Gen II Prius Individual Battery Module Replacement

привет
Seems like "uzuri" drink in Greece did not spoil you English skills at all mate
Folks here on Priuschat would not have a clue what are you talking about when you compare 40-module pack to Prius - they have never had NHW-10 in US and they talk about Gen-1 being NHW-11.
Just have a look at my site on Testing Complex - HYBRIDS - I have 20-channel HV Analyser ready to be shipped (can courier to Greece) and have chargers for 20 modules. 20-channel Analyser will allow you to test pairs as well as individual modules. Charger will allow to charge 1/2 of the pack at a time. I have on my "to-do" list to finish charger for 40 modules - just had no time for that yet.
Do not waste your time with DIY charger/discharger - that takes forever. - замучаешься тестить,
удачи

 

Did someone say something?

 

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Delta peak is a voltage peak sometimes called a knee in the charging voltage of NIMh cells. The voltage rises as the battery charges, and at full charge rises faster then falls. The delta peak.
Some chargers can detect this and end the charge at that point. The problem can be however that with a string of cells in series in a module there will be a delta peak for each cell that can fool the charger into shutting off early before all the cells in the string have reached full charge.
If you are using so called hobby chargers do not set a delta peak cutoff. Set a maximum charge MAH limit. This should be high enough to charge fully the rated capacity plus an amount to allow for the charging losses "inefficiency" of the cells.

I now await Kiwi's trashing response that I will ignore possibly because I am not in the US as he suggests.

John (Britprius)

 

Thanks for answer! since did not found a option on my charger to turn-off the delta peak sense i will set it to maximum possible(15mv/c), and cut-off at 7000mah, maybe delta peak setting will be ignored automatically when cut-off set by capacity...

I will post the results when will done

 

Even 7000mah may not be enough to overcome the charging inefficiency of the cells. This would calculate them to be 93% efficient a very high figure. I agree it is a reasonable starting point, but if you see capacities being reported at around 5600mah after cycling this could be the reason.

John (Britprius)

 

a_triant,

I am now working on 2 modules per suggestion of John. Looks like I may have the same issues you're facing but my Delta V though set at default is not being triggered. However, the highest discharge capacity I get on 4 modules were 5926, 5948, 5795, 5783. First 3 cycles at 7200 mAh, last 2 at 7500 mAh. So close yet not quite there yet.

Last night after some conversations with John (Thank you John again for bearing with me), I set 1 module to discharge>charge at 0.7A, 6V and charge to 8000mAh. The other I set to 0.7A, 4V, 8000mAh both for 2 extra cycles more. I think this time I'll get to >6000mAh which is the threshold I set for rebalancing my modules.

I'll post the results when completed.

Danny

 

Danny,

If the modules have lived in a warm climate, you shouldn't expect them to recover to full capacity. Note that if the capacity measurement were done at a high discharge rate (you are averaging about 0.2C), the capacity would be noticeably lower.

JeffD

 

JeffD
Average California temp is 70F and I'll consider that paradise already . But from the point of climate condition for the battery, I'll have to think on that. Anyways, would I still be fine at around 5800>5900 mAh if I can balance all to this capacity?
Danny

 

A capacity of half that number will still give good MPG.

JeffD

 

I also thinking to charge all the modules at 0.7A since i did not found option to disable the delta peak, with that charge rate it will not heat much and will be more dificult to peak delta, and also will be safe charging since we overcharging the modules

 

This maybe why I was not triggering my Delta V cutoff.

 

JeffD,
Should I then change my discharge rate to 0.1C to improve my module capacity measurements? I'm not press for time so I can afford longer discharge hours.
Danny

 

Just keep your discharge rate the same for comparing modules. Remember that you should also "load test" them (draw a heavy current for a short interval and record the drop in voltage - a halogen headlight using both filaments is a good load). If a module shows a larger drop than others, don't use it.

JeffD

 

And the results are:
Settings: 0.7A, 6V; charge to 8000mAh (Module #26)
D1: 6167 C1: 8000
D2: 6059 C2: 8000

Settings: 0.7A, 4V, charge to 8000mAh (Module #28)
D1: 5464 C1: 8000
D2: 5887 C2: 8000

Have to do one more step in fine tuning the discharge rate but I am very happy with reaching my threshold of >6000 for Module #26.

 

I think discharging to 4V is not a good idea, i'm not an expert but as i read everywhere peoples saying 0.8v per cell is the edge for NiMh, and if the cells are imbalanced, when we doing a cycle we starting from discharge then the low voltage cells can go even lower than others.

 

You maybe right. One weird thing I noticed during discharging from 5 plus V to 4V as I happened to be watching was that it jumped quickly to 4V with almost nil capacity change. Just went to the DRY mode of 5 minutes (Cool Time).

 

Danny at 1.0 volt per cell the cell is discharged. Below this point the voltage rapidly falls away "in graph terms it falls off a cliff" this is perfectly normal and does no harm. See the graph below of an eight cell 9.6 volt battery.There is virtually no capacity below 1.0 volt per cell. The only danger in going to low voltage in a string of cells "a module" at high discharge rates "amps" the lowest cell or cells can be reverse charged damaging them. At low current discharge levels this does not happen.
It is recommended that NiMh batteries should be stored in a completely discharged state "this does them no harm at all", and not in a charged state as with lead acid batteries.
The reason for taking the voltage down to a low level slowly and then recharging is to break up the large crystals that are be formed when NmHi cells are not fully cycled in use. Going to even much lower levels can be beneficial as recommended by "Jeff 652 with his grid charger, and dis charger".

John (Britprius)

 

Interesting information now i can't decide how to start rebuilding

Charge at 0.7A cut-off 8000mAh, Discharge at 2.0A to 1v per cell
or
Charge at 0.7A cut-off 8000mAh, Discharge at 0.7A(maybe even 0.6 better) to 0.4v per cell

Maybe should i start with discharge to 1v per cell and if the results are bad then next discharge to 0.4 per cell?
or discharge to 0.4 will be good in any case no mater the in which condition is the battery?

the car is 2006 so the battery is alredy 9 years old, and looks like the DTC tells about high internal ressistance, because the voltage of pair modules look not bad at all.

Any recomendations?

Thank You!

 

A 2.0amp discharge rate is beyond the capability of most hobby balancers. My Supermate DC6 can only handle a 5 Watt discharge rate (about 0.7 amps for a module)

Discharging to less than 1v per cell has a risk of reversing a weak cell and killing the module

Again, do NOT discharge to below 1v per cell (6.0 volts)

High internal resistance will limit module usefulness, but unequal module pair resistance will cause alarms.