NexPower V3 hybrid battery unveil - Sodium-ion battery

Wow, that is big on the accusations, claims and the likewise, without much to back it up ..... When did the Chinese govt start testing products for sale to overseas markets?

T1 Terry

 

With so many different sodium ion (Na+) cell construction methods and manufacturers, the number that are the real deal and the number that are failed production test runs are near impossible to identify one from another.
About the only Sodium ion cell that could be taken on face value as being thoroughly tested, would be CATL, and they don't sell to small enterprises, their second gen products are the cutting edge as far as commercial level production and OEM are taking these as fast as the pass CATL testing procedures, those that failed the testing are available on the open market .... not sure how much faith I'd put in them though, no one says why they failed to meet specs, they just didn't make specifications so were rejected.
Doesn't matter what letter of the alphabet they put on the claimed quality, it either passed CATL specs and went on to the OEM suppliers, or it didn't ........

T1 Terry

 

Maybe you missed all the fun here at priuschat, on the two projects youtube channels and the other projects followers (beta testers) at the insightcentral forum last year (24). As well as the banning frenzy (timed and permanent ) that happened here as a result of all the fun.

@PriusCampers comment about rigorous was referring to the testing Jack has done and published on his youtube channel which you can find by reading the documentation on the projects web site.

 

Why does Nexpower have to survive?

My in house rigorous testing (driving normally for 2 years in CA) caused their $2000+ pack to fail, with the only recourse from the company being the "opportunity" to purchase a $980 sodium replacement. That's $3000+ spent for crossing 1/5 of the life expectancy of a sub-$2000 oem pack.

There are claims being made that sodium is better than lithium and won't fail the same way, but these claims are coming from the same people who made the big lithium claims years ago (yes I was foolish for drinking the koolaid back then).

Additionally, Mudder's videos show that certain design deficiencies that lead to the lithium packs' failures are still present in the new sodium packs.

I can personally say confidently that I would have been better off (money, time and anxiety wise) without Nexpower. I am willing to bet that the overall prius community would've been better off without them too with the reliability of oem replacement packs.

 

Exactly. They never had a convincing story and never answered technical questions from the beginning.

 

I remember jack azausa telling me that Toyota’s bms in the ecu will keeping the lithium battery pack within range. If so, then why does the nimh cells are out of voltage range.

 

Caution, there's at least one recent thread reporting it's harder to find Toyota packs at sub-$2000 prices anymore.

 

The Prius balancing is done per 2 modules, allowing one module to go high and the other to go low, yet still have the same voltage across the BMS measuring points.
Add to that, there are 6 cells in each module, what hope is there if the attempt is to use 12 cells in series to establish the voltage as a comparison to the other 12 cells in series ..... what is supposed to keep each of the 12 cells in the group's voltage the same?

That is the real reason Toyota only use such a small amount of the battery capacity, the balance across the cells in each 12-cell group is an unknown, so they allow a very wide margin of error.

A replacement chemistry battery could use the same technique, but if they used the same safety margin to allow for the out of balance between the cells in each module group, the battery would need to be a much larger capacity and the area available just won't accommodate that .....

A purpose built BMS and dynamic balancing system could be designed and built to make these alternate chemistry batteries function as intended ..... but I doubt anyone would pay the extra to add that, it would more than double the price.

Well worth the cost if the plan was to fit a much bigger capacity battery than the one that fits in the area available at the moment, an additional $2,000 to protect a $10,000 battery pack makes more sense that $2,000 to protect a $2,000 battery pack .....

T1 Terry

 

Toyota is taking heavy advantage of chemistry-specific facts about NiMH. The chemistry has fairly benign behavior under a slight overcharge. A single series string of cells can be kept charging for a while, with the cells that are first to reach full charge simply tolerating a bit of overcharge while others catch up. That strategy definitely doesn't generalize to all battery chemistries.

In my gen 1's later years, I noticed it on several occasions going through such a controlled overcharge cycle. I don't recall catching such a cycle in my gen 3, but I don't know if that is because the programming was revised not to do it, or my gen 3's battery just isn't that old yet.

Toyota's NiMH battery ECU is just a voltage monitor, not a balancer in the sense of being able to direct currents from some cells to others for balancing. Charging current only passes through the whole stack in series.

They can't use that strategy for their Li-ion packs, of course; the battery ECU for those has connections to every cell.

 

I have experienced higher than normal nimh charges but only after a normal full battery sits overnight and ambient temps changed dramatically. This is followed by more regen down a 150 elevation drop in the first mile.

The v then burns off the charge with ev operation up to 35 mph without having to nurse it or force ev. The ev response can be impressive under this condition.