Gen II Prius Individual Battery Module Replacement

I'm curious, isn't the point to overcharge the units to allow for the weaker cells to get caught up?

 

Guys, why don't you use temperature sensors with your RC chargers - they are geared for that and sensors are cheap - and you do not have to buy special one - it is just a component you can buy online from other suppliers.
Or just use standalone temperature sensors with a temperature display, and an output trigger to strat fan, busser or LED - like those used in standalone PC to control fans. Little bit more DIY but doable.
It is better way to control the charge with temperature sensors and you can be comfortable that you would not overcharge even with high current.
With my High Voltage Analyser I specifically recommend using temperature sensors for monitoring charge. Normally set for 30-35 Degrees Celcius in our Winter time when ambient is 19C.

 

Yes, you are overcharging it through capacity (ie 7000mAh vs 6500mAh rated) not charge current (in use the modules may see up to 100A for a short time but the battery is always between 40-80% state of charge so as you get near maximum SOC the current must be kept low, the lower the better with the only sacrifice being time to cycle them). The point of is to always keep the temp and internal pressure as low as possible throughout the charge cycle and prevent possible damage to the modules. So given all this I have found it best when using RC chargers to keep it around 2A maximum.

I actually agree with you on this and most of these quad charger do have an input and settings for hooking up a temp sensor for monitoring. I did my cycling during early spring up here when ambient temps outside were around 0C, I kept a fan on them and kept the charge current at 2A max so there wasn't much chance to generate any heat (used a FLIR infrared gun on them and they might have rose a few degrees but not much), but if someone was doing this in the summer down in the southern US in a garage without AC then heat could really be an issue. I think as long as people keep the current down and don't make the mistake of running the charge the module before discharging first, then most of the potential problems will likely be avoided. Getting a temp probe certainly wouldn't hurt though.

 

First post on a forum ever, but I have learned a lot from this thread and thought I would contribute. Rebuilding my pack for a second time. First time was a patch job just to get the car running again. It worked out fine for about a year. The replacement module matched close enough in capacity and voltage that I got away with it. Recently I was deployed for four months and had to let my car sit while I was gone. Disconnected the 12v battery and the service plug in the hope that the batteries would not self discharge too far while it sat. Came back hooked everything up and ran for a week but with unusual SOC readings from the MFD. Upon cold start the battery would show 5-6 blue bars, after engine warm up and about 5 min. of driving the bars would drop to 1-2 bars very quickly but recover to the usual 5-6 bars in about 5-6 min. Then after any regen (event the slightest amount) the bars would quickly jump to 7-8 green bars, the engine would run to dissipate extra charge and the bars would drop back to 5-6 blue bars. This all seemed very erratic and troubling as I had seen this behavior right before the "red triangle of death" the first time I fixed my battery. Pulling the pack confirmed that 2 more modules had bit the dust measuring 6.2-6.4v each. If anyone is compiling data they were modules #7 and #17. I ordered replacements and installed them but decided to rebalance and equalize all modules this time. I will post the spreadsheet numbers with results of the discharge and charge cycles when finished and update with overall results when I start driving again. I bought 4 Genuine Imax B6's from hobbyking and am in the middle of the rebalancing process right now. One lesson learned so far, I do not recommend setting the charge cutoff higher than 7500. On my second set of four modules I had the cut off set at 8000 and charge rate of 2.0A so it would not cut off before delta peak. This seems too high due to the minor swelling (still clamped in HV pack) that occured on my #11 module. The module has now unswelled (lack of a better term) and has the same resting volts as the other balanced packs. Not sure if I damaged the module or not but ordering a new one to avoid removing the HV pack again for a long while. One question though about the swelling, if it was swollen and is now not swollen, how is this possible given the theory some hold that the batteries do not vent? The temperature of the module only rose 4°F during charging as I am using a temp sensor monitor/cutoff due to unattended charging. I could understand expansion due to temp change but not for 4°F. I think they do vent, just very slowly. Anyhow I will keep updates posted here if anyone is interested, I know I have enjoyed reading all the posts.

 

Are you doing any load testing? Voltage does not tell you the battery's ability to hold under load.

