Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

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MrCreosote
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Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by MrCreosote » Sat Nov 13, 2021 10:22 am

The power cord is wired for 230v single phase.

However the schematic for this welder indicates the 3-phase does not go directly to a 3-phase transformer. Instead it is immediately rectified into a 2-wire supply that goes to the welding power circuitry.

2 3-phase legs are sent to the electronics circuitry. (The power cord is wired to these 2 legs.)

My concerns are
  • powering 2 3-phase legs with 2 leg split phase is going to not produce the "smooth" DC 3-phase legs would
  • smoothing capacitors after the rectification may be over taxed
  • the 2-wire welding circuitry may not function properly due to 180* instead of 120* phase difference

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BigDumbDinosaur
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Re: Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by BigDumbDinosaur » Sat Nov 13, 2021 10:50 am

MrCreosote wrote:
Sat Nov 13, 2021 10:22 am
The power cord is wired for 230v single phase.

However the schematic for this welder indicates the 3-phase does not go directly to a 3-phase transformer. Instead it is immediately rectified into a 2-wire supply that goes to the welding power circuitry.

2 3-phase legs are sent to the electronics circuitry. (The power cord is wired to these 2 legs.)

My concerns are
  • powering 2 3-phase legs with 2 leg split phase is going to not produce the "smooth" DC 3-phase legs would
  • smoothing capacitors after the rectification may be over taxed
  • the 2-wire welding circuitry may not function properly due to 180* instead of 120* phase difference
First off, can you post some more info about this machine, e.g., make, model, nameplate ratings, etc? Also, it would be very useful to see the schematic.

Meanwhile, I WOULD NOT connect any three-phase welder to a single-phase line. You may end up losing the rectifiers, as well as the filter capacitors, not to mention fill up your shop with vile-smelling smoke. Also, while it should be possible, in theory, to power it from a static phase converter of sufficient size, I'd be leery of trying. Welders are not as forgiving with three-phase power in which one leg is leading or lagging the others, or one leg is lower or higher voltage than the others.
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MrCreosote
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Re: Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by MrCreosote » Sat Nov 13, 2021 1:29 pm

It is a KEMPPI PS 2800 / 4J 6142254

The spec plate on back is all symbolic.
I have no idea what F1, F2, U0, U1, U2, I1, I2 and S1 mean

https://imgur.com/jtN1KHV spec plate on back
https://imgur.com/O4bBkDy schematic zoom of 3-phase input rectification
https://imgur.com/Dj8qHSA schematic full

The following is technically off topic. There is a "mysterious 6-pin connector" on the back panel that is not shown in the user manual. Because of the circled V and A beside it, I'm speculating it is a control for constant voltage or current since this box can also be used for MIG. The following images show the connector and have a schematic zoom to the only 6-pin connector I can find.

https://imgur.com/AGYCzXX schematic zoom of mysterious 6-pin "V - A" connector
https://imgur.com/FvYsyhM Mysterious 6-pin "V-A" connector on rear panel not mentioned or shown in user manual

NOTE: There was a post from a fellow who supposedly ran a PS 2800 on single phase the trick being to connect the 2 legs that powered the electronics. The fact that this unit does not have a 3-phase power transformer at the power input suggests it may be "single phase friendly?"

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SteveR
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Re: Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by SteveR » Wed Jan 26, 2022 1:13 pm

Contact the factory and ask an expert. https://www.kemppi.com/en-US/. Better than burning up a good machine.

Alternatively, I knew a guy who built a motor-generator combo to make his own real 3phase from 2 phase at his house.

SteveR
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Re: Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by Harold_V » Wed Jan 26, 2022 4:30 pm

SteveR wrote:
Wed Jan 26, 2022 1:13 pm
Alternatively, I knew a guy who built a motor-generator combo to make his own real 3phase from 2 phase at his house.
Hmmmm. Two phase? That's not real common here in the US. Do you mean single phase 240 volts?

Two phase power was typically made up of four wire service, two wires per phase, with no regard for grounding.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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SteveR
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Re: Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by SteveR » Thu Jan 27, 2022 3:01 am

Harold_V wrote:
Wed Jan 26, 2022 4:30 pm

Hmmmm. Two phase? That's not real common here in the US. Do you mean single phase 240 volts?

Two phase power was typically made up of four wire service, two wires per phase, with no regard for grounding.

H
Hi Harold, No, not 4 wire - just the regular power that comes in to our house. We have 2 hot legs and a ground/neutral. Hot-Hot is ~230V (220?) and Hot-Neutral is ~115 (110?). To me it makes sense to call it two phase. My introduction was years ago when the neighborhood pole mounted transformer blew up. Only half of the lights in the house were working until they replaced the transformer because each phase runs about 1/2 of the main panel.
Best,
SteveR
12x36 Enco Lathe, 9x42 Bridgeport, SMAW, O/A, Miller MIG w/gas
Not enough measuring tools...
1.5" Allen Models Consolidation in progress
1" FEF in progress
1" LE Pacific "Project"
3/4" LE Northern Project
Measure twice, cut once, make it again....

