Does it have to be 10Kva

[GRW]

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

I think that it's really one of those "suck it & see" jobs. The problem is there are WAY too many variables - & even working out sensibly what should work, does not mean it will work.

I'd start with clamping the welder to see what it pulls off the mains (& note what voltage your mains is at).

Does your welder manual state the input voltage & frequency range? I.e. how "tolerant" it is? Given how much variability there is in even Mains supply these days (plus wanting kit to function in several different markets) - most stuff is pretty tolerant. If so, you can "cheat" a bit by winding your genny up off-load to (say) 54Hz (so a 3000rpm at 50Hz set is running at 3240rpm off-load to give you a tad more "wiggle room" & that bit more "oomph"). Note that peak hp of lots of small engines is at 3600rpm (60Hz) or even higher (so a 13HP GX390 isn't giving 13hp at 3000rpm, probably closer to 10-11hp.... which is why the 6kva-ish rating).

Weight & portability (& Money). A petrol set is way lighter, & way cheaper than its quality equivalent in diesel. That makes it easier to hump about, while the cost saving pays for a LOT of Petrol. Then folks like Stephill will fit an LPG Conversion (dual fuel) for a few hundred quid - so you CAN get diesel running costs for less money.

Esp if not running lots of hours - then a petrol makes sense, & the weight saving is a biggie if transporting it. Heavier petrol sets can be had in a 2-wheel "Barrow" type frame to make moving one about possible single-handed on hard surfaces (though loading / unloading still challenging).

When you factor all that in.... its obvious that IF a 1-cyl Petrol CAN be got by with - then it ticks every box.
If not, then a Honda GX610/620 V-twin will give you 10KVA, 8kw absolute overload max cheaper than just about anything else of reasonable quality..... but its still a LOT of money, and still a hernia-inducing lump (which would enjoy a drink of unleaded as well!).

You're in the dilemma I used to see people in all the time with mobile equipment - mobile caterers tended to be the stuff of nightmares - needing big power, with nowhere to put it, no way to handle it, not enough weight-carrying capacity etc etc.

If (IF) your measurements hinted that you might get away with a 1-cyl GX390 set - it'd probably be money well spent to drop £100 or whatever on a Hire Set from a Tool Hire place & actually test it - you'd lise a lot more if you splashed out on a set that didn't work!
(I used to see a chap who ran some kind of plastering machine off a Honda Petrol... on paper there was no way, but if the genny was tip-top and run at slightly higher rpms, voltage & frequency than you normally would - pushing the envelope, and I'd bung a new capacitor in it whenever it came in - it manfully stood up to being battered flat-out on a regular basis. I warned him it was damned marginal, to change the oil at least every 100 hours, and to bring it in for a tweak and a new air filter to give it every chance - and he used that setup for a long time).

(That's a very long-winded way of saying you need to do your homework - see if you've any hope, then actually try it & see if you get lucky )

 

[sako243]

Just stop messing about and just get a decent sized one.

 

[GRW]

Just stop messing about and just get a decent sized one.
View attachment 531184

That's a golden oldie! Late 70's, early 80's?

 

[Bornfree]

Just stop messing about and just get a decent sized one.
View attachment 531184

4 cylinder ford around 40kva at a guess.

 

[sako243]

4 cylinder ford around 40kva at a guess.

I think it's only a 28kVA alternator on the back. Yup old ford, forget the model name.

 

[Bornfree]

I think it's only a 28kVA alternator on the back. Yup old ford, forget the model name.

They were called Dorset probably a 2712 or 2711 fitted in the smaller D series trucks.

 

[sako243]

That's the badger

 

[GRW]

That's the badger

Don't leave old coolant in them - porous liners were a common Ford issue of that era.
Basically sound old lumps though - simple & reliable.
Has it got a "Markon" or "Newage Stamford" alternator on it?
(28kva does sound low - but iirc the 6-pot variants were only 40-45kva, so ...)

 

[Bornfree]

Don't leave old coolant in them - porous liners were a common Ford issue of that era.
Basically sound old lumps though - simple & reliable.
Has it got a "Markon" or "Newage Stamford" alternator on it?
(28kva does sound low - but iirc the 6-pot variants were only 40-45kva, so ...)

I've got a 75kva 6 cylinder turbo model at work. And a bedford 220 engined 33kva model which is why I thought the ford one would be nearer 40.

