Open discussion for projects on this forum.

[bistander]

At rated speed: 100 Volts +/-40 and 1 to 2 Amps.

[Ufopolitics]

At rated speed: 100 Volts +/-40 and 1 to 2 Amps.

Nope, sorry...way off...keep trying...


Regards


Ufopolitics

[bistander]

EDIT: Problem I have so far...is that an inline Amp Meter would short circuit the exciter, so voltage will collapse to zero. Therefore, I would need a fixed Low ohm but very high wattage resistor (200Watts) in order to run a test where I could read amps (with clamp DC Amps Meter) and voltage simultaneous variations under different and heavier loads.

Sounds like you are not taking measurements correctly, so I'll stick with my estimated values.

bi

[Ufopolitics]

Sounds like you are not taking measurements correctly, so I'll stick with my estimated values.

bi

Bistander,

What do you mean by "not taking measurements correctly"?

Simple stuff Bistander, an Amp Meter closing the circuit, so I am getting straight AC from stator exciter coils converted to DC through rectifier/cap circuit (since I am shorting out Rotating Field is out on this measurement)...measurement works only as a flash time before field collapses.

And reading Voltage is even simpler...I do not think you need an explanation on how it is done...However, you are off there as well.

EDIT: Like I wrote before, I know that in order to read proper running amps the field must be on...and shorting it with meter causes to collapse field, and of course...no field no juice...that is why I need a high W resistor there to measure it with the clamp.


Ufopolitics

[citfta]

Since I have not been following that thread I went back to the post Bistander gave a link to and looked at the schematic for the generator. I don't understand why an inline ammeter connected properly would short out the exciter circuit. Trying to follow what you are posting I think you are saying you want to measure the voltage and amperage of the exciter circuit under changing conditions. If you disconnect the wire going from one side of the cap to the slip ring brush you should be able to connect an ammeter to the cap and to the wire going to the brush and measure the current with almost no effect whatsoever on the exciter circuit. There may be a very slight drop in voltage because of the shunt in the ammeter but it would only be a few tenths of a volt. Then to measure the voltage just measure the voltage on the cap. Now you have nice simple DC measurements for your calculations.

I have worked on this type generator many times. Since they are designed to operate at a fixed speed the exciter circuit puts out a steady voltage no matter what the load as long as the engine has enough torque to overcome the load requirements for more current. In this type of generator the voltage and frequency are determined by the speed of the engine. As we add more load the engine has to provide more torque to keep the speed up and thus keep the frequency and voltage up to the required level. I can explain the difference between this and an automobile alternator if needed. They are quite a bit different in operation.

Respectfully,
Carroll

PS: As regards the aliens on other planets. Only God know why He does what He does. So if He desired to have other planets populated or not is certainly His choice. I don't have any reason to believe one way or the other.

[bistander]

Below I drew a black and white, plain circuit of a typical brushed generator type:

[IMG][/IMG]

Do this: put the generator back to original configuration. Run it normally. Record AC Voltage and frequency (if easily done) from the standard NEMA output plug. If reading normally, like 118 VAC & 60 Hz, measure DC Volts across the capacitor terminals while it is running. What do you get?

bi

[Ufopolitics]

Since I have not been following that thread I went back to the post Bistander gave a link to and looked at the schematic for the generator. I don't understand why an inline ammeter connected properly would short out the exciter circuit.

Thanks Citfta!

I was not doing it correctly...I was shorting out the field...

Typical of me for a change right?

But no problems, I will rewire it no big deal at all...only 4 bolts R&R and some wire butt connectors.

Trying to follow what you are posting I think you are saying you want to measure the voltage and amperage of the exciter circuit under changing conditions. If you disconnect the wire going from one side of the cap to the slip ring brush you should be able to connect an ammeter to the cap and to the wire going to the brush and measure the current with almost no effect whatsoever on the exciter circuit. There may be a very slight drop in voltage because of the shunt in the ammeter but it would only be a few tenths of a volt. Then to measure the voltage just measure the voltage on the cap. Now you have nice simple DC measurements for your calculations.

Many thanks, that is exactly what I will do!

I have worked on this type generator many times. Since they are designed to operate at a fixed speed the exciter circuit puts out a steady voltage no matter what the load as long as the engine has enough torque to overcome the load requirements for more current. In this type of generator the voltage and frequency are determined by the speed of the engine. As we add more load the engine has to provide more torque to keep the speed up and thus keep the frequency and voltage up to the required level. I can explain the difference between this and an automobile alternator if needed. They are quite a bit different in operation.

Respectfully,
Carroll

Exactly like that...Engine have an idle controller, called a governor...which acts automatically when engine goes below running RPM's (Load applied), then bring it back to normal operating spec's.

PS: As regards the aliens on other planets. Only God know why he does what He does. So if he desired to have other planets populated or not is certainly His choice. I don't have any reason to believe one way or the other.

As You have observed some anomalies where "usual explanations" do not work...I have seen also many of those...except this time... on the skies at plain day light as at nights as well...


Regards


Ufopolitics


Still Bistander was off on Voltage...it was exactly 175 Volts DC...

