Gen II Prius Individual Battery Module Replacement

Those are probably lab quality clips (which would be great) but most of what people would buy are the ebay "5A rated" version from China and they are absolute junk......this was what prompted me to finally make my own test leads after having so many problems using the off the shelf ones. There's no real time gained in using alligator clips vs ring terminals when the cycle time is days and false readings are costly in terms of time with the vehicle down so in the DIY situation I would stick to those, but in your case where you do this for a business with much lower cycle times the high quality croc clips make alot more sense.

 

So I am now done running all the cycles and reran a few I changed to ring terminals but it doesn't look like any improvement really. Now I am torn what to do next I was going to leave every cell in that reached the high 3k level or better in and replace the lower ones but I am considering buying 17 more cells and removing all the ones that are below 5k. Please eveyone let me know what you think. I can get cells for about $25 each.

 

It's your money, but I originally decided that anything below 5000 mAh was going to be unacceptable to me. Ended up with my modules doing better than that but that was my cutoff point to avoid extra work in the future.

 

X2

Hard for us to spend your money for you, but to me time is money too so I would make the cutoff a reasonable amount and replace any that don't meet the criteria. On setting a capacity limit you need to look at the discharge figures not the charge side of things. Looks like most of your good ones aren't returning more than 4000-5000 mAh (in this range your good modules would be 1,2,3,11,13,27,28) and even at that only 1/4 of your old modules are in that range so you might look at a full set depending on what the "new" modules test out at. I have seen somepacks go back together with very low average capacity but you need to do a very good job pairing them to make it work. Also be sure to load test the ones that meet your capacity cutoff too before ordering new ones. I had a situation where my capacities were all good across the board, but load testing quickly revealed the bad one. After that make sure to capacity and load test the new ones to be sure they will match up fairly well with what you already have. Then when reassembling the pack use your load test results to try and create an even average response across the entire pack.

Example (voltage drops over time on load test):
0.22v, 0.25v, 0.24v, 0.23v, 0.23v, 0.24v (avg 0.235v)

On reassembly I would order them 0.25, 0.22, 0.24, 0.23, 0.23, 0.24 (now you can see each pair/block averages 0.235v)

You try and always have the weakest modules on the outside of the pack because that is where cooling is best, those closer to the inside will degrade faster thus it will tend to even out your capacities over time.

 

Sometimes it just takes more cycle to get desired results. Keep running cycles as long as you see improvement. If they stop improving then replace them.

 

Good information there Roy. You may find it beneficial to go to 7000 mah when charging, but at a much lower charge rate from 6000 mah up to 7000 to avoid overheating the modules. There are losses when charging so that charging to 6500 mah capacity requires more than this in input. The typical charging efficiency of Nimh batteries is only 66% so to get a 5000 mah charge in a cell or module will require about 7500 mah input.

John (Britprius)

 

Hi John - I had read the number of 66 % but it appears to me that the prius Gen 2 battery is a little different. I am in the process of testing a group of (78) Gen 2 used batteries to use in my gen 1 batteries. I used a charging rate of 6 amps and 2 amp discharge at the 1v per cell and found I am getting discharge numbers from 5500 to 650o ma with a charge of 7500ma after 3 cycles. These Gen2's are very strong and have a higher efficency then the Gen1's. I have a friend who rebuilds the prius gen1 and 2 batteries as a business and he discards any battery that does not get 80%. Typically he discards about one in three and will only now use Gen 2 modules as the failure rate in the Gen 1 is so great. What do you think is the reason for these test results. My friend and I have different chargers so I don't think the error is in the instruments.













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Roy I do not know what happened there, but my reply did not come out in the usual format.

John (Britprius)

 

A little more to add. If you charge at 6 amps a module that is fully charged it will rapidly overheat as you are putting into that module approximately 54 watts of heat energy. Imagine holding a 60 watt light bulb. Charging at 350 ma will input only 3.15 watts of heat energy. About half the heat of your car tail light.

