Arc OK intermitent issues on torch fire

tommylight wrote: Again, lower the pierce height.
Try 3 or 2.5mm, see if that happens again.
If the torch is high it can not reach the threshold to activate the arcok signal, although the arc is established and cutting.
Or raise the cutting current a bit if possible.

Yer still having the same problem unfortunately

phillc54 wrote: That will give you around 24mA which would "probably" be adequate.

24 mA is well below the min current rating of most internal Arcok relays of 100 mA (certainly hypertherm, Everlast and Thermal Dynamics).

You need to add a pulldown resistor of around 90Ω 10W assuming a 24 volt ArcOK circuit and a Mesa card. Connect it from the Mesa input to -24 volt.

To achieve this from readily available parts we recommend to:

Get 3 x 270Ω 5W Resistors (Jaycar PN RR3284) and wire them in parallel. This will give 90Ω with 267mA and 6.4W of dissipation. 3 x 5W resistors in parallel will give you 15W power dissipation capability, so plenty of margin. Leave an air gap between the resistors though.

Expect to have to cycle the ArcOK a few times to burn off oxidisation. The last time this came up the user said
"After all this, and Rod's new arc ok resistor resistor blowing away the built up oxide, I am getting reliable cuts with about 30 minutes of cut time not throwing up a single error yet."

I'll leave it to you to find the thread.

rodw wrote: 24 mA is well below the min current rating of most internal Arcok relays of 100 mA (certainly hypertherm, Everlast and Thermal Dynamics).

The Hypertherm one I saw was 100mA @ 5V which is 0.5W. This equates to 21mA @ 24V.

phillc54 wrote:

rodw wrote: 24 mA is well below the min current rating of most internal Arcok relays of 100 mA (certainly hypertherm, Everlast and Thermal Dynamics).

The Hypertherm one I saw was 100mA @ 5V which is 0.5W. This equates to 21mA @ 24V.

I read that too but on checking this out with some research and conferring with my go to electronics expert, that not how it works with relays. The Hypertherm relay is also rated to 10 amps max so you need to be well within the minimum current. Regardless of the voltage passing through the circuit, you must respect the current ratings! eg. In this case, >100 mA at 24 volts (or whatever you are using).

We've had this discussion before and those who chose to take the advice I offered above fixed their problem.

Here it is.
forum.linuxcnc.org/plasmac/39985-valid-arc-lost-2?start=0

rodw wrote: I read that too but on checking this out with some research and conferring with my go to electronics expert, that not how it works with relays. The Hypertherm relay is also rated to 10 amps max so you need to be well within the minimum current. Regardless of the voltage passing through the circuit, you must respect the current ratings! eg. In this case, >100 mA at 24 volts (or whatever you are using).

The manufacturer of the relay in the Hypertherm quotes: NOT minimum current...