Measuring INPUT Power Accurately and with no Oscilloscope

[poynt99]

Using a "switching circuit" that exhibits self-oscillation as an example, let's examine the possibility of making an accurate INPUT power measurement using only two readily available digital multi-meters set on DC Volts, and a 0.25 Ohm CSR.

The schematic multi-fet-schema04.png illustrates the 3 measurements taken for all scope shots.

The purple trace is instantaneous power p(t) taken directly from the battery as shown. In the last scope shot, the average of this trace is shown to indicate the real power supplied by the battery.

The red trace is the voltage across the CSR, including the parasitic inductance associated with it. The trace value is divided by the CSR value 0.25 to indicate the instantaneous current i(t).

The green trace is the voltage measured at the point shown. Some experimenters erroneously call this "the battery voltage", and as such it has been labeled "BAT" in the scope shots. This is the instantaneous voltage v(t) representing what is supposed to be the true battery voltage. We will see however that using this two-DMM measurement method does not appear to be detrimentally-affected by the dislocated battery voltage measurement.

The scope shots multi-fet-wave07.png through multi-fet-wave09.png illustrate the wave forms we are dealing with here; quite dynamic, high frequency components, burst-mode oscillation, trace values above and below zero. This is not necessarily a situation that is easy to nail down in terms of an INPUT power measurement. However, by examining the values shown, you will see that the averaging method is "un-phased" by the oscillatory nature of the traces, and is able to extract the correct values for both the average battery voltage and average CSR current.

Simply multiplying the average battery voltage (60V) by the average CSR current (2.8A) produces a result that is the same as the actual real power being supplied by the battery (168W), as determined by the Watt probe placed directly on the battery.

Providing this works in all cases and is not erroneous, this is good news for experimenters. It would appear that stray inductance both in the battery feed lines and that associated with the CSR resistor have no affect on the true values required to obtain the INPUT power measurement, if this measurement method is utilized.

1) Now an accurate INPUT power measurement is readily obtainable by anyone, and there is no reason not to perform this measurement.

2) In cases where excessive heat is claimed as the output, the true COP can now be calculated by comparing this INPUT power measurement with the power required to produce the equivalent output heat using a simple DC source as a control.

3) This method can be applied similarly to any circuit using an input DC voltage source.

.99

[poynt99]

Quite curious how so few seem interested in a simple, accurate and inexpensive method for measuring INPUT power.



.99

[WilbyInebriated]

perhaps they are waiting for you to provide this works in all cases and is not erroneous. i know i am!

[poynt99]

perhaps they are waiting for you to provide this works in all cases and is not erroneous. i know i am!

I will provide results. However, there are many folks on this forum, including Stefan, that ought to be showing some interest in this, and perhaps testing it out themselves as well.

15 downloads and zero responses tells me that very few are even interested in the possibility that this is viable.

Having a simple method like this at hand would readily put to rest (one way or the other) many people's claims; recent past, present and future. Perhaps that in itself is the reason little interest has been shown.

Glad you're interested Wilby.

.99

[WilbyInebriated]

I will provide results. However, there are many folks on this forum, including Stefan, that ought to be showing some interest in this, and perhaps testing it out themselves as well.

15 downloads and zero responses tells me that very few are even interested in the possibility that this is viable.

Having a simple method like this at hand would readily put to rest (one way or the other) many people's claims; recent past, present and future. Perhaps that in itself is the reason little interest has been shown.

Glad you're interested Wilby.

.99

yeah you're probably right.

true that. i noticed the same apathy at yOUR forum. just one response, from milehigh who used it as a segue to poke at rosemary. and i'll resist commenting on the irony of his irony sentence...

i can't argue with that.