 

Yes, i am going to load test after batteries are done balancing but before equalizing. I plan to use the headlight as used in an earlier post. When I am finished I will post all data for everyone to digest. Finished last night on odd number modules and started even numbers. Then I am going to go back and hit all the lower discharge capacity modules with two more discharge/charge cycles to see if they improve. Only four more days until I am finished. This is definitely not for someone who does not have another vehicle or a really good friend to carpool with for a week or more. Unless you don't mind spending more on chargers to get more modules at once. One thing I found interesting is that my module #11 that exhibited swelling was the one I replaced last year. I have also noticed a slight recovery after discharging to 6.0V. If allowed to recover the module stabilizes at about 6.3-6.5V. Discharging a second time down to 6.0V shows a discharge of an additional 500-900 mAh. Is this normal or something factored in by industry standards when determining module capacity? Or is it only the first discharge to 6.0V that industry standards consider as the module capacity?

 

When I did mine I found that really anything over 7000 mAh on the capacity cutoff didn't show much improvement over just running additional cycles and risked the swelling you experienced above. I completely destroyed one test module with overcharging myself and yes, it only ballooned out and never vented at all nor did it even feel warm to the touch. I have not seen heat to really be a problem as much as the modules just don't vent during outgassing except under extreme circumstances (http://hiwaay.net/~bzwilson/prius/pri_batt_400.jpg classic example of where modules were way overcharged but still didn't vent!) So best off keeping capacity cutoff down and just run more cycles to check for any improvement.

 

I agree that heat is not really a problem. I also agree that running a higher charge cutoff is seemingly fruitless. I have run some modules charging at 7000, 7250, and 7500 mAh cutoff. I have only noticed any swelling above 7250. It seems that these modules have a 7000-7250 mAh charging sweet spot. The change in discharge capacity by the third cycle was not significantly improved by running a higher cutoff. I agree with MTL_hihy that if higher discharge capacity is desired run additional cycles to avoid the risk of overcharging and swelling your modules. This requires patience and time though. Do it right once so you don't have to do it often.

 

Also does anyone know how they determine the modules actual rated capacity? Is it the first discharge down to 6v even though the module recovers to higher than 6v, or the sum of discharges to get it down to 6v resting voltage?

 

The hobby chargers repeatedly pause the discharge as they get down to 6v to determine when to stop. The accumulated milliamp-hour is then stored for each discharge cycle. The capacity is the reported milliamp-hour for the final discharge (before the final charge cycle). Note that this is a low rate discharge and the rated capacity would normally be measures at the rated capacity (6.5 amps) discharge rate which usually would result in a lower reading.

JeffD

 

X2

This was why I bought 2 quad (4-channel) RC chargers to speed up the process.........cycling them properly does take alot of time. Also like Jeff stated, the rated module capacity will almost certainly differ from what you register on the RC charger, but the good part is that this testing gives a relative capacity which allows you to match modules properly (key part of DIY battery pack rebuilding)

 

Hi I am looked for some guidance for my battery issue as well. I am in the process of balancing the cells. I am using 1 hitec x4 unit I am doing 3 dsch/chrg cycles with the discharge as high as i can get it usually around 1.1amp and am charging at 2amps I set the mah to 7250. Don't think I am missing anything else. I left the Delta V at default.
The cells voltage after a 2 minute drain with a 55 watt halogen light where as follows and some cycle results also my cycles aren't leading to anywhere near 7250 mah. Any suggestions would help. Are most of these cells so weak I guess they work but look like they will die soon. The 2006 Prius has 183k on it.
1. 7.47 2988/6762/4284/6550/4486/6666
2. 7.56 2901/5912/4000/6801/4403/6609
3. 7.48 3065/6207/4048/6609/4219/5799
4. 7.46 2408/5181/3408/5517/3512/5270
5. 7.37 1470/4533/2369/4383/2392/4310 / 2134/1228/1070/4407/2397/4059
6. 7.28 363/1824/942/2020/963/2079 / 702/2155/990/2180/986/2181
7. 5.89 <--Dead Cell
8. 7.36 1194/3204/1847/3401/1878/3603 /1606/3898/1879/3531/1861/4152
9. 7.33 883/3056/1508/2857/1503/2856
10. 7.36 1268/2911/1892/3400/1930/3450 / 1599/3728/1946/3357/1914/3673
11. 7.63 3397/7250/5023/7149/4987/7250
12. 7.28 559/2168/1098/2512/1124/2512
13. 7.37 1534/3944/2406/4065/4286
14. 7.30 807/2375/1363/2560/1384/2738
15. 7.29 609/2176/1164/2428/1184/2368
16. 7.35 1247/3155/1855/1013/903/3302
17. 7.31 1023/3103/1686/3398/1676/3300
18. 7.32 1474/3800/2154/3854/2159/3996 /1788/4023/2213/3776/2184/3653
19. 7.32 1475/3710/2224/4013/2281/3944
20. 7.32 1610/3597/2271/3694/2302/3839 /1827/4427/2364/3955/2325/3938
21. 7.31 1338/3314/1517/3107/1511/3108
22. 7.32 1169/2762/1766/3055/1830/3156
23. 7.34 1439/3353/2178/3793/2244/3748 /1887/4284/2284/4065/2268/3898
24. 7.42 1973/3845/2851/4441/3039/5186
25. 7.47 2492/5085/3429/5538/3552/5437
26. 7.50 2694/5270/3683/6669/3970/6477
27. 7.57 3295/6933/4384/7005/4556/7019
28. 7.53 3512/6609/4265/7050/4140/7250

