Gen II Prius Individual Battery Module Replacement

I picked up those Hitec X4 chargers a few days ago and a car battery. I connected the 12v@ 6amp trickle charger to the car battery with the Hitec chargers.

1st mistake:
The first set up I selected was completely incorrect. I have never used chargers like these before and even though I read the manual I still screwed up the first over night charge. I accidently set the modules to drain to .6V instead of 6V. I check the next day and the log says that was what happened. Hopefully that drain does not kill those 8 modules...

Anyways I set up my new setting which I think are a bit more correct.

5 amp Charge
.7 amp Discharge to 6V
6750 mAhr
dsch<chg 3 cycles

So It discharges that module until it hits 6 volts. Then there is a 5 min cool down period before it charges it at 5 amps from 0 to 6750mAhr. Then it repeats the process two more times. (three times total)

2nd mistake:
So after getting the correct settings I let it run overnight and checked on it in the morning. When I looked at it all of the chargers were displaying the "low input Voltage" error. Apparently the car battery/trickle charger was not enough to power all 8 chargers at once. It managed to get through 2 cycles and stopped during the discharge phase.

I went ahead an grabbed a 450watt ATX computer power source that was in my office. I cut off the heads, combined the black wires for the ground and the only only green wire to turn in on. I combined all the yellow wires together for the 12v power source. The power source is suppose to deliver 24 amps at 12 volts.

And that is the set up I have going right now. Eight of the battery modules are finished so far. The car battery is powering one of the Hitec X4 chargers and my ghetto rigged computer power source is juicing the other.

I figured I would upload some pictures of the progress.

My latest set up with the computer power source.




This was the original set up with a single car battery and two multichargers


The trickle charger to the battery.


The was how I managed to get the modules to go back in correctly. That was a pain.




A view of the temperature sensors below the battery modules.


I believe this was one of the original modules that went bad.

 

Here is what I have collected so far. One thing to remember is my power source died during one of the 8 charging times so you will see an a 4th set of charge discharge data. That is where I set up a single discharge/charge. If there is a **** that means the discharge cycle was not written down.

LET THERE BE DATA!!!

Battery Module #1
Discharge: 3921mAh | 5706mAh | 4226mAh | ****mAh
Charge: 6750mAh | 6750mAh | 0000mAh | 6750mAh

Battery Module #2
Discharge: 4710mAh | 5619mAh | 5723mAh
Charge: 6750mAh | 6750mAh | 6750mAh

Battery Module #3
Discharge: 2190mAh | 5737mAh | 5208mAh | ****mAh
Charge: 6750mAh | 6750mAh | 0000mAh | 6750mAh

Battery Module #4
Discharge: 4180mAh | 5314mAh | 5433mAh
Charge: 6750mAh | 6751mAh | 6750mAh

Battery Module #5
Discharge: 1949mAh | 5655mAh | 5554mAh | ****mAh
Charge: 6750mAh | 6750mAh | 0000mAh | 6750mAh

Battery Module #6
Discharge: 2453mAh | 3002mAh | 4072mAh
Charge: 5056mAh | 6287mAh | 6641mAh

Battery Module #7
Discharge: 1758mAh | 5681mAh | 5756mAh | 2920mAh
Charge: 6750mAh | 6750mAh | 0007mAh | 6750mAh

Battery Module #8: Cycles are Pending

Battery Module #9
Discharge: 2983mAh | 4262mAh | 5096mAh
Charge: 6028mAh | 6750mAh | 6750mAh

Battery Module #10 -- #19: Cycles are Pending

Battery Module #20
Discharge: 4075mAh | 5164mAh | 5255mAh
Charge: 6751mAh | 6751mAh | 6750mAh

Battery Module #21

Discharge: 4647mAh | 5472mAh | 5585mAh
Charge: 6750mAh | 6750mAh | 6750mAh

Battery Module #22

Discharge: 0680mAh | 5616mAh | 5637mAh | ****mAh
Charge: 6750mAh | 6750mAh | 6446mAh | 6750mAh

