Generator question

[chris88]

I was thinking about something. Moes AEA 200 with a 10 hp makes like 250 amps. I forget the exact number but thats in the ballpark. But an SA 200 with a big 4 cylendar makes only 200 amps. Why is this? That AEA 200 makes more amprage then my AEAD 200 with a 20 hp on it.
Chris

[cnslmva]

Compare duty cycles. The SA200 will give you 200 amps at 60-100% duty cycle all day long. It also has a much larger generator that can stand up to severe use like carbon gouging. The smaller twin cylinder machines won't take that kind of abuse for long if even at all.

[Sberry]

Yup, the SA200 will run long after the smaller ones are dead and buried.

[chris88]

Does an SA 200 have anything special other than being able to run all day with out trouble? How come a lot of big welders only have DC current? My dads boss has 3 welders one big 40 (sitting outside going to **** ), one trailblazer, and one other miller that might be a big 40 but this ones diesel also going to **** outside and all of them are DC only. If the SA 200 wasnt so big I know where I could get one if my welders no good. My AEAD 200le is 100% duty cycle at 200 amps according the faceplate.
Chris

[cnslmva]

Durability. Like Sberry said the SA will be there long after the others are buried. I know of several SA200's built in the 50's and 60's that are still welding all day. The bigger machines will last a lifetime if taken care of.

[david_r]

I think you guys may want to check the duty cycle on the AEA machines. 100% means 100%. IOW, you won't burn up the alternator running full tilt 225 amps. Then again, how long is that air cooled engine going to last? I've heard about 2k hours and they go bye-bye.

[david_r]

chris,
The reason alot of the big welders are DC only is because they have a generator head, not an alternator head that can be rectified into DC. If you want pure DC, you need to start with it. Rectifying AC to pure DC just isn't realistic.

[Terry Lingle]

Originally Posted by david_r

chris,
The reason alot of the big welders are DC only is because they have a generator head, not an alternator head that can be rectified into DC. If you want pure DC, you need to start with it. Rectifying AC to pure DC just isn't realistic.

All rotating converters create AC.
A generator has reversed construction with stationary fields and rotating power uotput section. iIt use brushes and a segmented commutator to convert the ac into dc thus there is no "AC" available at ihe output. The brushes must carry the full output current.

An alternator brings the power out without mechanically rectifieing it and allows us to choose ac or dc. they use the stationary windings for the power eliminating the big brushes . In fact there need be no brushes at all in an alternator but often welders use multiple fields and small brushes on slip rings for better control in welding aplications.

Generators are constructed to run with an overlap and are normally wound to more "poles" than alternators.( this is the equivalent of 6 phase ) The main advantage that generators have is in the ease of tailoring the feedback to produce the desired output. (.generators are quite expensive to manufacture)

there may be a reactor with a gererator based welder or it's function may be built into the windings often as an extra field winding .

Alternators can be wound 3 phase or more( 6, 9 or 12 phase) and set up to produce very pure dc directly off the diodes. For most welding it is not required and the manufacturing cost eliminate 6,9 or 12 phase designs as practical welders . The control feedback is also slightly more complicated for an alternator based welder.

The reactor in an alternator based welder is what makes it constant current machine . Multi capacity machines (CC CV ect ) have more complex control over the reactor's characteristics at of course greater cost and increased risk of failure .

The main reasons the rectified alternator generators replaced the generator welders are lower overall manufacturing cost and increased reliability.

What I started to say was a generator is a mechanically rectified alternator.
a Welder is so much more than that. The "SA" is so nice that it is almost a cult machine..
Terry

[Terry Lingle]

To post on the original topic

The larger machines run at lower speed than the smaller lighter machines . Tthey are more costly to manufacture but can be more feature rich and should live about 4 times as long thus the end user is better off with the bigger machine if (s)he intends to use the machine 40 hours or more/week if the machine is just for occasional use the smaller high speed units are a better deal .
The output power is about the same but the " control" is better on the larger machines.

The larger machines are where the bleeding edge features are implimented. If they become easy and cost effective to incorporate into less expensive units , or become desired features they are put on the lower end machines as well.
Terry

[moe1942]

Chriss,

My AEA-200-L is basically a 200 amp, 100% duty cycle, AC machine. The highest tap is rated 200-240 amps. This machine doesn't have a fine current adjustment. Variations in output can be obtained by varying engine RPM.