John (Britprius)

 

Roy we all make mistakes. What counts is what we learn from them. Call me a geek or whatever, but it makes my day to learn something new.
I do appreciate where you are coming from with needing to keep cars on the road and do things as quickly as possible.
I bought up the idea of "bulk" charging the complete pack several years ago on PC, but there was no enthusiasm for that idea at the time. The downside to going that rout is there is no real method of getting information on individual modules.
The idea is good I believe to maintain the balance particularly of older batteries by charging them fully but gently. This I see you are doing. Keep the current down to or below 350 ma and the cooling fan on, but do not do this to often as you are putting full cycles on the battery.
Do not beat yourself up over these mistakes, and learn to duck when cooing pans come your way.
Your idea of having a spare battery is a good one that will allow more time to rebuild other batteries at your own pace. Keep an eye out for gen3 batteries as the modules are the same size as gen2 and in theory are superior. Gen3 batteries are to new to be failing in any numbers, but there must be many salvage batteries available.
PS. Grab some of them modules your friend is discarding and see if you can rejuvenate them. You could even try adding a little distilled water.

John (Britprius)

 

Thanks John -

On the subject of Bulk charging and looking at the battery modules. When I charge and discharge of the batteries in the car I use the minivic techstream to look at the state of charge as a percentage as well as the actual modules voltages in pairs (19). The connector on the 2001 to 2003 prius when used to charge or discharge the battery shows up in techstream as the process is ongoing. I take the SOC to 90 % and down to 20% and then finally leave it at a state of charge of 60% when I am done. I can also turn on the battery fan with techstream during this process and monitor the battery temperature in 4 spots.
The techstream software is a marvel to look at what is going on with the battery during charging/discharging or after you have installed a new battery under load.I picked off the bad module group under load in one of my batteries and was able to swap out the correct bad module.

Roy

 

Yes I to have Techstream and a very useful tool it is. A lot of people are not aware it works on any Toyota, Lexus, or Scion, but it also works on most other cars for engine diagnostics.
I do not think you are charging the battery high enough to balance the cells. A voltage check would confirm this at the end of the charge. It should be held at 342 volts for a battery with 38 modules to fully top them off but current limited to 350 ma.

I have to quit for tonight but I will be back online tomorrow.

John (Britprius)

 

I like the last part about 342 volts at 350ma ,will try that next.
cheers

Roy

 

The voltage used by the available grid chargers is 250 Volts DC for the gen2 battery with 168 cells (28 modules) this equates to 1.5 volts per cell. Your battery has 228 cells (38 modules). So 228 x 1.5 volts = 342 volts. You may have to increase the voltage steadily to keep the current down to the desired level, or use light bulbs to limit the current. Perhaps you could private message me with the method you are using if you are not comfortable with it in open forum due to safety concerns.
To balance charge your battery all the cells within the battery must reach full voltage. Some cells will reach this figure earlier than others so the charge has to be maintained "at a low current so as not to overheat the cells" for a period long enough for the cells with a lower level of charge to catch up.
I have two methods of charging. One using an old variac (variable voltage transformer) the second uses a 12 dc volt to 230v ac 300w inverter.

John (Britprius)

 

Hi John: My HV charger is made with a 120/140volt, 750 va variac with a voltage doubler circuit (capacitors) and a 50 amp diode bridge to convert to DC and two 50 amp/400v guiding diodes to stop the battery from feeding back into the charger. The charger puts out up to 500 v dc depending the load. I also built in a 575 v ac 30 amp contactor (120 volt control) with start/stop station I had around the garage to apply the voltage or discharge the battery. I can charge up to 2 amps at 350 volts dc but I charge at 1 to 1.5 amps. As the charge progresses I have to keep raising the charger voltage, if I leave it alone the charge current will back off to zero as the battery voltage rises. I discharge the battery at 2 amps with two 750 watt 240 v AC house electric heaters wired in series using the 30 amp contactor to apply the battery voltage to the heaters. I never leave the charge process unattended.

Cheers Roy

 

By the way john I am going to do my daughters prius battery in her car for the first time and will take note of the voltage at the end of my charge discharge cycle. I did not use voltage as a criteria as I was using techstream to view the cars state of charge and stopped at 90%, did not take note of the voltage at that point. I was not sure what would happen if I went to 100% SOC with the cars computer. I always discharge and recharge to 60 % SOC so the cars computer is happy at the end.

Roy

 

If you only charge to 90% only then only cells that have more than (about) 10% more charge than rest of the cells start to balance.

If you want battery to balance you need to charge it a bit more than 100%. You just need to use small enough current to stop cells that have already reached 100% from overheating.