generator over voltage

[Justme]

I am a mere Mechanical Engineer, but from my distant memory I have to ask A=are you measuring RMS voltage or Peak voltage.

RMS x √2 = Peak.

So, if you are measuring 230 V and your meter is set to Peak then it will indicate 325V. 240V would indicate 339V.

Good point, many cheap multimeters have a peak hold function now... Make sure its not peak holding!

I use this meter all the time for mains. Its not a meter fault.

[Justme]

Put a load on it, like an electric heater 2-3kw and then measure it.

It needs to be stable off load.

Or the inverter chargers will never accept the input.

[billi]

Put a load on it, like an electric heater 2-3kw and then measure it.

It needs to be stable off load.

Or the inverter chargers will never accept the input.

Well as you say 333 Volt , thats quite a lot , and for sure that overvoltage is a common well known problem as no off grid inverter /charger will accept an unstable voltage generator to be allowed into the system , hence tho old fashioned method advice from Roger, to attach a parallel load to the generator to balance its Voltage and see if the generator then is accepted by the off grid inverter/charger .... that parallel load may be possible then to be switched off , once the generator is under load while charging through the off grid inverter
I think my Victron Inverter was only accepting a Voltage range of 180-265 Volt (about) of the generator and so i attached an electric heater to the generator as the no load voltage was mostly to high , but never was close to 333 Volt

But i am sure , you know about this anyway
Best Regards Billi

[Westie]

Need a bit more info mate, is it brushed or brushless, if brushed how many sliprings 2 or 3?

Brushless.

Any circuit diagrams available? I would be trying to measure the excitation coil voltage, sounds like it my be permanently at max, it should obviously change with the load. Check the excitation levels and load the generator up and down , see if the AVR is trying to do its job. ie. changing the excitation voltage to maintain the alternator output voltage.

[Justme]

Put a load on it, like an electric heater 2-3kw and then measure it.

It needs to be stable off load.

Or the inverter chargers will never accept the input.

Well as you say 333 Volt , thats quite a lot , and for sure that overvoltage is a common well known problem as no off grid inverter /charger will accept an unstable voltage generator to be allowed into the system , hence tho old fashioned method advice from Roger, to attach a parallel load to the generator to balance its Voltage and see if the generator then is accepted by the off grid inverter/charger .... that parallel load may be possible then to be switched off , once the generator is under load while charging through the off grid inverter
I think my Victron Inverter was only accepting a Voltage range of 180-265 Volt (about) of the generator and so i attached an electric heater to the generator as the no load voltage was mostly to high , but never was close to 333 Volt

But i am sure , you know about this anyway
Best Regards Billi

Yes I know this. Mostly used on smally crappier typoe gennies with non AVR control.

This genny has been fine for 2 years with rock solid stats.

So I am not going to bandaid the fault to make it "work".

I want to find the fault & fix it not just the symtom.

[Justme]

Need a bit more info mate, is it brushed or brushless, if brushed how many sliprings 2 or 3?

Brushless.

Any circuit diagrams available? I would be trying to measure the excitation coil voltage, sounds like it my be permanently at max, it should obviously change with the load. Check the excitation levels and load the generator up and down , see if the AVR is trying to do its job. ie. changing the excitation voltage to maintain the alternator output voltage.

I think 333v is far outside the normal ability of excitation.

Plus till the voltage is down the system wont accept the input to load it.

Nor would I be putting 333v into a 240v device.

Re diagrams, so far I cant find this exact one.

Some that are similar but not the same.

[Oldgreybeard]

My suspicion is that the rotor has a shorted turn, perhaps not really a turn, as such, but part of the winding is shorted so there is a self-energising closed loop. If this happens the residual magnetism will cause the shorted part of the rotor winding to self-excite, and the AVR won't have any effect as it can only see the other side of the short.

Hard to think of anything else that could cause this fault, given that the AVR module has been replaced.

[billi]

Nor would I be putting 333v into a 240v device.

Wky not ?

If you dislike the idea of reducing revs or applying a load then i guess you wont find out


https://www.amazon.com/Clover-Stainless ... B09XB13N75

[rogeriko]

Not for your current situation Justme but general information about matching generators to off grid setups.

If you have a dodgy generator of any type or voltage you can put a fullwave rectifier on the output to give you DC voltage. It could be a three phase generator with a 3 phase rectifier or a 110v generator. Anyway this DC voltage you connect to the PV input of a regular cheap Grid Tied Inverter. The AC output of the inverter you connect to your Off Grid setup. The GTI must be smaller than the output of the generator because it will just run at full power. The PV GTI inverter will think the DC voltage is solar power and start feeding your grid. As long as you have an Off grid battery inverter like SMA or many others this will charge your batteries from the GTI output and when the batteries are charged or there is no more demand on your grid it will shut the GTI down and no longer take any load from the generator which will just idle.

[Justme]

My suspicion is that the rotor has a shorted turn, perhaps not really a turn, as such, but part of the winding is shorted so there is a self-energising closed loop. If this happens the residual magnetism will cause the shorted part of the rotor winding to self-excite, and the AVR won't have any effect as it can only see the other side of the short.

Hard to think of anything else that could cause this fault, given that the AVR module has been replaced.

The exciter coils are sepperate from the main windings by some distance so cant cross short internally.
Possibly the wires between could so will look at that.

However all the coils meter the correct resitance & show no shorts to each other.
Plus with avr disconnected the output drops to 30vac.

Got a new avr coming in next day or two just in case previous new one was faukly.