Powermax 45xp lost arc delay (Solved)

snowgoer540 wrote:

From the Hypertherm owner's manual (65-85 but I'd bet the others are similar):

With reference to Start (start plasma or Torch On): "Normally Open. Requires dry contact closure to activate."

With reference to Transfer (start machine motion or Arc Ok): "Normally open. Dry contact closure when the arc transfers."

Being as they are using the same term "dry contact closure", and seeing as I took apart my Hypertherm and found the exact part number for the mechanical relay they use, we could safely apply logic and deduct that they are wanting the end user to use a mechanical relay to provide dry contact closure and start the torch. Also, further logic applied could take us to the fact that a manual torch uses a simple momentary on off switch to start the torch. Neither are SSR's and therefore, a mechanical relay should be used (as the manual states).

I suspect there is not enough amperage to properly bias the SSR, and Hypertherms are particularly sensitive to this.

I'm not disputing that a mechanical relay fixed your issues or that the 7i96 on board relays are unsuitable. But its not appropriate to extend "further logic" to extend the definition in a machine manual to suit your own argument.

Dry contact means a switch controlled by another circuit with independent power where no current passes through the switch. It does not mean that there has to be an air gap between the contacts and it does not mean it has to have a coil. Here is another quote:

All relays, including solid-state relays, use dry contacts.

control.com/technical-articles/the-diffe...et-and-dry-contacts/
So by that definition, any SSR can achieve a "dry contact closure"

As with everything here, its up to you the machine builder to select suitable components for the application. Sure a good old fashioned mechanical relay has been proven to work in this application but that does not mean its the only solution. There are other solid state or opto isolated relays that will also surely work. You just have to choose wisely.

To fire the torch, all we need to do is to close a switch as we are providing the dry contacts.

But when it comes to designing a circuit that is responding to a remote "dry contact closure" such as the Arc OK circuit, you the builder need to take additional precautions to ensure that adequate current passes through the remote "dry contacts" for reliable long term operation. Using a Mesa output on its own is not enough to guarantee this. Its quite remiss of Hypertherm not to specify the minimum current required to pass through their "dry contacts" but from Snowgoer's tireless efforts we know that its 100 mA and those "dry contacts" can handle a maximum of 10 amps. Coincidentally, they are the exact same values I found Everlast used when I conducted similar surgery to an Everlast machine. It might work for you without any additional components for a while or possibly even forever but when and if oxide builds up on those contacts and intermittent operation starts, you will be in a very stressful and frustrating place. I've been there. Thats why any machine I build will have an appropriate pull down resistor and heat sink to ensure > 200 mA passes through those remote "dry contacts" to ensure reliable operation for the life of my machine.

The 7I96 outputs should be fine firing "torch on"
In fact it should be considerably more reliable than
a relay as it has no contact wetting requirements.
and near 0 voltage drop at the typical torch-on currents
(and unlike typical a SSR, no minimum or bias current
requirements, in fact, it is a better dry contact than a relay)

Arc OK is a different issue if its a dry contact output from a relay
contact, and they will require wetting current. Note that the wetting current
can be as low as a few mA in small non-power relays.

tommylight wrote:

Rod is right, they all have a rated minimum and maximum current, but it will work without it for at least 20 or 30 years before failing.

But that has not been the case for everybody. If you are affected its a very stressful position to be in. Sometimes compounded by disbelief of others who don't understand.

tommylight wrote:

After all this, i still agree with Rod, when building a machine add a resistor, it will most probably come in handy after 5 or 30 years of use, or even faster if there is a lot of humidity around.

Sometimes a lot sooner than that so defensive building is worth it at the beginning.

PCW wrote:

Arc OK is a different issue if its a dry contact output from a relay
contact, and they will require wetting current. Note that the wetting current
can be as low as a few mA in small non-power relays.

I think this depends on the quality of the plasma cutter. When this fault was first diagnosed for me, we used a 1 K pulldown (41 mA) and it resolved the issue. But then I sold my Everlast to Little Sparky and he got caught out again until he replaced it with a 90 R (267 mA) pulldown and then it came good after a while. There have been a couple of Hypertherm users afflicted.

So for safe operation over a broad range of machines, I think > 100 mA is required. Then power dissipation is a concern.

Nice to know the 7i96 relays should work as "dry contacts"

Wow you guys are impressive. All your knowledge can be overwhelming to a newby like me.

It would be nice not to have to add an additional relay to my system since the 7i96 have ssr's, but it makes for a quick test and if it "fixes"the issue, then I can cut metal again. That is after all the goal here. Right?

Let's just say for sake of argument that I wanted to try the diode or pull down resister. Would I put that on the ssr output pin of the 7i96? How would I go about tieing the resister to ground? A schematic of what you guys are referring to would sure go a long way. I'm very graphically driven. Text doesn't always make sense to me.