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Running 3 Phase KEMPPI PS 2800 Welder on 1 Leg

MrCreosote

Aluminum
Joined
Aug 27, 2011
Location
Pennsylvania
Welder power cord is wired for single phase.

Unit is 3-phase, however, the actual circuitry is single phase: The 3-phase power is immediately rectified to a single phase, 2-wire circuit. NOTE: The line cord is connected to the 2 legs that powers the electronics.

My concerns are
  • powering 2 3-phase legs with 2 leg split phase is going to not produce the "smooth" DC 3 legs would
  • smoothing capacitors after the rectification may be over taxed
  • the 2-wire welding circuitry may not function properly due to excessive ripple
 
Depends if it’s designed for both 1 and 3 phase. I have a miller cst280 which is similar. It’ll run on either single or three phase power. It’s an inverter welder so pretty sure it it’s just derated some on single phase.
 
I want to run this 3-phase welder on single phase. (The unit was wired for single phase as discussed below and owner said it ran on single phase.)

I believe the Hass Kamp does not apply because it deals with a 3-phase transformer fed directly by the legs - the output of this transformer is then 3-phase rectified.

This KEMPPI has no such transformer.

The 3-phase legs are immediately rectified.

So the difference would be feeding the DC circuitry with rectified 3-phase or rectified (full) single phase.

While the single phase would have more ripple, the real question would be the electronics are powered from taps on 2 of the 3-phase legs.

I came across someone who said they remember doing this many years ago with the same welder. The key idea was that KEMPPI made this series of Power Supplies very "multi voltage friendly"

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Hi Creo, and welcome to the group.

Your suspicions and concerns are correct in most everything. Thank you for posting pix of the diagram, as it saves me the research 'on a guess' of what you really have... (it's not unusual for someone to ask, and upon a search, I find 30+ flavors of the same model, right?)

It's a transformerless inverter, so no need to do any 'conversion' antics to make it wake up... just pick

Ripple would be a concern, but note that L001 is an iron-core series inductor immediately downstream of the 3-phase bridge rectifier... that will not only 'smooth off' any 3 phase ripple to the primary link capacitors, for single phase input, it will ALSO have the effect on preventing high ripple loading from occurring at the two segments of your input rectifier array.

The only concern I see,is the same as any OTHER inverter system designed for 3-ph in... you have only 4 diodes of the bridge carrying full load current, rather than 6.

Now, see L002? That's a sensory device- it's looking at the lower leg of LINK current... but since it's an INDUCTIVE device, it's not measuring DC current- it can't... it's effectively measuring CHANGE in current. It could be set up specifically to read LOW FREQUENCY incidence of change (immense current spikes during welding op), OR it could be wide-banded, basically looking for ripple-yielding fault conditions.

See ZG101?? That looks like some sort of plug-in assembly, and it appears to be a combination noise and surge-supression component. The 2.5" wire going form GV107 to the far side of L001 is probably 'freewheeling' suppression (a highly inductive component does NOT like to have it's current supply interrupted, when it does, it adopts the attitude of an ignition coil).

Use L2/L3 and give it a whirl. I would not be surprised to see VG101,102,104 and 105 working fine at all loads, but if one DOES go, just replace it with a larger flavor. keep an eye on C001, C002, C003, and respect their terminals- I see no identified bleeder resistors across them... they MAY have them integral to the cap bank assembly, or they MAY have opted to leave them out, and rely on the output thyristors' firing on shutdown to 'crowbar' the link caps to 0V. If they did, don't TRUST it- electrolytics may go to 0V on a shutdown thyristor firing pattern, but long afterthe microprocessor is down, the capacitor electrolyte is STILL chemically equalizing, and can rebuild a charge. Make a 'chicken stick' and short them down manually before you get body parts in the circuit.
 
Thank you so much for your help and time you spent inspecting the schematic!

Good point about 4 diodes now doing work of 6.

I was looking to see how the A001 board (electronics I'm assuming) was powered. There is a T003 transformer that takes input legs (2 and 3) and converts to 24v.

XX601 looks like some kind of jumper for that. I believe that is the "little wire jumper" at the "voltage jumpers" pic follows.

The heavy weld current jumpers are at X006 on the schematic.

As received, they had this box wired for single phase (actually 2-phase) on L2/L3 and both jumper groups correctly set.

I'm also adding the symbolic spec tag on the back of the unit. Deciphering is beyond my pay grade. I'd sure like to know what f1/f2 mean in the top symbolic description of the welder itself.

View attachment 334483
View attachment 334484
 
RE: Using 4 instead of 6 diodes:

Connecting single phase to L2 and L3, what about jumper L2 to L1?

That would halve current in the L2/L1 diodes - of course the L3 diodes would be unchanged.

It should reduce the probability of blowing a diode: 1 in 4 twice as likely as 1 in 2. ...like when they turned ENIAC on, the first step was to replace all the tubes that failed from turn on.
 








 
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