DC amps vs AC amps

[JB4310]

First off let me say, after reading the threads in this forum, I never knew how much I never knew about welding If I ever knew what I never knew, I'd of never started!

Couple of questions,

Just wondering why on my ac/dc machine, max amps on the ac are higher than on the dc?
225 for ac and only 150 for dc, are they equivalent?? or is ac capable of welding heavier/thicker steel?

Also, just recently replaced my ground clamp, I had used a battery jumper cable clamp for all these years til the spring wore out, it had a little insulation on the handles, all the ground clamps I've seen have no insulation on them. What is the reason for no insulation on the ground? I find myself with both cables in my hands sometimes, and some times with no gloves. what's the rule, never hold both at once or never handle cables with no gloves?


What is the general consensus of a miller thunderbolt AC/DC. strictly homeowner/hobbyist or slightly better?

Couple of pics of my buzz boxes, I replaced the ac only with the ac/dc 2 years ago. I have not used ac since. Found that ac machine on the side of the road, in a pile of garbage, cobbled it back to life and it served my needs for 30 years!!!


Thanks JB.

 

[rankrank1]

...Just wondering why on my ac/dc machine, max amps on the ac are higher than on the dc?
225 for ac and only 150 for dc, are they equivalent?? or is ac capable of welding heavier/thicker steel?...

What is the general consensus of a miller thunderbolt AC/DC. strictly homeowner/hobbyist or slightly better?

Both welders pictured are transformer based welders which means they transform your household power (lets approximately say 240 volts, 40 amp input power from your breaker panel which is AC power) to roughly (225 amps max , 75 volt open circuit voltage or about 30 volts when actual welding is happening still all in AC power though). From here to get DC power, diodes and bridge rectifiers are used inside the welder to convert the AC power to DC power. During this conversion process from AC to DC there is parasitic power loss. Kinda like how the motor in your JD 4310 has more hp at the motor flywheel, than it does hp at the rear wheels due to parasitic loss from the driveline, accessories like alternators and hydraulic pumps, and transmission parasite loss, etc.

Either of these two welders will weld thicker metal on AC than DC. If you happen to stop by a TSC that has the Hobart Stickmate AC/DC with the Hobart advertsing literature posted; it even states DC capability up to 1/4" material and for welding material over 1/4" thick then the use of AC power is recommended. (FYI the Hobart Stickmate is the same as the Miller Thunderbolt - both Miller and Hobart are owned by ITW).

That said, 100 amps on DC is stronger than 100 amps on AC all other variables being equal. The arc is going out 60 hertz on AC power just like your household lights are going out at 60 hertz even though it is hard to see this with human eye. On DC power the current is continuous in one direction and never goes out so DC is slightly more efficient. Very generally speaking, if you look at detailed weld charts for rods that are suitable for either AC or DC use: The manufacturers typically recommend a 10% to 15% higher amp setting when using an AC power source as compared to a DC power source for the same rod. (e.g. a rod that requires 100 amps on DC will probably require 110 to 115 amps on AC all other variables remaining constant of course). To aide my memory, I typically consider AC power to be the happy medium located inbetween DC Electrode Positive (70% of heat into rod and 30% of heat into work) and DC electrode Negative (30% heat into rod and 70% heat into work). No such thing as polarity on AC since AC is constantly switching back and forth on polarity at 60 hertz so in my mind that should put it roughly in the middle (50% heat into rod and 50% heat into work) - not exact science but helps me keep things somewhat in perspective.

The Miller Thunderbolt, Hobart Stickmates, and Lincoln AC/DC buzzboxes are all three considered very good and durable welders for a farm/hobby type shop. You can weld almost anything that a homebased shop would ever encounter with any of these units (excluding very thin metal under 1/16 of an inch or so which is better suited to MIG or TIG, but even thin metal can be done in a pinch with practice). You are pretty much limited to 1/8 rods or smaller on any of the 3 units on DC power, but you can easily burn bigger diameter rods up to about 3/16 or so on AC power if the need ever arises. In short, Lots of welder for very little money and they are all durable too. It is not uncommon to see welders like these 50 - 60 years old still in use when used as recommended.