 

[Jack Ryan]

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).

Conventional generators require inertia. The stored energy is used to maintain voltage and frequency when the load changes.

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.

The size of the engine is determined by the design load. Using an under sized engine will result in poor performance in either type of generator.

An undersized inverter generator is not much good for anything at all. A properly designed inverter generator can supply a large intermittent load probably better than a conventional generator and with less distortion.

The inertia of generators used to maintain the voltage and frequency of the grid is slowly being replaced by (hopefully) properly designed inverters that support solar, wind and other power sources.

Jack

 

[Shedendman]

Just stop messing about and just get a decent sized one.
View attachment 531184

Thats bigger than the inside of the van

 

[roofman]

I have an industrial wet n dry vac which has 3 x 1000W motors, i can run it from a 4KVA genny but need to run the genny at a constant 3000rpm or it bogs down on vac start up...my other 8KVA genny runs it almost on idle. What i am saying is if you up the rpm constant on the generator it has less load shock on start up, this solution could be used for a small welding job but to have the engine screaming for hours at 3000rpm would not be feesable.

 

[GRW]

Conventional generators require inertia. The stored energy is used to maintain voltage and frequency when the load changes.


The size of the engine is determined by the design load. Using an under sized engine will result in poor performance in either type of generator.

An undersized inverter generator is not much good for anything at all. A properly designed inverter generator can supply a large intermittent load probably better than a conventional generator and with less distortion.

The inertia of generators used to maintain the voltage and frequency of the grid is slowly being replaced by (hopefully) properly designed inverters that support solar, wind and other power sources.

Jack

Power is Power.
Energy is Energy.
It has to originate from somewhere, & in a Generator it is Fuel Energy, converted to mechanical energy & inertia that does this.
If you don't create it, put it in - then you cannot get it out... the laws of the universe at work.
Already, the notion that Solar & Wind Energy can totally replace conventional Energy - is now being "reconsidered" because quite simply it just doesn't work like that.
(Massive cascade grid failure events in chunks of Spain & the USA & already proved that the hard way. Even a senior WEF figure recently stated that for key Manufacturing Processes like steel & cement, that "Alternative Energy" simply cannot sustain the kilojoules of energy for such processes.
Neither solar nor wind energy (or indeed small engines) can instantly "find" the extra power to react to additional load - they get overwhelmed & fall behind (or fall over, & as one falls, it trips another, and another......

An inverter as a Producer is still utterly reliant upon the available Energy to power IT. It is no magic bullet that sidesteps the laws of physics.

Generators - will never be "replaced" entirely.

 

[GRW]

I have an industrial wet n dry vac which has 3 x 1000W motors, i can run it from a 4KVA genny but need to run the genny at a constant 3000rpm or it bogs down on vac start up...my other 8KVA genny runs it almost on idle. What i am saying is if you up the rpm constant on the generator it has less load shock on start up, this solution could be used for a small welding job but to have the engine screaming for hours at 3000rpm would not be feesable.

All small portable (non-inverter) gennys run at 3000rpm at 50hz & have 2-pole alternators.
Industrial 4-pole stuff is 1500rpm at 50Hz.
Mechanical Governed stuff is set up off-load typically at 52.5Hz to allow for a bit of rpm loss approaching full load - & even a fit set will sit at 49.5Hz at 100%

Electronically governed engines are at 50Hz offload.

If an alternator has an AVR, then upping rpms won't alter the Voltage.... but Capacitor regulated alternators can volts with frequency - so just whacking revs on can see output volts jumping to 260v plus - so you have to know what you're doing, & what your load can tolerate without going POP & emitting Magic Smoke

 

[GRW]

The size of the engine is determined by the design load. Using an under sized engine will result in poor performance in either type of generator.

An undersized inverter generator is not much good for anything at all. A properly designed inverter generator can supply a large intermittent load probably better than a conventional generator and with less distortion.

You need to factor in "Sales & Marketing" and Price.

1. Yes the engine power is determined by the alternator size & vice versa.... but with lots of wiggle room for "interpretation". E.g. a smaller capacity turbo engine will hit the same peak kva on load test when ramped-up... as a non-turbo.... so they are both able to meet the Regs to be rated at (say) 60kva Prime, 66Kva Standby.
But the non-turbo will spank the turbo unit for Load Acceptance / Motor Start / Impact Load.
Yet you will not find a 60kva non-turbo set for sale today. Why? The smaller turbo unit is cheaper & more competitive on sale price.

