Power inverter design for a welding machine

Amps? Volts?

Vector MFG. make real nice basic low cost inverters.

A 4000 watt version could run a commercial version. And i do encourage using commercial methods when welding. Homemade welders are bad because they are required to have small importent things obvious to the expert but not to the untrained.

And on/off switch must do two thing I believe, Cut power and interupt the main welders line. BUt maybe I am wrong and my advice is dangerous!

Bottom line get a certified design from a reliable source. NO expermentation.

Even running a power inverter driven welder requires advice, can it be done. I do not know, but it sounds simple.

I would it go be able to deliver around 100 to 120 Amps at 25 Volts. Thanks

current mode buck regulator, anyone ?? International Rectifier has some 70A IGBTs that derate to 50A at 100C that should handle the job if you use 2 or

3 in parallel on a hefty heat sink with cooling fans... dont forget a thermal cutout :)

might be a little easier to work out compared to a transformer design at those currents.. ground reference would be the only real issue to cope with...

or pick one up on ebay for less than $100

M. Williams

I am afraid that the amount of energy through the freewheeling diode might destroy it, hence the need for a snubber circuit. Have you got a schematic of your induction heater?

Thanks

Check my website, I'm building an induction heater. Same thing, just a different output.

If the IGBTs are co-pack with diodes and the H-bridge is constant voltage (stiff voltage supply, bypass capacitors aplenty), the flyback energy will be shunted back into the power rail by the diodes.

When driving a pure inductive load, the voltage waveform is a squarewave, so the current waveform is a triangle wave. When the current passes through zero, the diode turns off and the IGBT part starts carrying the current, producing a visible step of a few volts on the flat part of the square wave. When real power is being drawn, the position of the transition changes.

Tim

-- "Librarians are hiding something." - Steven Colbert Website @

Actually, that's my brother (or mother).

The diode IS the snubber. The energy doesn't go into the diode, it is directed by the diode. The diode sees amperage, but not energy.

Umm..? It's in every post of mine...you even posted it in quoted text.

Tim

-- "Librarians are hiding something." - Steven Colbert Website @

OK, found it.

Thanks

Modern is single , low cost NPN forward

converter . Use a low cost Thyrister

to soft start , if the choke is not enough

to control inrush .

I have all the parts for a 10KW welder .

--------------------------------- MJE13007 will drive 1KW into a microscopic

ferrite core . IGBT are CRAP , MOSFETs

a bit better , 20 year old bipolars work best .

13007 will have a winding to drive the

base , and a pull down circuit to shut down

the oscillator .

This is the latest technology in switchers .

You can rectify output for D.C. welding ,

This oscillator starts in less than 10 microseconds

so you can "control" it to produce any waveform .

by merely turning it on for 100 to 1000 cycles

then controlling another , opposite circuit .

Oscillating is safer , cause its the "failure"

of the core , that shuts off the drive to the

13007 . Self limiting ...

Buy a $17 450 Watt , IBM PC power supply from MCM , open it up . The core is TINY ! Its 1/3 the size used , just 10 years ago in all PC's . 450 watts , 100% duty cycle . But many still use push pull circuits . A few use the newer , better single drive .

Its really mind bending watching a welder do 1/2" steel plate , with a tiny box , with no heat , 100% duty cycle ..

And if ya build/design it yourself , its better .

about $300 will do for 10KW .

You cant buck regulator , its too much

voltage drop .

You will use 310 vdc up to 600vdc

"forward converter" .

IGBT are Vsat = CRAP .

old MJE13007 can beat the IGBT .

buy the new round center ferritte E cores .

and use copper sheet for secondary .

30 amp Shottky diodes ...

I got parts , just need time to build it .

Circuitry is much simpler than the old Push-Pull , 2 transistor PC power supplies 10KW , 100% duty cycle ..

Non sense , there is no flyback energy .

No Catch diodes , because there

is no energy !

Open up a NoteBook computer power

supply and draw the schematic !

Single bipolar , forward converter ,

but it is oscillating , control is to simply short

the base drive to ground .

It is the most elegant , low cost and hi

power switcher ever .

This "controlled" oscillator starts in less than

10 microseconds , so you can get any

waveform you need .

Want a perfect sine wave for your R.V. ?