But as has been stated, these small machines are not in the same league with the SA-200. They are however 100% duty cycle. They will weld longer than you care to hang onto the stinger... Mine is a 1960 model if that says anything, and it is in like new condition operational wise..

[moe1942]

Her is my former Onan powered, now Kohler powered AEA-200L.

[TRG-42]

Hi Chris, your questions is a good one . First off , the fact that generators such as the Lincoln SAs and Classics require far more horsepower to run has nothing to do with duty cycle, longevity etc . Ironically, by nature of the design the duty cycle ratings are actually less on the generators . I will explain that later

Alternator Machines

Machines, such as the Bobcats , Trailblazers , Rangers etc ( basically ALL engine driven welders except Lincons SA , SAE , SAMs and Classics ) have two components to make the welding power

1. Rotor ( the round part that the engine spins )
2. Stator ( the steel part with windings that encase the rotor )

The stator on a Trailblazer / Ranger is small and light ( can hold it in your hands )

In an alternator design the welding current is carried buy the outer portion ( Stator ) that doesn't spin so the rotor doesn't have to be large.

Generator Machines

Generator machines have 3 main parts

1. Armature ( the round part that spins )
2. Exciter ( the part that extends out the front )
3. Generator Frame ( outer portion that doesn't spin )

The Armature and Exciter are all on the same shaft and it is very heavy compared to the stator of an alternator

In a generator design, the welding current is carried by the armature ( part that spins ) so it has to have large copper windings to carry the current . This makes it far heavier ( well over 100 lbs ! )

Lastely, the resistance of the armature spinning in the magnetic field of the frame is much higher. The shaft on armature is far larger in dia than the shaft on a alternator welder

Because of this , it can be said that generator desinges are not as efficient . It takes more horsepower to turn to yield the same welding amps

Another issue with generator machines is the peak amps they can produce. A alternator machine , like a Bobcat , full out when carbon arc gouging will only give a bit more than its nameplate rating. A generator machine on the other hand will give far more than its nameplate rating. The 300 amp generator when gouging will hit peaks over 500 amps ! ( this is why for equivalent rating, the generator machine is a better gouging machine ) . This takes some serious torque to keep the armature from slowing down

Back to the 100% duty cycle comment . Pretty well all alternator style machines ( Rangers , and all Millers etc ) has the output rating at 100% . Recall that in an alternator the welding current is generator on the outer portion that does not spin. Because of this it is very easy to cool

However , on a generator style the welding current is producted by the inner rotating armature. Two problems with that

1. There is far less airflow and cooling on the inner portion
2. You now have to carry the welding current from somthing that is spinning around to your output studs. They use great big carbon brushes for this. The amount of current is now limited by the brushes and the commutator ( part that the brushes rub against )

This is why generator machines typically have their output rating speced at 60% ( they are capable of 100% but at a lower amp

[Sberry]

You made a good point about the momentary torque demands when arc gouging and as was eluded to, sort of, was when we were talking longevity we were also considering the engine at high loads, 4 cyl water cooled by nature should outlast a small air cooled machine.

[chris88]

So for someone like me who welds every now and then and not at an extened period of time a smaller altenator welder is better and more efficent but for someone who welds 8 hours a day 6 days a week should get something like an SA 200 or a big 40 or anyother big generator welder. With a generator you can only get DC constant current, is this correct? Too bad these things are so big and I have no way to move them. I could prolly get that Big 40 for cheap but I have no way to move it. Thanks for all of your replys.
Chris

[Sberry]

yes, the part timer doesnt need a big machine, too heavy and no AC power. The first one I bought was a SA200 and found out it was too much weight to carry around for the use it got. I have it trailer mounted now but have a Lincon GS8000 I carry on my service truck. It has AC , is small and light, fits on the truck well, could be enclosed and didnt take up my bed room. If I had to do it over again I would have got small machine to start with. I do occasionally take the big one where I can park it and there is going to be a lot of welding or for having another man. I have 2 smaller ones and they are great. On the truck it is installed so I can reach thru the back of the tool box to operate it.