Onboard welder using a GM Delco 140 Amp alternator
out of a '94 Chevy Camaro
Page 1 | Page 2 | Page 3 | Page 4 | Home
Finding the right one...
Alternators are capable of generating increasingly higher voltages relative to the their RPM. When they're used in automotive charging circuits they are always regulated by an external or internal regulator circuit to maintain output voltage below 15 volts so that the battery will not be damaged. The regulator simply reduces the field input voltage from below 12 volts to almost nothing to maintain the <15 volts output. We need to eliminate this regulator and apply the full 12 volts to the field positive so we can get the maximum available output from the unit. This can be a relatively easy matter or more complex depending on the specimen. The amperage rating of the unit also gives us a clue as to what kind of output we can accept. The bigger the better. Well almost...(see later) You can start with an older 66 amp Delco model that has a Y wired stator that can be rewired to a D (delta) configuration effectively almost doubling it's output (more on this later). You can go up to the 100-120A Ford style Delco or Motorcraft alternators and to some similar 130A Chrysler Delco models also. I've seen a big 120A Bosch unit in a yard that also looked promising. The biggest car alternators available are the big case 140A GM Delco-Remy models out of mid 90s Camaros and Firebirds. This is what I picked up for $40 but there is a catch!
The good...
These monster big case alternators are able to withstand great loads and heat. Their big case provides adequate cooling, has a heavy-duty rotor with an external fan, a beefy delta wound stator and good quality bearings. Their electronic components are also rated over 140A. Since we're going to mostly gut it out though the most important factor remains the rotor and stator cooling and stout bearings.
The bad...
Apparently GM got real fancy with their charging circuit by actually using the engine management computer also as part of the regulating circuitry. What this means is that instead of a simple beefy field input stud there is a special four prong connector on the alternator where the field power would go. This takes the field power and other inputs from the engine computer and there is no easy way to use this connector to supply field voltage to the rotor. Another bad thing I found out about these beasts is that while the rectifier diodes are able to handle over 140A they are only designed to handle 32 volts! That's right. They're designed to burn out at 32 volts as a form of protection. It's a bummer since we're hoping to generate over 100 volts here. I quickly found this out during the first test where at idle I got 30V and as soon as I throttled up a diode blew and the alternator started straining terribly almost killing the engine. I quickly shot it down and inspected the damage with a multimeter. Later I found out on the Transpo Electronics website that this rectifier has a working voltage limit of 32V! :( So now I was in for a fight.
And the ugly...
I decided to stick it out and work with what I have. After talking to an alternator repair guy about replacement diodes and finding none that would fit and would work up to 200V he gave me a couple of stout looking rectifiers rated 100A at 200V off some monster Ford Motorcraft truck (Transpo part# FR1270) alternators to use as an external rectifier. Now I had what I needed to make it all work so it was on to making the necessary modifications.