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clarify AC vs DC welding on my miller thunderbolt

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diggerdave

11-11-2004 10:59:58




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Hi. wondering if someone can clarify a topic that was posted here a while ago. I have a miller thuderbolt stick welder. Ive done a bit of welding learning by reading then trial and error. Using 7018 rod (recommended by dealer as an easy rod for a beginner)I fabricated a pretty cool loader for a tractor i have. I cant be certain if i had it set to AC or DC, but I got real strong and nice looking welds. A while later I was using it and had trouble keeping an arc and the welds looked horrible an noticed that it was switched to the other (AC or DC). Being a little green here..my question is since the welder is plugged into the wall (AC) shouldnt the machine be left on AC? Im pretty sure the post from june of this year said that AC is not as smooth as DC with 7018 due to current stopping and starting 120 times a second. If this is true then why the DC selector option?? will I hurt it running on DC? thanks for any advise. dave

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George G

11-12-2004 13:50:39




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
I think you need a manual. Get you model and s/n, and click on link below.



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Big Jim

11-11-2004 21:19:22




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
The general rule for stick electrodes is even numbers are designed for DC and odd numbers are designed for AC. 6010 - DC, 6011 - AC
DC is preferred in most cases.
Be sure to keep the 7018 warm and dry. The coating will absorb moisture and function poorly.
My favorite for maintenance welding is 7014. Very easy to use in any position.



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bubba

11-11-2004 18:29:44




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
7018 is a low hydrogen rod.It is imperative to use low hydrogen rods when welding high carbon steel and needs to be welded with DC current(not reverse current setting).Most all modern farm and construction equipment is manufactured with high carbon steel.Using 6011 or 6013 on high carbon steel will cause hydrogen bubbles to form in the molten metal and causes cracks in the weld which destroys its strength.6011 is fine for most other structural metals and is much easier to weld with over 7018.6013 should only be used on very thin metal where burn through can be a problem since it penetrated very poorly. 6013 can be used for temporarily tacking metal together where the weld may have to ground off later.

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txblu

11-12-2004 06:18:03




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 Re: clarify AC vs DC welding on my miller thunderb in reply to bubba, 11-11-2004 18:29:44  
Sir, your chemical analysis is exactly the reason this amateur switched from 6011's to 7018's.

Mark



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buickanddeere

11-11-2004 17:48:15




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
DC will let you run either polarity for thick or thin metal.



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lucass

11-11-2004 17:40:27




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  

i use dc on thin stuff and ac for heavy stuff because ac penetrates deeper on a 225 type welder. 6011 and 6013 are for cold roll and 7018,7014 are for tougher high carbon made steels. lucas



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seth_ia

11-11-2004 16:49:15




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
7018 is not a rod for amatures to use on ac, but dc will work very well. 99% all 7018 rods are ac or dc. It's just that they are very difficult to run on ac. while they do have easier to run ac only rods, I don't even think that I have ever even seen a dc only rod. If you are not very experienced the problems you had with 7018 on ac are normal with rod sticking and poor bead. ac is always harder to run than dc regaurdless of what rod you are using. 6013 is the easiest rod to run. I call them idiot proof as that you can drag them. 6011 is a great rod for dirty steal, but the bead is not quite as good as other rods. It also has a high dispostion rate, which mean it takes less heat to melt the rod and you move faster. Remember good welders don't get married to just one rod. It should be noted that 7018 is a stronger rod than say 6011 or 6013, and must be used on things like grader blade. The 1st two numbers * 1000 is the strength of a rod( 6011 is 60*1000=60000lbs and 7018 is 70*1000=70000lbs). You will know you are a very good welder when you can run a vertical UP with 7018 on ac output. Not imposible, but very very difficult.

