Gen II Prius Individual Battery Module Replacement

I just had my pack taken apart recently and noticed the 2 modules at the very ends of the pack were .1 volt lower than the rest. 7.6 volts for everything but the end 2 modules, they read 7.5 volts.

 

Yes, the 2 terminal bulbs are just high (65w) or low beam (55w), 3 terminal have both (55w + 65w) which is great if you want to load test the cells. Don't use the light to equalize the voltages, far better and easier to just build a harness to balance all the modules together.

Any chance you can get the Hitec X4 instead over there? Should be quite a bit cheaper than the H4.

Strongest modules should go to the middle of the pack and try to match them in blocks (pairs) to even out the capacities as best you can.

 

This is where I don't quite understand. There seems to be a contradiction. If strongest modules go to the middle then how can you account for matching capacities in pairs. In my case, matching in pairs will result in 1/28, 2/27... but the strongest modules (by capacity) which are 1,2,3,4...should go to the middle first and 28, 27, 26 ... will go to the outside. Here is my capacity again. Would you mind clarifying?
1 5941
2 5876
3 5852
4 5850
5 5818
6 5625
7 5591
8 5580
9 5512
10 5502
11 5468
12 5459
13 5458
14 5447
15 5440
16 5423
17 5422
18 5419
19 5398
20 5393
21 5373
22 5319
23 5298
24 5285
25 5282
26 5257
27 5210
28 5155

 

I would match pairs based on effective series resistance, not capacity. When you do the load test you will see a delta voltage drop. put together pairs so that all module pairs have the same total drop (sum the two module drops). That will minimize the deltaV that the Battery ECU sees under load (after you equalize the modules) and prolong the period without HV battery alarms.

JeffD

 

No because it will not be cycled above 80% or below 40% (theoretically anyway). Additionally the strong #1 will balance out the block (theoretically).

 

I agree with Jeff completely, but without seeing the load test voltage drops you would have to resort to capacity to sort modules. However I would strongly suggest it was beneficial to do the load test because you may have some with good capacity that are actually NG when load tested (this is precisely what happened to me). I also find it very interesting that instead of seeing capacity sag in the middle of your battery pack, it appears to be quite linear across the entire pack. Given this fact I would just reverse the order in the pack (#1 becomes #28, #2 becomes #27, etc) and then load test them all to make sure you don't have any bad ones (and voltage drops are close to one another). Over time heat should even the drops and capacities out so you have a closely matched pack at the end.

Here you can see what I mean (passenger side had a higher avg voltage drop than the driver's side):
Gen II Prius Individual Battery Module Replacement | Page 13 | PriusChat

 

But isn't a load test and a capacity test theoretically the same? Isn't testing capacity done by placing a known load on the module and monitoring to see how long it can feed that load?

 

In a Load test you also measure the voltage drop under load to determine the effective series impedance of the battery module. It is a short term terst whereas capacity is a long-term test. It is this series resistance that can contribute to module pair voltage differences under load (or when charging) and trigger an alarm. The other contributor is a difference in module pair voltages due to differences that develop over time (corrected by re-equalizing the modules)

JeffD

 

Thank you so much everyone. Great info!
I only have a 12.4v 55W bulb (not the high/low beam). Would you mind shedding some light for me on how long I should put each module under load in order to have meaningful data for delta voltage drop? Rationale with backed-up calculation would be greatly appreciated. I remember reading some info in this thread but for the life of me, I cannot find it now.

Also, should I connect all modules in parallel for half a day before doing the load test in order to have a good baseline voltage reading to compare the voltage drop with?

 

The delta voltage drop is instantaneous, but i would do the test more than once to see that the module voltage recovers when the load is removed. If you measure the load current, you can calculate the series resistance (~ 10 to 20 milliohms in a typical module) by dividing the delta voltage by the current.

The equalization step does not take more than a few minutes and is done after the load testing of each module just prior to reassembly.

JeffD

 

Think of a battery like a swimming pool hooked up to a fire hose. The capacity (mAh) is how much water you have in the pool and the load test is how much water flows from the nozzle over a given period of time. If the nozzle (series resistance) is out of spec (sort of like a clogged nozzle) , then you can't flow enough water to meet the demand (as measured by the size of the voltage drop under load). In the second case this is what the ECU is looking for and why it will set the "weak block" trouble codes. Also shows why just testing for capacity (as I did initially until Jeff explained my error) is really missing an important step in doing a reliable battery pack rebuild.

This isn't rocket science here, so if you have only around half the load I would simply double the time you have it loaded for in order to make any bad modules more obvious. I used 60 seconds with 120w so running them with 55w for 120 seconds should be enough to see any issues (start voltage minus end voltage equals voltage drop.........make sure to run the load for exactly the same amount of time each test, stopwatch is key). The modules should be reasonably balanced (similar starting voltages, doesn't need to be exact at all though because the differential is what you're interested in.......again re-read my link above and look at the photos of my load test setup) when starting. I balanced them overnight (be sure to include any replacement modules on this balancing process), then load tested in the morning, replaced any bad modules, then balanced again until lunch and then installed the pack for good.

 

After the modules are load rated, pairing to get the averaged as even as possible, how are they loaded into the housing? Is mod 2 and 3 a pair and 1 and 28 a pair and 4 and 5 a pair and so forth?

 

Thanks all of your guys put lots of valuable information here. I successfully replaced one faulty module and equalized 28 battery modules by using a custom wiring harness made of ring connectors that I saw here. I just returned from my first 15 mile test drive and everything was clean and flawless. I did not have any code came up by checking with my OBD2 scanner. However, there are two things that puzzled me.

1. Whenever I engage the power to the ready mode, I hear click-click-click from the ECU unit. Is it normal? I did not put any interior trim yet and I might suspect that I did not hear this because the ECU was covered with the seat and etc.

2. I cannot open the trunk. I used a manual release to open it. It seemed like all the wires and sockets connected correctly, but I cannot open the truck. No wire was broken or cut.

I am so happy that I change the battery without paying several thousand dollar to the dealer.
Thanks.

 

The clicks are normal, it's when you don't hear them you should worry.
No idea on the trunk.

 

KhaPhoRa,

Thanks for your reply. Now I do not need to worry about the click sound. For the trunk problem, I wiggled the trunk latch few times when I opened the trunk manually, it suddenly started to work. Maybe the latch was not in a proper position or so.

My Prius started to work perfectly fine and I couldn't be happier.

 

Zelium,

Are you saying that you did not put all of the batteries through 3 discharge>charge cycles before balancing the voltages? This would save me a lot of time and money buying the chargers. Are you still driving without any problems?

 

xtrmbkr,

No, I did not do those discharge/charge cycles. I just balanced the voltage by connecting all the + terminals and - terminals in parallel for 48 hrs. And after that I checked the voltage of all 28 batteries and the voltages I got were all equal. Then, I just put the battery back and it worked. I have driven it for 2 days and have not seen any problems (approx 80 miles so far).

I hope this helps.

 

I am still trying to figure out the pairing of modules. Counting from the left or the computer end with the first one # 1 how are the pairs installed? I thought maybe the bar with the sense wire would make a pair and #1 and #28 a pair, is this correct?

 

I really don't know but shouldn't it be 1 and 2 make a pair, 3 and 4 make a pair and so on up to 27 and 28????

 

You are correct, usnavystgc.