20 kva generator head on CS6

[Reg Burn]

Good morning.

I have a Lister CS6/1 600 to 650rpm driving a Lister 3kva lighting plant at the prescribed 1500 rpm. As expected the voltage gradually decreases as the engine speed decreases until the engine is doing 350rpm to 300rpm when the voltage suddenly drops to virtually nil.

But I want more power and have been offered a 20kva/1500 rpm alternator. My engine should be able to turn this alternator at 1500 rpm, but at just six horse-power the engine will not be able to achieve the full 20kva.

What should I expect?

Reg

[listard-jp2]

That sounds like an ideal alternator to connect to your Lister FR4 engine 

[38ac]

I assume that in your given example that as you apply your load needs  the engine begins to slow down and as it does the voltage is dropping?

If so then engine power, not alternator capacity is your limiting factor and switching to a 20 KW unit will do nothing for you.

You may have an engine performance problem or may be expecting too much of the 6/1. To know which you need to know how many KW you are producing.

What should you expect from a 6/1 driving a generator? The rule of thumb  is 1/2 KW per engine HP or 3 KW. My 6/1 'roid and 5KW head will do a little better than 3KW at max output but is much happier around 2.5.

[Reg Burn]

Hi

to Mr listard-jp2, yes that's the plan once I get the project finished but getting a decent amount of electricity to my workshop (dilapidated shed at the bottom of the garden) is the priority.

to Mr 38ac, the deceleration of the engine was not due to generator load, it was a manual deceleration using the governor to restrict fuel flow. This was an experiment to see the affects on voltage and to see the minimum rpm at which the generator would illuminate a light bulb.

The generator output is determined by the size and capabilities of the alternator but this is limited to the HP of the engine/prime mover. So if I attach a 20 kva alternator to my CS6/1 the engine will limit the power output to 3kva regardless of the fact that the engine is turning the alternator at the prescribed rpm. Is this correct?

Reg

[38ac]

The generator output is determined by the size and capabilities of the alternator but this is limited to the HP of the engine/prime mover. So if I attach a 20 kva alternator to my CS6/1 the engine will limit the power output to 3kva regardless of the fact that the engine is turning the alternator at the prescribed rpm. Is this correct?

Reg

You are almost correct.

This part is right on
"The generator output is determined by the size and capabilities of the alternator but this is limited to the HP of the engine/prime mover"

The rest is not quite right or I am misunderstanding you. With a 20KW head driven by a 6/1 it will maintain RPM (within the capibilites of the governor) up until you reach maximum engine output., 3KW is close enough for this discussion. After that point adding additional load will cause the engine to slow down and the voltage will drop along with the frequency.  If the original 3KW head has some reserve it will behave exactly the same way as the 20KW head in a overload situation. If the 3KW head does not have any reserve capacity then there may be a  gain in performance  in a very small area of operation between where the 3KW head falls short and you run out of engine power.

[Tom]

The 6/1 I have will run 3120 watts out of the alternator continuous. I do long runs charging batteries and can set how much load the engine sees, it is currently set to 13a at 240v. I ramped up the load until the exhaust was just starting to show grey and then back off an amp. So that's probably about what you can expect from yours too.