[MarkinSK]

Since I just sold my Miller Bobcat, trying to use my Miller Dynasty 200DX off regular generator. I wonder what watt is enough to run at least 175 amp?

[Coldman]

http://www.millerwelds.com/files/owners ... AF_MIL.pdf

see page 15

[MarkinSK]

Thank you for input. I never seen that page before.
I was looking at Single-Phase Stick Process 130A-says 4.7KW. I'm expecting that if I connect it to 6500W generator then I could run 150A or close to 175A, am I right?!

[cj737]

You also need to know the amps available on your generator if using 230v power. It's not just about the wattage... Striking the rod will draw the most amps but then settle in once lit. The higher amps your Dynasty is set to, the greater the wattage seen at the generator.

[Otto Nobedder]

Look for a figure on your 200DX called "Maximum inrush amps", probably abbreviated "Im" (or "Ip" for peak current) on the data chart on the back of the machine. That's the figure your generator must be able to provide, briefly, each time you strike an arc. "Amp continuous", probably "In" (n for nominal) is the most it will continuously draw while an arc is established, likely at the machine's 60% duty-cycle point, possibly 40%. (Specs vary by maker.)

Actual consumed watts are hard to measure on a welding machine.

Steve S

[noddybrian]

Many inverter welders seem to draw they're maximum when first switched on as the large capacitors charge - when trying to weld from a generator if the welder senses voltage / frequency out of acceptable limits it will switch off with an error code so you really need a generator at least as big as the maximum that Otto mentioned or as the revs drop on the generator before the engine governor can recover you will have problems - it is also very hard on the generator - ones with an AVR do not like such use - the much hated brushless inductive type will tolerate much higher momentary overloads - its possible that as most Millers have auto input voltage sensing they are more forgiving - if you want to know a wattage draw at a specific welding current simply use a clamp ammeter on the input lines & multiply by line voltage - remember though if you have the dig function enabled that power will change a fair bit depending on arc length.

[Keith_J]

Power (kW) advertised is a big variable for generators. For example, my 1970s era milsurp MEP 002A is rated at 5kW but it easily powers my 200 DX when hooked in 3 phase..being a wye connection, that is 208 VAC. I've load tested the genset with three 3500 watt water heater elements (phase to phase) and freqency drooped to 59.5 Hz from 61.5 Hz no load.
This is an 1100 pound rig, 70 cubic inch indirect injection air cooled Onan beast. The generator is brushless and weighs in alone at over 350 pound of iron and copper.

Now a one lung gas powered 5kW from a bigboxstore might do fine if you don't go above 150 amps in GTAW but no way SMAW.

I also have a milsurp Lima MAC 12 kW 3 phase( again in low wye, 208 VAC) that is PTO driven in my M 1031 truck (1986 militarized Chevy K30 with Deyriot Diesel 6.2). Main circuit breaker is 45 amps. Mind you, the power cord on a 200 DX is 4C 12 AWG SOOW, good for 20 amps if it is cold outside. Which brings me to that point. Ampacity.
20 amps single phase at 240 volts is 4.8 kW. But the inverter inrush can be as high as 40 amps due to power factor correcting capacitors. So if you run a generator with less than a 12 horsepower engine, you risk the power cord due to reactive heating..current lagging voltage in the waveform.

I spent a few years as a generator operator and mechanic in the US Army..could you tell?

[MinnesotaDave]

When I had this question for my maxstar 150s (power factor corrected machine) I sent Miller an email.

They told me any modern 5000w continuous generator would power it fine.

I'm sure they will have the answer to your question as well.

@keith J, that was a very interesting post

[noddybrian]

Agreed - even if we're getting borderline " Sheldon " ! generators & power in general is quite a complex subject - a point touched on is that older built stuff especially if built to a spec rather than a budget will have more reserve available & tolerate overload / surge's way better than modern ones - big box store units are usually " over rated " to start with at low duty cycles & true continous output is nowhere near the sticker wattage - you get a feel for what a unit should make based on the engine advertised horsepower / displacement against claimed output but it takes some experience - so when shopping for a generator it's best to take the sticker claims with a pinch of salt & go with a good safety margin over your requirements.

[Keith_J]

Well put, Brian. Two horsepower per kW is about right for a 3600 RPM (two pole) unit using gasoline engines. "But wait, one horsepower is 746 Watts " you ask? Yes, that is the math but that engine also has to cool itself (hp is often stated gross, neglecting cooling) and the genetator itself needs cooling plus that heat is also lost power. Then we have single cylinder issues where a power stroke happens once every two revolutions. When that piston is on its compression stroke, the frequency droops horribly. Then on power stroke, frequency overshoots to as much as 67 Hz.

[noddybrian]

Well put Keith - you clearly have a good knowledge on this - I would actually go 2.5hp per Kw minimum on the single cylinders - partly because a lot are now using import copy engines based on Honda's & the claimed Hp is un-proven - they just assume if they roughly copy a design the copy will work identically to the original which they usually don't - partly the rotational mass of both engine & generator is getting cut year on year to shave manufacturing costs - part because the Hp is based on a brand new engine & once it's done a few hours they soon lose some - partly because over here ( UK ) our standard supply frequency is 50Hz so governor target revs are 3000 on a common 2pole so is lower in the power band of the engine - peak power on the little singles is often 3600 > 4000 rpm's so we are not getting the same power out of the same motor.

[Keith_J]

Totally missed the 50 Hz on that side of the Atlantic. Spot on too regarding copied engines. I know the US military engines of last century were FAR under rated. OHV engines that produced a rated 1/5 Hp per cubic inch or so. And they ran forever.

If you run an engine at 100% of its rated max, it might last 200 hours. 75% and that goes to 2000. 50% and it should last 10000 hours. Since most don't run generators heavily, they can get by with undersized engines. But not welding.

[MarkinSK]

I'm very appreciated for very knowledgable info. Looks like around 7kW might do the trick. I will use it till I get another engine driven welder, probably Trailblazer EFI.

[noddybrian]

If your going trailblazer / Ranger I would go Kubota diesel every time.

[Oscar]

I've tried my HTP Invertig 221 off my 7 kW TroyBilt generator with stick welding. Running 7018 at 125A will momentarily draw a power spike close to 7kW, but then settle to around 65% load. So it all depends if you will only be TIG welding, or also stick welding which will draw larger spikes due to hot-start settings.

[Keith_J]

Yes, SMAW will draw a lot more than GTAW, especially on inverter machines. The larger the generator, the greater the inertia to pull the load. And bigger engines also have greater inertia. My Onan MEP 002A has two flywheels plus the generator so it never struggles. It weighs in at 1100 pounds wet yet is only rated at 5kW into a 0.8 power factor load. I've tested it to8 kW.