how much h.p. for a 300 amp welder?

[wippin' boy]

i got my hands on a CP300 3 phase welder
it says full load on 230 3/phase is 30 amps
any guesses on hp for a rpc?

[macplus]

I would go with a 15hp RPC

[precisionworks]

full load on 230 3/phase is 30 amps

30 x 1.73 = 52 amps single phase. At the very minimum, 11 hp is required, and the next standard size motor is 15 hp.

I would go with a 15hp RPC

+1

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Barry Milton

[DaveKamp]

Kev-

Before you dedicate yourself to running it on 'invented' 3-phase, 'cmon over and take a look at what I did with my CP-200... ;-)

[wippin' boy]

show me

[JL Sargent]

I have never used my welders at FULL load so I don't think I would be too worried about an RPC that would carry the full load of that welder. What amperage do you typically weld at? Back engineer that + 15% to get an accurate RPC size.

[wippin' boy]

i think your on the right track JL
.045 calls for 21 to 27 volt
thats a little over half the max possible of 44 volts
and its gonna be rare that i need that much power
.035 is plenty for most my play
so i'm thinkin' 10 horse will light 'er up way good most the time

sounds like a perfect spot for a multi idler system with a couple 10's in line

still lookin' for daves "magic phase eliminator mod"

[Avanti]

If you could cut the one set of windings loose from the "Y" inside the transformer, you could then parallel each ½ of the orphan winding with L1 and L2 at the 230/460 tie bars for 230 1ø operation. I wonder how deep the center of the "Y" is buried in the transformer?

[Perry Harrington]

I don't see any reason why you can't just power 2 phases and leave the 3rd phase floating.

[PWP]

I have a 10hp converter. I'm limited on how hard I can push my 325 amp Lincoln. I'm going add a temporary 10hp next time I come across one.

[wippin' boy]

If you could cut the one set of windings loose from the "Y" inside the transformer

i would imagine that one is over my head

I don't see any reason why you can't just power 2 phases and leave the 3rd phase floating.

what do you suppose that would do to the output power?

[Marcibb]

Hello, hope this helps.

This is the response I received from a friend that maintains and installs electrical motors for a living, when I asked him what would be the best way for me to go.

There are a few ways you could go the main ones are either an electro/mechanical rotary phase converter or a static phase converter.

An electro/mechanical rotary phase converter is like a 3 phase generator built in the same frame with a single phase electrical motor. These devices once up to speed require relatively little power to keep them going; you get a true sine wave and clean power out of them. Thy will give you the closes thing to commercial 3 phase power. I think your machine has a 8HP motor so a converter rated at 10HP should do the trick, you need more power than what is call for to power the 8HP motor to allow for powering the rest of the machine.

These devices can be run at 3 to 4 times there rated power for short period’s (main motor start etc). A new 15HP converter will set you back somewhere between $1,800.00 and 2,200.00 a used one in good shape about 1/2 of that. You may be able to get by with a smaller unit, even an 8HP unit may do because the mill’s motor does not draw full power continuously. So if you do not plan to run the machine hard and are really strapped for cash then you may take a chance. Not really a good idea.

An other method is with a static phase converter, these perform the same function as the electro/mechanical rotary phase converter but do it electronically the newer ones are about as energy efficient as the mechanical phase converters, thy are much smaller make no noise to speak of and are simple to install in most cases thy can be mounted right on the machine. Thy do not produce a true sine wave and some are very electrically noisy so much so that thy may interfere with the electronics on the machine and require filters to remove the noise from the circuit.
The can be found new for $350.00 to $400.00 for a 12HP unit.

The best way to determine the size of the unit you need is by looking at the data plate and finding out the power requirements roughly 750 watts equals 1 horse power so if your machine requires 7,500 watts of power to operate then you need a 10 HP unit. If the wattage is not listed on the data plate then you can computed it by multiplying the applied voltage in volts by the maximum current in amps.

