Small gasoline AC generator theory

[buba2011]

Hi there
I have this schematic of a small gasoline AC genetator. Could somebody explain to me how the AC voltage is regulated in this stuff?
Thank´s

 

[waross]

The resistor is new to me. The voltage is determined by the value of the capacitor. The effect is linear in the range of operating voltages.
It is not uncommon for the capacitor to drop in value with age. It is a common fix to add another capacitor in parallel with the existing capacitor.
I own a light tower. That is a trailer mounted crank-up 30 foot mast with four 1000 Watt flood lights, powered by a 6 kW diesel generator. I needed to use the generator for a few months without using the lamps. Without the contribution of the capacitors in the HID ballasts the voltage was about 105 volts. a second small capacitor in parallel brought the voltage up to exactly the anticipated voltage.
Hint; Don't use motor starting caps. Motor running caps are good.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[OperaHouse]

I believe it won't build up a field without the resistor. Larger power designs use two coils in series with diodes in oposite directions so one or the other field is excited. All these generators use a host of magic tricks.

 

[buba2011]

Thank´s for the replays.
The reason of my posting was to learn how to alter the frequancy of my HYUNDAI 800W 220V 50Hz gasoline generator to 60Hz. Actually, the schematic I posted is not for this model but it is the only one I found on the Internet since Hyundai provides no schematics nor any tech instructions. I managed to adjust the speed governor to 3600RPM all right but the voltage rised too high. Then I reduced the capacitor from the original 12uF to 7uF and everythig was fine but only with 600W resistuve load. With 40W load or with no load at all the alternator does not exite itself and produces no power. I reached 240V 55Hz with 10uF cap but I still would like to reach 60Hz.

 

[waross]

There are several things that i would check:
Instrumentation-
Speed >- How are you measuring the speed/frequency? Is your instrument accurate?
Voltage >- What type of volt-meter are you using? Is it accurate? Is it true RMS? Is it tolerant of unusual wave forms?
Capacitors >- Have you checked the value of the capacitors? Are the capacitors rated for a high enough voltage? A very good method of measuring the actual capacity of these capacitors under working conditions is to energize them with 120 VAC or 240 VAC and measure the current.
Use the formula for capacitive reactance (1/{2 pi x F x C})and Ohm's law to calculate the actual effective capacitive reactance at the working frequency and a reasonable voltage.
If all your values are correct the 10 uF cap should do the job. I suspect a failing capacitor or a capacitor used at a voltage above its safe working voltage.
I don't know what the voltage is in the capacitor circuit but I would use a capacitor rated for at least 350 VAC.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[buba2011]

waross
I use an osciloscope to check the frequeny and a professional multitester for AC voltage measuring. The capacitor is rated at 400AC.
I can´t rise the frequency to 60Hz with 10uF capacitor because the voltage rises too much.

 

[ccjersey]

It appears to me that the resister could be used to tune the voltage.

Is it brushless?

 

[buba2011]

Yes, it is brushless alternator.