3 phase bridge rectifier selection for DIY TIG welder.

[albersondh]

Hey guys. So Im building a TIG welder with a 200A alternator. The alternators internal bridge rectifier will presumably make the smoke once I by-pass the field regulator, send a full 12VDC to the field, turn up the RPM's, and the volts go way up. Soooo, I need to select a stout 3 phase bridge rectifier that is good for 200A and ?? Volts.

I dont imagine this thing can spin up more than maybe 200VAC at max RPM and full field. If you think otherwise please correct me. I have been looking a these: Three-phase rectifier SQL200A/1200V(bridge rectifier,rectifier,diode rectifier)

3 Phase Diode Bridge Rectifier 250A 1000V SQL250A. Thinking that may work for me. However, I see some specs on this that Im not sure about. I see a spec for " Mean on-state current 50-300Amp". What exactly does this mean, please define this for me. My best guess tells me this may not produce current below 50A? Which would be no good for me.

Another spec that Im curious about is "peak repetative reverse voltage 200-1800V". What exactly does this mean to me.

I need to have the ability to control this welder to a very low DC current and as high as the alternators max output of 200A. Do you think the Bridge Rectifire I listed abouve will work?

 

[tcmtech]

Your alternators diodes will work just fine as most now a days have around 150 - 200 volts ratings. I doubt you will get more than around 60 - 80 volts open circuit.

For TIG welding you need a regulated current with variable voltage. Plus you will need a reactance inductor in line between the alternators output and the TIG gun as well to stabilize your arc.

Most decent TIG welding often times works better with HF AC or PWM DC not strait DC.

 

[albersondh]

Your alternators diodes will work just fine as most now a days have around 150 - 200 volts ratings. I doubt you will get more than around 60 - 80 volts open circuit.

For TIG welding you need a regulated current with variable voltage. Plus you will need a reactance inductor in line between the alternators output and the TIG gun as well to stabilize your arc.

Most decent TIG welding often times works better with HF AC or PWM DC not strait DC.

What is the purpose of the reactance inductor? As I understand things, RPM will raise/lower Hz and volts. I plan on regulating current output with a rheostat feeding the field. Your thoughts?

My alt is from an 04 Ford Crown Vic Police Interceptor. If the stock bridge rectifier will allow 150+ volts to pass, wouldnt that be pretty bad if the reg ever crapped out and just full fielded the field? I would think those extra volts would boil the battery pretty fast. This is why I have thought that an additional higher volt rated bridge rectifier would be needed. I cant find specs on alternator bridge rectifiers, do you have a source?

Since Im building this as a DIY rig, Im obviously a poor ******* that cant afford an off the shelf unit. Im not sure if pulsed DC is in the budget. Could this be accomplished on the cheap?

 

[tcmtech]

The reactance is to help smooth out the arc and stabilize the weld characteristics. In any type of welding its very necessary.
The resistor current control will work just fine provided it gets its 12 volt power from a constant source.

Alternators failing to full on is not all that uncommon. Your battery usually takes the massive amp input and limits the voltage for a little while. The cars electronics are protected to take that level of surge just long enough for the fuses to blow. The smoking belts tends to put a fairly fast stop to the over charge situation if common sense doesn't tell you somethings horribly wrong in the first place.

Rectifiers dont limit voltage. They just work as check valves up to a peak reverse voltage where they then conduct both ways and usually burn up causing a dead short.

I am not sure how you plan on building a TIG gun being they are very application specific to TIG welding and the required shielding gas flow characteristics that go with it.

Stick and MIG (wire feed) welding systems are fairly easy to make out of an alternator for the power source but TIG is a whole different method of welding and its typical applications are far more application specific which is also why the power source has to be considerable different in its over all design as well.

I worked as a service tech for Praxair and I have the schematics for a large number of different types and brands of welding machines and plasma cutters. So if you need a referance schematic I can easily provide them for any of the common welder types.

 

[albersondh]

The reactance is to help smooth out the arc and stabilize the weld characteristics. In any type of welding its very necessary.
The resistor current control will work just fine provided it gets its 12 volt power from a constant source.

Alternators failing to full on is not all that uncommon. Your battery usually takes the massive amp input and limits the voltage for a little while. The cars electronics are protected to take that level of surge just long enough for the fuses to blow. The smoking belts tends to put a fairly fast stop to the over charge situation if common sense doesn't tell you somethings horribly wrong in the first place.

Rectifiers dont limit voltage. They just work as check valves up to a peak reverse voltage where they then conduct both ways and usually burn up causing a dead short.

I am not sure how you plan on building a TIG gun being they are very application specific to TIG welding and the required shielding gas flow characteristics that go with it.

Stick and MIG (wire feed) welding systems are fairly easy to make out of an alternator for the power source but TIG is a whole different method of welding and its typical applications are far more application specific which is also why the power source has to be considerable different in its over all design as well.

I worked as a service tech for Praxair and I have the schematics for a large number of different types and brands of welding machines and plasma cutters. So if you need a referance schematic I can easily provide them for any of the common welder types.

Great information thank you.

I wouldnt even attempt to make a TIG gun and the argon/reg and stinger I already have with existing MIG/stick welders. Ill be buying the TIG gun.

My AC TIG will be full wave and Hz/volts should follow RPM so that should give me a bit of cleaning control over the process. No % wave electrode +/- adjustment but I think I can live without this and just supplement with RPM controling the Hz and volts. Current I can control by minipulating the field. DC will be non-pulsed unless I find an economical way to control DC PWM at pretty high current. DC volts and current will be controlled in the same manner as AC.

Am I oversimplifying this? Everyone please feel free to make recomindations for improvments and asoceated additional parts required.

 

[tcmtech]

If you already have a stick welder, depending on what type of course, you may be further ahead to just add a homemade high voltage igniter/stabilizer unit to it for the TIG system and preferably a foot pedal for the heat control if your welder has a remote control capability.

The problem with doing high quality TIG work is its entirely in the power supply and user control systems. Cheap constant current TIG can be done directly off of any common stick welder power supply regardless of whether its an AC or DC output system.

I do mine with a standard issue Miller Shop master 300. It does fair welds and I have to scratch start my arc but thats not really much of a problem being I have a foot control so I can start my arc at minimum current. If I ever did get into it more I would add a high voltage igniter/stabilizer unit in line with the output leads and maybe integrate a pulser function into the remote control system.

The home built alternator system just doesn't seem like a wise choice to try and build a TIG system from. There are too many other factors behind TIG work that will be missing that are very important to the actual TIG welding processes.