Battery Voltages -- Surprise!

[JW50]

deleted, just too much





and I still would like to know the RMS voltage from a typical fully charged eGo?

If anyone out there has a "true RMS" meter, there is still interest in knowing what it reads on a fully charged eGo. If method to test loaded voltage not available even an unloaded, fully charged, reading would be helpful. Suspicion is that it should read about 3.7 volts (i.e. DC volts on cheapo meter divided by square root of about 0.85, believed duty cycle) but confirmation would be appreciated.

 

[Rocketman]

I just love all the equations, and "Exact" methods presented here

JW,
here's a "seat of the pants" analysis of the eGo output
1) unloaded cell voltage is in the order of 4.2 volts (the Li-ion cell on the inside), agree?
2) the instantaneous peak loaded voltage from the cell, through the magic circuitry, and driving a 2.0 ohm carto is between 3.9 and 3.7. Anyone not believe that? Would 3.8VDC +/- 0.1v be a reasonable assumption?
Why not 4.2 volts to the carto as peak?
3) the magic circuitry of the eGo generates a pulsed dc waveform with a rather high Duty Cycle. Agree still?
4) Knowing peak voltage (3.8 +/- 0.1) we can "Calculate" the RMS voltage for duty cycles ranging from 80% to 100%. Agree?
5) Knowing the squarish shape of the waveform, peak voltage, we can calculate Average voltage for that Duty Cycle range. Agree?
6) We can calculate the percentage difference for each of the hypothetical RMS values and Average values. Agree?
7) The percentage difference between the RMS and Average values decreases as Duty Cycle goes up. Agree?
8) The Average voltage approaches RMS as the duty cycle approaches 100%. Agree?

Now the questions:
At what duty cycle does the difference between RMS and Average become reasonable for measuring an e-cig (like maybe 3 or 4% percent, or about a tenth of a volt)?
Would the Average voltage from an eGo exceed the RMS value?
What duty cycle would produce an average voltage equal to the RMS value?

The measurement accuracy of the "Cheapo" meter when used to measure RMS voltage output from the eGo is:
A) +/- 50%
B) +/- 10%
C) +/- 3%
D) Better when the eGo is at a partial charge than at full charge.

You guys have fun with your equations

 

[jimho]

If anyone out there has a "true RMS" meter, there is still interest in knowing what it reads on a fully charged eGo. If method to test loaded voltage not available even an unloaded, fully charged, reading would be helpful. Suspicion is that it should read about 3.7 volts (i.e. DC volts on cheapo meter divided by square root of about 0.85, believed duty cycle) but confirmation would be appreciated.

Peak-Peak was 3.98V - RMS should read about 3.6- go back here and down the page....
http://www.e-cigarette-forum.com/forum/joye-510/65055-battery-voltages-surprise-12.html#post2301546

Sorry, I no longer have an eGo to test.

 

[Rocketman]

jimho thanks,
I've been through the thread and sooooo many posts.

The 900mah eGos I have for the wife (can't get her to carry a big honkin mod around) are what I'm measuring.
You really don't need one to approximate what is going on. Scottbee gave an implication that in addition to varying Duty Cycle to hold RMS output constant, it also does it for load (maybe). The 3.98 seems a little hot (I get a little overshoot on my storage scope that shows up in the PK measurement) but, it is a high quality cell in there.
So, 3.98 volt Peak into a load is what it is. At a duty cycle of 85%, full charged that is right at 3.6 volts RMS.
You have found the answer

As the charge deteriorates does the regulator circuitry keep that RMS somewhat constant?
By increasing the Duty Cycle?

 

[jimho]

jimho thanks,
I've been through the thread and sooooo many posts.

The 900mah eGos I have for the wife (can't get her to carry a big honkin mod around) are what I'm measuring.
You really don't need one to approximate what is going on. Scottbee gave an implication that in addition to varying Duty Cycle to hold RMS output constant, it also does it for load (maybe). The 3.98 seems a little hot (I get a little overshoot on my storage scope that shows up in the PK measurement) but, it is a high quality cell in there.
So, 3.98 volt Peak into a load is what it is. At a duty cycle of 85%, full charged that is right at 3.6 volts RMS.
You have found the answer

As the charge deteriorates does the regulator circuitry keep that RMS somewhat constant?
By increasing the Duty Cycle?

