Powermax 45xp lost arc delay (Solved)

The pull down resistor goes from your arcOK input pin to field power ground. When the arcOK circuit is energised, additional current passes through the resistor to ground and the 7i96 is unaffected. The resistor should be around 90 Ohms and be > 6 W. To use off the shelf components, 3 x 270 ohm 5 W resistors in parallel will give 90 Ohm, 15W. Keep them in the air for cooling. I have ordered a 100 Ohm 35 W TO220 style resistor with an appropriate heat sink which dissipates about 6W. More on that later.

If you use a mechanical relay to trigger your torch, you should place a diode (IN4004, IN4007 et al) across the coil contacts of the relay so that the band on the diode points back to the output pin. The other wire on the relay coil goes to field power ground. In view of your original post, I would try in this order.

1. Extending the THC delay as discussed.
2. Adding the ArcOK pulldown
3. Use an external relay for torch on but based on PCW's feedback, that is not necessary so hopefully you do not get to this step.

2 pence / 2 cents....

dry contacts (i.e. physical switch, relay or contactor) are used because electronic devices (SSR's, optocouplers or optoisolators) can and do normally have a leakage / quiescent current.

dry contacts have no leakage current, hence zero chance of being triggered in error or held in the on condition.

The problem is with high impedence circuits, and the impedence is not given by hypertherm in their datasheets just a requirement for "dry contact closure".....

diodes (and in part capacitors) are not required unless the switched circuit uses a coil / relay arrangement because the collapsing field can induce a reverse voltage which can kill electronic devices. It is HIGHLY unlikey that you wlll need to use a diode as the switched circuit is highly unlikey to be a relay..... because it would not need a dry contact closure if it was as it would not be affected by (low) leakage currents through the relay coils (they would not have enough current to energise / hold the relay closed in my opinion)

I would suggest using a relay.... Do not use SSR's / optocouplers or optoisolators....

If it works for you.... great.... if not.... use a RELAY.....

I use very high speed (repeatable) reed relays for firing the torch signal. But a small (low current rated) relay will work just fine....

1. All switches have leakage current (it may be small but its always there)
2. Proper low power OPTO or SSR circuits do not have significant leakage current
3. If the Hypertherm start circuit is quite high impedance, a relay would be a bad idea due to the lack of contact wetting current so I would suggest _not_ using a relay for reliability reasons

BTW it would be valuable if someone with a Hypertherm measured the Plasma Start
circuit current with a DVM set to say a 200 mA range (they specify 18VDC open circuit voltage
but not the closed circuit current)

Note that a normal external SSR block type relay's would not be expected to work well
as these often need a minimum current and have significant voltage drop because they use
bipolar transistors and must get their base drive from the switched power side

A MOSFET type SSR would be superior to a mechanical relay

tommylight wrote:

This has gotten so much out of hand that i need to source a 7i96 as soon as possible to test this.
I would venture a guess that all the issues stem from the interference caused by the high voltage torch start.
The smallest SSR i have are 12A AC ones so not really useful for this.

Where do you call home? Odds are really low you are near me, but if so you could use mine for some testing. I'm in Utah USA.