First test will be conducted to establish the polarity of Pbat for the condition where the battery energy is depleting. Once known, we will have a baseline to compare against our measurements on the actual circuit.
DSO Limitations
While taking some measurements I noticed that the "mean" of any trace will have a slight variance in value depending on where it is placed vertically on the scope screen. The degree of variance is enough to be of a concern, so I made a video illustrating this particular limitation one should be aware of when using DSO's. I've also outlined a method to virtually eliminate this slight flaw and get the most out of your critical measurements. Tektronix gives you the ability to add an offset to any trace, and doing so seems to eliminate this measurement artifact. I am not certain if Lecroy or Agilent, or any other DSO brands have this feature.
I will be utilizing this method whenever I can in the upcoming measurements.
The video will follow shortly.
Here's that video demonstrating the variance of the mean measurement value on a trace as it transitions from bottom to top of the screen. Assigning a counter-DC offset to the trace seems to correct this scope artifact.
This video demonstrates the use of a simple DC circuit to establish the polarity of the battery power measurement as per the connections on the schematic. In this case the polarity is POSITIVE. This circuit of course exhibits a battery whose energy is DEPLETING.
As such for the tests which will follow, a battery power measurement that is positive will indicate that energy is being depleted in the battery, and a measurement that is negative will indicate that the energy is being increased in the battery.
Poynt
I must say that i don't know why the simple test hasn't been carried out on Rose's circuit. This is so easy even she could do it. No scope's or fancy equipment required-just a plain old DC volt meter of any description,and nothing more.
Test as follows.
Place volt meter across battery.
Run circuit for 10 minutes.
Disconnect circuit from battery
If battery voltage rises,then you were drawing more than you were returning to the battery.
If battery voltage drop's,then you were returning more than you were drawing from the battery.
When you charge an SLA and disconnect the charger,the voltage will always drop to a rest voltage. When you draw from an SLA,the voltage will always rise to a rest voltage when the load is removed. I am yet to see any device that shows otherwise when it comes's to SLA's.
This is going on your comment
Quote: As such for the tests which will follow, a battery power measurement that is positive will indicate that energy is being depleted in the battery, and a measurement that is negative will indicate that the energy is being increased in the battery.
But i was under the understanding that her circuit wasn't so much a loop circuit,but able to dissipate more heat energy than watts of power from the batteries to do so?. In this case,the test above is no good to use. The test above is for the loop system's where people claim to be charging the supply battery faster than it's being depleted.
tinman,
You are absolutely correct about the battery voltages after running the circuit. It would most certainly tell you if the battery energy was depleting or increasing before you disconnected the circuit. Maybe Rose has already noticed this, maybe not. I doubt she would admit it.
In terms of the circuit and test I posted above, that has little to do with RA's circuit actually. It is presented ONLY to determine the polarity of a battery power measurement with the given probe configuration. And since it is easy to determine this when the battery is depleting, that is what was done. The same probe configuration will be used on the RA circuit, so we can carry forward the rule we established with this simple circuit.
Hope that makes sense.
It make's a lot of sence,but what is this about the DMM's,and people doubting what about them?
Quote from: tinman on 2013.06.23, 15:16:55
It make's a lot of sence,but what is this about the DMM's,and people doubting what about them?
The doubts are whether two DMM's can be used to obtain an accurate Pbat measurement with oscillating/switching circuits such as RA's.
Attached is a drawing of the circuit I'll be testing with added protection and CSR components.
Quote from: poynt99 on 2013.06.23, 17:12:04
The doubts are whether two DMM's can be used to obtain an accurate Pbat measurement with oscillating/switching circuits such as RA's.
Well up until a couple of days ago, i would have been one that believed they could.I have always relied on my DMM's for P/in , but now i will have to be a little more careful i believe. That new device i am messing around with (the dovada transformer) was the first time i couldn't get an accurate P/in with my DMM's. What made this apparent was the DMM reading I/in went to a negative value. Apon adding a large cap between the device and DMM, the DMM then went back to a positive value-and we are only talking about a 90mA draw @ 12 volts here, with the DMM set on the amp scale. First time i had ever seen that(the DMM go negative),so now i will be taking a little more care with DMM's and pulsed circuit's.
tinman,
I'd be interested in seeing the circuit you were measuring with your DMM's, and where the measurement points are. I want examples I can try so as to determine if the method is fool-proof or not.
Quote from: poynt99 on 2013.06.24, 13:44:52
tinman,
I'd be interested in seeing the circuit you were measuring with your DMM's, and where the measurement points are. I want examples I can try so as to determine if the method is fool-proof or not.