 

Finished balancing the modules and equalized the voltages. Load tested with the headlight as described earlier. Timed for one minute each and none of the voltages dropped signifcantly so I did not include the spreadsheet for that. The rebalancing spreadsheet is attached. One module required seven discharge cycles. I did not expect to get anywhere near 6500 mAh from the modules but I was content with anything over 6000. I matched pairs of modules to try to get them all as close to equal as possible. It is all back together now and I have just over 100 miles on the rebuilt pack with no problems and averaging 51 mpg. One thing I did not do was discharge the modules down before reinstalling. I left them all at 7.8V and had no codes thrown. The MFD battery didn't even go into the green. I will post any updates if they seem relevant.

 

Great job loadmaster. Thanks for your service too.

 

Great update. Way to persevere! Good data collection. And now you will have a reference point for the future.

I know this is the second time in about a year that you had to do work on your hybrid battery.

How much time was involved in this process, hour-wise?
When you do it next time do you think it would take less time?

Looking forward to ongoing updates (every 6 months?) So we can follow along with your project's outcome.

 

Good job, this is exactly the sort of organization and attention to detail that makes for a very successful and rewarding rebuilding experience.

 

Did some tests with different gauge wire and attachment options to try to replicate your results on two extra modules I had ordered for my rebuild. It seems when I used 18 gauge or thinner wire with alligator clips on the output side the charger would get erroneous voltage readings and falsely trigger the Delta peak feature to stop charging the modules early (a quick search confirmed my results showing others with similar charging lead problems, both input and output leads). If you haven't already I would make better charging leads with thicker wire and ring terminals to hold them onto the module using the terminal nuts and use a wire brush if corrosion is present (make sure all bus bars are removed before wire brushing terminals though). Run 3 cycles with better leads and see what results you get eliminating poor connections as a culprit. Out of curiosity I am going to run 3 cycles on a known bad module and see how many mAh it will take before triggering delta peak if at all. I may break something, we shall see. Maybe someone else has a different idea though?

You're welcome, and thank you likewise.

From start to finish it took me approx. 10 days. I started mid wednesday one week and finished mid saturday the next. A long time but most of it was waiting on the cycles. Total hours I spent actively doing work on the project I would estimate at about 10 hours if you include research time.

When/if I do it next time I definitely think it will take less time. I know what tools I need and can have the HV battery out of the car in about 15 minutes. I will certainly get either four more chargers like I have or a 4 channel charger to cut my time at least in half. Things I did not factor in were time to run extra cycles on stubborn modules, or the fact that I was not always around/awake when a module finished it's cycles in order to move the leads and start the next module.

I will post an update every 6 months or so. Sooner if anything goes wrong of course but so far so good. Ordered a ScanGaugeII so I can keep a closer eye on things.

 

Thanks I used 14 gauge wire but I will replace the alligator clips with ring terminals. I was going to make a wiring harness with them to equalize the voltage but i will also use them for the charging.

 

True 14ga wire should be fine (thinner wire can be a problem as well) but I would definitely crimp on spade/ring terminals because there's not enough contact surface with alligator clips and you will get very inconsistent results using them for the rebuilding process.

 

We call "crocodile" and you call them "alligator" in US.
I looked at the specs of those I use with my HV Analyser and those are actually called "buldog" clips, rated 5A (for voltage detection lines) or 10A (to load/charger), made in Japan. No problems with those at all.