Screenshot from TechStream - HV battery aficionados rejoice

1. You would normally expect the module pairs which register the highest and lowest voltages to change around as you continue to watch the screen (assuming the car is READY). If one module pair consistently reads lowest, that is a leading indicator of a failure about to happen.
2. A maximum difference between module pair voltages of only 0.11V is quite good. I believe that a difference of 0.3V is required to cause the traction battery ECU to log a fault code.
3. Based upon your screenshot there is no reason to think that your traction battery has a problem.

 

Your traction battery module voltages are normal and I doubt that the grid charger would improve the behavior that you have seen. However if you want to try it and see what happens, that would add a data point to the discussion about grid chargers, and whether they actually help Toyota traction batteries or not.

 

I all looks pretty good PriusGuy. The internal resistances look very well balanced too.

BTW. Do you happen to remember how many bars of SOC were showing at the time (eg 6 blue, or 7 green). Just wondering what 1.34 volts per cell (which is about what you've got) corresponds to.

 

I may have to be corrected by others, but I'm under the impression that battery behavior under load is a more useful indicator of module health.
I know from playing around with 'Torque' for Android that I can log over time the greatest voltage delta between pairs of modules while I am driving. I presume anything 'Torque' can do, Techstream can too, or better

Any dissenting opinions regarding the utility of this test ?

 

Yes, one is really wanting to look at dynamic data, especially during periods of acceleration or braking, when the battery current is well over 50 amps. That will show the weak modules, if any. If the highest delta voltage continues to switch around in the pack, then no worries. Techstream can graph that data.

As for the grid charger, I would say that is mostly applicable to those who never see a fully charged pack just due to driving conditions. I see all green bars for extended times, and the attendant battery thermal sensor increase, every time I go down the mountain. I would not expect to see much imbalance that would be corrected with a grid charger. Those in flat areas, where they might never see all green bars, would be more likely to need the balancing at some point.

 

When I did a similar test with an average module pair voltage of 15.25 volts the state of charge registered at 55.5%.

John (Britprius)

 

Thanks Brit. That 15.25 volts is about 1.27 per cell, which sounds about right for that SOC level. The "mid range" of the NiMH discharge characteristics is extremely flat, so very hard to deduce SOC from voltage without also having Coulomb counting, but 1.27V and 55% certainly sounds about right. BTW. That would have been either right at the bottom of the sixth bar or right at the top of the fifth, so I guess you had either 5 or 6 bars showing at the time.

The reason I was interested in the SOC of PriusGuy's is that it was over 8 volts per module (about 1.34 per cell), so reasonably high. I was just wondering if his battery was showing more than 6 bars at the time.

 

Admit it already -- you are jealous.

 

I will run some tests at various levels of charge and list the voltages.
For what it's worth the charge on my battery generally is five blue bars and often into the green range at 6 0r 7 bars. This may be due to the terrain or my driving style.

John (Britprius)

Here are the voltages with % state of charge, and MFD state of charge bars as reported by Techstream. There will be some movement on these figures because of the variability of the level of charge within each bar of the display.

2 Pink bars = 14.5 volts at 42%
3 blue bars = 14.6 volts at 47%
4 blue bars = 14,8 volts at 52%
5 blue bars = 14.9 volts at 54%
6 blue bars = 15.3 volts at 56%
7 green bars = 16.3 volts at 71%
8 green bars = 16.4 volts at 76%
8 green bars = 17.1 volts at 81%

The maximum cell voltage at 81% charge (17.1v / 12) = 1.425 volts. The voltages for the module pairs are an average of the 14 pairs.
As you rightly assumed 15.25 volts (55.5%) would be near the top of the 6 blue bar level according to these new figures.

John (Britprius)

 

Thanks for that data John.

I was interested to see how well it correlated with the voltage/SOC measurements on my NiCd and NiMH power tools. Actually it correlates quite well.

I know that the underlying relationship is not necessarily linear, but for what it's worth I made a plot of your data and a line of best fit.

BTW. In the formula (V = 11.40 + 6.84*SOC), the SOC is taken as a decimal (0 to 1) instead of a percent.

 

X2

OP, the testing needs to be done while driving not just at vehicle ready. As it stands your info shows the sign of a healthy battery pack (ie lowest/highest voltage blocks move around randomly throughout the pack while driving). A battery in poor health will typically have the same blocks being the lowest voltage under acceleration and then highest under deceleration.