Hi Poynt
What i did was wound another coil around the dovada transformer, using fine copper wire. This was to get away from using the FG to drive it,so as i could eliminate any power coming in from the FG. I just used the berdini ss/ssg circuit to run it and see what happened. The DMM (for I) was between the power supply and primary coil. All was good until i hit one spot on the 1k pot when tuning. The DMM then started reading a negative current. Now a year ago,i might have started to get excited,but now i know better. So i placed a large cap(10 000uF) between the coil input and the DMM,and negative of the cap to common ground.The DMM then started reading a positive current draw again. The odd thing was,the power supply always read a positive current flow,even when the DMM was reading a negative current flow. I believe the reason the power supply kept reading correctly is because it has large smoothing caps on the output.
First time i have seen my DMM's swing to a negative current though.
If you like, i can throw a video together showing this happening,and then add the cap,and show the DMM read correctly again. But the circuit was just the ss/ssg-nothing more.
So you were pulsing a primary coil with your FG, and the DMM was in series with the FG?
If so, that would explain it. The Pbat measurement I am referring to is with a battery, i.e. constant DC voltage.
Quote from: poynt99 on 2013.06.24, 15:05:56
So you were pulsing a primary coil with your FG, and the DMM was in series with the FG?
If so, that would explain it. The Pbat measurement I am referring to is with a battery, i.e. constant DC voltage.
No-as stated above,the DMM was between the power supply and the primary coil-no FG in the circuit. The secondary coil i wound over the top of the primary was only to trigger the transistor. The power supply was reading a positive current,and the DMM was reading a negative current until i placed a cap between the primary and DMM.
Sounds like you need to draw it out. I think there may be more going on and I don't want to guess.
Quote from: poynt99 on 2013.06.24, 23:26:40
Sounds like you need to draw it out. I think there may be more going on and I don't want to guess.
Hi Poynt
It seems that it may be an effect only with the benchtop power supply,as when i use batteries,there is no reverse current detected by the DMM. So with batteries,it seems the DMM's read correctly-but with the power supply they can read wrong. This may be because of the capacitors within the power supply being on the wrong side of the meter? ,as when i put a cap between the DMM and load,the DMM reads correctly again while using the power supply.
Could be Brad. I'm just not sure I understand what you are doing exactly? :D
Quote from: poynt99 on 2013.06.27, 01:00:17
Could be Brad. I'm just not sure I understand what you are doing exactly? :D
Hi Darren
It is just a simple circuit as drawn below,sory for not posting the schematic sooner.
So in this case using the bench top power supply gives me a negative current reading on the DMM,but using a battery as our power supply gives me a positive current reading on the DMM.
I am glad i found this,as i will have to be carful using the power supply for P/in when taking measurement's. I will now make it a habbit to place a cap after the DMM to make sure it's reading correctly.
Brad,
Thanks for the diagram. I would try placing the caps directly across the PSU. The PSU output impedance may be high, and connecting some caps there will effectively lower it.
Hi Poynt
How is this testing comeing along?.
It's coming OK. Trying to be thorough and comprehensive, so taking my time.
I'm also eager to see how the demo goes tomorrow morning ;)
Stay tuned for more results.
Do you have the link where we can watch this demo?
Brad, I could only find this (https://plus.google.com/u/0/b/106757863561134167356/events/c0cknd87s3qj3qusg2k7s0qsdnk) on Mark's website.
Somehow I got an invite.
Well dont hold your breath Poynt
Quote Rose; The team member doing the demo is away in Namibia until Saturday morning. So we're cutting a fine line for the demo and it may be as well to delay this until our time 18.00 hours - 6.00 pm. But I'll check with him. But he'll most CERTAINLY guide you in how to get this setting. I'll post the time on WEDNESDAY - as I undertook - and when I've had some feed back. The downside of the 6.00 time is that it's dark here by then - as we're in mid winter. And my study is not really that well lit. But we could do the demo in the living room. Anyway. That's a detail.
Seems like this is a leadup excuse in the making for another bail out on the demo.
I'll give 8:1 odds on it.
Just a couple of scope shots looking at how a power transistor fired circuit looks,insted of using mosfets.
.99,
The Google+ thingy did jam my computer totally, using up 100% of my CPUs. So I left the Google+
and did look at the live Youtube link instead. http://www.youtube.com/watch?feature=player_embedded&v=zDsc-UAHHAQ
The video quality was crappy at best, the audio did drop out a times. The camera was NOT if focus all the time.
GL.
Quote from: Groundloop on 2013.06.29, 17:05:11
.99,
The Google+ thingy did jam my computer totally, using up 100% of my CPUs. So I left the Google+
and did look at the live Youtube link instead. http://www.youtube.com/watch?feature=player_embedded&v=zDsc-UAHHAQ
The video quality was crappy at best, the audio did drop out a times. The camera was NOT if focus all the time.
GL.
Yes,two minutes was enough for me. How anyone will get any usful info,and a close look at that setup is beyond me C.C
Nothing but problems with the link, in end watched on youtube
Mike 8)
As pretty much expected, we did not see a faithful reproduction of the Fig. 3 scope shot presented in Rose's first paper.
The key fail was when +12V (or less) Gate voltage was present, there was a significant current flow as shown by the shunt voltage. Fig. 3 in the paper shows pretty much zero current with at least +12V Gate voltage.