I think somewhere down the thread (around that time frame) he indicated it didn't really do much to the duty cycle to push towards 100% as it drained, but that was with the versions they were shipping a year ago.... There were a few revs since then.

I think they keep the RMS constant using a boost switching regulator (which is why you see a bit of overshoot).... so as the battery drains and its voltage drops, they just draw more current from it.

 

[Rocketman]

That would be nice to find a boost circuit in the new eGo
Scottbee sort of stoped (maybe on purpose) giving details about circuit operation.
But if they went to 100% Duty Cycle, it would be cell voltage (under load) less resistive losses.

Here's a hand drawn chart of three of the wife's spares. Two new, one a couple months old.
The measurements of course are cheapo meter readings. And the time scale is "as vaped", tested every half hour or so.
(a lot of vaping )

With the Peak voltage and RMS voltage that the earlier posts show, this gives a reasonable error estimate of the cheapo readings. If $4 gets you 10%, how much more would it cost to get to 5% accuracy?, 1%?

 

[jimho]

That would be nice to find a boost circuit in the new eGo
Scottbee sort of stoped (maybe on purpose) giving details about circuit operation.
But if they went to 100% Duty Cycle, it would be cell voltage (under load) less resistive losses.

Here's a hand drawn chart of three of the wife's spares. Two new, one a couple months old.
The measurements of course are cheapo meter readings. And the time scale is "as vaped", tested every half hour or so.
(a lot of vaping )

With the Peak voltage and RMS voltage that the earlier posts show, this gives a reasonable error estimate of the cheapo readings. If $4 gets you 10%, how much more would it cost to get to 5% accuracy?, 1%?

Well, I just needed an excuse for a new meter... for other things - my cheapo meter was a pretty good DMM for 1981. To get to .001% cost me about $350 and I got the software and cables for $30 on ebay- If I were to do it again, I would probably have picked up one of the DSO's that Scotbee was using for around $150 on fleabay- trade off is portability....

The thing is, looking at a trace (or a digital sample presented like a trace) tells a much better story with these things than a DMM will- especially when your DMM isn't telling you what you expect...

If you've got a storage scope though, can't you see what's going on as the battery winds down?

 

[Rocketman]

Well, I just needed an excuse for a new meter... for other things - my cheapo meter was a pretty good DMM for 1981. To get to .001% cost me about $350 and I got the software and cables for $30 on ebay- If I were to do it again, I would probably have picked up one of the DSO's that Scotbee was using for around $150 on fleabay- trade off is portability....

The thing is, looking at a trace (or a digital sample presented like a trace) tells a much better story with these things than a DMM will- especially when your DMM isn't telling you what you expect...

If you've got a storage scope though, can't you see what's going on as the battery winds down?

0.001% is pretty good. My TEK 310 or even my 3478A won't do that on AC.

Jim, the point I'm trying to support is people making measurements can still get reasonable results with less than world class instruments IF they understand the potential errors inherent in the instruments and techniques they use.
Some don't even have a cheap meter. If we keep dogging them about getting expensive meters, they never will.

How much trouble would it be to apply an "educated guess" average to RMS correction factor for cheap meter measurements to get the result into a "reasonable for e-cigs" accuracy?
One thing the cheap meter does is make it easy to monitor the performance of your e-cigs, batteries, chargers, attys/carto.

Thanks again for the help,
Rocky

 

[JW50]

Peak-Peak was 3.98V - RMS should read about 3.6- go back here and down the page....
http://www.e-cigarette-forum.com/forum/joye-510/65055-battery-voltages-surprise-12.html#post2301546

Sorry, I no longer have an eGo to test.

If unloaded, just off charger, 3.98V as peak sounds a bit low to me. But, if an aged batt, maybe. But still, charger is seeking a 4.2v charge. But, OK, 3.98V it is. Then what seems to be case is that eGo voltage from cheapo meter (DC scale) is usually about 3.5V, unloaded. To make a 3.98 peak average 3.5V a 88% duty rate is implied (i.e. 3.5/3.98=0.8794). So, my belief, RMS volts is 3.5 divided by square root of 0.88. 3.5/0.88^0.5 is 3.731. So, I believe that RMS volts is ~3.7 volts. You believe 3.6 volts. 3.7 volts is approximately 6% above the cheapo meter read. 3.6 volts is approximately 3% above the cheapo meter read. But both above the cheapo read. Consider saying RMS voltage is cheapo read plus 0.15. Then using this convention in this case we could say "RMS voltage is 3.65" (3.5 coming from cheapo read plus 0.15). Now, my belief that the RMS voltage is 3.7 is only 1.4% above the 3.65 and your belief that RMS voltage is 3.6 is 1.4% below the 3.65. So, cheapo read plus 0.15 takes one to the RMS voltage - plus or minus 1.4%. That is, within the typical duty cycle limits of an eGo, estimating RMS voltage as cheapo DC meter read plus 0.15 is pretty close.