Harold_V
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Re: Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by Harold_V » Thu Jan 27, 2022 4:30 am

Thanks for the reply, Steve.
Unfortunately, that's not two phase. It's single phase. If you put the voltage on a scope, you'd get just one wave. Two phase would provide two waves, and three phase would provide three waves.
I'm not much of an electrician, but Patio worked as one for years and has the credentials. If he happens to see this maybe he'll chime in.
Mean time, here's a link that might help explain the difference: https://en.wikipedia.org/wiki/Two-phase_electric_power

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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Re: Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by John Hasler » Thu Jan 27, 2022 10:38 am

Harold is correct (as usual).

BTW do *not* try to run any three-phase equipment other than a motor from a "static converter". It would be more accurate to describe a static converter as converting a three-phase motor to run on single phase than to describe it as converting single-phase to three-phase.

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Re: Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by BigDumbDinosaur » Thu Jan 27, 2022 1:34 pm

SteveR wrote:
Thu Jan 27, 2022 3:01 am
Hi Harold, No, not 4 wire - just the regular power that comes in to our house. We have 2 hot legs and a ground/neutral. Hot-Hot is ~230V (220?) and Hot-Neutral is ~115 (110?). To me it makes sense to call it two phase. My introduction was years ago when the neighborhood pole mounted transformer blew up. Only half of the lights in the house were working until they replaced the transformer because each phase runs about 1/2 of the main panel.

Harold is correct. Household power in the USA is single-phase, so-named because if scoped across the hot legs a single sine wave will be observed. The neutral is a grounded center tap on the transformer secondary and therefore is not a reference leg for determining number of phases.

If the power source is two-phase, connecting the inputs of a dual-channel ’scope to the hot legs would reveal two sine waves exactly 180 degrees out of phase. Similarly, if one has access to a multichannel ’scope and connects it to the three hots of a three-phase line, one will see three sine waves exactly 120 degrees out of phase with each other.

True two-phase power never caught on here, as three-phase is more economical of infrastructure—only three conductors are required for transmission, versus four for two-phase power. This characteristic became very important early in the history of commercial power generation, as loads could be hundreds of miles from the generating station. Clearly, a three-wire distribution system stretching several hundred miles has a cost advantage, both in installation and maintenance, when compared to a four-wire system.

High-leg, delta-connected three-phase services have a grounded center tap on one of the three secondaries in the transformer, conventionally between phases L1 and L2. Measured from L1 or L2 to neutral (the center tap), the nominal voltage is ~120. Measured across L1/L2 it would be ~240. Measured from L3 (the high leg, aka “wild leg”) to neutral, the output would be approximately 208 volts (120 × √3). Due to that “odd” voltage, the wild leg connection is rarely used with single-phase loads.

Another three-phase supply scheme is wye-connected, which is what is at my shop. In this arrangement, all three secondaries have a common connection, so when schematically drawn out, the secondaries appear to be in the shape of the letter Y. The usual voltages provided by the wye connection are 208 between any two phase hot legs, e.g., L1 and L2, and 120 volts between any phase hot leg and the common center connection. The latter is the grounded neutral.

As 120 volts can be obtained between any phase and neutral in a wye setup, loading on the transformer tends to be more balanced than with the delta arrangement in an installation with a lot of single-phase consumption, assuming the wiring is properly laid out. This characteristic results in more closely-matched voltages between phases (which is very beneficial to motor life) and less harmonic distortion being kicked back into the line. The downside is current draw by three phase motor loads at any given horsepower will be higher than on a delta setup, since the somewhat lower voltage has to be made up with higher current to maintain motor power.
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BigDumbDinosaur
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Re: Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by BigDumbDinosaur » Thu Jan 27, 2022 2:26 pm

John Hasler wrote:
Thu Jan 27, 2022 10:38 am
BTW do *not* try to run any three-phase equipment other than a motor from a "static converter". It would be more accurate to describe a static converter as converting a three-phase motor to run on single phase than to describe it as converting single-phase to three-phase.

It depends on the converter. The higher-end ones produce a good-quality output, with approximately equal voltages on all legs. They could be used for non-motor loads, although I would draw the line at powering an arc welder with one.

On the other hand, the “low cost” converters are barely suitable for running a motor. I'd use one to run a three-phase light bulb, though. :lol:
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Research is what I'm doing when I don't know what I'm doing.

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SteveM
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Re: Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by SteveM » Thu Jan 27, 2022 4:03 pm

OK, for the uninformed, please explain how something like a welder can be 3-phase.

I can see in motors where the different phases kick in to provide rotation, but 3-phase welder sounds like a 3-phase light bulb to me.

Steve

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Re: Running a 3 Phase KEMPPI PS2800 Welder on Single Phase

Post by rrnut-2 » Thu Jan 27, 2022 7:18 pm

It depends on the welder or plasma cutter. Some welders and plasma cutters have a 3 phase bridge rectifier that will supply a DC voltage for welding or cutting. Most of the later units use SCR's that are fired at the correct time in the AC cycle to provide the final results. The SCR's (silicone controlled rectifiers) are controlled by a microprocessor circuit. Some of these units will run on single phase, but not well.

Even the newer single phase welders and plasma units use the SCR method rather than a transformer.

Jim B

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