Portable Generator Regulated By Capacitor - What Does That Mean?

[Deleted member 36384]

Hi,

I have a Rockworth Powertask Generator, 230 V, Single Phase, 6kVA max (5kVA continuous). The generator is stated as brushless, self exciting, 2 poles, single phase and the that the voltage regulator is a capacitor.

What does the capacitor do and how does it regulate the voltage? I assume that it just charges up and releases 230V at 50Hz i.e. a very basic form of control. At the moment I have an extension lead running to the yacht and I have the Sterling Pro Charge Ultra plugged in and a heater. Why would the fuse not blow in the 3 x Pin plug when the sterling is showing 20A? Is this because this is 20A on the 24V side of the charger, I assume so.

I have just received my new shore power inlet and my intension is to plug the generator into this. This will be with a normal 13A 3xpin domestic plug crossed over to a new 32A, 3 round Pin, shore power inlet.

Final question. Even though the generator is technically capable of providing approximately 20A (5W/230V) up to the consumer unit, the 13A fuses in the extension cable will be the limiting factor. There is no 32A outlet on the generator, just 2 standard UK style plugs. I assume that the design of the generator is such that the maximum amperage of the generator, if needed, would be taken from the two plugs (via 2 consumers).

On the boat I have a 1kW immersion heater, the Sterling charger, a fridge and 3 outlets (typically I have 1 kW heater running and power tools). I have not run all these yet but I assume that if they were then I would exceed the 13A rating (so I need to be sensible here). In a marina, shore power side, could I expect 32A to be supplied upto the consumer unit using a correct 3 x round pin shore power cable? The cable that runs from my shore power inlet to the consumer unit is thick and is rated for the 32A.

I am really just trying to understand the difference between the mains shore power and my generator shore power.

Thanks,

BlowingOldBoots

 

[nigelmercier]

Using a capacitor as a regulator is meaningless, it probably means it isn't regulated.

Generators are often regulated by varying the speed, so I guess they could rectify the output, smooth it with a capacitor, amplify it and drive a servo. The best type for running electronics is the inverter type.

 

[Deleted member 36384]

Okay, thanks. The operating manual specification table just states "capacitor" accross all models in the regulator row. The generator will not be used to power any of the boats electronics, just heaters, power tools a and the immersion heater. Do you think this unregulated power supply could damage the Sterling Pro Charge Ultra and if so would a device like a surge protector be a good idea?

 

[NorthUp]

en.m.wikipedia.org/wiki/Induction_generator
Explains better than I can!

 

[jdc]

en.m.wikipedia.org/wiki/Induction_generator
Explains better than I can!

I don't think that engine powered generators are usually asynchronous induction motors which is what the Wiki page covers - mine (Whispa) certainly isn't. As I understand it, asynchronous motors vary output voltage and frequency with load (due to variable slippage), so are poor for supplying a fixed frequency to variable loads. But fixed frequency and Voltage whatever the load is the exact characteristic one desires form a petrol or diesel generator hence the normal small generator is a 2 pole synchronous motor.

The power comes from the stator and the field from the rotor. The complication in the OP's case (and with mine) is that the normal big generator system uses a DC feed to control the current in the rotor, via slip rings (which is how our alternators work) whereas small gen sets seem to do some trick whereby instead of the field winding in the rotor being fed by DC via brushes it's fed by some kind of rotating transformer - for which the capacitor is essential, although whether to provide a resonant circuit or simply a phase lead of current versus voltage I don't know. The 'transformer' output is then rectified to DC by diodes on the rotor itself.

There is no regulator per se, but the open circuit emf (Voltage) is determined by the design and for a constant speed is constant, and under load is thus the open circuit Voltage less a little for the small internal resistance. The generator runs at constant speed due to the engine's governor, which is probably not electronic at all.

However, in response to some other of the OP's questions, the generator should provide a well behaved supply at least as good as some continental mains supplies! My generator's spec is to always be within 5% of 50Hz, and 230V AC +/- 5%, and equipment is normally rated for supplies anywhere between 220 and 265V AC, so are compatible with the generator.

As to load, it seems that you can't just add up the stated wattage ratings of the various loads since these typically (i) draw higher current at start-up (esp power tools and compressors), and (ii) don't necessarily have unity power factor, so although drawing '1kW' for instance of real power may also draw another 1kVA of reactive power - which they don't mention. So it's all too easy to overload the (k)VA rating of the generator even tho the add up of the purely resistive loads would suggest you're drawing less.

Hence I wouldn't count on it supplying a stated load of more than 13A say at 230V = 3kW despite it being a 5kVA generator. Thus a single lead with 13A fuse is probably ok for the OP.

Nonetheless this should be adequate I'd have thought: the fan heater will be 1kW, the battery charger a bit less (50A at 12V = 600W, plus maybe 10% for efficiency). Power tools are usually 600W ish. If the fridge is 12V, then it's load does not need to be taken into account separately from the battery charger's.

 

[Deleted member 36384]

Thanks everyone for the information. The generator has a torque arm which is connected to the carburettor and provides constant rpm, so I guess as more load comes on (a slight blip is noticed on the engine, then it stabilises again. I am very happy with unit but not being electrically competent, I just wanted to get some stuff better understood.

Cheers,

BlowingOldBoots