2 mirror circuits , one starts the positive

sine , the other rests .

No H bridge , no hi-cost components ..

Simple , fault tolerant , for the ferritte

cores are saturating 200 times a millisecond.

100% duty cycle . No heat .

yeah right. although at these puny power levels a BJT wouldnt be too awful, go read an MJE13007 data sheet.

for a start, Vceo = 400V, Vces = 700V. So Vdc = 350V (unless you fancy emitter switching which is a lot messier). So for 2500W out at say 85% efficiency, thats about 9A. it fits in the SOA, just (best not to think about lifetime).

then the gain is ~ 6. For Ib = 1.5A, Ic = 8A, Vcesat = 2V. Hmm, thats about what the IGBT does.

now make it switch fast (and dont forget your floating gate drive has to supply 1.5A continuous, along with hefty turn-on and turn-off spikes). at those sorts of current levels, you will need to do something pretty special. and dont get it wrong, lest your SMPS explode.

the humble IGBT is looking pretty good.

I think its pretty clear from the data why you dont see 2.5kW SMPS using MJE13007.

1mOhm = 10W. better be a good transformer. Still with MJE13007 it will barely be above 20kHz, so that helps a bit. except when you count how many layers in the transformer, and try to keep Fr = 1.5. Then there is the lead-out.

at 100A? thats a good trick.

yeah right. big bipolar SMPS did exist, but they were complex, and very hard to make work correctly. way, way beyond a do-it-at-home project, unless you happen to be an expert in that particular field.

this is why IGBTs are the clear winner above a few kW, and FETs below that - the removal of Rdson = k*Vdsmax^2.5 pretty much killed the need for BJTs in smps.

I caught the tail-end of big bipolar drives, using tralingtons. even then the 300A parts had a gain of about 30, so the base drivers were substantial.

for several kW, FETs are the best bet here, you can get nice 600V FETs fairly cheaply (although you need Rdson < 0.3R to beat an IGBT in terms of conduction losses), and some awesome LV FETs for synchronous rectification. even then its not trivial, but a shitload easier when you can ignore SOA and the gatedrive is comparitively easy

by the time you get above a couple of kW, the required Rdson makes the FET very expensive (assuming you want high efficiency), and a non-starter above about 10kW.

Cheers Terry

what, no leakage inductance in the transformer, and no stray inductance in the layout. thats a good trick.

LOL

betcha the output doesnt ramp up that fast.

not in a forward converter they dont.

ROTFLMAO!

Cheers Terry

OK, build one then post an MPEG of it welding. Tim has plenty of pics of his induction heater working.....

thats a bit different from 10kW.

well it was in 1963.

this is a blocking oscillator. again, all the rage in 1963.

thats because using FETs allows them to switch at 100kHz - 200kHz, as opposed to 25kHz - 40kHz with bipolars.

and, of course, its 450W. now incre3ase the power 22x. Wow, I^2R losses just got 500x higher. Hmmm.

perhaps you should look a bit harder at a modern PC SMPS. no blocking oscillator circuits there, nor will you find a saturating core (except perhaps as a mag-amp auxiliary regulator, but even then not likely)

next you will say it runs first time. and never fails. LOL

Cheers Terry

I am using some International Rectifier IGBTs in the "H" bridge that have, the specs are similar to the one you describe. I am using a "H" bridge do drive a transformer because it seems simpler to me and it is also safer, because of the isolation factor, and by driving a transformer, the current going through the IGBT should be smaller and It might work with 4 IGBTs in the bridge instead of 8 or 12.

Tim

How much current where you able to pass through the IGBTs. How much current did it draw from the utility line.

Thanks

Well, I've seen peaks up to 200A (maybe even 300), under very unusual circumstances. I think I fixed the suspect that was causing that. Don't want too many like that through the 4PC50's, though!

I haven't had power draw more than about 1kW, which is around 10A from the

120V line. The transistors appear to be good for at least 50A and 300V, which corresponds roughly to one fat ass weld bead in your case.

Tim

-- "Librarians are hiding something." - Steven Colbert Website @

Tim,

Isn't your circuit connected to 240 Vac?

Thanks

It will be... still in the testing stages (regardless of what any of my drawings may indicate).

Tim

-- "Librarians are hiding something." - Steven Colbert Website @