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dirt man

11-11-2004 16:30:28




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
Dave, make sure that you keep your 7018 rod clean, dry and fresh. wet or contaminated rod does not work well at all.
Phil



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txblu

11-12-2004 06:15:38




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 Re: clarify AC vs DC welding on my miller thunderb in reply to dirt man, 11-11-2004 16:30:28  
Good point. I use an old Igloo beer (er ah pop) cooler.

Mark



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Charles (in GA)

11-11-2004 15:04:07




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
" will I hurt it running on DC?"

Its designed to be used for AC or DC output, so you won"t hurt it a bit using it like its intended to be used.

Charles



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Vern-MI

11-11-2004 13:27:35




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
Hi Dave

To answer your question: "Being a little green here..my question is since the welder is plugged into the wall (AC) shouldnt the machine be left on AC?" Your welder uses regular 60 cycle AC input to operate while it gives you the option to use either AC or DC on the output. The DC output is rectified AC from the input side. So the welder is converting the AC to DC for you.



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txblu

11-12-2004 06:14:24




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 Re: clarify AC vs DC welding on my miller thunderb in reply to Vern-MI, 11-11-2004 13:27:35  
True sir, but you can bypass the "swinging choke" and rectifers and have your output AC like the input. That's why it's called AC-DC.

Slight problem with the DC is that due to the rectifier dissipation (I'd assume) or they only have half wave rectification, anyhew the DC rating is limited to 110 amperes whereas the AC is rated for 220.....at least on my Miller.

Mark



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TimV

11-11-2004 13:14:07




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
Diggerdave: More than likely you originally had the machine set to DC, then switched to AC and your weld quality went south. Much of the 7018 rod sold will only work with DC, and if you try to use it with AC it will weld terribly, if at all. While you can get AC7018 rod, it still works best on DC. The input current type (AC or DC) has no bearing on the output current type of the welder--it is changed (via a transformer setup) to whichever mode you set the welder for.

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txblu

11-11-2004 12:28:59




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
Have the Miller 200 AC-DC. Recently graduated from the infamous 6011 to the 7018. Will never return.

The AC function reverses current 60 times per second. That means that your arc starts and stops 60 x 2 (1+, 1-) times per second. That also means that electrons are going into and out of the stick and the metal at that rate; back and forth, back and forth.

DC is just that Direct current. You set up the polarity so that the electrons leave the rod which is what you want for the sacerifice element. There is a big inductor in series with the DC line that keeps current flowing during the humps in the rectified AC; like a filter capacitor on the power supply of your radio to get rid of 60 cycle hum. The inductor is used rather than the cap as it is better suited for high currents.

Result is smooth steady current and smooth steady erosion of the rod. Result? Perfect welds.

To weld on AC you need the 7018 AC rod. I only use AC when I am remote operating off an Aux power unit and need all the current I can get. For reasons given, welds are substandard, but they work.

The 7018 really puts out a super weld in strength and beauty for me..... a self appointed, self taught, master welder..... of old iron and associated parafanelia.

Mark

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old

11-11-2004 11:54:04




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
DC will make a stronger, better looking weld and with 7018 rod its also easyer to keep an arc. DC will also get better penatration so makes better weld. Most people I know never use the AC side of there welders.



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seth_ia

11-11-2004 16:53:44




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 Re: clarify AC vs DC welding on my miller thunderb in reply to old, 11-11-2004 11:54:04  
Ac has to be used when welding around magnetic feilds, other wise your ark will blow around. Granted most people never weld around a magnetic feild.



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Ron Anderson

11-11-2004 11:35:17




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 Re: clarify AC vs DC welding on my miller thunderb in reply to diggerdave, 11-11-2004 10:59:58  
You must have been using your welder in the DC mode when it worked good for you and switched it to AC later. I leave mine on DC since it is easier to work with. Funny when you think of progress made from a common AC welder to option of AC DC welder then to modern wirefeed.I have both AC DC stick and wire feed and they compliment each other. Wire feed is easy to operate but when it comes to dirty metal or heavy steel stick is the way to go. Your welder is designed for both AC and DC use which ever you want to. Ron

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