Does it have to be 10Kva

[E T]

I did some tests a while ago on both my 150A Kemppi and 180A Fronius stick welders with a clamp meter and found that arc length also plays a big part in current draw from the mains not only strike-up.
On the Kemppi I saw values up to 28A while welding and on the Fronius up to 30A.

 

[GRW]

There is another possible "curve ball" that the Welder Mfr is trying to side-step with their "10kva" stipulation - & that is Total Harmonic Distortion (THD) & its effects upon Generator Voltage Regulation.
THD is a phenomena where (simplified) "interference" on the supply circuit to an Inverter is caused BY the inverter.... which in turn "confuses" the Automatic Voltage Regulator of the supply Genset.
The result is the supply voltage moves outside the operating parameters of the inverter. (Basically the inverter creates an issue, then cannot cope with the issue it created).
Once a non-linear load (inverter) on a genny exceeds 50% of the Alternator rating - the chances of THD becoming an issue increase exponentially..... so again this MIGHT be another reason why ESAB state 10kVA

It can all get a bit "Black magic" tbh... because you get stuff that should not work on paper that does - & vice versa.

E.g. I've seen supposedly "better" AVR regulated gennys fail to run a non-linear load, but a basic Capacitor Regulated set of the same size run that load with no apparent issues (my best guess here is that the "dumber" slower-reacting Capacitive setup "damps" out THD by not reacting as quickly as AVR's, thus avoiding voltage instability).

On the flip side I've seen Capacitive regulated sets eat capacitors in just 2 or 3 hundred hours running inverters (best non-boffin guess is the much higher frequency THD accelerates degradation of the capacitor ).

So... the 5kVA mathematical power does have a couple of real-world possibilities as to why ESAB would state "10kVA".
Chances are it'll operate on a smaller genny - but which smaller genny will, & which won't gets too big a minefield for them to get into - there's too many variables for them to "go there" i suspect.... so they just pick a safe oversize at 10kva as a minimum that should always work.

(e.g. The German off-grid Inverter Mfr SMA had so many issues with customers & installers blaming their kit & slating it - when the issue was that those people had no clue about any of this stuff, & were trying to run their kit off nasty little genny's - that they issued a "White Paper" document where they stipulated a genny a minimum of 2x the Inverter output rating, and that the alternator had to be a 2/3 pitched winding industrial grade unit before they would consider a generator supply to be of acceptable standard).

 

[8ob]

I have an esab rouge em180,now according to the spec i need a 10kva genny,really? For something that small?
10Kva gens are massive and costs fortunes,wheres 8's and 7's are far more cheap and portable,this has to go in and out of my van
Theres a guy i know running his rig(Stahlwerk 200 mig)at full tilt off a 6kva and has never had a problem(forgotten what genny now)
I just cant see how for mine i need such a monster of a genny
Cheers

My small 130 amp inverter tig/stick welder that runs off a 13amp plug almost stalls my 6kva Hondal genny. I dont bother taking that set up out any more, I use a welder generator now.

Bob

 

[Woody.v8]

This is definitely a common experience & Factor. MIG does seem "easier" on a genny than MAG for a given Welding Current.
(E.g. Plenty of peoplr inc me have no issue with a 180A transformer MIG off a 13A Plug - where a Stick Welder would be popping fuses often).
I'm not sure why exactly this is, but guess it could be the thicker welding rod & flux demands more power over Wire arc
Inverter sets also are less energy-hungry than Transformer sets (though aso are arguably more "fussy" about voltage & frequency & not as robust as a Transformer lump).
That said - modern inverters are much more accepting of much wider voltage and frequency windows than they used to be.

[Pedantic mode on] Mig and Mag use the same machine, just different gas. MMA uses flux covered electrodes .[Pedantic mode off]

 

[GRW]

[Pedantic mode on] Mig and Mag use the same machine, just different gas. MMA uses flux covered electrodes .[Pedantic mode off]

OK, OK- I always get the terminology wrong somewhere .
Mig seems to use less juice than Stick - I'll stick to that then

 

[Jack Ryan]

I checked a couple of manuals on different ESAB sites and I can't see a 10kVA requirement.

