Control board of a plasma power supply (start, arc transfer and divided arc voltage at the machine interface)
The control board of a plasma power supply as the CNC and height controller see it · start input closed by a dry contact, transfer (motion) output rated for a relay, divided arc voltage at 50:1 or a selectable ratio, ELV outputs that are not SELV, and the Arc OK signal a controller prefers
Inside a plasma power supply, the control board runs the start sequence and arc current, and it is also the source of the signals the cutting machine depends on: a start input from the CNC, a contact that closes when the arc has transferred to the plate, and a scaled-down arc voltage for torch height control. Their electrical type and ratings decide how the CNC and height controller are wired to it.
Control boards of plasma cutting power supplies, viewed through their machine interface signals to CNC and torch height controllers. The power supply as a unit is covered on the Plasma power supply: the power source unit of a mechanized plasma cutting system page; height control on the Plasma torch height controller: the arc-voltage control unit and Z lifter that keep the torch at cut height page; contract board assembly on the PCB assembly (PCBA) service page; general relay I/O boards on the Control and monitoring I/O board with relays, isolated inputs and RS-485 page.
CNFX editorial research · Sources checked October 13, 2026 · 2 sources
Start input, transfer output and divided arc voltage
Hypertherm's Field Service Bulletin 806180 (Revision 5, December 2013) for the Powermax45, 65, 85, 105 and 125 lists the machine interface signals: Start is a normally open input with "18 VDC open circuit voltage at START terminals" that "Requires dry contact closure to activate"; Transfer is a normally open output giving "Dry contact closure when the arc transfers", rated "120 VAC/1 A maximum at the machine interface relay or switching device (supplied by the customer)". [1]
The Powermax45 has a built-in 50:1 divider; the Powermax65 and 85 have an optional five-position divider set by DIP switches to 20:1, 21.1:1, 30:1, 40:1 or 50:1, preset at 50:1. The bulletin gives open-circuit maximums of 7 V for the Powermax45 divider and 18 V for the Powermax65/85. [1]
Signal
Type
Rating or ratio
Sockets
Start (start plasma)
Input, normally open
18 VDC open circuit; dry contact closure
3, 4
Transfer (start machine motion)
Output, normally open
Dry contact; 120 VAC/1 A max at customer relay
12, 14
Ground
Ground
—
13
Voltage divider
Output
50:1, 7 V max (PM45); 20:1–50:1, 18 V max (PM65/85)
5 (−), 6 (+)
Ask the supplier for the interface table of the exact power supply and board revision, including divider ratios, maximum output voltage and the transfer contact rating.
02
Wiring the board's outputs to a CNC or height controller
Hypertherm cautions that the divider output is an impedance-protected functional extra low voltage (ELV) output, that "The voltage divider is not fault tolerant and ELV outputs do not comply with safety extra low voltage (SELV) requirements for direct connection to computer products", and that the interface cable must be terminated inside the enclosure of listed and certified height or CNC controllers. [1]
The LinuxCNC QtPlasmaC documentation advises that "If the plasma power source has an Arc OK (Transfer) output then it is recommended to use that for Arc OK rather than the soft (calculated) Arc OK" derived from arc voltage, and names a reed relay on the work lead as an alternative where the source has none. When the CNC port's divided voltage is used, it says "A common ratio used is 20:1"; where full arc voltage is taken through a resistor divider instead, it warns for HF start power supplies that "EACH OF THESE RESISTANCES SHOULD BE MADE UP OF SEVERAL HIGH VOLTAGE RESISTORS". [2]
State which controller will read the arc voltage and Arc OK, its input range, and whether isolation is provided between the plasma interface and the controller electronics.
03
Plasma control board interface details
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Power supply: [model; board revision]
Start input: [voltage; contact type]
Transfer output: [contact rating]
Arc voltage: [divider ratio; max V; full arc option]
Controller: [CNC; THC; input range; isolation]
Cable: [length; termination; enclosure]
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
What closes the start input on a Powermax?
A dry contact closure across terminals that sit at 18 VDC open circuit, per Hypertherm's bulletin. [1]
Can the transfer output drive a logic input directly?
Hypertherm rates it as a dry contact up to 120 VAC/1 A at a customer-supplied relay or switching device. [1]
Which divider ratios are available?
50:1 on the Powermax45; 20:1, 21.1:1, 30:1, 40:1 or 50:1 on the Powermax65/85. [1]
Should Arc OK come from the power source or be calculated?
LinuxCNC recommends the power source's Arc OK (Transfer) output where one exists. [2]
Sources and what still needs a direct check
Sources checked 2026-10-13. Hypertherm's Field Service Bulletin 806180 is read from a copy posted on the LinuxCNC forum; the LinuxCNC project publishes the QtPlasmaC documentation.