If the relationship of RMS voltage to cheapo meter read is RMS=cheapo DC divided by square root of duty cycle then RMS voltage will always be greater (or equal) than the cheapo read because the duty cycle will always be less than 1 (or equal to 1 just prior to cut-off). If we call RMS volts the cheapo read plus 0.15 then, at most, we will be 0.15 volts off the mark.

Given the above I suggest this as poorman's RMS meter. Use cheapo DMM. Test for DC volts and record. Then test for AC volts at one polarity and AC volts at reverse polarity. If AC volts at one polarity is double the DC read and reverse polarity is zero - consider it PWM. (May also consider PWM if AC read, both polarities, is other than zero in either polarity.) If PWM - RMS voltage is DC read plus 0.15. If not PWM, RMS voltage is DC read. RMS volts may not be "exact-exact" but - pretty close.

 

[Rocketman]

JW,
I agree with the accuracy percentages, and "Cheapo RMS" approach.
As far as the Peak voltage, you can't use the 4.22 off the charger value.
The very first electron going to the atty will travel at "loaded voltage".
The atty will never see a 4.22 volt electron, not a single one
Cell and circuit resistance is already "in the path". Peak to the atty is always loaded.


Late Edit:
My always loaded comment is just asking for it
Yes, it would be possible to put a capacitor at the cell to supply cell unloaded voltage to get an initial peak a little higher than cell loaded voltage. You would still have wiring and Mosfet losses at the atty.
I doubt 4.22v would even make it to an atty that wasn't open.


If you want to find out if a eGo or clone is PWM, use the earphone from your IPOD. Just don't put it in your ear

 

[JW50]

jimho thanks,
...
You really don't need one to approximate what is going on. Scottbee gave an implication that in addition to varying Duty Cycle to hold RMS output constant, it also does it for load (maybe). The 3.98 seems a little hot (I get a little overshoot on my storage scope that shows up in the PK measurement) but, it is a high quality cell in there.
So, 3.98 volt Peak into a load is what it is. At a duty cycle of 85%, full charged that is right at 3.6 volts RMS.
You have found the answer

As the charge deteriorates does the regulator circuitry keep that RMS somewhat constant?
By increasing the Duty Cycle?

Not that I am right here, I don't agree that Scottbee implied that RMS voltage was held constant. I suspect there is circuitry that might do that but it would have the expense of something on order of "true RMS" meter as compared to cheapo DMM.

 

[Rocketman]

Just an "algorithm" in the control chip to vary Duty Cycle with declining cell voltage.
An approximation of RMS control.
The "algorithm" could be as simple as a multiplication factor.

Draw a "cell voltage line" and "correction line" on the cheapo chart I posted. Straight line, offset plus slope, would do a pretty good job of correcting the cheapo values

 

[JW50]

I think somewhere down the thread (around that time frame) he indicated it didn't really do much to the duty cycle to push towards 100% as it drained, but that was with the versions they were shipping a year ago.... There were a few revs since then.

I think they keep the RMS constant using a boost switching regulator (which is why you see a bit of overshoot).... so as the battery drains and its voltage drops, they just draw more current from it.

Not that I am necessarily right, don't agree that there is any boost at all. I think more straight forward - vary duty rate to produce output that is ~3.5v (average volts) unloaded.

 

[JW50]

That would be nice to find a boost circuit in the new eGo
Scottbee sort of stoped (maybe on purpose) giving details about circuit operation.
But if they went to 100% Duty Cycle, it would be cell voltage (under load) less resistive losses.

Here's a hand drawn chart of three of the wife's spares. Two new, one a couple months old.
The measurements of course are cheapo meter readings. And the time scale is "as vaped", tested every half hour or so.
(a lot of vaping )

With the Peak voltage and RMS voltage that the earlier posts show, this gives a reasonable error estimate of the cheapo readings. If $4 gets you 10%, how much more would it cost to get to 5% accuracy?, 1%?

