Can a Chopper Realistically Be Built

[Peter Hurley]

I have a newly acquired Lincoln Engine Driven Welder. The Vantage 300 is a great machine and this one is runs excellent. It has a diesel Kubota powering a 12.5kw generator that powers a 300 amp welder.

The generator operates as it should. I checked all the wiring, voltage, current, etc.... and it's spot on. The welder is another issue...... the chopper had been found to be bad and was removed. I acquired it less the chopper and a new chopper hovers around $2,000. This welders NEW counterpart is $2500 and is a better welder.

As it is.... I am happy to have it as a portable generator. But I would LOVE to have the welder back in action.

Can a chopper be built? Can the chopper be circumvented? You get the gist. All the other items are still with the welder. The inverter, control panel, choke, etc.... The research I have done at Lincoln Electric states the chopper was a 20,000hz unit. A potentiometer feeds its current to the chopper telling the chopper to feed the welding circuit the desired juice.

What can be done?????????????
Thanks
Pete

 

[davenn]

Can a chopper be built? Can the chopper be circumvented? You get the gist. All the other items are still with the welder. The inverter, control panel, choke, etc.... The research I have done at Lincoln Electric states the chopper was a 20,000hz unit. A potentiometer feeds its current to the chopper telling the chopper to feed the welding circuit the desired juice.

What can be done?????????????

hi ya

without knowing the actual circuit, it would be highly unlikely for one to be built
Unless of course some one had the identical unit and could take photos etc of the board

 

[kellys_eye]

The cost and effort involved in building one would exceed the cost of purchasing a used (good) one.

This is often a problem faced when trying to circumvent the facts of 'mass production'.

 

[BobK]

Well, $2000 does not sound like a cheap mass-produced item. I know nothing about welding, so, what does a "chopper" do?

Bob

 

[kellys_eye]

Well, $2000 does not sound like a cheap mass-produced item.

nor does it when talking about a sedan or coupe..... but you get my drift?

 

[BobK]

Well, if the chopper requires as many parts as a car, I will cocede your point.

Bob

 

[BobK]

Lincoln Electric’s Chopper Technology is the simplest form of high frequency power conversion. A chopper is composed of a transistor switch and a diode. DC input power is “chopped” to a lower output voltage, and a choke is placed in the path of the output to smooth current variation.

Sounds like a description of a buck converter to me. And the frequency is only 20KHz. Yes, 300 Amps is a lot, but I would think I could build one for less than $2000.

There is another reason why it might be so expensive. Lincoln is the only company that offers this, so the likely have an active patent on it and are therefore a monoply.

Bob

 

[Peter Hurley]

The cost and effort involved in building one would exceed the cost of purchasing a used (good) one.

This is often a problem faced when trying to circumvent the facts of 'mass production'.

That may be true............. and I would buy a used one in a heartbeat (at the correct pricing of course) but they are far and few between. I would suspect, even a used one auctioning on eBay will go for very steep dollars.

 

[Peter Hurley]

Here is a photo of Lincoln Electric's brochure regarding Chopper Technology. Hope it helps. It has a small photo of the Chopper Board in question here.

 

[kellys_eye]

Such welders will have a variable output voltage (around 10V to 80V).

Currents of 300A are relatively easily handled with paralleled MOSFETS but finding the right ferrite core is probably the most difficult aspect of a design.

Unless you get it completely right you risk blowing up a lot of parts and I imagine in a quite spectacular fashion too!

 

[Peter Hurley]

Correct. Most welding in this size arena hovers around 20v +-.

 

[Peter Hurley]

Here's a thought......

What component or components would be required to eliminate the chopper and its controlling potentiometer? The input voltage to the chopper is 90v DC with an output of 30v (constant and 30v is correct and what most welders output) having an AMP range of 40 to 300, give or take.

Does any of that make sense??????

 

[BobK]

The "chopper" or the more complicated "inverter" are what we call a buck converter and a flyback converter in the electronics world. These are the only reasonable ways to reduce 90V to 30V at that kind of current.

