Generator Overvoltage at no-load and other questions

rascalsailor

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Aug 5, 2019
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I recently got a bargain generator; It has a Briggs I/C 8Hp engine. I'm not sure what the generator head model is.
(see the pics - anybody know?) Assuming 90 - 95% efficiency and given that 8hp = 6KW, maybe 4.5KW output ??
The output does give about 220 under load. (I tried a 550W drill and a 2Kw heat gun both together and separately)
The interesting thing is that with no load, I measure a bit over 500vac, this then drops to 220 when loaded.
Even if I plug in a small battery charger without connecting the output, the generator output voltage shows about 217 Vac
I plugged in a mains powered led lamp which works fine.
Is it possible that the unloaded voltage is a 'floating level' which is in fact not likely to supply any significant current?
I assume that the unloaded output is due to the AVR not regulating under no-load conditions.
I tried with another voltmeter, it reads the same - I thought perhaps, I'm getting EMI or spikes which is causing unstable readings.
I had installed one those digital ac voltmeter displays (see the pic). This reads also reads an unstable over-voltage with no load, but shows 217 vac or so as soon as I load.
If I power up the heat gun as well, the voltage goes up slightly to 220V, so I guess the regulator is doing its thing.
Further questions below:

What are the diodes for? Does this give a DC voltage to drive the avr? voltmeter.jpg pic1.jpeg pic2.jpeg pic3.jpeg pic4.jpeg

Is the AVR that module with the 4 terminals?

thanks and regards
Russell
 

thehuman

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Nov 2, 2004
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Maybe try make a "wiring diagram" of what wires come from generating part .

My feelings is the avr is Maybe not doing its job
 

The_Traveller

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You better have insurance cover you when that generator destroys all your devices thats connected to it.
 

Jaws677

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Dec 3, 2009
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You could add a permanent load to the generator. Something like a 50 W globe. It should sort out the the problem.

The issue is that the Automatic Voltage regulator in this case probably set its it lowest excitation current to the field winding, but with no load connected the terminal voltage generated is 500 V. With a load connected ie current being drawn this voltage will be pulled down, and only then can the AVR start controlling the output voltage
 

Geoff.D

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Aug 4, 2005
Messages
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I recently got a bargain generator; It has a Briggs I/C 8Hp engine. I'm not sure what the generator head model is.
(see the pics - anybody know?) Assuming 90 - 95% efficiency and given that 8hp = 6KW, maybe 4.5KW output ??
The output does give about 220 under load. (I tried a 550W drill and a 2Kw heat gun both together and separately)
The interesting thing is that with no load, I measure a bit over 500vac, this then drops to 220 when loaded.
Even if I plug in a small battery charger without connecting the output, the generator output voltage shows about 217 Vac
I plugged in a mains powered led lamp which works fine.
Is it possible that the unloaded voltage is a 'floating level' which is in fact not likely to supply any significant current?
I assume that the unloaded output is due to the AVR not regulating under no-load conditions.
I tried with another voltmeter, it reads the same - I thought perhaps, I'm getting EMI or spikes which is causing unstable readings.
I had installed one those digital ac voltmeter displays (see the pic). This reads also reads an unstable over-voltage with no load, but shows 217 vac or so as soon as I load.
If I power up the heat gun as well, the voltage goes up slightly to 220V, so I guess the regulator is doing its thing.
Further questions below:

What are the diodes for? Does this give a DC voltage to drive the avr? View attachment 1043041 View attachment 1043031 View attachment 1043033 View attachment 1043035 View attachment 1043037

Is the AVR that module with the 4 terminals?

thanks and regards
Russell
Have you tried to get hold of a copy of the manual?
 

Nemesys

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Dec 7, 2017
Messages
291
The function of the AVR on the generator is just to smooth manor fluctuations in voltage output. Maintaining the correct engine speed (3600 RPM) is required to generate electrical power at 60 Hertz. The correct speed is required to insure the proper voltage levels. The governor of an engine is the device that keeps the speed at or near 3600 RPM. The more sensitive the governor is to changes in speed as loads change the closer frequency will stay to 60 Hz.

You can read all you need to know at

 

Colin62

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Apr 23, 2008
Messages
8,260
The function of the AVR on the generator is just to smooth manor fluctuations in voltage output. Maintaining the correct engine speed (3600 RPM) is required to generate electrical power at 60 Hertz. The correct speed is required to insure the proper voltage levels. The governor of an engine is the device that keeps the speed at or near 3600 RPM. The more sensitive the governor is to changes in speed as loads change the closer frequency will stay to 60 Hz.

You can read all you need to know at

You are aware that we use 50Hz in this country?
 

Nemesys

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You are aware that we use 50Hz in this country?
Yes I am aware of that and also that the local generator are governed at 3000 rpm to maintain 50Hz. The object of my post is to highlight to the OP that there may be more to his problem than a faulty AVR Judging from the photos it is obvious that the gen has seen better days and that the problem may well be over revving of the engine and not a faulty AVR. Understanding the principle may give the OP more options to look for a solution.
 

Jaws677

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The correct speed is required to insure the proper voltage levels.

Incorrect

Engine speed = frequency of AC output

Field current (magnetic field strenght) of the rotor determines the output power of the alternator. The AVR simply measures the output voltage of the altenator and controls the current to the rotor winding. The greater the current output from the AVR to the rotor winding the stronger the magnetic field will be rotating inside the stator, that will inturn generate more power
 

rascalsailor

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Aug 5, 2019
Messages
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Have you tried to get hold of a copy of the manual?
I can't find a type on the generator head anywhere. That said, I traced the schematic, see attached. The 4 terminal device is another rectifier - (Siemens, SKB 30/06A1). Strange schematic - I'm pretty sure I traced it correctly. How does it regulate? schematic.JPG
 

Stokstert

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What does that matter? It works and it is an interesting project to do some servicing and repair to get it back to pristine condition. It will outlast plenty of the new crap on the market.

It was posted as a joke, I personally appreciate ancient tools and equipment when it still does the job.
I am sorry if I humiliated anyone.
 
Last edited:

Geoff.D

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The function of the AVR on the generator is just to smooth manor fluctuations in voltage output. Maintaining the correct engine speed (3600 RPM) is required to generate electrical power at 60 Hertz. The correct speed is required to insure the proper voltage levels. The governor of an engine is the device that keeps the speed at or near 3600 RPM. The more sensitive the governor is to changes in speed as loads change the closer frequency will stay to 60 Hz.

You can read all you need to know at

except it is 3000 rpm and 50Hz in SA. ........
 

Geoff.D

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It was posted as a joke, I personally appreciate ancient tools and equipment when it still does the job.
I am sorry if I humiliated anyone.
Accepted, but no need for an apology. Just getting so sick of the new is better. Most "new" stuff is just not made to last.
 

Geoff.D

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Messages
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I can't find a type on the generator head anywhere. That said, I traced the schematic, see attached. The 4 terminal device is another rectifier - (Siemens, SKB 30/06A1). Strange schematic - I'm pretty sure I traced it correctly. How does it regulate? View attachment 1043853
Here is a pretty good explanation:

 

rascalsailor

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Aug 5, 2019
Messages
6
I've not seem this type of circuit using two bridge rectifiers though. I found some high rated stud diodes. I'm going to make up a replacement bridge.
 
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