not enough friction on the bottom pulley
I know this is an old post but I just had to say something. This isn't an rpm issue or a problem with the alternator. It is a mechanical engineering problem. The belt touches the bottom alternator just slightly, maybe 10-20% of its circumference. When you get 20 amps or more of current of welding off that alternator, it may be 30 volts at 20 amps or 600 watts. No matter how tight that belt, you can't transfer almost a horse power with that little bit of surface area. In other words, when you get up to a certain power, the pulley for the welding alternator is slipping. But you can't see that at the time and of course you can't hear it with the engine going and revving up. The easy fix is to swap the two alternators. The one on top doesn't need a lot of power so should do fine in the bottom position. The top pulley has a good wrap with the belt.
The other option is to get a tensioner pulley. They aren't there to keep tension. The real purpose is to make the belt wrap around the pulley more than it would without the tensioner. You would have to get a longer belt though.
Just remember, you might try to weld with up to 80 volts and 100 amps. That is 8,000 watts of power. That is 10 hp. But even if you just wanted 5 hp (plenty for welding most things) then you would need a couple of hundred pounds of bearing force due to the belt tightness. And that is based on 180 degree belt "wrap". In the current setup with only 60 degree wrap, then you would need so much belt tension that the belt would snap.
Anyway, hope this helps.
This is old but I've tried to do this too with a CS130. It just doesn't work. I have mine mounted to an AMC 360 engine that resides in my jeep. I wanted to build an on-board welder but it won't arc. It just sparks. I got my engine up to 4000 rpms and it stil doesn't work. It gets extremely hot but will not weld.
I was really hoping the OP could come back with some updates. My thread about my build is here:
Why not just get a Used HO alt from off a Car audio site, I see them all the time. SInce its not specific to a car (in your case) You can get them.
I had heard you could do this with the CS130s so I gave it a try. The best alternator to use is the Ford's with the external regulator. Simple and easy. I got this one for $10 so I figured I'd give it a shot.
Also, the voltage coming out was only 29 volts. You'd need at least 60 or better. I'm still hoping the OP will show up with a few answers.
Originally Posted by McCracken
Lol mine to, never got it to work, I tried all kinds of stuff,
but never tried a wider belt, its sitting dissembled right now,
I was going to look into the Zena welder, but got side tracked and
needed a welder right then and there ended up getting the
Miller Thunderbolt XL 225 AC/DC stick welder, I set it at 90amps AC
and weld all day with it, - I still want a portable welder, but its
going to be a long time
BTW I hear its better to use 24 volt alternators
also look here
BUILD A $20 PORTABLE DC ARC WELDER
we must be doing something wrong
I figured it out a while back but never came back here with my results. The alternator uses Avalanche diodes. These diodes will not allow welding because of the voltage drop across them. It doesn't matter how fast you get it it'll never weld. The only way to get these to work is to replace the rectifier bridge. That or rig up some other diodes outside of the alternator.
I found the bridge you need. I could only find it at one place. Mobi-Arc. The guys that are already building welders out of alternators for $700+. The cool thing is though that they will sell the bridge for roughly $30. So if you want to build it, you can do it for the cost of the alternator and a $30 rectifier bridge without the Avalanche diodes.
Hope this helps someone.