A machine that draws 75 amps and operates at 440volts will require 75 X 440 = 33,000 watts or 33 kilo watts and 33,000 divided by 750 = 44 HP you will need a 45HP unit to power that machine.

[wippin' boy]

I'm limited on how hard I can push my 325 amp Lincoln.

what kind of numbers (dc volts) are we talking?
what do you see when you pull on it to hard?

[precisionworks]

If you run wire, especially gas shielded flux core like Dual Shield 7100 Ultra, you'll have the machine cranked way up. In .045" size, that wire needs 30 volts at max deposition rate, which equals 308 amps. If you do much structural welding on heavier plate, the gas shielded flux core wires are pretty popular.

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Barry Milton

[DaveKamp]

Marci- Nice answer, but Kevin's not gonna drop a huge chunk of change to come up with 33kw of 3-phase power, and it's really not necessary to go that far.

Avanti/Perry- Yes, you CAN disconnect and leave the center core floating, but you have to look closely- the machine is wired in delta on the output, so that results in a substantial power pentalty.

Running it in single-phase only, with the two outside cores, knocks the crap out of your output, especially if you're running with the high-smoothing reactor tap. It puts about a 68% crimp in your output. Welding with 32% efficiency ain't great. Lots'a ripple, and no balls.

I did some messing around with numbers, and volleyed some Emails with Peter H, and came up with a novel way of making all three active, and if what I'm seeing here (on my CP200) is true, I should be at about 90% efficiency.

First: Separate out all three primaries. They all land at a long terminal strip on the right side (facing the machine) panel.

Second: Wire the coils for 480v configuration. This will make the set (in series) operate at 240.

Third: Connect the FIRST coil so that it is fed in phase with the 240v line.
Fourth: Connect the LAST coil so that it is fed 180 out-of-phase (flip the wires).
Fifth: Connect the CENTER coil so that it is fed through a capacitor on EACH side.

The result: The center coil runs 90 degrees out of phase with the first and last coil, hence preserving MOST of the figure-8 flux pattern which the transformer normally gets in 3-phase delta operation.

The reason for doing this, is because the SECONDARY side is also in DELTA, and the rectification scheme needs a certain amount of symmetry in order to keep stable output.

The catch is, you'll need to do some wiring, and some trimming. You'll need to calculate the capacitance, get in the ballpark, and then work with it a bit to get the right amount to suit your setup, and realize that as you change, the effectiveness will change, so 'trimming' capacitance will be required if you go from 1/2" plate to 23-gauges sheet steel.

[wippin' boy]

1) so after thinking about this sunday i was wondering why this is not just a "static converter" in disguise
2)

so 'trimming' capacitance will be required

i'm wondering why this is better than a rpc

thanks barry but the numbers i was after are what PWP gets for the top end on his 10hp RPC feed machine

[wippin' boy]

for the record
this mornings test welds reveal
.035 er70S-6 with (Praxairs') Stargon (3 part) gas, 21volts dc pulls right at 100 amps
when welding 1/4" plate, on a 2F position weld

[JL Sargent]

Thats good info. But remember as far as your RPC goes your concerned about amperage on the primary side of your welder, not the secondary. So your incoming amps was less than 15 or so?

[wippin' boy]

correct....
the 10 horse is half built as we speak

[precisionworks]

So your incoming amps was less than 15 or so?

That sounds about right for small diameter solid wire with gas shielding. The problem will happen if you ever run larger diameter higher voltage wires - these include hard facing wires, metal cored wires, gas shielded flux core, etc. Or if you ever want to air-arc. Then you'll sometimes need 100+ amps on the input side.

Even mid sized wires, if you run in spray transfer mode, take a bunch of (welding) amps. .045" solid, 3G or 4G position, runs at 25 volts & 260 amps. .062" solid, 3G or 4G, runs 26 volts & 290 amps. Both are decent choices if welding plate that's 1/2" or thicker. In the flat position, the amps get even higher

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Barry Milton