misfires on lower amperage

[Rockchucker]

Good morning kids!
I'm having trouble with my MAXPRO200 misfiring on lower amperages. When im running 130-200 amps it works flawlessly but when i dial it down to 50 amp to its very unreliable. sometimes it will run a whole complex program with no issues at all and others I have to babysit it constantly because it misfires every time it tries a new pierce. Ive tried dialing down my pierce height and it seems to help a bit but I dont want to go any lower because its hard on consumables. Will bumping up my arc voltage help or is there another parameter I'm missing. I'm not great with computers so i dont want to just start mashing buttons and screw something else over. Im using flashcut CNC
Thanks for the help and for the great community!

[weldguy]

Arc voltage is just a number the controller reads to determine the torch height, turning that number up will only get you a taller cutting height. I think that reducing your pierce height was a good idea, what is your current pierce height at when cutting at 50 amps? The actual measured height, not just the number you set on the screen.

[Rockchucker]

On 10ga the book says .160. I’ve lowered it to .140 but still not great. I’ve measured with feelers and the actual height is within .002” +\-of the target.

[weldguy]

I wonder if your ground clamp needs to be cleaned or moved.

[SegoMan DeSigns]

You check all electrical cable ends for tightness? both supply and plasma sides. I always buff & ground to metal on rusty materials.

[Rockchucker]

I was using a magnetic ground and it appears the spring wasnt strong enough to make really good continuity. put on a brand new solid copper ground clamp and it seems fine now. I never thought to look to the grounding as it works perfectly on higher amperages. thanks again for the help!

[SegoMan DeSigns]

Good Deal.

I use magnetic grounds myself and buff the bottom to keep it conductive. As for it working at higher amps I could see it arcing to complete the circuit.

[tcaudle]

Dealing with high current and connections: Like when you use jumper cables to start a car with a dead battery if the clamp connections are not really good it just wont get enough voltage/amps (power) tot he car to start it. The connection is Resistance (ohms + R)
So a bad connection has high R and that limits current flow and drops voltage .

There is a fixed relationship between Resistance(R) , Voltage(E) and Current (I) that follows the formula E = IXR
So if you change one value the others change in proportion. Normally in Plasma the Current (I) is fixed (by the Plasma Cutter) and Voltage varies based on Resistance . It's assumed that the Resistance between the workclamp on the Plasma and the actual point of the cut (i.e. through the material) is minimal . That allows ALL of the POWER to flow right at the cut with only the arc gap (height) as the resistance factor. A bad connection introduces resistance tot he flow .
If you understand the relationship of the voltage/current / resistance then you have a good idea of how Plasma cutting works .

[weldguy]

I was using a magnetic ground and it appears the spring wasnt strong enough to make really good continuity. put on a brand new solid copper ground clamp and it seems fine now. I never thought to look to the grounding as it works perfectly on higher amperages. thanks again for the help!

That's awesome, glad my suggestion was able to help