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Up Topic Welding Industry / General Welding Discussion / Miller Big 40 and LN 25 problems
- - By harl Date 10-11-2008 01:48
I'm having some trouble with my Ln 25 everytime I hook up to my big 40 2002 model the ln 25 goes to the max voltage 40volts.  I didn't have a problem with it until a friend of mine hooked up his miller briefcase with a control cable to my welder.  I found a work around to my problem I switch the process selection until my LN 25 drops off max volts but I'm afraid it is under load when I do this and I might end up burning something up.  I have a selection for constant voltage wire feeder and thats what I use when I get it to drop off max voltage.  Does anyone know if my big 40 has a memory like a computer and it keeps going back to the miller briefcase or is there something else going on?  Has anyone else had this problem?
Parent - - By aevald (*****) Date 10-11-2008 02:05
Hello harl, if I'm following you correctly here you are saying that when you hook your LN 25 up to the machine in the CC mode that you see 40 volts on the volt meter and you think this means something is wrong? If this is what you are seeing while hooked up this way it is normal. It is likely that if you start welding with the LN 25 you will note a voltage drop that will be based on the amperage setting that you have set on the machine.   I don't do a lot of welding with LN 25's on CV capable machines so I can't remember the exact difference there, however it is possible that you will see the actual voltage from the Big 40, as it is set, when using the CV tap. The main difference between the CC output and the CV tap output should be that the CC output will start out with maximum open circuit voltage and then drop to actual welding voltage upon welding start-up, whereas CV voltage will be determined by the setting on the machine and will remain relatively constant even after welding has been initiated. Hope this somewhat explains what you are seeing if I have understood your post correctly. Best regards, aevald
Parent - - By harl Date 10-11-2008 02:41
I hook up my ln 25 in the cv mode I have a selection for cv wire feeder and a setting on my amperage control for constant voltage.  When I start welding with the ln 25 in cv mode the wire burns back to the tip and melts because the ln 25 is at max volts and doesn't drop off of max volts.  I switch the process selection through stick, tick, stick remote and tig remote then it drops off to what I have the welder set at usually 18 volts. I switch the process selection back to constant voltage wire feeder, then I'm able to weld and adjust my voltage its like it remembers the miller briefcase and goes to max voltage because I don't have the control cable with the ln25. I didn't used to have this problem used to I would set it on constant voltage wire feeder, set the amperage selection to constant voltage and hook up my LN 25 and start welding.
Parent - - By aevald (*****) Date 10-11-2008 02:47
Hello harl, have you also set the internal toggle on the LN 25 to the CV mode? I am just wondering if you might have missed this switch as it is kind of small and inconspicuous. Or possibly someone else switched it and you didn't notice it? Best regards, aevald
Parent - - By harl Date 10-11-2008 02:52
Yes I already checked it, it was set to cv
Parent - - By aevald (*****) Date 10-11-2008 03:10
Hello harl, I'm out of suggestions for the moment, maybe others out there have experienced similar occurrences and can offer some suggestions or explanations for you. When you figure it out please post up so the rest of us can be enlightened, I would really be interested to know what is going on. Good luck and best regards, aevald

One final thought here, when you attach the remote cable for operating a regular feeder or the Miller suitcase does the machine automatically sense this connection or do you have to activate a switch for it to know there is a connection? 
Parent - By harl Date 10-11-2008 07:21
it has a switch for remote you have to tell it when your gonna use the pin connection and I believe it is located just above the pin connection.  I always have it set for panel instead of remote I'll check again to see if it is set to panel.  I have alot of switchs, one on the briefcase for cv, panel or remote on the welder, process selection and voltage.  Thanks for helping I'll go over everything again cause I get fustrated when I burn a .80 cent tip and I could have overlooked something. 
Parent - By sbcmweb (****) Date 10-11-2008 14:21
I cannot say for sure, not knowing exactly what model of Big 40 you have & the actual serial #, but the technical manual troubleshooting guide refers to possible PC 1 malfunction. Miller is usually very vague when it comes to board problems & in the case of this machine the main control board is hermetically sealed in a protective box Miller refers to as "the Vault" There is an LED board (PC 9) that will give indication as to whether the PC 1 board is functioning correctly. There is a series of LED sequences you can use to troubleshoot PC1 in a very general sense. Your owner's manual should have a sequence guide to follow.

I took this info from a Big 40 CAT diesel manual. There are several variations of machine & engines, I am assuming the electronics for late model machines will be basically the same. I could be mistaken though. It sounds as though you have a signal issue & I didn't see anything pertaining to a "memory" when using a remotely operated device. I take it you are connecting the LN 25 to the terminals on your machine & setting the BIG 40 to VS wire feeder, remote 14 switch OFF (or panel control) the contactor, being on & the lines "HOT". You set the coarse A/V range switch to the desired setting & set the fine adjustment as well. This machine, if I am looking at one similar to yours, only has two output terminals for weld current, not a separate set for CC & CV. It sounds like a control signal issue to me & I again, may be mistaken, but the machine electronically connects to CC & CV, not physically, like with a knife switch, or a separate set of terminals.

I would check PC 9 out & see if you have an obvious problem linked directly to the main control board. It seems odd, that if you spin the selector switch, it will start doing what it's supposed to. Something may have malfunctioned with that switch, or another control function when your buddy hooked his suitcase up to it using the remote 14 out. I can't say doing what you are now is going to fry something. As a rule, switching polarity, or TAP style range selector switches while under load will cause arcing & is very bad for them. Not recommended. The switch you are using is electronically controlling the weld selections & process options. That's probably where the problem's coming from. Wherever the switch is sending a signal to. I'm believing it to be PC 1. I hope this helps you out. If you take it to service, they will give you a better idea. If the PC 1 board is bad, I can direct you to a couple places that repair them for much less the cost of a new one.

Good luck. S.W.
Parent - By sbcmweb (****) Date 10-11-2008 14:43
One other thing you can do, is call the factory & ask for Performance Engine Drive division. Don't waste your time with the sales guys at your LWS, unless they know their stuff  & know it well. John is REALLY good in PED & has walked me thru a few problems. I have a toll free number for them, PM me & I'll give it to you. This is for dealers & service techs ONLY, so I do not like to post it.

I believe your machine is using solid state electronics to create CV current, unlike a true CV machine with a separate tap or transformer windings you physically connect to. The problem most likely lies somewhere in that area, or in the control signal activating it. Again, I may be wrong. I have never worked on this machine & have no real familiarity with it. :-)

Good luck. Steve.
Up Topic Welding Industry / General Welding Discussion / Miller Big 40 and LN 25 problems

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