For Welding Machine

Yes, a motor generator can be used.

Motor-generator - Wikipedia, the free encyclopedia

Use transistor in CE configuration but be careful about stability,gain,frequency,temperature withstanding capacity etc.

In theory you can step up current without the use of a transformer but a transformer is a much more cost effective method most of the time. For the brief bursts of high current that spot welding requires, some welding machines store energy in a capacitor. For continuous welding, the non-linear effects of saturating the core of a transformer nearly perfectly matches the changing load conditions of starting and maintaining a welding electric plasma without causing power distribution protection circuitry (breakers and fuses) from tripping OFF.

For a "buz-box" type welder, there is probably no other practical means to provide the necessary voltage and current other than use of a power transformer. Welders with a.c. output, connected to an a.c. source, use a transformer to convert the higher source voltage to the lower voltage required for welding. In the process of converting the voltage, the rated current is increased across the transformer. Therefore, if the source voltage is 240 volts, the transformer reduces the voltage to perhaps 24 volts using a transformer with 10:1 turns-ratio. The rated current is increased across the transformer by a factor of 10. So if the welder draws 20 amps on the primary (240 volt) side, it will output 200 amps of current (minus losses) on the secondary side to the welding "stinger".

Welders, however, usually have current regulators so the current flow is consistent and somewhat independent of the arc distance between the rod and the work. The heart of this regulation is often series connected inductor(s).

Inverters.

http://en.wikipedia.org/wiki/Welding_power_supply#Inverter

http://www.millerwelds.com/resources/articles/welding-inverters-decrease-maintenance-downtime/

http://www.lincolnelectric.com/en-us/support/process-and-theory/Pages/inverter-based-power-detail.aspx

http://www.everlastgenerators.com/what-are-inverter-welders.php

Now thats funny! Miller inverter welders decrease down time! HA!

I worked at a local welding supply company a number of years ago and I can tell you from experience that the entire line of Miller inverter based welding systems are junk and then some.

I used to order replacement parts in what the stock system considered bulk volume meaning regular quantities of 10 or more of each single item! The entire time I worked there there was not one single day that I did not have one or more of those POS machines in the shop for a major repair and most were in under warranty too.

The three year warranty was about 2 years too long is what it came down to and the few that made it past warranty where rarely ever cost effective to repair.

Good to know. What parts had high failure rates? Have you heard of problems with any other manufacturers?

The easiest way I can sum it up is that everything on the inside of them fails way too soon.

Control boards, relays and contactors, switching devices, HF transformer, the high current handling cabling, the fan, the twist lock connectors.

Basically the massive aluminum heat sinks and the case are what I never replaced on any of them!

As far as other manufactures went they didn't hold up any better. Inverter welders do have good welding characteristics and great portability but that portability and power to weight ratio comes on a sacrifice in life expectancy.

We purchased quite a few Miller Pulse Welders (first generation) because of the service we received from the old 650 units, with the exception of the aluminum connectors used to tie the transformers together. The pulse units were not hardened for factory use. We replaced control boards, power supplies, and complete units. The next generation had "Tunnel Technology" and were slightly better. The next generation was Lincoln. it should have been Fronius from my stand point but there was no local distributer. The Miller was an excellent machine, it just didn't live up to the sales pitch. I will say that our local SJS welding supplier was exceptional servicing these Miller machines. We still use them.

When I read the comment, I scrolled down quickly in hopes of correcting the misconceptions about inverter welding machines....only to find you had beat me to the punch.

GA

I would like to add that Miller Inverter Welders do excel in one area; incredibly stable very low amperage control used for things like welding very thin walled titanium or aermet tubing. No welding machine I know comes close. If that is desired, the effective very low duty cycle requirements are just something that must be dealt with.

I have a "Buzzbox" WIA 200Amp stick welder. It's about 35 years old, was in daily commercial service before I bought it at auction. It has a 65% duty cycle which I suspect is at full rated current. I usually use it in the 60 to 120 amp range (more than 120 and I start to melt power plugs )and using it at that range I can weld all day and night without it getting much more than warm.

I've looked at invertor welders, and the ability to lift (my welder weighs around 50+kgs/120 odd #) them with ease is about the only benefit I can see over my "little green" welder.

I also have a gas/gasless mig welder which is more portable but I tend to use the stick welder more often than not especially on big outside jobs.

sure... just increase the voltage or decrease the resistance.

Its just not done unless you want to commit suicide.

Inverter welders use a transformer also.