Gen II Prius Individual Battery Module Replacement

I took a shortcut and I am caught . I'll let the guilt build up while I replace the ebay modules into the pack. I want this car back ASAP: my backup vehicle only gets 12mpg!!

 

No worries. Your car. If you're okay with doing it again in the near future, so be it.

BTW, MERGED, .. you're also likely setting yourself up for imbalance at the outset.

If you're fully charging modules and letting them sit for days while you test other modules, self-discharge is likely going to create imbalance between old and freshly charged, particularly at 100% SoC where SD is the greatest..

Best to discharge all modules to a set voltage, say 6.6 and input a small amount at high current, say 1000mAh @ 20A . At that point, you know your modules are all at a lower SoC and the 1.5 hours it take you to charge all the modules with 1000mAh@20A. SD won't be a factor at all, and you'll have more than enough charge to start the car.

Good luck,

Steve

 

I read previous posts where people had individually discharged all of the modules to the same nominal voltage, then hooked up all the battery terminals in parallel and let it sit overnight prior to reinstalling in the car. I was planning to use that method to balance the modules..?

I've started running some cycles on the ebay packs now that they're in the battery assembly, and will probably hit a few more cycles on some of the other modules you pointed out.

Thank you for your feedback!

 

that method later proved to be a total waste of time! you will get much better results from Steves above recommendation

 

Skip the parallel. It's worthless.

 

Well, I thought I found the leaking module, but after reassembling the vehicle and trying the battery health test, I got the triangle again.

Once again I had a leak. This time, I left the cells in the case, grounded my Multimeter to the case, and attached the positive lead of the meter to each of the positive terminals to test for voltage. Bingo, found my culprit. Oddly enough, it was leaking from the negative end, so it wasn't from over torque on the bolt.

I believe that the battery health test caused the module to rupture. Evidently there was too much compression on that cell in the pack, so when I force charged the pack in the vehicle, the module swelled and popped.

This time when rebuilding the pack, I matched modules together that minimized the amount of bulging, and I didn't need the pipe clamps to reassemble the pack. It was tight though, and the modules were compressed a bit when I put in the 4 bolts that hold the pack together. A bit of compression is normal, correct?

I am hesitant to try the health test again for fear of popping another module. Thoughts?

 

Terminal leaks are due to 1) manufacturing defects, 2) nut over-torque, 3) blow-off valve failure.

The battery health test did not cause the module to rupture. For healthy modules, there should be little to no swelling at or below 80% SoC unless there are high temps and aggressive cycling. If a module failed during the health test, it was a bad module. Your conclusion is analogous to a right, front tire with visible tread separation on the inside where you can't see it. Then the next time you make a hard right turn, the tire blows. You would not conclude that the problem was making a right turn. The difference here is you can't see the defect, but it's there.

Pipe clamps? It took pipe clamps to assemble your pack before? That's a problem. The bolts are more than long enough to compensate for any normal swelling in a pack during assembly. I have never had more than about 1 module's worth of swelling across a pack, i.e., I'm able to place the end clamps, thread the bolts and then tighten to solid-height with the bolts alone.

Matching the modules on the basis of bulging is probably the least effective means of matching. Modules either bulge or they don't, and I can't imagine rearranging them could have much impact on the total assembled length as they contact on the stand-offs first, then the faces. You match modules in block for performance and longevity, not bulging. If you have bulging to the extent that you can't clamp up 28 modules with the bolts alone, you may have bigger issues.

I don't remember what you did in your recondition. Did you overcharge the crap out of the modules?

 

Agreed, I only meant the health test exploited something that was already going on with the module. I should have been more specific with my statement.

It wasn't matching per say, but for the last 5 or 6 modules in the pack, I weeded out any overly fat ones by putting them side by side until I found a good fit. They are all within 200mAh of one another.

The bolts are more than long enough. I had to use the clamps to get the bottom screw holes aligned with the case prior to installing the end cap in my first rebuild. I didn't have to use the clamps on the last rebuild.

I cycled each module 3 times, or until it achieved a discharge over 5k. Charged at 5A with delta peak enabled and capacity cutoff of 7.5k. I set the discharge 6.3V @ 2A.

 

Ah... you're doing it the hard way.

Disassembly:
Remove bus bars
Disconnect inlet air temp sensor from far end of pack.
Remove ECU bay (3 nuts and a few connectors)
Remove two nuts holding plastic clamps to base.
Stand pack on non-ECU end facing the bottom.
Remove all mounting screws from bottom of case
Remove bottom of case
Note installation and remove temp sensor harness.
Now you have all your modules clamped between the two plastic ends.
Flip clamped modules to other end (now sitting on ECU end)
Remove 4 bolts securing top clamp
Remove/rearrange/replace modules as you see fit.

Assembly:
Reverse of above EXCEPT
After you start and snug the clamping bolts, you need to lay the pack flat and ensure it does not rock when you put the final torque on the bolts. If you do it in the vertical position, the pack will twist.
When attaching the case bottom to the clamped pack with screws, don't just start at one end, start the extremes and work inwards in a random fashion. The idea is to get all of them started before screwing any of them down.