2. Inverter sets follow the same market forces thing as above - but with the added "bonus" they can be lighter and smaller if they use a smaller, higher-revving but ultimately less torquey engine as the source..... so they do!

 

[henry Kadzielski]

Mechanical Governed stuff is set up off-load typically at 52.5Hz to allow for a bit of rpm loss approaching full load - & even a fit set will sit at 49.5Hz at 100%

Just trying not to be tooooooo pedantic.
52.5Hz no load mechanical governing as 5% variation (droop) from no load to full load. Full load being 110% @50Hz. Electronic governers that I have delt with have .5% droop. I haven't built a generator for a while now but that's the figures I worked to. The smaller the sets the lower the alternator efficiency. Some engines will produce their rated output easily and go to 120%, whilst some barely make what the manufacturer claims.

 

[GRW]

Just trying not to be tooooooo pedantic.
52.5Hz no load mechanical governing as 5% variation (droop) from no load to full load. Full load being 110% @50Hz. Electronic governers that I have delt with have .5% droop. I haven't built a generator for a while now but that's the figures I worked to. The smaller the sets the lower the alternator efficiency. Some engines will produce their rated output easily and go to 120%, whilst some barely make what the manufacturer claims.

Not wanting to be too pedantic ..... but 100% Load (Prime) IS 100%, with (iirc) the definition being the set can be run at variable load, with the 100% rating not exceeded. The 110% "Overload" rating is an emergency power rating, and cannot be for more than1 hour in any 12-hour period.
(There is a 3rd "Base Load" category which is for continuous max load - which is a de-rate from the Prime rating of typically 10% (dependent on the engine Mfr statements).

So.... any genset engine that achieves 120% has been mis-rated according to the Industry Standard classifications, and indeed the Proof Load-Testing Criteria..... & (because every Mfr wants the biggest most impressive kva number for a Sales angle) - no-one under-rates a genset - they generally quote the highest value the regs will possibly let them get away with
(Unless it's Chinese, when it seems they claim anything).

Addendum. The Standard is ISO 8528 which outlines ERP & PRP etc Criteria.
Mfr Datasheets will usually have the qualifying statements on them, including the Relative Humidity (typically 60%) and the Ambient Temperature (40% or 27%) and the height above sea level the ratings are relevant at (typically 500' ASL).

 

[henry Kadzielski]

After reading my responce again, I see clearly how it was worded very wrongly. You are 100% and even 110% correct. The 120% that I put forward was from Kubota load tests on a load bank that I have done. The engine is rated for X kw however on the load bank I could get 120% of X, knowing full well that that is not where it should be run. I built a Isuzu 4BG1T based genset 3 phase. 70amps per phase at 100% load (variable load) 77amps per phase for short burst to start bigger loads. I was informed by the customer that it does 84amps per phase no problem. Go figure.

 

[Robotstar5]

Just stop messing about and just get a decent sized one.
View attachment 531184

And put it on wheels so you can move it around

 

[GRW]

After reading my responce again, I see clearly how it was worded very wrongly. You are 100% and even 110% correct. The 120% that I put forward was from Kubota load tests on a load bank that I have done. The engine is rated for X kw however on the load bank I could get 120% of X, knowing full well that that is not where it should be run. I built a Isuzu 4BG1T based genset 3 phase. 70amps per phase at 100% load (variable load) 77amps per phase for short burst to start bigger loads. I was informed by the customer that it does 84amps per phase no problem. Go figure.

The Japanese Mfrs (like the Germans) used to be very focused upon the reputation for reliability & every unit meeting the performance on the datasheet of their products - where arguably everyone else picked a strong unit & used every trick to enhance the output claim to be as impressive on the Sales blurb as possible.
So if any industrial motor (of a few years ago anyway) - was going to punch well for its weight, a Kubota, Isuzu, or a German Deutz would be arguably more likely to excel than a Perkins (esp. some in their bigger nodes).
Kubota, Isuzu & Yanmar made some cracking small industrial diesels - I'd offer them over a Perkins 400 or a Lister-Petter Alpha option where I could.... they were just better.