For the trolls

Doesn't matter if you clicked the link I sent. Given that you embedded the same video (with your suggestion that other people "will learn something or maybe not"!), it's fair to presume you've watched the video you chose to embed.

Whether to have a single BMS unit or a distributed one is a simple choice in the packaging design.

It's not the number of sense wires that dictates your choice of a single or distributed BMS. It's the other way around: the choice determines how many wires you need.

Toyota likes a single BMS, and Toyota understands what that choice means: when they are building an NiMH battery, they can get away with one sense wire for every twelfth cell, and when they're not, they need per-individual-cell sense wires. That's why their non-NiMH BMS needs so many more sense wires.

Had they wanted their non-NiMH version not to have so many wires all running to a single BMS, they could have gone distributed, and moved some of the BMS functionality into each module. One way or another, the BMS needs to respond to every single cell's condition, and it doesn't matter which way they do it. What matters is Toyota knows they need to do it, and they do it.

Nexcell's lithium pack chose a module packaging of ten Li cells (5s2p) per module and fourteen modules. That would be ok if there were also five sense wires coming out of each module and there was a replacement BMS with 70 sense inputs to go in place of Toyota's NiMH one.

If that seemed like too many wires, there was the alternative of moving some BMS functionality into each module to use fewer wires. One way or another, the BMS needs to respond to every single cell's condition, and it doesn't matter which way that's done. What matters is needing to do it and not doing it.

The V3 (non-GT) seems to be two big modules of 35 cells each. 35 sense wires out of each module would do the trick, again replacing Toyota's NiMH BMS with a 70-input sodium one. Or, again, five sense wires out of each V3 GT module (if those are 5s, I haven't seen one's insides).

Or, again as an alternative, move some of the BMS logic into each module to avoid all those wires out. The choice of how to do it doesn't matter. What matters is needing to do it and not doing it.

 

What ChapmanF describes in post number 22 on this thread really is key.

And he summed it up quite well.

As far as Azusa Price's idea about coming up with a pack that works better...

I don't imagine anyone is going to come up with their own cells for a replacement.

It's more likely it would use some sort of off the shelf automotive cell.

Once the cell has been chosen then if required by the chemistry, some sort of hardware software battery management system would also need to be created.

(This is the part ChapmanF and others have noted)

For the Honda Insight world there is a n aftermarket drop in lithium replacement packs that use OEM Honda modules repurposed from other vehicle's modules.

In conjunction with those modules is a separate hardware / software packages that does the battery monitoring and management.

The battery monitoring and management package is open source. And likely could be adapted in some way to be used for the prius.

Heck, nextcell battery designers could take a look at that and use it to add the additional battery monitoring and management function to any or all of their products.

 

So, whom shall we learn from here? Toyota, for having designed and built cars, and knowing when a battery chemistry calls for per-cell monitoring, and doing it?

Or Azusa, for having "worked on the Prius system for 10 years and knowing its limits and needs."? (And for so adroitly changing the subject once shown that Toyota knows to do per-cell monitoring with framedrops from the exact video he pretends to school others with?)

 

Is it legal to completely change the batteries without going through government safety approvals? Maybe even crash testing? Not sure. If it doesn’t meet standards it shouldn’t get a license plate.

 

Take a look at the 14:04 mark of the video that you linked. He explains that each 3.6 volt lithium-ion cell has a voltage sensing wire connected to it. Why do you think that Toyota did this for the litium-ion chemistry (Gen 4 Prius) and Toyota only used one sensing wire for every 12 cells for the NiMH chemistry (Gen 2 and Gen 3 Prius)? The answer is that it is needed to safely control the battery (keep the cells balanced to each other).

Why were there problems with the V1 and V2 LiFePo4 batteries that Jack sold? It was not the chemistry of the battery, it was that each cell did not have a sensing wire to keep all the cells in the pack balanced to each other. Jack was trying to use the Toyota one sensing wire for every 12 cells, which did not work out too well because the cells became unbalanced with each other over time

Jack is doing the same thing for the V3 sodium-ion battery. He is using the same Toyota supplied one sensing wire for every 12 cells. The results will be the same as the V1 and V2 batteries. The cells will become unbalanced with each other, and then you will have battery failures. Again, it is not sodium-ion chemistry of the battery that is the problem, it is that each cell does not have a sensing wire.

The key point is that you need to keep all the cells in the battery pack balance to each other no matter what the chemistry of the battery.

It is like Jack is putting his head in the sand and does not want to face the fact that every cell needs to have a sensing wire for the LiFePo4 and sodium-ion chemistries. I think that the V3 will be the death of NexPower Engery. It may take a few years to get to that point, but I predict that it will happen. It is a real same, because I was rooting for Jack to succeed.

 

Before you get called needlessly on a quibble, Jack did include a rudimentary balancing circuit in each of those modules. The 5s2p cell pairs are wired to a small board inside the module capable of (slowly) bringing overcharged cells back within range (though it hasn't got any way of comparing those cells' voltages to cells in other modules).

What he didn't do was bring individual cell voltages out to a BMS interfaced with the car, so the car could change its behavior if there's a cell in trouble. There's just one wire per module, being monitored by the car's original firmware tuned for NiMH, and so the car has no way to know it should back off or signal an error unless the overall voltage of a whole 5s2p cell group happened to look like twelve NiMH cells in trouble.

He could have tried to find a way to get adequate information to the car, by putting a separate stud on each module for the sense wire, and driving that stud from an internal circuit, so that if any internal cell was in trouble, an 'out of range for 12 NiMH cells' reading would be put on the sense wire. Kludgey, but at least the car would know there was an issue. (If I remember right, mudder suggested an idea like that at some point.)

But instead of doing something like that to give the car's BMS more-usable information, the V2.5 business with the signal soother went the opposite way: with that, instead of even seeing the voltage from a single 5s2p group of cells, the car's BMS would be shown the average of that group and the next group over—thus making the car strictly less able to recognize and head off battery trouble.

The sodium batteries have at least dropped that idea, but are still stuck with the car having no sense data for individual cells.