If you calculate the requirement:

Imax * V * 1/PF * 1.3 will give the VA requirement with 30% headroom

21A * 230V * 1/(0.8) * 1.3 = 7850 kVA (that's continuous, not peak downhill with a tail wind)

The manuals I looked at specified a 7 kW generator with good AVR.

Of course, that is for flat out operation.

On the other hand, do you trust the specs of your generator?

Jack

 

[GRW]

Small portable gensets (even reasonable quality ones) .... their kva rating is invariably:

Reasonable Sets (e.g. Stephill, Pramac)
1. 110% "Overload" rating
2. Assumes a 0.8 power factor.
So take 10% off straight away for max kVA, then a further 20% off that for KW resistive load capability.

Chinesium generators (though the odd Kipor one might actually be ok):
1. Whatever made-up figure looks good, at least 110% & invariably exaggerated nonsense that will be out of reasonable parameters if you try to actually get close to claimed power.
2. PF. Irrelevant due to 1. above.
3. Any output you get liable to have questionable stability & reliability
So - A total lottery what you actually get.

(You can see why ESAB might want to play it safe when stating what minimum generator requirement is )

 

[Shedendman]

@GRW
You know your onions indeed
Reading what you've put up has quite eased me in a way
Thanks

better add,most is for mig gas and gasless,i very rarly do stick

 

[GRW]

@GRW
You know your onions indeed
Reading what you've put up has quite eased me in a way
Thanks

better add,most is for mig gas and gasless,i very rarly do stick

If you've got access to a clamp meter & can strip back a bit of cable so you can clamp the Live & measure the Current on strike-up and welding at 180A (& lower if that's where you'd typically use it)..... see if you can capture the peak strike Amps at mains voltage.

It's not quite the same off Mains as off a Genny - but it should give you a starting point to convert to kVA & get a number.

The problem.... is that the most powerful 1-cyl common genset engine (twins get lots more expensive as well as heavier/less portable) is the Honda GX390.... which always used to be 110% peak rated at 6.5kVA, 5.2kW.
Mathematically that gives you 28 Amps for strike-up (given the ESAB states its power factor is 0.8, same as the genny baseline for its kVA rating)..... so there are several factors that do indeed suggest that a 1-cyl genny might be somewhat marginal.....
..... but its possible.

 

[Munkul]

We had a mosa 200 genset (4kva) that we used to use a minarc 150 on cos it was nicer to stick weld on than the mosa built in welder.
We burnt out the alternator eventually.
Not sure if it wae linked, but I'd guess it was.

 

[GRW]

We had a mosa 200 genset (4kva) that we used to use a minarc 150 on cos it was nicer to stick weld on than the mosa built in welder.
We burnt out the alternator eventually.
Not sure if it wae linked, but I'd guess it was.

Almost certainly.

 

[henry Kadzielski]

My two cents worth.
The main reason for stating a larger generator is for the 'engine' that drives the alternator. The electronics, voltage regulation can react quite quickly, however the engine 'prime mover ' takes time to react causing a voltage drop. The bigger the generator, the bigger the alternator and such the revolving mass. This is the kinetic energy used to handle the sudden increase in the load (current draw). To big a load to start the generator will stall out. The governor needs time to react, and only reacts when the prime mover starts to slow down, not before, there is no preemptive governor application. This is assumed that the alternator is at the required rating.

 

[Jack Ryan]

My two cents worth.
The main reason for stating a larger generator is for the 'engine' that drives the alternator. The electronics, voltage regulation can react quite quickly, however the engine 'prime mover ' takes time to react causing a voltage drop. The bigger the generator, the bigger the alternator and such the revolving mass. This is the kinetic energy used to handle the sudden increase in the load (current draw). To big a load to start the generator will stall out. The governor needs time to react, and only reacts when the prime mover starts to slow down, not before, there is no preemptive governor application. This is assumed that the alternator is at the required rating.

