# Silly question: Alternator Welder?



## R.G.

I've been very attracted to the idea of using a 200A car alternator for a welder. I've collected a 200A GM alternator and a 12HP Honda engine from a stuffed-up pressure washer, including the rollaround frame. As soon as I can get to it, the idea is to adapt the engine to the generator and attach leads. 

Any experience with this genre of welder?


----------



## Hawkeye

There are several sites and videos on the Net which deal with making a welder out of an alternator, or just car batteries for that matter. Some use a spoolgun to make a wirefeed welder. Run it through Google and see what comes up.

I think the limitation will be that most arc welders run in the area of 28 to 36 volts. 12 volts may not work too well for sustaining the arc. You may have to bypass the built-in regulator and build one to work at the required voltage.


----------



## Tony Wells

Seen it done, and have a 16hp Kohler waiting on a dead welder to come my way, but thought about it myself. Couple of things. The diodes in an auto alternator are only rated for about 32v, and will blow if you run the rpm up where you want it to get a stable arc. Easy enough to sub larger ones from a welding supply that services welders. Need to control the tickle voltage to the field for current control. A wirewound rheostat will work for that. 

Google and youtube have many examples of people's successes and failures.


----------



## Tony Wells

Here's a guy that did it on a service truck:

http://www.metalwebnews.com/information/alternator-welder.pdf


----------



## R.G.

Tony Wells said:


> The diodes in an auto alternator are only rated for about 32v, and will blow if you run the rpm up where you want it to get a stable arc. Easy enough to sub larger ones from a welding supply that services welders.


Absolutely correct. I found a major supplier of alternator diodes that makes 100V diodes for alternators. Turns out that the auto industry solved the problem of overvoltage transients killing the computer modules in cars by down-rating their alternator diodes so they would break over and protect the computer modules. Hence the 32V rating on most of them now. Older high voltage ones are available. 

But on the way to that, I found 200A 200V diode modules on ebay, along with 10milliohm shunt resistors rated for 200A so I could sense current and do some electronic controls stuff (I'm an EE, not a machinist; that parts easy for me) to make the welder portion do the right voltage per current action for stick. Stick, MIG, and TIG all want different voltage/current 'hardnesses' to give good weld operation.



> Need to control the tickle voltage to the field for current control. A wirewound rheostat will work for that.


Correct. I can do that. I designed power supplies for a living for a few years, so it comes naturally to me to use a power semiconductor to control the field current. I have that stuff in my junk boxes. I just don't have any steel bars or rounds to turn. 

I'm thinking about attaching a big disk brake rotor as a flywheel for the engine, as the start-up transient is a big deal on these things I read. Conceptually, this is straightforward; in practice, turning a pulley with keyway, and setting up a plate to hold  stuff on is a mountain to me.


----------



## Tony Wells

I get a mix of both worlds. I play in electronics, antique stuff mostly, but some new technology as well. I did it as a hobby until I married and left home. Dabbled since then. Have a bench in the shop for it though, couple of scopes and misc equipment. But then I did the metal thing for a living, so know more about that. 

I'd be interested in your progress on this project, because I may want to take a stab at a similar piece myself. As if I had the time!


----------



## Rbeckett

ANy AC/DC genset can be converted fairly easily and can produce some fairly large amps too.  There are several fora that have the conversion process spelled out for just about any alternator you could wish to change over.  Before you buy anything have a look at those threads and then buy or source accordingly.  Some of the newer GM alternators are 150 to 200 amps and only require a higher voltage regulator to get enough OCV volts to do a nice bead in some pretty thick material.  As a "can it be done?" project  it is a fun thing to do, as a cost saving idea is is not so good.  But the learning that will come along with it is priceless.  Hope this helps if you decide to build one from your stuff at home.  And don't forget  the pics, no pics means it didn't really happen....Have a great day.
Bob


----------



## aametalmaster

My buddy has one with car Delco alternators and a lawnmower engine. Maybe i can get him on here to decribe how he did it...Bob


----------



## aametalmaster

My buddy says he got his info here http://diy-welder.com/weldernator.shtml ...Bob


----------

