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Old 06-01-2016, 04:32 AM   #11 (permalink)
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On another voltage-related note, I swapped back in my 010/030 BCM/MCM, replacing the 305 combo I've been running for a while -- and discovered that my 305 BCM reads pack voltage about 5V higher than the 010 BCM. I posted about that here:
BCM, MCM & ECM Revisions

So keep in mind that different BCMs don't necessarily measure and/or report the same pack voltages. 5V is a big difference...

EDIT: turns out I had been reading Mvo on the 305 BCM and comparing to Bvo on the 010 BCM. Both BCMs read Mvo and Bvo the same. Mvo is +6V higher than Bvo. Mvo is +2.8V vs. actual and Bvo is -3.2V vs. actual...
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Old 06-08-2016, 08:26 PM   #12 (permalink)
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Default Voltage Taps Part 2

I stumbled upon a graph I had saved, that Eli Bumblebee Master must have posted in one of the threads at IC (couldn't find it), that goes a long way toward illustrating what's going on in terms of battery management at the tap level.

Eli must have logged tap voltages during a long assist event. The upper blue curve shows assist current, on the right hand Y-axis, while the 10 tap voltages are on the left hand Y-axis. Time in seconds is on the bottom.

The general sweep of the graph goes like this: Start with full assist. Full assist is quickly throttled back to acceptable levels. Assist continues until, most likely, the car's 'empty' threshold. I think we can reasonably take the values at the key transitions as approximate Insight BCM/MCM management thresholds. Plus, the values generally fit with what we know about NiMH electrochemistry/use.

You can see how assist current initially peaks at about -75 amps. Voltage for the lowest 2 taps drops to about 10.5V (average of 0.875V per cell), while other tap voltages range from about 12V to 13V at this point (avg. of 1V to 1.08V per cell).

This is an old, weak pack - so current is quickly throttled back. Time from peak current to throttled-current looks like it takes no more than about 5 seconds. Assist current is throttled to about -25 amps. Voltage for the lowest taps rises to about 14V (avg. 1.17V per cell), while voltage for the others ranges from about 14.5V to 15V (avg. 1.21V to 1.25V per cell).

The assist discharge continues for another 500 seconds or so. Over this period, current gradually decreases to a low of about 15 amps at about 540 seconds. Voltage for the lowest taps at the end of this period is about 13.0V (1.08V per cell avg.), while voltage for the others is about 13.5V (1.13V per cell avg.)...

Overall, the BCM and MCM adjust assist current lower and that keeps voltage for the lowest taps between about 13V and 14V, or roughly 1.1V to 1.2V per cell average...

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Old 06-08-2016, 11:14 PM   #13 (permalink)
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It is a very interesting graph which I guess I missed somewhere along the road. The specific values of the taps are useful in confirming my "severe" sorting routine - as Keith calls it. I have found that "good" sticks will support 6 volts @ 35A for pretty long periods of time, and that becomes my measure of quality when separating the good from the bad. Thanks you for the refresher.
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Old 06-09-2016, 03:26 AM   #14 (permalink)
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Strictly speaking, "6 volts at 35A" wouldn't be so good. The worst sticks in the pack graphed above are at about 7 volts after the current gets throttled to about 25 amps. The others hit about 7 volts at 20 amps midway through the discharge; they don't fall below 6 volts even at the initial 75 amp discharge. And this is for a bad pack...

Plus, at 6 volts you're already below the level the car allows - and that's at only a 35 amp rate, yet the car demands more like 80 amps+ at max, 45 amps typical max sustained in 1st, 4th, and 5th gears...

Maybe your 6 volt figure is a typo?, or maybe you're measuring voltage through the loaded wires (kind of doubt that though since you're an expert)...

Some posts up I listed some discharge rates and voltages we might expect for good cells/sticks, assuming they were all at about 3mΩ; it'd be more like 7.35V, 1.22V per cell, at 35 amps... (permalink to post #4): The quintessential Insight NiMH voltage thread

In fact, you posted just above post #4 that you were seeing 1.08V per cell at a 70 amp rate. That's more like it... 6V at 35 amps isn't good, basically. I want to make sure people get that straight.
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Old 06-09-2016, 09:50 AM   #15 (permalink)
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Quote:
Originally Posted by eq1 View Post
Strictly speaking, "6 volts at 35A" wouldn't be so good. The worst sticks in the pack graphed above are at about 7 volts after the current gets throttled to about 25 amps. The others hit about 7 volts at 20 amps midway through the discharge; they don't fall below 6 volts even at the initial 75 amp discharge. And this is for a bad pack...
It is a little difficult to make direct comparisons since my loads are fixed at approximately 70A and 35A, mid discharge cycle, and there is no BCM/MCM management involved. I was just making the observation that the data for good sticks seems to generally agree with what I was seeing by entirely different methods. I define good sticks as those which can reach 5500 mAh capacity under the my test conditions. I won't go into methods because it just leads to interminable arguments, sorry, but suffice it to say that I'm just trying to find good sticks. I am doing nothing to try to heal sticks. I have accumulated enough sticks that I have that "luxury."

I just don't have the time right now to respond to this kind of very detailed discussion. But one quick point, the 6 V is right at the end of the exhaustion of the capacity test. I'll try to take some evening time to respond if I think I can do it adequately, but the long winded discussions are generally the reason I avoid discussing the topic at all. Plus it seldom leads to any agreement at all
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Old 06-10-2016, 10:29 AM   #16 (permalink)
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Quote:
Originally Posted by eq1 View Post
Strictly speaking, "6 volts at 35A" wouldn't be so good. The worst sticks in the pack graphed above are at about 7 volts after the current gets throttled to about 25 amps. The others hit about 7 volts at 20 amps midway through the discharge; they don't fall below 6 volts even at the initial 75 amp discharge. And this is for a bad pack...
I got curious about my previous 6 volt exhaustion number, so I went back and checked a so-so stick at half discharge. It read 7.05V at 35A. It would obviously read higher at a lower load. It is not a number that I usually document within my procedure, so I didn't have data.

Later I want to make some observations about this specific pack example and discuss/question some technical points, but right now the lawn mower calls.

Thank you for reposting Eli's data. It is instructional!
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Old 11-29-2016, 02:27 AM   #17 (permalink)
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Has anyone installed a voltage logger/monitor on these taps? It might be interesting. Also can you recondition pairs of sticks through these taps (keeping in mind pack reconditioning probably does as good a job as working with individual sticks unless you want to get philosophical).
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Old 11-29-2016, 08:41 AM   #18 (permalink)
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Quote:
Originally Posted by andr0373 View Post
Has anyone installed a voltage logger/monitor on these taps? It might be interesting. Also can you recondition pairs of sticks through these taps (keeping in mind pack reconditioning probably does as good a job as working with individual sticks unless you want to get philosophical).
Yes. Search for JimIsBell posts. I think Retepsnikrep just did one recently.

Conceivably, yes, but the wire is very fine gauge, so currents would be severely limited.
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Old 11-29-2016, 12:46 PM   #19 (permalink)
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Quote:
Originally Posted by S Keith View Post
....Conceivably, yes, but the wire is very fine gauge, so currents would be severely limited.
I thought the resistors in each line was the main problem...
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Old 01-10-2017, 07:36 PM   #20 (permalink)
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Here's a link to a portion of a current thread that has some new-ish tidbits concerning NiMH, Insight packs, and voltage:
Grid Charging in Q3 2016?
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