[Ufopolitics]

Do this: put the generator back to original configuration. Run it normally. Record AC Voltage and frequency (if easily done) from the standard NEMA output plug. If reading normally, like 118 VAC & 60 Hz, measure DC Volts across the capacitor terminals while it is running. What do you get?

bi

Yes, exactly from Cap terminals it reads 175 Volts DC


Thanks

[bistander]

Yes, exactly from Cap terminals it reads 175 Volts DC


Thanks

So I was a little low: 140 vs 175. Puts field current at 2.7 - 2.0 Amps depending on temperature. That's a safe calc. I wouldn't bother to measure current if you're sure of resistance value. If you do measure current, it has to be running normally.

bi

[Ufopolitics]

So I was a little low: 140 vs 175. Puts field current at 2.7 - 2.0 Amps depending on temperature. That's a safe calc. I wouldn't bother to measure current if you're sure of resistance value. If you do measure current, it has to be running normally.

bi

Bistander, After all my work to get Gen running...I would absolutely want a real amp measurement. But I know what you meant...Ohms law should give Us the Amps if we know V and R...

Only thing here is the way we look at those three coils forming the whole exciter circuit...in order to obtain (calculate) Rt

And the "dilemma" here is that if we look at both stator coils in series like forming one single coil...then relate it to the Field Coil...then coil at stator and field coil are connected in Parallel.

Plus, if we assume connection by the source feeding side, we will notice the feeding terminals are exactly located at the two brushes and cap terminals. And from here both set of coils (stator and rotor) are in a perfect Parallel Connect.

However, if we just simply look at a "plain" three coil circuit (neglecting that each group of coils have completely different functions, as they are dependent upon each others.)...then all three coils are in series.

Calculations in Parallel (based on Rt= R1XR2/R1+R2)From 65X1.5/65+1.5

according to Ohms Equation:

I=V/R...so if we divide 175 V by 1,5 ohms...then we have 116.666 Amps

So, definitively this can't be calculated like that in a "Logical form"...

In series if we add them all...we have 66.5 Total Ohms (65+1.5)

Then go to Ohm's Law and have:

175/66.5= 2.69 Amps...which seems more logical, just like you have predicted...right?

So, the more I go through this dilemma...the more I need a real read out...and please re read if you want my analysis above, which I did not just made it up now...but have been dealing/thinking about it for a very while by now.

Of course I will check output with an Energy Meter on the Load at the time to read amperage.


Thank You and Citfta for your time


Regards


Ufopolitics

[bistander]

Exciter

[IMG][/IMG]

This exciter is a small generator (~400VA) within the big generator (4400VA). The small generator has a dedicated load which is the field coil. That field coil happens to provide the field for both the large and the small generator.

Speaking only of the small (exciter) generator, you must analyze it as a generator and load. So this means not putting armature coil resistance in series or parallel with the field coil resistance, but seeing them as separate circuits. So let's do that.

In the diagram above, disconnect the slip rings from the capacitor. Connect the slip rings to a 175 VDC battery. Connect a 65 Ohm resistor to the capacitor. Now you have 2 separate circuits; a rotating field coil powered by a battery, and a generator armature with a 65 Ohm load.

Ohm's Law applies directly to the field circuit. However, in the armature circuit you must consider the generated voltage, voltage drop across the armature coil impedance, rectification (AC to DC), filtering and load (65 Ohm resistor).

bi

[citfta]

Hello Bi,

I hope you don't mind if I disagree slightly with your analysis of the exciter circuit. I don't think you can use Ohm's law only when looking at the exciter coils. They are producing AC power so the impedance of those coils also has to be considered. I agree with your analysis of the armature circuit.

Respectfully,
Carroll

[bistander]

Hello Bi,

I hope you don't mind if I disagree slightly with your analysis of the exciter circuit. I don't think you can use Ohm's law only when looking at the exciter coils. They are producing AC power so the impedance of those coils also has to be considered. I agree with your analysis of the armature circuit.

Respectfully,
Carroll

Hi Carroll,

Ohm's Law for the field coil works as it is a pretty smooth DC current. It certainly is when the 175 VDC battery is powering it. When connected normally, to the cap, the cap and the inductance of the field coil itself are excellent filters and again you get low ripple DC. It may* not be perfect, but typical deviation is negligible.

Regards,

bi

2nd edit: don't forget the rotor is the field.

[citfta]

Hi Bi,

Ok I agree the rotor is actually the field coil as the field from it is what induces the current in the exciter coils. But now I don't understand what you meant when you said the armature coil impedance had to be considered in your previous post. I have always considered the armature to be the part that moves. So in this case it would be the rotor. Are you referring to the exciter coils as the armature? That would explain my confusion.

Regards,
Carroll

[bistander]

Armature

Hi Bi,

Ok I agree the rotor is actually the field coil as the field from it is what induces the current in the exciter coils. But now I don't understand what you meant when you said the armature coil impedance had to be considered in your previous post. I have always considered the armature to be the part that moves. So in this case it would be the rotor. Are you referring to the exciter coils as the armature? That would explain my confusion.

Regards,
Carroll

Hi Carroll,

You're not the only one confused. I just looked at Google armature definition. Numerous places say it is the rotating part. That is incorrect. If you go to an expert and reliable source like an electric machinery textbook you'll see the armature can be either the movable or the stationary member of an electric dynamo (generator or motor). It is the member which contains the coils or conductor(s) passing the armature current. Armature current being that which interacts with field flux to produce torque.

Almost all BLDC (brushless DC motors ( and generators)) have PM (permanent magnet) rotors. Obviously a PM rotor does not have wires and current to produce torque or any means to generate voltage. Those functions necessarily are confined to the stator. The PM rotor is the field. The stator is the armature.

The rotor in your typical automotive alternator is the field and the stator is the armature.

Regards,

bi