Gen II Prius Individual Battery Module Replacement

Are there some alternatives besides Prolong that does balance the voltages of modules in the pack?

 

You can wire all the modules in parallel and leave them for a few hours, and this will bring them all to the same level.
The capacity of the modules is automatically measured by the DC6 or equivalent charger.
John.

 

1. Make sure that the modules are all close in terminal voltage so that you don't get high currents flowing when you put them in parallel.

2. It is the total discharge amp - hours that gives the capacity measure. Note that since the small charger - balancers are limited to low current, the reading will be artificially high compared to the specified 1C discharge rate of 6.5 amp - hours.

JeffD

Posted via the PriusChat mobile app.

 

That looks hard to do practically.

 

It has been established that this "equalisation" process does little and is of dubious benefit. You are better off, just using your load tester to discharge all modules to the same voltage which remain close after they have rested. But really, as long as each module is within 0.3 V, it will be close enough. Bear in mind that each module will also need to remain with that same 0.3 V when being charged or discharged in real life use, as well, so getting them all the close as possible in the first place is a better idea.

The biggest problem you face is having modules that charge and discharge at different rates, in real life use, and then go outside the 0.3 V differential that the HV battery ECU is looking for. The only way to fix this is to ditch the errant modules and find replacement modules that more closely match the remaining ones.

 

The current flow really is irrelevant when connecting them in parallel as the voltage difference will or should be minimal, and the modules are capable of withstanding much higher currents in use both in charge or discharge scenarios.

John.

 

Are you using the thin wires that came with the charger? I’m new here but I have read the wires that come with the chargers don’t work. You have to make heavy duty ones yourself.

 

No, I made that mistake the first go around. Made some custom 10ga wires with ring terminals and banana plugs.

 

Sorry, maybe a silly question. How do you get mAh ? Will that be on the chargers?

 

REally, what is the logic behind?

 

When you charge everything to 7250 mAh, will you have different volts on modules?

 

Cody,

The Prius battery has a limited cooling system using the cabin air and the modules in the center of the pack tend to be at a highed temperature which causes them to age faster than those at either end of the stack

Each module has a capacity to store energy that slowly and unevenly goes down as the battery ages. Modules with a lower capacity will end up at a higher voltage than those with a higher capacity. So, no they will not all end up at the same voltage after charging all of them with 7250 mAh (note that some modules with lower capacity will cause the charger to shut down early and not reach 7250 mAh).

JeffD

 

I kind of understand the process. But why 6 volts ? Why not 4 volts for instance?

 

Cody,

6 volts is one volt per cell (assuming all 6 cells are balanced, not always the case) and fully discharging a cell to 0 volts will destroy it.

JeffD

 

Ok. But why not do 0.7 volts per cell which totals 4.2 volts per cell. This is in comparison to 24 volts of discharge using hybridAutomotive dischargers. 24/168 = 0.14 volts per cell.

I mean discharging modules individually, why we can go low as hybridautomotive guys recommend us for better reconditioning.

 

I understand this. Is it ok to discharge a module to 4.8 volts or 3 volts after charging it fully?

 

Yes, but more precisely, after thoroughly but carefully overcharging it. It is important that the cells are all at an equal state of charge. If one cell is at a lower state of charge, it might be discharged below 0 Volts during deep discharging, which might cause permanent damage.

Also, the deep discharge itself can cause SOC variations among cells which have different degrees of crystallization. That's why it is often recommended to do the deep discharge in stages, bumping the discharge voltage lower in each cycle, and rebalancing SOC after each deep discharge until the lower end of the discharge curve is more uniform between cells.

 

This is a gray zone. There is a tradeoff between lower voltage being more effective and more likely to destroy a cell. There is also a point of diminishing returns, where the tiny bit of extra capacity gain is not worth the extra time of discharging to lower voltages. Also, every minute of cycling degrades the electrodes by a tiny amount, so that at some point you are doing more harm than good.

Since it's impractical to analyze each and every cell beforehand, the exact optimum discharge voltage is unknown for a random module. So these different values are based on different peoples past experiences with different batteries and different equipment.

So the answer to your question is that there is no definitive answer.

Edit: Speculation: The Prolong system cycles all the modules simultaneously, but at a low discharge rate and with very good cooling. So it might be "gentler", even when it takes less time to do the whole battery pack to a lower voltage, than with one or two hobby chargers.

 

Right now, I am discharging individual modules to 4.8 volts with a rate of 0.9 amps.
When I discharged a module at 0.7 amps, I got ~8000 mah when charged back.

So, I can not make any inference for now.

 

Look at the table posted by @ryousideways , he is putting in 6750mah (rather than charging to delta v as you have done), and the modules that are good are putting back out 5500mah or more, weak modules are returning 4000mah or less. Weak cells can absorb a lot of energy (turning it into heat) but they can only put out so much because they didn't store it. By putting in a measured amount of energy and seeing how much of it you get back you expose the weak modules (or rather cells within those modules).