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Old 12-29-2012, 06:23 PM   #41 (permalink)
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Ron, where on Earth did you hear that? That's not true at all, and it's disturbing that you would even say that. I am guessing something must have gotten lost in translation, because you've been around these things long enough to know that isn't true.
I'm not sure we are talking about the same thing.

Are you measuring the output of the cell, or the voltage of the circuit? Take the charge off and read the voltage output of the cell and see what you get.

You will never read a voltage off a pack higher than 174 unless it is connected to a charger.

No matter what amperage we used (up to 100A charge), we could never exceed 1.45V on a cell. That number held true for 0.1A up to 100A.
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Old 12-29-2012, 06:38 PM   #42 (permalink)
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I'm not sure we are talking about the same thing.

Are you measuring the output of the cell, or the voltage of the circuit? Take the charge off and read the voltage output of the cell and see what you get.

You will never read a voltage off a pack higher than 174 unless it is connected to a charger.

No matter what amperage we used (up to 100A charge), we could never exceed 1.45V on a cell. That number held true for 0.1A up to 100A.
Reading the cell's voltage while charging and seeing 1.6V is the same as reading the cell's voltage while discharging and seeing 1.1V. That IS the actual cell voltage. Saying that a cell can't go over 1.45V is like saying a cell can't dip below 0.9V. Obviously this is false.

Sure, it drops down to ~1.45V or less once current input is removed, but the voltage you're reading across the cell during charge and discharge is real.

I figured this was just a semantics issue. If you would have said resting voltage, I would have agreed.
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Last edited by Eli; 12-29-2012 at 06:41 PM.
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Old 12-29-2012, 07:44 PM   #43 (permalink)
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Discharge voltage nearly doesn't matter with six cells in series without monitoring at the cell level. 0.9 * 6 = 5.4V.

That could be five cells at 1.0V and one cell at 0.4V, or any combination thereof. With this in mind, it actually makes more sense to use a higher minimum voltage if you're truly worried about overdischarge. At the same time, you want to give the cells the maximum workout you can. I use 0.750V in the testing rig currently, which is rather arbitrary.
Since he's charging it first, 5.4V basically ensures that no cells will reverse unless the stick is totally unusable anyway. He's trying to separate the wheat from the chaff.
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Old 12-29-2012, 07:51 PM   #44 (permalink)
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Reading the cell's voltage while charging and seeing 1.6V is the same as reading the cell's voltage while discharging and seeing 1.1V. That IS the actual cell voltage. Saying that a cell can't go over 1.45V is like saying a cell can't dip below 0.9V. Obviously this is false.

Sure, it drops down to ~1.45V or less once current input is removed, but the voltage you're reading across the cell during charge and discharge is real.

I figured this was just a semantics issue. If you would have said resting voltage, I would have agreed.
Eli, by that reasoning, a resistor in circuit would have that voltage.

This is a battery. All that matters is what we can get out of it.

What I'm saying is the the resting voltage (which is the only voltage that counts in my book), will be 1.45V or less the instant you take it off charge, therefore that is the maximum voltage of the battery. And it will fall to 1.4V over time as it cools down and settles. (Less than 1.4V if damaged.)
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Old 12-29-2012, 10:06 PM   #45 (permalink)
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Eli, by that reasoning, a resistor in circuit would have that voltage.
Yup it does.
V=IR

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What I'm saying is the the resting voltage (which is the only voltage that counts in my book), will be 1.45V or less the instant you take it off charge, therefore that is the maximum voltage of the battery. And it will fall to 1.4V over time as it cools down and settles. (Less than 1.4V if damaged.)
And the dV from resistance will drop in an instant ... but the chemical distribution is not that fast ... and for a short time after the charge is initially taken off the cell the cell itself on the terminals can be over 1.45 V , before the terminal voltage begins to quickly fall back.

Graph added if it helps.... shows the time after a charge cycle ... the AMPs of charge current go to zero ... but you can see the terminal voltage of the cell takes a bit longer to drop back down ... when the minor 1Amp charge current drops out there is an imediate drop from the loss of that external current of the voltage doing down to 8.83v for a 6 cell stick ... average cell is still over 1.45v per cell or 8.7V total ... and you can see the voltage continue to drop but the chemicals take a bit longer than the electronics .... and this is just an example from 1Amp .. 100A would see an even larger effect... I agree it will continue to drop down to 1.4 and under over time ... but it takes time to even get under 1.45v.
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File Type: jpg Settle.jpg (104.0 KB, 8 views)
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Last edited by IamIan; 12-29-2012 at 11:27 PM. Reason: graph
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Old 12-30-2012, 08:56 AM   #46 (permalink)
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And the dV from resistance will drop in an instant ... but the chemical distribution is not that fast ... and for a short time after the charge is initially taken off the cell the cell itself on the terminals can be over 1.45 V , before the terminal voltage begins to quickly fall back.

