Generators - need some help

[Chicken Drumstick]

I’d like to get a generator to have some power down at my unit. But I’m a little lost on what I’ll need. 

I’d like to run a compressor off of it. And maybe the odd power tool such as a grinder, drill etc and some lighting (most likely led). But not necessarily all of these at once. 

I’m not sure what kind of power rating I’ll need. Is something like this likely to be stout enough:

https://www.machinemart.co.uk/p/clarke-pg2500-22kva-petrol-generator/

[steve b]

Unlikely , the problem would be the compressor - what sort do you have ?   2.2kw would not run a 9" disc cutter to give you some idea .

cheers

Steve b 

[FridgeFreezer]

Anything with an electric motor is likely to take a big kick when starting so I tend to guesstimate at least 2x the power rating.

For running big dumb tools you are best off with a big dumb generator (not a sine-wave or inverter type) as they won't get upset so easily by abuse.

[Chicken Drumstick]

Happy for any recommendations. Generators aren’t really my think. So just started at machine mart for looking. I notice some are rated in kw while others are rated in kva. Not sure how these really compare apart form making it harder to compare to each other. 

I’ll have to try and find some info on my compressor. Suspect it might be difficult as it’s oretty old. I know it has a plaque on it with a 4 digit telephone number or similar. But tbh it’s a really good compressor and does all I want from one. 

[lo-fi]

I bought an old Petter diesel powered generator on ebay for that kind of money. The engine is rated at 12hp, I believe, and its man enough to power my welder at a decent whack. Its a big old unit at 3 ft long, 2 high and 1.5 wide. Crank start and kicks like a mule, but can be dead handy. 

As Steve points out, 2.2kva isn't going to get you very far, particularly with the massive startup current of a compressor. 

[Cynic-al]

The kW of a power tool might be the motor output or the current draw depending what information they're trying to give you. If it's the motor output then the electrical input will be higher depending on how efficient the motor is and what other electrical control stuff might be running as well. The kVA of say a lamp will be the same as the kW, but for an AC motor it won't as there will be a phase angle difference, you should get given a power factor correction figure so you can convert the two. Don't ask me to explain in any more depth than that as it was a long time ago so if you need any more information ask google or someone who actually knows  But basically you'll need bigger than you think.

I don't know what you want to run with your compressor but it might be worth considering an engine driven one? Put it on a trolley so you can wheel it outside whilst your using it?

I've used the cheap generators that come under a dozen different brands for an angle grinder and arc welder when somethings broken. It did the job. Spluttered and slowed down but didn't stall. Maybe if it's your only source then something a bit better might be nice for a bit more control.

I find LED lights are on or off, if your voltage is going to be up and down a bit a filament lamp might be less annoying? Have to try it an see!

Edited April 29, 2018 by Cynic-al

[Blanco]

I tried to start a small compressor once with a 4kva  generator, it didn't get close. Pay attention to the specification,... the headline capacity and the actual rating are often very different, also unless you can tuck it away somewhere the noise becomes a strain, (neighbours?) so then easy to start and stop is nice to have.

[FridgeFreezer]

Also, if you can get one with a genuine Honda GX 4-stroke it will live forever and be worth more 2nd hand.

[qwakers]

On 30/04/2018 at 7:41 AM, Blanco said:

I tried to start a small compressor once with a 4kva  generator, it didn't get close. Pay attention to the specification,... the headline capacity and the actual rating are often very different, also unless you can tuck it away somewhere the noise becomes a strain, (neighbours?) so then easy to start and stop is nice to have.

i had that same problem with a 3.5 kva generator. i found overriding the governor with a  stick (and rev tits off it) whilst the compressor started and it would the run it fine.

[FridgeFreezer]

1 hour ago, qwakers said:

i found overriding the governor with a  stick (and rev tits off it) whilst the compressor started and it would the run it fine.

That's how landrover598's welder died in a field in Wales  did do a nice weld though!

[muddy]

I bought a nice quiet diesel Stephill ~4.5kva one for just over a grand sh and it seems to run our freezers, van tills and kettle at shows with absolute ease unlike the 2.5kva petrol one I once hired. 

 

Id definitely go diesel and big unless you have a tractor/landrover  for a pto one?

[steve b]

Take a look at Genset 6 or 10 kva 240/110v second-hand they come on a good wheeled frame and are in a noise reduction case , good industrial level stuff .

Have used one quite a lot with a 200a 240v 16a plug inverter MIG/TIG/Stick and they do work really well . Kubota 3 pot diesel so pretty economic on the diesel too .

cheers

Steve b

[jason110]

For a motor, eg compressor, the starting current Is generally 8x the running current. So you’re going to need a fairly big genset to run a smallish compressor just to cope with the start up without over speeding it to cope with the droop effect as the load comes on the genset during compressor start up 

 

 

[simonr]

What about driving the compressor with an engine and using a small generator for everything else?

https://www.ebay.co.uk/itm/AIR-COMPRESSOR-50-LTR-NEW-PETROL-ENGINE-5-5-HP-INCS-FREE-10-MTR-AIRLINE/163032269806?hash=item25f57b03ee:m:mCm0ycFfSa9YZsxDDYI_QvQ

Si

Edited May 5, 2018 by simonr

[Chicken Drumstick]

Thanks for the replies. Liking the idea from Simon. Hadn’t thought of going that route. 

 

Btw this is the compressor I was wanting to run. 

[lo-fi]

That's quite some beasty of a single phase compressor.... Assuming a conservative four times startup to running current, 28a at 240v is a big ask. It's likely higher than that, though! 

The petrol engine suggestion is a good one of you're looking for that kind of grunt from a compressor. You can get electric clutches for mower decks quite cheap, which could be adapted to a horizontal output four stroke and used to convert what you've got. Hard to beat the price on that one Simon posted, though! 

[FridgeFreezer]

The days of it being worth cobbling up things like that are pretty much gone unless you happen to have lots of bits laying around - new stuff is cheaper than ever, you can likely buy a petrol-powered compressor, flog your electric one and not be massively out of pocket plus have exactly what you need for the job. Life's too short to make tools unless you have to.

[lo-fi]

Sad, but true! 

Keep us posted what you end up doing

[Cynic-al]

I just scrapped a 3ph 3hp motor that looked just like that off an old machine and replaced it with a modern one. The casing had cracked at some point and someone had gone to the effort putting a formed plate on the inside with countersunk screws before welding it up. I felt quite guilty throwing it away instead of fixing it!

[cackshifter]

You might want to consider something like this https://www.ebay.co.uk/itm/lister-8-cs-diesel-engine-generator-5kw-240-volt/222999794945?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D49130%26meid%3D7f710615a68b43099048713876de501c%26pid%3D100005%26rk%3D3%26rkt%3D12%26sd%3D122948288613%26itm%3D222999794945&_trksid=p2047675.c100005.m1851

The large flywheel helps overcome the start surge of induction motors. It's 5 KVA so has a bit in hand for the compressor. And it'll run on all sorts of fuel, and they are reasonably quiet once started.