What size generator do I need?

[Kidds]

I want to run some equipment with motors on, three motors, 2.2kw 1.5kw and .75kw. All single phase
Would also need lighting but nothing more than a couple of battens and boil a kettle. Kettle can be turned on when motors are off.
I would usually have all three running at some point but no biggy to just have 1.5 motor off when other two are running.

What size generator would do that?

 

[Exfarmer]

I want to run some equipment with motors on, three motors, 2.2kw 1.5kw and .75kw. All single phase
Would also need lighting but nothing more than a couple of battens and boil a kettle. Kettle can be turned on when motors are off.
I would usually have all three running at some point but no biggy to just have 1.5 motor off when other two are running.

What size generator would do that?

its the start up load on the motors is the issue, they can be three times running load. I would advise speaking to a sparky about the motors , there are ways of having soft start etc. but it will probably be cheaper to go for a larger Genny.
I suspect the absolutely smallest you will get away with is 7.5Kw, but always remember to start them in the right order.

 

[jellybean]

Or you could do what I have done and guess. I wanted a generator to run the house and the borehole pumps etc in case of a prolonged power cut. We already have cabling from house to workshop and back to take the generator although switch gear and distribution board need replacing as they no longer meet regs. Found an 18 kva diesel generator for £2000. I know we will have to switch things on and watch the amp meter to see how much it will take but I am sure it will do enough to keep us going.
Generator says 80 amps.

 

[TheTallGuy]

I want to run some equipment with motors on, three motors, 2.2kw 1.5kw and .75kw. All single phase
Would also need lighting but nothing more than a couple of battens and boil a kettle. Kettle can be turned on when motors are off.
I would usually have all three running at some point but no biggy to just have 1.5 motor off when other two are running.

What size generator would do that?

Depending on the motors & what they're running on my estimate would be minimum of 10kVA to account for startup loads, plus sometimes you can get seriously bad oscillation in either the AVR or throttle control if the genny isn't strong enough.

 

[Thick Farmer]

Depending on the motors & what they're running on my estimate would be minimum of 10kVA to account for startup loads, plus sometimes you can get seriously bad oscillation in either the AVR or throttle control if the genny isn't strong enough.

Sounds excessive. 5kVA should do it.

 

[Bongodog]

How many hours are you thinking of running for ? if its just a few you could go for something just capable, regular use though and it will be far better to go for 15kva or so and not put a big strain on the generator. Alternately if you have spare tractor get a pto generator, that way you get a lot more kva for your money.

 

[Mur Huwcun]

A 5kva petrol engine one will be no good. We have one here that really hates motors. It will run three shearing machines as long as they start them up individually but works really hard on something like a concrete mixer or 9” grinder!! You’ll never regret having one that’s too big but an underpowered one will be a big PITA!!! You need quite a capable one for a kettle. Oh, and go for a diesel one with electric start!!!

 

[TheTallGuy]

Sounds excessive. 5kVA should do it.

It all depends on the the motors & what they are driving, the general rule of thumb I was always taught was to rate for 3x nominal power on motor startups. Thus the 2.2kW is potentially looking at 6.6kW for startup & that's without anything else running. If we assume the power factor to be 0.8 then that 6.6kW equates to 8.25kVA. Okay a smaller generator might work, but then again it might not - or it might only work on warm days or not on a full moon. I've seen many cases where the generator trips out or the AVR goes unstable - even to the point where the angry pixies release the smoke.

A useful point of reference is the calculator here https://www.atlascea.com.au/generator-sizing-kva-calculator/

Putting in 2.2kW, 240V single phase DOL suggests 8kVA is required for startup....

 

[TheTallGuy]

A 5kva petrol engine one will be no good. We have one here that really hates motors. It will run three shearing machines as long as they start them up individually but works really hard on something like a concrete mixer or 9” grinder!! You’ll never regret having one that’s too big but an underpowered one will be a big PITA!!! You need quite a capable one for a kettle. Oh, and go for a diesel one with electric start!!!

That sounds like a China special - a 4 or 5HP engine strapped to an alternator that's only capable of sustained delivery of around 3kVA... but still has a sticker to claim 5kVA.

I wouldn't be inclined to go too mad on over powering with diesel generators though as you need to give the engine something to do or the bores will glaze, etc.

 

[Mur Huwcun]

That sounds like a China special - a 4 or 5HP engine strapped to an alternator that's only capable of sustained delivery of around 3kVA... but still has a sticker to claim 5kVA.

I wouldn't be inclined to go too mad on over powering with diesel generators though as you need to give the engine something to do or the bores will glaze, etc.

Can’t remember off top of my head what the alternator is but it’s got an actual Honda engine not a copy cheepy. This one actually starts everytime not like the Chinease ones that start for most of the first season!!!
Well yes I’m nit suggesting an 80 kva one but a 15-20 would be much more usefull! We used to have a 15kva PTO one years ago intill someone borrowed it off Dad them someone else borrowed it then in the end no fu**er knew where it went

 

[borderterribles]

Got a 15kva single phase, pto generator here, was working fine when removed. Bit of age about it( probably dates from a time when Made in England meant something), but hasn't done a lot. Comes complete with pto shaft, changeover switch etc. Bid me above scrap price and its yours!

 

[Kidds]

Got a 15kva single phase, pto generator here, was working fine when removed. Bit of age about it( probably dates from a time when Made in England meant something), but hasn't done a lot. Comes complete with pto shaft, changeover switch etc. Bid me above scrap price and its yours!

I'm hopeless at bidding things, just tell me how much and I will bring the cash. And thanks.

 

[Farmer Roy]

Ask an electrician for a definite answer, or a business that sells generators . . .

 

[Exfarmer]

Got a 15kva single phase, pto generator here, was working fine when removed. Bit of age about it( probably dates from a time when Made in England meant something), but hasn't done a lot. Comes complete with pto shaft, changeover switch etc. Bid me above scrap price and its yours!

I am sure you are genuine, but just make sure it works before you sell it, if it has not been used for a long time.
Lister I think made many of those Pto generators and we had one, only really used it during the the miners strike. We actually had it built in to a shed and it never went outside, permanently plumbed in. As said tried to fire it up some years later and it was dead and could not be restored. They want running fairly regularly or the damp gets in the windings.

 

[Hesstondriver]

Ask an electrician for a definite answer, or a business that sells generators . . .

Whats wrong with the panel of experts on here ??

 

[TheTallGuy]

Ask an electrician for a definite answer, or a business that sells generators . . .

It's rare these days to find a sparky that actually knows what they are talking about - mostly they are trained (if you can call it that) to tick boxes rather than understand what is going on.

 

[Doing it for the kids]

Get a sparky to test their start up individually, then add it together and hire a geni to test it first I would.

my drying fans are 4 x 36kw units. The start up on one pair is about 300 kw so they have to be wired in to turn on one at a time. Full runNing load is about 150 though

 

[Exfarmer]

Years ago the Wind tunnel at RAF Thurleigh, when it started up would drag the voltage down so much in Bedfordshire all the TVs with in a fair few miles would shrink to a white dot