While the above sounds like a lot of work, it's MUCH faster than trying to futz about with trying to get a single module worked in, with much better results.

Can't see you did anything wrong with those charge/discharge numbers.

If the force charge results in another leaking module, it's going to leak at some point in the near future. Personally, I'd rather know now than later.

 

Man, that sounds MUCH easier. I hadn't thought of leaving the pack clamped together and just removing the bottom, and vice versa. Wish I had known this.

Thank you for all the helpful advice. It is very much appreciated.

 

Tested my two ebay modules and found capacity of only 2100mah on each, and didn't bother testing the 3rd. These replacements look more like my reject modules than good modules. Can't find any sellers that guarantee any type of capacity, they only list whatever surface level voltage they can measure with their $2 multimeter!!

 

I'm sorry to hear that. It's an all too common occurrence. I would encourage you to try the 3rd.

Thank you for following up.

 

I performed the test again, and this time all the bars filled on the battery, and the engine didn't come on until the end of the discharge. The only thing that I didn't follow precisely was temp. When I first got in the car it was 73, by the time I finished it was 66. 7 degree drop in roughly 20 minutes.

My test time was 7:28.

 

Sounds like it worked. You probably pulled a little less current towards the end of the test due to the lower temps. Assuming you lost a minute as a result, that's still 7.5* 9.5 = 71.25%. I'd drive it for awhile (month or so) and re-run the test when the temps are solidly above 70°F.

 

I'd be happy to sell you some capacity tested modules.
What is the cost for non-capacity tested modules?
What is a reasonable price for capacity tested modules?

 

^^^^^ This is the fellow you should be getting used modules from, NOT ebay.

 

Eric,

I sold my 27 tested/balanced modules for $30 each (they had 6.5 AH capacity measured at 0.1C so maybe 3-4 AH at 1C). That was a good deal for the buyers as unreliable sources were selling them for $25 to $40 on eBay at that time (about 3 years ago).

JeffD

 

So 3 years ago, $60 for 2 modules from a private party. How much for shipping/handling?
Or did that include shipping/handling?

 

Cheap! they are around $55 each plus postage via ebay AU

 

Eric,

I charged $10 S&H for the first one and $5 for each additional module in a multiple unit sale (Two fit in a medium prepaid Priority mail box). I dug into my archives and found that it was 5 years ago (how time flies). Here is the text that I had on eBay about these modules.

"I have 25 good Gen2 Prius battery modules left that came out of my 2004 Prius (the 28th had a bad cell and two were sold and used locally). Each of them has been rebalanced, charged and measures better than 6.5 amp hours of capacity after the re-balancing protocol which takes about 32 hours per module with the equipment that I purchased to do the job. I am selling each of these tested, good modules for $30 plus $10 S&H.

If you are rebuilding a 2001-2003 (Gen1) Prius battery, these modules are a great choice and can be made to fit, but you need 38 of them (don't mix Gen1 modules with Gen2 modules). If you are repairing a 2004 - 2009 (Gen2) Prius battery, these modules are as good as or better than the ones you have. In either case please be careful as when the bus bars are connected as the battery can kill.

Before you assemble your battery make sure to slowly discharge all of the modules to the same voltage before attaching the bus bars so that the battery ECU doesn't complain about mismatched module pairs. Of course, you should also re-balance your existing modules if you want a longer life out of your repaired battery.

Each module was charged to higher level than normal for a Prius as part of the re-balancing cycle. They have slowly self discharged somewhat with the first ones done at 7.7 volts after 6 weeks of storage, but the rate of self discharge is very slow (about 0.1 volts/month) which is a good sign of their condition. You will find them as advertised. If there is any problem with one of these modules, let me know and we will resolve it. I expect prompt payment via PayPal when you make the purchase and will ship as soon as I can get to the post office.

If you want multiple modules, Let me know and I will save you some shipping cost on the additional modules shipped at the same time.

Jeffrey N. Denenberg
Professor of Electrical Engineering

Update 1: 3 of these modules were sold and shipped today (19Aug2011) to an eBay buyer so there are 22 left.
Update 2: 6 more modules were sold and shipped today (20Oct2011) to an external buyer so there are 16 left
Update 3: 10 modules were sold and shipped to another eBay buyer (He left positive feedback!) today (20Oct2011) so I only have 6 left"

Note: I do NOT have any modules currently for sale (Two were sold directly to a PCer before the eBay sales and the last 6 were sold and shipped Dec 13,2011. The buyer of a block of 10 negotiated a $250 price plus $50 S&H). These were ones I removed from my original 2004 Prius HV battery at 195K miles. They were refurbished as described and sold in 6 blocks so that others could use them to fix their Prii. Two updates to the description would be required now that I know more about the rebuilding process. First, the capacity measurement at 0.1C id optimistic and should be redone at 1C (6.5 amps) which would result in a lower capacity measurement. Second, the advice should include a "Load Test" (check the voltage drop under a medium load (3C-5C or 20 to 30 amps) to weed out weak modules.

JeffD