Voltage taps after the first full charge and 3 hours into my first discharge with 2 60watts in series
from left to right
end 27hrs charge, after sitting idle 12 hours, 3 hours into discharge.
17.83 16.88 15.58
17.88 16.85 15.55
17.88 16.87 15.58
17.84 16.86 15.61
17.87 16.85 15.57
17.85 16.85 15.54
17.80 16.87 15.55
17.79 16.89 15.57
17.87 16.89 15.55
17.87 16.86 15.58
179.6 168.4 155.4V
draining at .380amps
I know its still quite early but at this time, this pack appears to be in better shape than the one which came with the car. .07v variance highest to lowest vs I think over .1 with the pack in the car (probably far worse now)
This pack so far is less predictable too, pack A the weaker taps would be higher during charging and lower during discharge but I see no correlation yet.

EDIT: 6 HOURS LATER IT'S ONLY LOST AMOTHER 5 VOLTS!

 

That looks good so far. It's possible that the low SoC of the pack as-received put the resting voltage of all the cells below the voltage depression threshold, i.e., they self-discharged all the voltage depressed capacity, and your capacity will be at max.

6 hours is only 2.3Ah. 9 hours is only 3.42. At such a low current, you won't get much voltage drop until the 132-144V range. It will then fall comparatively rapidly but will be metered somewhat by the reduction of current with reduced voltage.

If you compute > 5.5Ah of capacity to 144V with uniform taps, Additional cycling is likely unnecessary, but it may provide some other benefits as cycling can improve SD.

 

the last check I did yielded ONE outlier on the low end, 3 at 15.94 and then one at 15.86

I started this thinking "you know it would be really great if I could just find four or six good sticks that act just like the ones that are in my pack, that I can take and replace, or even just 2 to solve my really poor single tap" and now I'm thinking, s***, I might cannibalize the pack in my car to Sure up this one!

I left the low-wattage bulbs in because I wasn't sure how this thing was going to fair over the 8 hours I was sleeping and didn't want to wake up to a very unfortunate surprise. I'll do at least one more full charge to try and balance out the voltage taps and then use my dual 90 Watters to discharge it that time.

As far as going all-in and taking out all 40 sticks and load testing all of them like you were saying: really the only additional time and effort for doing that instead of just identifying the weakest sticks and replacing them with candidates closest to the average of the pack is the removal and load testing right? Just replacing a couple vs testing all isn't really saving any significant time or disassembly is it?

as for pack A I don't think that it was actually disassembled I think that guy was just full of s*** and had done a whole boatload of grid charging.

EDIT: 14 hours later, beginning at .38Ah and now at .365. Still at 145V
Even doing math for .36 x 14 I'm over 5Ah
so looks like you were right on that one. Guess I'll be able to move onto grid charging pack A ahead of schedule (car won't move for this week so they can both be out of service)

 

I wouldn't regard .08V on a tap as an outlier unless the other 16 were much higher.


You sleep for 8 hours? Lucky.


"identifying the weakest sticks" = load testing. You can't conclusively say "identifying weakest sticks" based on tap results or stick voltages during grid charges/discharges because it's inconclusive as to whether it's capacity, IR, SD or a combination thereof.


A 7 day wait and a load test gives a much higher likelihood of "identifying weakest sticks".


A stick with low IR, low SD and say 4500mAh capacity is likely "stronger" than a stick with 6500mAh capacity, higher IR and poor SD as it relates to in-car performance.


The 4500mAh stick in that example will maintain its performance level. The 6500mAh stick in that example will likely deteriorate over a weeks to months timeframe, particularly if it's SD.


You could further enhance your testing with TWO load tests...


24 hours after grid charging will give you a good indication of the "strength" of a freshly charged stick. Since the 15 second test only consumes about 250mAh, it can be done without significantly impacting the 7 day results. A comparison of the 24 hour results with the 7 day results will scream the SD issues at you and weed out bad sticks with a high degree of certainty.


I'm also pretty sure you could do load testing without disassembling the packs. Just pull both end plates to expose the sticks and install the spacers on the stick to be load tested.

 

Well... this is sad inducing.
my little outlier has become a big one....
14.09
13.98
14.21
14.33
13.82
13.32
13.87
13.66
14.10
full pack at 139.1 now

I am curious though, how could a stick have such reduced capacity but still be relatively good in the other metrics? ( SD, IR, etc) I thought they somewhat went hand-in-hand, if less electrons are able to flow this would lower voltage (Which would essentially be voltage depression right?)

 

On average the sticks are almost completely empty as the load you're using is very low. Once you hit nominal at low load, there's not a lot left. I wouldn't be too worried. Ideally, at 144V, you'll see 10 very near 14.4. You're at 140, which would put them at 14.0V, and you have .33 above and .68 below - not at all a catastrophe.


It's not uncommon to see a full cell drop out at this voltage with low current when a cell is in bad shape.


How long to get to this level, and what is the current now?

 

yeah just in the course of checking the taps the low one lost 20ma! (From 10.58 to 10.38)

It really dropped out fast toward the end,
Between 1645 and 1715 it went from 130.1 down to 106!
I saw the decline was picking up but it accelerated much more rapidly in the last half hour.

Spent the vast majority at .37A down at .34A at 130v
at 107v it was .3A.
15 hours at .365
Then average an hour at .33

oddly the 4th tap held at 13.08v while all the rest were under 11.5!
problem child landed at 6.76

My capacity math is landing around 5.8Ah.

just finishing up letting it rest and then beginning charge 2.

 

The behavior you describe is a very good sign.


What does your capacity math say between the start and the ~140V readings?


There is zero need for "let it rest" at either end of the process unless you're doing it deliberately to gather data, e.g., the voltages 12 hours after grid charge or 1 hour after discharge termination, etc.


In the interest of expediency, I would eliminate those unless you feel strongly about those data, except for comparison purposes, you need to keep the 12 hour post-charge rest.

 

For the first half hour discharge was .39 at 0040
.38 from 0110 to 0340
.37 When I checked it at 1245 (total discharge time 12.08 so far)
and I want to say .355 when I checked it at 1610
So .38 x 3 (chop the extra 10ma off the front)
let's say .37 x 9
.36 x 3.42. (This last one more speculative)

in the neighborhood of 5.5Ah
I noted taps meticulously but failed to note current flow near as often. However I do remember it being .38 and .37 for the vast majority of the drain, only heading south toward the end. At 130volts it was draining at .34. And that was 35 minutes after my previous data point when the pack was still at 139V (a half hour later and it was at 106!) I think I should be able to math out the current if i can pin down the resistance of the drain circuit.

Are you familiar with Peter Perkins?
he appears to be an engineer. Has some pretty crazy contraptions on display on YouTube!

if I were to get a bumblebee battery I'd get one of his assist boosters but I know better than to try that with a pack that's in a little less then ideal shape.

 

Yes. He's a retired UK cop with a passion for tinkering. I've referred to him as "Merlin" on multiple occasions - fitting given he's from the UK, and he's a wizard of sorts.

I have one of his OBDIIC&C for the G1 Insight. It's the one for monitoring.