 on topic plasma control panel
Thanks for the hints guys.

John, did you go with the raw arc voltage interface or the simple series resistor network that seems to be common here.

Rod, you are a bit over my head with your idea, I will contact you off list later.

Cheers, Phill

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27 Mar 2019 23:49 #129806 by rodw
Replied by rodw on topic plasma control panel
I think John has built his own divider but the simple THCAD resistor works fine. I did try that on my Thermal Dynamics recently. Most machines with a CNC port add a 1k resistor on both sides of the raw arc voltage input and you need to count that as part of the THCAD's resistor divider network. PCW says you can overdrive the THCAD so you get more resolution in the 0-150 volt range and it will clip at full scale but you need some headroom to sense kerf crossing.

But I don't think you have an interface so just mount the THCAD in a metal jiffy box at the plasma cutter and power it with 5 volts from your control box. I think Hypertherm uses the same AMP connectors as Thermal Dynamics do so if you take care, you might be able to build this box with sockets on it so you can move it to your next machine.
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28 Mar 2019 00:19 #129807 by islander261
Replied by islander261 on topic plasma control panel
Phill

The voltage divider I built (I up loaded the schematic earlier today) was originally met to work with any plasma box, blowback, HV,HV/HV and not cook the THCAD or other AtoD. You are using the THCAD with a well behaved HT box so a simple series resistor will work. If you are using a THCAD 10 then I would shoot for a full scale of about 180V. That is higher than any cutting voltage you will have. I removed all the caps from my original circuit when I was fighting the OE branch. I later found that any delay in the arc voltage sensing can play hell with the thc working. I think that using the F divide by 32 as PCW recommends should work well and provide good enough noise protection. Fast forward to now and more black ops on how the pros do it. It seems that most mechanics are way faster response than the constant current loop in the plasma box. The big boys seem to be limiting the both the Z speed and Z acceleration according to material thickness and desired response. Sorry for the long winded response. I put my voltage divider inside my plasma box and wired the output to the appropriate CPC sockets. Your HT does use the same connectors as the TD for the CNC interface, it is a standard AMP CPC series connector and you should be able to get pins and sockets from an online stockist ( no idea about where to buy this in Oz). My THCAD lives in a small box under my plasma power supply and connects to the main control box through a piece of shielded stranded cat 5 cable. I will up load a photo later when I am in the house. I send 24vdc over the connecting cable and then use a small ebay made in China buck converter to get 5v (don't like sending my logic supply all over the noisy shop). I do have a several LEDs on the box to indicate power, torch on and arcok.

John
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