 

[JB4310]

Thanks, that explains alot.

I got pretty efficient with AC, but I do like the DC now, cleaner and quieter.

Mostly been running 7018 rod 1/8" got some Hobart rod that says it's good for dc or ac, man it is deep penetrating, but the slag is like ceramic and does not want to release. I might be running it a little to hot to help with the restrike that 7018 is known for.

JB

 

[rjmack]

Mostly been running 7018 rod 1/8" got some Hobart rod that says it's good for dc or ac, man it is deep penetrating, but the slag is like ceramic and does not want to release

thats the weld, hanging onto it.

these are 5/32 and 1/8 7018 you need to let it cool at least until the colour has gone out of the slag. if the weld is smooth, the slag should just peel itself right off.:thumbsup:

 

[JB4310]

thats the weld, hanging onto it.

these are 5/32 and 1/8 7018 you need to let it cool at least until the colour has gone out of the slag. if the weld is smooth, the slag should just peel itself right off.:thumbsup:

The welds look pretty good, not quite as nice as yours, but the slag is not releasing except with alot of hammering and chipping. definitely getting good penetration, but not getting as much of that crowned look like in yours.

I've never gotten slag like this before, don't know if it's the brand of rod or what, but it looks like glazed tile.

7024 are known for self releasing slag, with those I get it curling up and off by itself

JB.

 

[Brad_Blazer]

7018 slag. I think the rods were Radnor.

 

[rjmack]

I've never gotten slag like this before, don't know if it's the brand of rod or what, but it looks like glazed tile.

that's normal, it's also why it's a bit harder to strike an arc with a partially burned rod... there is a layer of glass stuck to the end of the electrode. you have to break the glass off the end of the rod to close the circuit.

when the slag starts peeling itself off, then you are making some headway.:thumbsup:

 

[JB4310]

7018 slag. I think the rods were Radnor.

that's normal, it's also why it's a bit harder to strike an arc with a partially burned rod... there is a layer of glass stuck to the end of the electrode. you have to break the glass off the end of the rod to close the circuit.

when the slag starts peeling itself off, then you are making some headway.:thumbsup:

So is it more about the correct Amp setting dialed in or the experienced welding technique ?

Also I've always heard about DC only 7018, but I always see 7018's rated for both ac and dc. Is there a big difference in performance using the dc only rod ?

.

 

[rjmack]

So is it more about the correct Amp setting dialed in or the experienced welding technique ?

experience tells you when you are too hot or cold.

the amp range is usually noted on the box 1/8 7018 max 125 amps. it's a good rule of thumb to weld as hot as you can.

Also I've always heard about DC only 7018, but I always see 7018's rated for both ac and dc. Is there a big difference in performance using the dc only rod ?

25 years, mostly construction, i've never seen a box of ac/dc rated 7018. i was always told (by pros) 'no self-respecting welder uses alternating current'.

i guess there are some exceptions, like hi frequency a/c for aluminum tig, but you never see a/c stick in industrial construction or fabrication. if you can't beat the arc blow on things like structural steel, they will get somebody else who can.

 

[JB4310]

experience tells you when you are too hot or cold.

the amp range is usually noted on the box 1/8 7018 max 125 amps. it's a good rule of thumb to weld as hot as you can.

25 years, mostly construction, I've never seen a box of ac/dc rated 7018. i was always told (by pros) 'no self-respecting welder uses alternating current'.

All I see is the ac/dc 7018 in the home centers, even TSC. have to ask at the weld supply shop.

What rod, amp setting and thickness of steel are shown in your picture here? Looks like what I am typically working with, around 1/4 inch material.


Anyone wish to comment on the bare ground clamp, and standard protocol for handling welding leads ?

Also on my machine is a warning about electrocution hazard using AC. Why is there greater electrical shock hazard on AC ? I thought it was amps that kill.
JB