Calling Kubota Experts - choosing the right engine and 1800 rpm versions

[threeReefs]

I am kicking off a project to build a generator. It will be a smallish Kubota diesel driving a chunky 48V alternator, which can put energy into my 48V batteries which in turn feed an inverter. I'm going for this approach because the inverter will be my main power source - good output, clean sine wave, versatile - and most of my power needs are intermittent, so having a genny run all the time is not a good fit. Plus, this way is a lot less fussy about alternator speeds.

I think I'm looking at a small Kubota engine like the supermini range, Z482 etc, but Kubota seem to advertise some of these - and their larger 3-cylinder brothers - as "1800 rpm" versions like this :
https://global.engine.kubota.co.jp/en/products/detail/126/
They have derated it in the spec to 5kW / 4.5HP, but is this engine "special" in any other way ? What have they done to it, I wonder, to make it a "1800 rpm" version. Am I going to get different results getting a "normal" 482 and just running it slower ?

I want to end up with a slow-running engine for noise and reliability, so 1800 is kind of a goal for me, and 4kW would be a good-size output... just trying to understand the range here.

Anyone have any thoughts ?
Thanks !
Richard

[keith71]

Hi three reefs, I am not a Kubota expert but I do have a Kubota D722 that I still deciding on whether to use my meecalte 7500 watt head and belt drive it or go 48 volt with a pma with a bell housing setup, or regular heavy duty truck alternator. Remove the factory rectifier and diodes and externally rectify the three phase ac windings into 2 150 amp rectifiers. Depending on the voltage output, might run it into a charge controller, or in the case of a pma run it at whatever rpm is needed to output 56-57 volts and 100 amps to directly charge a 48 volt bank of lifepo4 batteries. Enough of me.

As for the Z482 for use at 1800 rpm. They may retard the injection timing, Add more mass to the flywheel. The one you posted looks to have a beefy one.  With 5.5 HP at 1800 rpm You would be doing real good if you were getting 3000 watts continuos. I dont think it would like running like this. A more realistic goal might be 2500 watts, maybe 2700 max cont ? I am not sure. The listing you posted does not describe what the engine is used for. But looks to be generator type.

Henry here on the forum has lots of knowledge and could better answer your questions. In fact I think he actually did build a z482 and if I remember correctly he ran it at 2600-2800 rpm? I think he has a build thread if you search the forum. Or better yet you could pm him... He is a nice guy and is willing to help to the best he can.. Have fun, Keith.

[keith71]

I meant to ask what Alternator Or Generator do you plan to use ?

[Henry W]

Been working on a project. I need to start checking in more often.

The Kubota Z482 runs much smoother in the upper range that Keith71 mentioned. (2800 rpm)

When I was testing a Z482, I found that 1800 RPM's was too low. This was also verified from some acquaintance's I got to know that work for a very well known manufacturer that builds Kubota powered generators for marine, standby, and continuous use.

A Kubota Z482 powered 1800 rpm direct drive generator is very rare. It will not be able to put out anywhere close to 4000 watts.

Over ten years ago, I called Kubota engines in the US and had an opportunity to speak to an Application Engineer. He mentioned that the Z482 engine's sweet spot is near 2800 rpm's. He also mentioned that the engine will live a much longer life due to less vibration and stress. The oil pump will also be operating at full continuous output. Even when the oil reaches high temperatures. The Z482 operates much quieter near 2800 to 3000 rpm. At 1800 there is much more noise. (Combustion and mechanical noise) The engine was just not happy running there.

Peak torque is near 2600 rpm's. One of the things the Kubota application engineer went over was how important it is to stay 200 rpm's past peak torque curve. The reason why is, when an engine starts getting a load, the governor speed will drop and in turn the engine normally not dip below peak torque curve. This is healthy for a diesel engine.

Any time an engine goes below peak torque curve, it becomes much easier to overload an engine. (One terminology is called lugging an engine)

I also built a Z482 powered direct drive two pole generator. The engine seemed stressed. It had a good amount of vibration. I would not recommend running a Z482 engine at 3600 rpm, or 3720 rpm unloaded.

My recommendation is belt drive a Z482 engine equipped with a 3600 rpm flywheel. And, run it near 2800 to 3000 rpm. See where is runs best with the least amount of vibration.

Hope this helps.

[Henry W]

If you're going to build a generator using a 4 pole head, and you want to use a Kubota engine, I would highly recommend D1005 BG.

If you can find  a used D905 BG engine, it will also work. This model was discontinued years ago. "Do not mistake a D902 for one it's a lighter duty engine.

If you can find a used D905 BG or D1005 BG, it comes with a much larger and heavier mass SAE flywheel and shorter SAE housing than the industrial engines. These are needed for making an 1800 rpm generator. The smaller diameter and lighter flywheel will not work. There is a super thick smaller diameter SAE flywheel also available that is used with a much thicker SAE housing. Some have used them but noticed some flickering of lights when engine is fully loaded because of less rotating inertia.

I have built and documented a complete build using a D1005. Was a great generator. But it used more fuel than I expected because I had to run a constant load bank to keep the engine loaded properly so it would not wet stack and coke up.

Try to build a generator that is able to handle your minimal critical power requirements with the engine loaded no less than 50 %. Preferably 75%.

If you need to produce more power at a certain time of the year, consider a second generator to handle the heavier loads.



Below is one of the surviving pictures right after the forum crashed a while back. I built this Kubota D1005 powered generator over ten years ago. I no longer have it. At times I sure miss it. It was a great project.:

You cannot view this attachment.

[Henry W]

Here is a design that can be used with either a generator or alternator.

https://hardydiesel.com/product/kubota-5-5-kw-micro-diesel-generator/

[keith71]

That is a great generator there.. Like the belt pulleys. Next gen builds some great gen sets.

[keith71]

 I need to start checking in more often.  Yes you do..

[Henry W]

I been so busy with the Truck engine.

The details of the build is almost complete. Than it's gathering the rest of the parts to build it.