As kelleys_eye says, the current can be handled by parallelled MOSFETS. I would use what is called a synchronous buck converter to use MOSFETS in place of the diode as well, since the diode would otherwise need to dissipate 100s of Watts. I suspect their board actually does the same, despite the simplified diagram they show, which is a classic buck converter.

Let's do some math on the inductor.

Assuming we need to step down 90V to 30V at 300A.

Let's allow a generous ripple of 10% because I can't imagine it is that critical.

The equation is:

Vout = Vin * Ton / Tperiod

So to get 30 from 90 you would use a 33% duty cycle. The transistors would be on 1/3 of the time and off 2/3 of the time. The change in current over that 2/3 off time would be 30A (10% of 300A).

The equation for an inductor is:

dI / dt = V / L

where:

dI / dt is the change in current over time, i.e. Amps per second. For a change of 30 Amps over 2/3 of a 20000 Hz cycle, we get:

dI / dt = 30 / (1 / 20000 / 3) = 1.8 M A / sec

V is the voltage across the inductor, which is the difference between the output voltage and the input voltage, which is 60V.

1,800,000 = 60 / L
L = 60 / 1,800,000 = 33uH

This is a pretty small inductance. No ferrite core needed, just a coil of very thick wire.

Using this calculator:

http://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtml

I find that 9 turns of wire one foot in diameter over 3 inches width would do it.

Bob

 

[kellys_eye]

How do they derive the 90V input?

I assume the generator side is a standard 120/240VAC output.

 

[BobK]

Pull up the brochure that the OP posted. Full wave rectified, and they sjow a smoothing capacitor as well.

Bob

 

[Peter Hurley]

How do they derive the 90V input?

I assume the generator side is a standard 120/240VAC output.

The generator produces single and three phase power. Possibly, they simply pull the single from the three phase. BUT I seem to recall watching a video from Lincoln in which the Tech was talking about the generator exciting from 12v and in turn producing 120v...... then the 120v was reintroduced to a second section of the gen head in order to produce 230v 3Ph. Don't quote me but I believe this is what they do.

Anyway, the Tech was talking about the 230v AC entering an rectifier and coming our 90v DC which was then sent to the Chopper..... the Chopper was told what to do form the Potentiometer and then released its appropriate current to the choke..... choke to welder's cable.

I am think (which is always dangerous for a hack) that I bet I could find an old school current adjuster from another welder and introduce it into this one. It may not be Gas Pipeline capable in the welding department...... but it will weld everything I ever want.

Hence the reason I was asking about replacement components to bypass the chopper, etc.....

 

[kellys_eye]

That would result in a 170VDC or 340VDC output assuming a standard 120/240V alternator side.

Accordingly they would require a power converter to get the 90V DC and a SMPS to get 90V DC @300A is no simple circuit!

Does the set the OP has still have the inverter part fitted and does it work?

 

[Peter Hurley]

Here is a video from Lincoln diagnosing a Vantage 400...... the Vantage 300 I have is built exactly the same. The chopper, etc.... are the same part numbers.

 

[kellys_eye]

It would be necessary to integrate any DIY chopper into the existing circuitry so do you have a system schematic that shows how the chopper is fitted as part of the whole?

The 'chopping' part of the design is (seemingly) straightforward however the CC/CV modes and their adjustment takes additional circuitry of somewhat rather more complication. The processor board visible in some of the Youtube video doesn't point to any DIY solution as being 'easy' by anyones standard!

Is there ANY technical spec, schematic etc available for us to look at?

 

[Peter Hurley]

Everything is there...... Whomever took the chopper out... also tagged all the wires. Plus, Lincoln numbers all the wiring..... it would be a walk in the park reattaching everything correctly.

When I bough this machine, I was hoping everything was inside. It would have been possible to diagnose the bad part and fix the part itself. It is a shame the chopper was removed.

Wiring Diagram.......