Miller Spectrum 875 THC Wiring

We have a Miller Spectrum 875 (NOT the auto-line version) we were planning on using with our soon-to-be-delivered CrossFire Pro and the torch height controller. I’ve read through the THC wiring instructions and wondered if others can confirm what I’ve found.

According to the Miller user manual, the rated open circuit voltage is 400V, which is greater than the 300V max listed in the THC manual.

Here’s my question - have I read this correctly? There is also an output voltage rating of 140V listed in the specs. Is this the value I use?

Assuming the 400V value is correct, can we still use the THC but just not turn the voltage too high? Or does anybody on this forum know if there is a divided voltage available on the machine somewhere?

Thanks in advance!

The Output Voltage Rating 140V DC (V volts not A amps typo) is the voltage you care about for THC. The 400v DC OCV is the voltage in the ‘air’ when it’s live but not doing anything. The THC will take the 140v down 50:1 for the height calculations. I think you’ll be using the raw voltage connections on the voltage divider for this machine. I’m using a 625 miller that has the 50:1 built in. All that said, may not be a bad idea to check with LS support to be sure.

Thanks for the reply. And for the typo catch! I’ll see what support has to say.

I do it (typos) all the time…good luck with your system!

I have the same unit and have the THC coming in as well. I am gonna need to know how to hook it up also. I did call Miller support and they told me that this unit does not have a 50:1 voltage divider nor do they sell a kit for this unit. He did mention that there maybe an aftermarket part that I can get and would not recommend any but no luck yet. Any information would be greatly appreciated. Thanks in advance.

Miller’s web site isn’t responding as I write this (get your act together Miller), but I was thinking something like this would work…

It says it won’t work with the Autoline model…your post says you don’t have the autoline…I wonder why Miller told you they don’t have a CNC option. It could be the link is wrong or something, but I’d probably call miller again to be sure…they have a few sku’s for the 875’s. Perhaps they were thinking a kit like a control board and wiring. From what I’ve read, it’s just a wiring kit and instructions on where to tie it in. They should be able to look up by serial number and tell you what’s up. Hope that helps…

James you’re saying the output voltage rating is only 140V Can I connect the LS “Raw Voltage Pigtail Cables” to the torch cable and work clamp inside of my cutter? If I can then I will mount the VIM box inside of my cutter and connect the LS “Divided Voltage Input Pigtail Cable” to the PV output soldering the spliced end to a 5.5 barrel outlet that’s mounted to the back panel of my cutter. Then I will have only 1 cable (Output Voltage Cable - Shielded) running from my cutter to the LS Control Box. I already have the touch firing cable installed from the crossfire.

Yeah - the VIM / Voltage Divider has an input for plasma cutters that don’t have the 50:1 cnc output internally - so it can take the “raw voltage” and divide it down for you and then output the lower voltage for the THC controller. I’m not sure about the splicing / cables you’re referring to, but yeah - that’s the idea. You’d have 2 sets of wires - one for torch firing on/off (which is sounds like you’ve got handled), and one set for the voltages if you are using the Torch Height Control - and that set will route thru the VIM box using the raw or 50:1 depending on plasma cutter output. In your case, you’d use the raw voltage…but be sure to double check with Langumuir support and or Miller on the wiring specifics - I’m not an expert on your cutter and don’t want to steer you wrong.

Well, we made a few test cuts and in theory everything is working although we very quickly burned up our remaining consumables.

Just for reference, however, we connected the THC red lead to the work terminal, this is easy to find, and the black lead to “Electrode_B”. We were cutting some 1/8 steel and voltages were in the 140v range I think. So at least it appears we wired the TCH correctly.

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I am looking to use my 875 miller as well. Is there any chance you have any pictures of your set up? New to all of this and understand little of it so far!