Upward move from zero time to just before avalanche does not seem right. Are you sure?

 

[Rocketman]

As measured, on three eGos.

Average gets closer to RMS as duty cycle increases.
Starts off a good bit less but gets pretty darn close to RMS at 100% duty cycle


Can you figure out which one is the used one?

 

[JW50]

Just an "algorithm" in the control chip to vary Duty Cycle with declining cell voltage.
An approximation of RMS control.
The "algorithm" could be as simple as a multiplication factor.

Draw a "cell voltage line" and "correction line" on the cheapo chart I posted. Straight line, offset plus slope, would do a pretty good job of correcting the cheapo values

Don't think I understand the correction. I think too complex for mainstream use. Think the constant add (of 0.15 or whatever that minimizes error of the estimate) is much more workable.

 

[jimho]

If unloaded, just off charger, 3.98V as peak sounds a bit low to me. But, if an aged batt, maybe. But still, charger is seeking a 4.2v charge. But, OK, 3.98V it is. Then what seems to be case is that eGo voltage from cheapo meter (DC scale) is usually about 3.5V, unloaded. To make a 3.98 peak average 3.5V a 88% duty rate is implied (i.e. 3.5/3.98=0.8794). So, my belief, RMS volts is 3.5 divided by square root of 0.88. 3.5/0.88^0.5 is 3.731. So, I believe that RMS volts is ~3.7 volts. You believe 3.6 volts. 3.7 volts is approximately 6% above the cheapo meter read. 3.6 volts is approximately 3% above the cheapo meter read. But both above the cheapo read. Consider saying RMS voltage is cheapo read plus 0.15. Then using this convention in this case we could say "RMS voltage is 3.65" (3.5 coming from cheapo read plus 0.15). Now, my belief that the RMS voltage is 3.7 is only 1.4% above the 3.65 and your belief that RMS voltage is 3.6 is 1.4% below the 3.65. So, cheapo read plus 0.15 takes one to the RMS voltage - plus or minus 1.4%. That is, within the typical duty cycle limits of an eGo, estimating RMS voltage as cheapo DC meter read plus 0.15 is pretty close.

If the relationship of RMS voltage to cheapo meter read is RMS=cheapo DC divided by square root of duty cycle then RMS voltage will always be greater (or equal) than the cheapo read because the duty cycle will always be less than 1 (or equal to 1 just prior to cut-off). If we call RMS volts the cheapo read plus 0.15 then, at most, we will be 0.15 volts off the mark.

Given the above I suggest this as poorman's RMS meter. Use cheapo DMM. Test for DC volts and record. Then test for AC volts at one polarity and AC volts at reverse polarity. If AC volts at one polarity is double the DC read and reverse polarity is zero - consider it PWM. (May also consider PWM if AC read, both polarities, is other than zero in either polarity.) If PWM - RMS voltage is DC read plus 0.15. If not PWM, RMS voltage is DC read. RMS volts may not be "exact-exact" but - pretty close.

You can believe what you want- it's a free country.
If your method works for you - good for you!!!
Whatever makes you happy.

 

[Rocketman]

Don't think I understand the correction. I think too complex for mainstream use. Think the constant add (of 0.15 or whatever that minimizes error of the estimate) is much more workable.

Agree for individual use. Just make an educated guess, add correction, pretty darn close.


But for a magic circuit like in the eGo a slope/offset correction to start-up loaded voltage would be easy to implement. Test the load for 100msec, set DC, go.

 

[JW50]

As measured, on three eGos.

Average gets closer to RMS as duty cycle increases.
Starts off a good bit less but gets pretty darn close to RMS at 100% duty cycle


Can you figure out which one is the used one?

I would think the used one is the blue dots. Still have hard time accepting cheapo DMM volts upward move. Basic cell volts are constant or falling (likely falling, but slowly) with vapes. Would have to know either expensive RMS volts at each dot or duty rate and cheapo DDM DC read at each dot to know whether RMS is being held constant - but avalanche suggests RMS (and average voltage) is not the keyed output.

 

[JW50]

You can believe what you want- it's a free country.
If your method works for you - good for you!!!
Whatever makes you happy.

No insults intended on my part. Looking for what is accurate. 3.6 or 3.7 - not a major deal. Most of volts read or derived headed toward "power". R is usually in that "power" and R will vary easily 10%. One can only hope the errors of R cancel out the errors in volts.