I've been trying to find a source for a portable PTO (Power Take-Off) generator which can be coupled up to a tractor as and when needed: Single phase 240V, around 5kVA or so.

This is a little out of my usual field, and so far most of my searches have only turned up PTO generators of much larger sizes, typically 20kVA upward.

Any ideas for a source?

Paul, I found Virtaucompany [which google] on e-bay US, selling a 13kw unit with PTO drive and gear-box, giving 50A x 240v, @ about £800+ ship. taxes etc. The problem is the PTO's 540 rpm, requiring a g/box of 3-1 on a 1500 rpm alternator or 6-1 on a 3000rpm unit, making a home-build very difficult.

Thanks Alan. Since posting (sorry, been tied up for a couple of days!) we've also managed to find a farm dealership here selling Mec Calte generators. 13kVA unit which requires 435 r.p.m. is retailing at £1075 incl. delivery (big beastie, over 400 lb.). Comes complete with volt/amp/frequency meter set, C/Bs, etc.

It's bigger than he needs, but I think he's going to go for it and have the spare capacity.

Paul ;

you mean you found a pto genny that can run at 435 RPM ?? is that geared for 4 shoeed [poles] genny unless i am figureing the gear ratio wrong there i came up 3.44 gear ratio so i figured out that with standard 60 HZ it will be very close to standard speed there i came up 523 RPM[PTO speed]let me know

Merci , Marc

also i think they have 2 bearing gennys as well you can add on to just have to get right combation of gearing or belt pulley diamater that useally called belt driven genny they have smaller size as well

Maybe you're asking for the wrong thing? There surely are smaller PTO generators around .... many are called "welders."

I'm not sure if it is actually a 4-pole stator on the model in question, but the gear ratio sounds about right if it is to get 1500 r.p.m. (for 50Hz).

Unfortunately I don't have the full spec. sheet with me at the moment. I've heard that he's ordered the genny anyway (rush job, as usual!) and will be taking care of the mechanics. I'll just be going to do the wiring when it's all ready.

I know for sure he's not going to be happy when I tell him that for the load he has in mind it's definitely going to mean rewiring all the hookups, and probably going to involve running a heavier SWA feeder up to the main electrical "cabin."

He seems to think that all problems are solved by having "MORE POWER!" at the source.

Guys,
Correct me if I'm wrong, but isn't the speed of the PTO shaft "adjustable" by which gear the gearbox is in?.
Or does the PTO come off a different set of gears inside the gearbox?.
Sorry, I haven't had a lot to do with tractors.

Mike ,

Normally most PTO gennys have gearbox just like car or truck tranny is they will increase the speed from the tractor pto speed [ useally either 540 or 1000 rpm ] to correct speed what the genny is set up but there is some do have belt drive it can change the speed on the spot if need to.

Merci, Marc

PTO rpm is set by the throttle. 540rpm seems to be the norm, but 1000 rpm can be optionally selected on most modern tractors, with a ratio-change effected by lever or by changing gearwheels.
You have to set the throttle to the necessary engine rpm to get your PTO speed. My Renault ticks over at 600rpm, develops full power, [30HP], at 1750rpm and 540 PTO speed is at 1500 engine rpm for instance.

But, a tractor diesel is governed for driving, that is +/- 10% on set speed. So at 1500 rpm idle, when a load is applied the engine will drop to, say, to 1350 rpm before the governor demands more power. On unloading, engine speed might rise to 1650 rpm before the governer reins in the engine speed. My Renault has an air-vacuum governor which might run out to +/- 15% on occasions.

A +/-10% governor regime is hardly ideal for electical generation. -4% to +0% is often specified for such work, but driving such a close-governed diesel in a vehicle would be virtually impossible, like riding a bucking bronco I'm told.

So unless there is some smoothing built into the alternator circuitry, the electrical quality could be very poor from this set up.

I'd been informed that the generator was delivered a couple of days ago, so I went out there this afternoon to take a look at what would be needed to complete the installation.

He'd already got it coupled up to a tractor to try out:



Apparently the units he wanted to order were out of stock, but the place said they could do a deal on a 20kVa set for only a little more, so that's what he's got. What he's going to do with the spare power I have no idea, especially as the feeder from the barn to the loads at the moment is about 250 ft. of 4mm SWA and I get the feeling he's not going to like the price for upgrading to something which would actually make a 20kVa generator useful. Sometimes you get involved in jobs you wish you'd never seen.....

Anyway, the generator is 2-pole:



No idea what combination of gears are in the box to achieve the correct 6.98 ratio.

At least we have a full set of meters, but having seen the old tractor he intends using, I have to wonder, like Alan, about how good the speed regulation is going to be.

It appears in the picture that there is some sort of gearbox that might speed the RPMs up to the generator. It's a pretty nice-looking and quality-built unit, but I can't imagine that it would be very efficient to operate.

So, is it safe to assume that the large connector can handle an 80 amp/ 230 volt load? That is pretty impressive when you think about it and it sure could come in handy in an emergency.

I have that feeling most days of the working week.

Yes, it gears up from 430 r.p.m. to the 3000 r.p.m. needed to obtain 50Hz from a 2-pole generator.



Yes, the big blue connector is a 125A IEC309/BS4343 type, 2-pole plus earth. These are the standard industrial connectors here these days. The smaller connector on the right is the 16A version, like these.

The pin configuration and locating lug position determine the voltage, 1ph/3ph, etc. The higher-rated connectors have the same general lug/pin positions as the 16A versions but are just physically larger.

The connectors are also color-coded for the highest voltage present (phase-to-phase or phase-to-neutral/ground).

Paul. This ATN series mecc alte alternator is specifically built by the OEM as a PTO tractor generator and is not something cobbled together by a backstreet shop. As far as my translation can ascertain, there should be electronic voltage control of +/- 1% of unloaded voltage on board, capable of holding the voltage steady with from -5 to +30% of nominal rated PTO speed. Frequency will be up and down though I suppose. On checking, I found that mecc alte also built my 6kva 3-phase workshop alternator, which has run as sweet as a nut for over 2 years.

Alan