Error Code P0A90-604

Will be done for gen 2 in january/february. Planning to make it commercially available

 

The 64sXYp would be rather happy with that range of voltages (low 3.04v and high 4.14v). Mine pack however is 58s. This would be on the high voltage side at 4.56v per cell. It is way to much which will lead to overheat and possible self ignition and explosion. You definitely don't want that. Additionally, even more don't want to charge you prius original pack up to 265v. This corresponds to 1.57v per NiMH single cell. Since they are an automotive grade NiMH cells, they are designed for enormous amperage output and inputs (power density), but not for high voltage and high capacity (energy density). Thus 1.57 volts per Ni cell is absolutely not recommended and extremely dangerous (speaking out on my personal unfortunate experience: my old prius gen 1 got its cells charged up to 1.55 volt (not by design, but by an algorithm error), what caused a thermal runaway, boiling of the base electrolyte and an explosion of the pack; i had to scrap the car after that). Some of the latest Toyota's (Panasonic) NiMH cells are okey with up to 1.54v. All the older cells up to including the third gen prius and all of their's derivations should not experience more then 1.48 volt per cell.

However, if you mean a peak charge/discharge that the pack may experience for a second or two while accelerating or decelerating, then it is fine, as the NiMH cell will exhibit somewhat a capacitor properties for some microseconds and will allow higher potential differences between the anode and cathode. Then the ion diffusion will take over and reduce the potential to its electrochemical potential. Sorry for the scientific terms, i work as an chemical engineer in a company that develops lithium batteries.

 

In two to three weeks i will try to post a video with the details.

 

It certainly can and does. NiMH batteries are much less thermally stable in comparison to Lithium chemistries. If the cell has seen lower than 0.9 to 0.8 volts, a permanent partial capacity loss is guaranteed. If the cell has seen over 1.5 volts (open circuit voltage) there will be formation of cristal dendrites on the electrodes, what will lead to short circuit and thermal buildup, -> internal pressure increase -> explosion of the casing

Here one needs to do a so called "PMA" test, Post Mortal Analyses. I think however, the tap voltage wires got blown up like fuses when the whole pack started to deform in order to prevent the voltage leakage from the individual modules onto the body. Additionally, those tap wires have an extremely weak metal bridge from the wire itself to the contact metal plate. Those wires hang under a slight tension therefore even under a slight change in geometry of the pack, the tap wires will lose their connection to the individual cells.

The Prius ECU would have normally indicated the wrong cell/cells and would not have let the car to go into "Ready" Mode. The algorithms in the ECUs are, to some tinkers kind of annoying , pretty strict and thus are safe.
To me it looks like there was one or several cells which experience a long turn out-of-range voltage and was rebalanced and used in the pack.
If so, then the HV ECUs will not be able to recognize a bad cell since it shows nominal voltages. However, may this call get warmed up during the ride, and then experience heavy charge (deceleration) / discharge (acceleration), the load resistance will strongly decrease (meaning if the cell is being charged it will get over its nominal charge profile very fast thus letting itself overcharged; beyond 1.6 volt) thus provoking the damages you've described.

Another thing could be that the electrolyte got breached through the cell's case and got shortened onto the body. However this should have also provoked an error message on the dash. But it would not have caused the explosion of the pack.

Interesting case btw.
You could also try to replace the original NiMH cells with the 18650: the math is simple
each NiMH module has 6x 1.2v cells = 7.2v
two 18650 (say NMC chemistry as an example) will deliver 3.6v each, thus 2x3.6=7.2v

 

Camry Hybrid is more powerful than Prius, awesome thing. I wish we had those in Germany.
Good luck!

 

Those are good points, thanks:

I don't have to, while the HV ECU will force the MG1 to discharge the battery when the system voltage goes above 251 volts or so (above 1.49), thus i went the safe way to charge only up to 243,6v (1.45v NiMH cells and 4.2 Li cells).

If i were to live on top of the mountain and drive down the hill with the fully charged battery, then yes, i'd have a short-turn overvoltage peaks into both of the batteries. On the other hand with the empty battery driving down the hill could almost top it up (keeping in mind the full capacity of both batteries 5.8 kWh lithium + usable 0.53 kHw NiMH), but it has to be a rather long drive down to generate almost 7 kWh of electricity (6.3 kWh + heat losses).

Correct, they get charged simultaneously.

Agree, the most extreme pulse (peak) charge/discharge values i've seen were 1.59 volts and 0.85 volts respectively.