This also assumes a conventional (non-inverter) generator.

Jack

 

[henry Kadzielski]

Invertor generators are similar. They run at a lower speed when demand is low and the governor then speeds up the prime mover as load increases, this all takes time. The larger the generator the higher the startup current is, the better the 'shock' loading is

 

[Jack Ryan]

Invertor generators are similar. They run at a lower speed when demand is low and the governor then speeds up the prime mover as load increases, this all takes time. The larger the generator the higher the startup current is, the better the 'shock' loading is

True, but an inverter doesn't rely on angular momentum for step load increases, it uses storage to help fill the gap between the new load and the engine powering up. As long as it is designed properly, the inverter can supply the new load - within limits. When using a welder, or other large intermittent load, it would be better to disable any economy mode that idles the engine.

The previous comments still apply though, the engine has to be up to the task, etc, etc or that won't happen. There is a big market for cheap generators and that's probably why they get a bad name.

Jack

 

[Jack_K]

Due to how manufacturers seem to rate generators now, I have a simple way to determine if I'd run a welder on it. If it is a single cylinder petrol, it is too small. I'd look for a twin cylinder.

Some single cylinder generators can do some welding jobs but what was once a 4 or 5kva now seems to be rated at 6kva or more. Chinese HP. As far as I'm aware, the Honda GX line-up has never had a single cylinder over 13hp. China sells their equivalents in 15 and 16hp. I doubt they've engineered extra HP, I reckon it's just a sticker. 13hp was about what used to be fitted to a 5kva generator.

 

[Jack Ryan]

Due to how manufacturers seem to rate generators now, I have a simple way to determine if I'd run a welder on it. If it is a single cylinder petrol, it is too small. I'd look for a twin cylinder.

Some single cylinder generators can do some welding jobs but what was once a 4 or 5kva now seems to be rated at 6kva or more. Chinese HP. As far as I'm aware, the Honda GX line-up has never had a single cylinder over 13hp. China sells their equivalents in 15 and 16hp. I doubt they've engineered extra HP, I reckon it's just a sticker. 13hp was about what used to be fitted to a 5kva generator.

Yes, it's hard to talk in terms of what ought to be, as it rarely (at least in the case of portable generators) is.

As it stands, ESAB specified a generator rated at 7kW. I'm sure there will be 7kW generators that can't supply that with a power factor of 0.8, there would be a current overload. It pays to look at the detail.

Jack

 

[henry Kadzielski]

I'd look for a twin cylinder.

I can tell you I used a 10kva single cylinder 3phase genset to run my TPS320i on 5mm alloy and no trouble. I was supprised how well it did it actually.

 

[GRW]

It's not "just" HP from an engine, but also type & mass.
E.g. Load Acceptance / Impact Load of a naturally aspirated diesel of say 100kva is usually 90% of its Continuous Rating, where on a Turbocharged engine that typically drops to about 70%.

Old Lister-Petter sets with very heavy cranks & very, very heavy flywheel assemblies would punch well above their rated power for motor starts - because they had so much stored energy in the Flywheel to carry through the motor start transient surge (& industrial Alternators will typically withstand a 300% overload for up to 10s as well as have extra tricks up their sleeve to help).

Small inverter gens I don't think are that great for impact loads.... because using an inverter alternator let's them get away with using a smaller engine (I.e. where a conventional gen is at 3000rm at 50Hz, a mfr will use a smaller engine & rev it 50% higher at 4500rpm to get peak power.

Small "portable" conventional "site" gennys are relatively simple in engine, governor and alternator design, plus are lightweight with little mass & designed really for hand power tools.. so given all that, a decent built one actually performs pretty well for what it is.

 

[Shedendman]

@GRW ok,so if you had my unit,what genny would you go for,out of curiousity
Cheers