Reactive power - Reactive Generator research from GotoLuc - discussion thread

[poynt99]

Hi poynt or anyone who know the poynt way of AC scope power calculations.

Please tell me what the power used from the source (grid) in watts from the scope shots below. Both are the same just one has 15 samples instead of 3.

The CSR is 0.1 Ohm 5% with both probe grounds on one grid side of CSR, channel 2 on circuit side of CSR and channel 1 on other grid side and is 100x probe with scope menu at 100x. Chanel 2 probe is set at 1x and scope menu is set at 10x with Inverted selected.

Thank you for your time.

Luc

Luc,

I would say that the second shot with more cycles is the better bet. Note, you need about 10 cycles of the MATH trace, not the voltage or current traces to get an accurate power computation.

I am finding that the GRID power measurement does not seem reliable in my setup at least. I am using a 10uF cap, and 10 Ohm resistor. Depending on which CSR I use, I get a different GRID power.

For example, with the 0.1 Ohm CSR, I get a GRID power of about +3.8W (your probe config. and not inverted btw). With my non-inductive 0.25 Ohm CSR, I get a GRID power of about +2.5W. The power in the 10 Ohm measures to about 1.5W using a DMM, and compared against a DC control it is close at about 1.3W. So the DMM voltage (4.3VAC) over the resistor value is close, but probably coming out a little high (3.6VAC is more correct).

My wave forms look quite close to what you posted above.

Unfortunately thus far with my setup I can not get the negative MEAN GRID power you have with a couple of your tests. Technically it is supposed to be positive anyway (since I have not inverted CH2), but I was hoping to be able to get close to your -3.15W.

More work ahead to see if I can figure out why it is behaving more or less the way it is supposed to, LOL. btw, you may have noticed that I still have 1W or so unaccounted for. I was able to measure about 0.6W being dissipated in the 10uF cap, but still short.

btw, I tried your little trick of using a x1 voltage probe as a "current probe" while setting up the channel to measure current directly with the proper scaling. Seems to work ok. Sorry for giving you a hard time about that.

[gotoluc]

Luc,

I would say that the second shot with more cycles is the better bet. Note, you need about 10 cycles of the MATH trace, not the voltage or current traces to get an accurate power computation.

I am finding that the GRID power measurement does not seem reliable in my setup at least. I am using a 10uF cap, and 10 Ohm resistor. Depending on which CSR I use, I get a different GRID power.

For example, with the 0.1 Ohm CSR, I get a GRID power of about +3.8W (your probe config. and not inverted btw). With my non-inductive 0.25 Ohm CSR, I get a GRID power of about +2.5W. The power in the 10 Ohm measures to about 1.5W using a DMM, and compared against a DC control it is close at about 1.3W. So the DMM voltage (4.3VAC) over the resistor value is close, but probably coming out a little high (3.6VAC is more correct).

My wave forms look quite close to what you posted above.

Unfortunately thus far with my setup I can not get the negative MEAN GRID power you have with a couple of your tests. Technically it is supposed to be positive anyway (since I have not inverted CH2), but I was hoping to be able to get close to your -3.15W.

More work ahead to see if I can figure out why it is behaving more or less the way it is supposed to, LOL. btw, you may have noticed that I still have 1W or so unaccounted for. I was able to measure about 0.6W being dissipated in the 10uF cap, but still short.

btw, I tried your little trick of using a x1 voltage probe as a "current probe" while setting up the channel to measure current directly with the proper scaling. Seems to work ok. Sorry for giving you a hard time about that.

Okay, thanks for the update!

but I'm getting a little confused... why are you measuring without channel 2 Inversion when you said without doing that I'm getting the wrong readings?

And can you please tell me what the power is on the scope shots I provided above with channel 2 Inverted since I no longer know how to read a scope.

Thanks for your time

Luc

[poynt99]

Okay, thanks for the update!

but I'm getting a little confused... why are you measuring without channel 2 Inversion when you said without doing that I'm getting the wrong readings?

The first task is to try to replicate your results the way YOU produced them. So I am trying the measurements the same way you are doing them. If and when I get the same or similar results (i.e. a negative MEAN GRID power), then I can move on.

And can you please tell me what the power is on the scope shots I provided you with above with channel 2 Inverted since I no longer know how to read a scope.

What do you mean you no longer know how to read it. It is the MEAN value as before. I see +194mW.

[gotoluc]

Unfortunately thus far with my setup I can not get the negative MEAN GRID power you have with a couple of your tests. Technically it is supposed to be positive anyway (since I have not inverted CH2), but I was hoping to be able to get close to your -3.15W.

If you Isolate your scope from grid then use 240vac and you should get a negative means

Luc

[poynt99]

If you Isolate your scope from grid then use 240vac and you should get a negative means

Luc

I guess I can try that, but you were getting it on a single phase. And I did isolate the gnd on my scope. Do you mean transformer isolation as well?