Though the cells display works pretty well, the balancing current display never reaches stability before the test cells reach 100% "fuel" or charge, and the test cell do reach balance, though the voltage display shows balance.
You can get better balancing by adjusting the profile to favor balancing.
For example .. I have used my 3 PL8s to balance the 48s LiFePO4 in my car 8 cells at a time .. 3 PL8s .. each doing 8cells at a time .. 1st one half (3x8= 24s) , then the 2nd half (2x8=24s) .. end result displaying within +/-1mV .. for example .. 2.800 and 2.799 .. this +/-1mV difference also represents a +/- 0.036% variation .. or a ~99.964% accuracy .. I don't actually believe the device is actually that accurate , that's just what is displayed.
---
'good enough' is subjective .. there is just a finite limited faith / confidence in any measuring device.
Always remember .. The number of digits on the display is arbitrary , and has almost nothing to do with the devices actual accuracy .. thinking that the number of digits displayed does in some way directly correlate to a devices accuracy is a psychological trick .. commonly exploited in every day life by gas station pump displays .. many U.S. state department of weights and measures allow for up to a +/-2% pump tolerance .. that sticker on the pump .. only tells you on that date the tester certified that pump was no more than +/-2% .. even if we for the moment ignore any error in that tester's own testing .. on 10 gallons that could be only giving me 9.8 actual gallons .. the number of digits displayed on the pump is arbitrary .. 10.000 displayed , is not any more of an accurate pump than 10.0 displayed .. it is a psychological trick to think the 10.000 display actually is anywhere near that accurate of a pump.
2.800 shown from a +/- 0.1% device .. doesn't mean it is 2.800 .. it means a display of 2.800 could be as low as ~2.797 and as high as ~2.803 .. an actual 2.803 could show as a 2.800 just as a 2.797 could show as a 2.800.
---
To increase / improve the PL8's final balance .. you just have to keep in mind how the PL8 does cell balancing when you make adjustments to the profile.
There is a main +/- current across the whole series string of batteries.
At whatever rate you've programmed .. up to the ~40A limit.
The balancing works by bypassing a certain % amount of that current around a given cell .. up to the maximum Amp balance rate you've set the preset to do.
The amount % of bypass (100% = the max Amps of balance you programmed) displays on the PC charge control software .. and is also (by default) logged in the data file.
Soo .. on a charge or discharge of 40A and a 1A max balance .. that shows at a given moment a 50% bypass of cell #2 .. 50% of that 1A set is 0.5A .. that means cell #2 only sees 39.5A of charge or discharge.
Soo .. because the PL8 gives so many options you can adjust .. this can be adjusted / improved numerous different ways .. or some combination.
Option#1> Increase the max Amp rate of balancing.
Given the OEM balance wire size (that came with mine) I don't myself go above 1Amp .. but the PL8 itself can go up to 3A .. but personally I would recommend larger than the 22ga OEM balance wire to go up to 3A for any prolonged period of time.
Option #2> Increase the % of operation spent balancing.
If balancing on charging .. do you start to balance with 10% SoC left to go .. or 20% or 30% .. etc .. the further out you start to balance the more time that gives the balancing to work.
Option #3> Lower the C-Rate for ending the top CV phase of charging.
It will reach C/3 sooner than it will reach C/10 .. this also effectively gives the balancing more time to work.
Subtle detail note about balancing in the CV phase :
If in the CV phase your total for the 8 cells is presently at 2A of pack charging .. you can not get 3A of balancing at that same time .. you can set it for that 3A, but you won't get that 3A .. even a 99% bypass would max out at 1.98A bypassed .. which means that cell at the top charges slower , but it doesn't truly go to 0% charging.
Option #4> Lower the total bulk charge rate.
40Amps of charging gives a 1A balancing rate less time to work .. than a 20A charge rate with the same 1A balancing rate .. 10A to 2A .. etc.
Option #5> Multiple Passes /cycle on reasonably matched cells.
If .. for example .. out of a 2Ah balance difference .. you corrected for 1Ah on the 1st pass .. you could get 1Ah more on a 2nd pass .. but only if the cells are reasonably matched .. if extremely far apart from each other the multi-pass might not be the best option .. but with all the balance voltage sense wires in place, it won't do any damage.
I don't think these hobby chargers were ever designed for testing huge batteries. Seems like if the supply battery is huge compare to the test battery things might work smoothly, but given same order of magnitude of the two, problems.
Agree-ish.
Especially on supply batteries that swing in voltage under a given power of charge or discharge.
For example .. my normal 'goto' supply battery is 4p4s A123 (~900Wh or so) .. if I were to do a significant number of cycles .. because of less than 100% round trip efficiency .. I would have a bench power supply setup with CC-CV settings to do refilling of that supply 4p4s battery as needed .. that is easily 16x the size of a test 1s1p A123 cell.
--
An idea I've sometimes toyed with .. would be to rig up bidirectional supply side power .. tell the PL8 it's using a supply battery .. but in reality .. it gets supply power from a AC/DC power supply , and it gives regenerative discharge energy back to a DC/AC grid tie inverter .. I have a 340W AC/DC power supply and I have a 500W DC/AC grid tie inverter .. the trick would be to coordinating the two so they take turns correctly .. oh well .. another project to stay on the back burner for a while yet.
Although I myself like the regenerative discharge feature .. if one wanted to use just a power supply and the PL8's internal discharge .. Keep in mind the internal discharge is resistance based .. as the test cell voltage gets lower and lower that reduces and reduces how much your max rate is for internal discharge .. This especially pops up as you get down to trying to test voltages of 1 cell at a time .. the regenerative discharge feature uses a DC-DC buck/boost (not resistance based) .. so .. in addition to the efficiency benefits of regenerative discharge there is also testing benefits for low voltage test cells.