Non stop problems with thc

Someone please help before I lose my mind. I have crossfire pro. Miller 625 hooked up raw voltage. I’m having problems with the thc during cuts. When I’m set at 40 amps I have 80-110 live volts. Cutting single pass parts it usually performs fine with live volts indicating. When I go to cut parts with multiple cuts it will start the first few passes fine then on the third or fourth cut it will lose arc voltage. Sometimes loses pierce delay. Sometimes not. If I turn thc off it cuts fine.

On the thc test I pass the resting voltage but fail the arc test at 10v every time. But when it’s actually cutting most times live volts is 100. I have tested the volts on single line cuts with the dmm and I get good volts at the banana connections. What’s going on? Anyone have ideas where to start.

What’s your pierce delay? Failure to fire is usually a pierce delay or air pressure issue.

For whatever reason, Firecontrol makes the first pierce delay longer than the set value. Subsequent delays are at the set value, so it will usually fire ok on the first pierce and fail on the next if the delay is too short.

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Oh that’s good to know. That might explain why it does good on parts with one cut.

I usually run 1.3 seconds on my 40 amp tip cutting 14 gauge. Today I tried 30 amp tip on 14 gauge with .7 delay.

.7 would work on straight line cuts but failed In parts with multiple passes.

I have never liked banana plugs. I have seen them fail and not make contact to many times or be wired wrong.

A good rule of thumb is to start your pierce delay at 1 second and work from there as every plasma cutter setup can be different.

Thanks. I have it at 1 sec now and .06 pierce with Miller drag cup. Cut height is .01, Still losing arc voltage.

Took ground clamp apart cleaned all components, ground work piece till nice and shiny. Was cutting a long cut today and it lost arc voltage after over 20 inches of cutting. Got it started again and was watching the live volts. 45-50 then would drop to 3 for a split second. That time it didn’t fail but I’m thinking it was close.

Why would I lose live volts during cutting after 2 feet?

If you have the drag shield on then take it OFF you don’t use it on a CNC table. Set your torch height to.060" from tip to metal. I am betting you are losing arc/ voltage because your tip it to far from the metal and it may also be warping a little causing it to be even farther away.

Thanks I’ll try that. Just heard may burn out consumables quicker without so I left it on.

Tried no cup. .060, 1sec., .12 pierce. Worked first three cuts in part then failed again. Very clean cuts before fail

80 volts into vim, 1.3 coming out on straight line cuts.

Still losing arc voltage??

Do you have the work clamp on the metal or the table or slats?

On the work piece. Ground metal nice and clean. Took clamp apart cleaned with wire brush. Replaced ring terminal of cable at clamp. Ohm’d the ground cable. No resistance.

Still does it

Clean the contacts in the THC.

Are you using a laptop with a 3 prong charger, or a desktop? The most common cause of low voltage readings are one of those two things. Similarly using a laptop with a metal case resting on a metal laptop stand can cause the same result.

If neither of those solutions apply to you, I recommend carefully walking through this troubleshooting flow chart. It has proven very effective at diagnosing these types of issues:

Hi. Thanks for the reply. I use a surface pro with a metal case. Never have had it charging on the machine. I isolated the computer from laptop stand with a piece of cardboard during the live voltage test and it still failed.

I have ran through the entire thc troubleshooting guide and my route was as follows:

  1. Verify THC voltage using test below: 80 volts at banana connectors, 1.2 at output cable

  2. Measure less than 5v resting voltage: yes

3)live voltage: fail at 1.2 volts

  1. Using Miller 625

  2. Yes, pin 1 and 2, 1.2 volts

  3. measure OL on 20000 scale on DMM for resistance check

  4. voltage on chip same as output cable

  5. went to flag 3. Did the computer steps with cardboard as mentioned above. No change

Today I started a part with thc on. Failed into the second cut. Makes it two seconds into cut then loses arc. Turned thc off continued with part. No lost arc. Watching the live volts with thc off while it was cutting were always 1.2-1.4. Not sure if live volts won’t read with thc off?

THC seems be failing almost constantly now where it started out intermittently. I’m thinking either vim box either loses giving an output or chip is defective. I don’t know?