Graph added if it helps.... shows the time after a charge cycle
What is the y axis of your graph? 1 second per row?
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Old 12-30-2012, 10:20 AM   #47 (permalink)
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What is the y axis of your graph? 1 second per row?
That particular test the measurements displayed in the file snap shot above were polled every 70 seconds.

In that test it took about ~8 minutes for the 6 cell sub pack initially being charged at a 1 amp rate to fall from the 8.887V pack voltage ( average cell ~1.48v ) to the 8.7V pack volt ( average cell ~1.45v )... later in the spread sheet after a total of about 30 minutes or resting from the charge before the discharge part of the cycle ... the 6 cell subpack had settled down to 8.612V ( or average ~1.435v per cell ) ... then of course the voltage dipped down more under the discharge load.

I've seen IMA pack voltages in my car go up over 185V ... ( which would be an average of 1.54v per cell ) ... when the charge current is removed ... there is drop of the voltage related to removal of the current flow ... but it does not instantly drop back down to 1.45v or less per cell ... the chemicals are not that fast at distributing the charge energy throughout the medium of the cell... it is a logarithmic decay , so the higher the voltage starts the steeper the initial slope will be back toward that ~1.45v ... my only point was that it will still initially start higher when the charge current is initially removed... it takes time for the terminal voltage to slope down as the chemicals distributed the applied charge energy through the medium of the cell ... the car can swing 150A in like a second ... that is a significant amount of non-distributed terminal voltage that will show up on pack voltage readings.

Another way to look at it in a different context is something like taking a blow torch to a solid block of aluminum ... the temperature difference cross the block will have a gap ... it takes time for the energy to distribute through the medium ... take away the blow torch and one side will still be hotter than the other for a period of time while the energy is still being distributed... chemical reactions are slower than electronics ... and it takes them time to distribute the chemical energy applied.
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Old 12-30-2012, 04:03 PM   #48 (permalink)
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i dont want to go off-topic, but since the discussion is dealing with internal resistance, I wanted to ask if anybody has experience with those chargers that can graph, measure IR and do many more things.

Here is one I was thinking of getting that has specs similar to the superbrain 989, but it also graphs and measures IR. There are others that do also, but this one seems to have good reviews.

Duratrax® IntelliPeak ICE Charger | 88X
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Old 12-30-2012, 05:11 PM   #49 (permalink)
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i dont want to go off-topic, but since the discussion is dealing with internal resistance, I wanted to ask if anybody has experience with those chargers that can graph, measure IR and do many more things.

Here is one I was thinking of getting that has specs similar to the superbrain 989, but it also graphs and measures IR. There are others that do also, but this one seems to have good reviews.

Duratrax® IntelliPeak ICE Charger | 88X
I haven't used that particular unit ... but the PL8 I have does IR measurements.
There are generally 2 common ways one can do the IR measurements.

#1> Look for the dV from no current to ___ Current ... use V=IR.
Even if your device doesn't offer this ... you can always check in the beginning or at the end of the charge and or discharge events and just do the V=IR math yourself.

#2> AC Impedance ... by carefully monitoring the results of the PWM wave a device can measure and track the AC Impedance not just in the beginning but continuously over use ... the advantage is the wide parts of the test cycle that can give you a Ohms reading ... just keep in mind they are measuring AC Impedance and converting to DC Ohms ... so it is an estimate , and not an actual direct measure of DC Ohms of resistance.

- - - - - -

The above having been said ... consistence is important ... if you are going to be picky about it you might have to measure the wires resistance to account for it ... and then use the same 'calibrated' test wires for all the tests to be consistent.

As long as you are reasonably consistent you should have no real issue comparing among your own tests... so in that sense the quantified actual resistance is less important than the relative resistance compared to the other cells and or sticks you have and will be comparing to.
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Old 12-31-2012, 08:03 AM   #50 (permalink)
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Followed the instuctiins on cell cycling and reinstalled the pack. Good news is it started right up and noIMA code. Still need to drine it more to see if it stays out. Idid notive it drives like a normal car now. Prior it felt like the clutch was grabbing, I was actually planning on replcing it thinking it was oil fouled. Charge and boost seems to work and battery level showing full.
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