The following video clearly demonstrates how parasitic circuit inductance can and will skew the battery power measurement "Pbat" when taken using a DSO oscilloscope.
Of note to remember for the video:
- A "positive" indicated Pbat tells us that the battery energy is depleting.
- A "negative" indicated Pbat tells us that the battery energy is increasing.
It's good if we can show some zoom in current waveform
When Power is negative (probes far apart)
When Power is positive (probes moves closer)
Replace the resistor with pure inductance
Of course this is for the electrodynamics crowd and not the OU crowd.
Nice vid .99. Distributed inductance in wiring
can be a real bugaboo in certain cases such
as you've demonstrated.
Has anyone determined how the stray inductance
causes the error you've demonstrated? It would
seem that sufficient kickback is produced in the
wiring which is superimposed upon the desired
signal at the precision resistor to create some
sort of "phantom" in the measurement/calculation
process when the scope leads are improperly
placed.
A scope display of that signal would reveal the
kickback spikes which cause the error?
Gibbs comments above seem to be directed at
the same question. Perhaps a followup would
be helpful in conveying more understanding?
The following segment "4" video illustrates essentially the same as segment 3 did, in that parasitic inductance between CSR probe tip and probe ref will significantly skew the Pbat measurement. There was concern expressed that I did not have the Vbat probe reference connected, and therefore it is connected in this redo. In this segment I only compare the CSR probe measurement in two positions rather than 5. The variance is dramatic still and changes from roughly -1.02 to +0.91 by simply moving the probe tip and ref 1" away on either side of the CSR body.
Video Link: http://www.youtube.com/watch?v=SietCns2r-M
The two attached pictures relate to those two probe positions and their resulting Pbat values.
The current amplitude drop as the probes moves close together. This means the inductive effect is reduced. It seems like the battery also subjects to parasitic inductance since the voltage observed spiked up much higher than its normal voltage.
It is questioned that can the current in this circuit reverse (or cross the zero reference). It seems that even if the current is reversed, there won't be much compare to the battery direction (unless it uses its own capacitance to resonate). So the negative portion of the current waveform could be a near complete result of inductive kickback while there is little reverse current.
The resistor true value should be IR and the inductive effect is Ldi/dt and L is the parasitic inductance. We can see that IR is highest when I is highest, but Ldi/dt is highest when di/dt is highest. di/dt is highest when current begins to flow and when it is cut off. Furthermore, the polarity for begin and end is opposite. It is possible that that the true current waveform does not have a negative portion.
Here is one more video showing the negative/positive mean battery power; this time with 20 cycles showing on the scope screen.
http://www.youtube.com/watch?v=CGDzic26qQs
Your vids are helpful in understanding
the importance of measuring device
lead placement to exclude spurious
signals which will affect calculated
levels.
It also helps to understand why in
radio frequency circuits and most
switching circuits good design practices
demand the shortest possible lead
length between critical circuit components.
It stands to reason that the inductive
discharge transient of the circuit wiring
would generate a substantial negative
impulse as that voltage is developed
across a relatively high impedance.
I'm wondering whether anyone has
captured a scope shot which actually
shows the offending transients? As
in a single pulse close-up?
It would be very interesting to see the
amplitude, polarity and time duration
of the offending spurious pulse compared
to the desired signal pulse.
I'm not sure why you fellows are talking about inductive discharges; they are not the cause of the negative mean battery power computation. The measurement skew is caused by the phase change of the oscillation portion of the wave form. In theory they should amount to almost zero power, but when parasitic inductance is allowed in between the csr probe locations, this phase change happens and the result is an erroneous computation.
That may be; increasing the inductive component
in series with the Current Measurement Resistor
would introduce both a phase change in the
measured waveshape and a change in amplitude.
So you're saying then that the negative error is
dependent upon oscillation? With simple pulsing
the error would not exist?
Granted, at the higher frequency of the oscillation
the effect would be more pronounced and possibly
easier to detect with digital sampling over the long
term.
If there were no oscillation component, the error would be non-existent yes.
But since there is an inductive resistor and plenty of wire, there is going to be at minimum a lot of ringing. In this case because of the miswiring of the MOSFETs, there is oscillation.
Quote from: Dumped on 2013.07.08, 05:38:46
So you're saying then that the negative error is
dependent upon oscillation? With simple pulsing
the error would not exist?
It's a good point. I've designed a circuit to demonstrate this. I could not access falstad to test it but it looks pretty straight forward.
The circuit does not have any capacitance so we can say the current cannot reverse. R1 is the current sensing resistor and L3 is the inductance that cause the measurement error. When switch S is closed, current increases because it bypassing R2. When S is opened, circuit energy stored in inductance release through R2. This simulates a pulse.
We can measure Pbat by multiplying its voltage with the current waveform. To simulate inductance error, the current waveform can be taken between L3. I think there will be a Pbat difference because R1 waveform and L3 waveform are different through out this pulse transient.