Battery Module #23

Discharge: 3392mAh | 4536mAh | 5052mAh
Charge: 6274mAh | 6750mAh | 6750mAh

Battery Module #24

Discharge: 1178mAh | 5567mAh | 5534mAh | ****mAh
Charge: 6750mAh | 6750mAh | 1527mAh | 6750mAh

Battery Module #25

Discharge: 4658mAh | 5241mAh | 5622mAh
Charge: 6274mAh | 6750mAh | 6751mAh

Battery Module #26

Discharge: 1321mAh | 5761mAh | 5777mAh | ****mAh
Charge: 6750mAh | 6750mAh | 1019mAh | 6750mAh

Battery Module #27

Discharge: 2343mAh | 3496mAh | 4182mAh
Charge: 5046mAh | 6267mAh | 6750mAh

Battery Module #28

Discharge: 1401mAh | 5786mAh | 5795mAh | ****mAh
Charge: 6750mAh | 6750mAh | 1501mAh | 6751mAh

Whew! At least there is only 28 batteries!

 

Yup. I ran into the same issue. I have actually been monitoring my Hitec X4 chargers once every 4 to 8 hours or so. I have been switching the trickle charger from 12 volts @ 2amps to 12 volts @ 6amps and back again. I use my multimeter to check the voltage of the battery. If I see it starting to spike close to 15 volts, I knock the trickle charger down to 2 amps. If it starts to drop below 12 volts I kick it back up to 6 amps.

The other Hitec X4 charger is being powered the computer power source I customized so its a constant 12 volts (as long as my power does not go out.)

 

I agree but not exactly sure yet. I think one of the prius gurus will pop in some time today for the assist.

 

I decided to use 6750mAh because I saw it on another thread somewhere on prius chat. I have also seen the limit set to 7500 mAh. I figured as long as it was above 6500 mAh it would be ok.

Does this mean I need to start the 3 cycle process all over again with all of the battery modules at 7250 mAh? Or should I just do another 3 cycle process to modules #6 and #27? Or just a one cycle discharge to charge?

 

I finally got to the point where I can attach the batteries in parallel. Thank you for the sugesstion. Took almost 2 hours to set up the wiring. Right now it is sitting in the garage equalizing out.

Another update with photos:

The crazy wiring you see below is the custom harness I created
to connect the modules in parallel. All the positive terminals connect to the positive
and the negative to the negative. It is just speaker cable I found in my garage.






This is the paper where I recorded all my data from the Hitec x4 chargers.




More info in a bit...

 

Sorry for the delay everyone. After I got it back together I drove it 120 miles with a mix of highway and stop and go traffic. Before I had balanced the battery pack I was only able to make it about 16 miles before the triangle would show and battery vent fan would kick on. Proper battery balancing is must.

I just got back from taking it for a 3000 mile test drive after putting it back together. Yes, you read correctly. 3000 miles. I drove from Cocoa Beach, FL to Atlanta to Washington DC, to Maryland and back. (Rock climbing trip) I am happy to report that there have been no problems! The trip averaged about 48 mpg.

That funky code I was throwing U0100 and U01111 was from plugging in the OBD II scanner while the car was running. It would trip the code as soon as I plugged it in. (You must plug it in while the car is off THEN run the scanner)

I will work on putting together a simple step by step process of exactly how to do this. In the meantime here is a quick overview:

Tools:

• Two Hitec X4 Multi battery chargers example: TowerHobbies.com |Hitec X4 Quad DC Multi-Charger(130.00 a piece)---OR---Two Thunder T6 Multi-liPo Battery chargers $85.00 a piece Thunder T6 Multi-LiPo Battery Charger (4X 6-Cell) Professional Balance Charger/DisCharger w/ LCD Display---OR---8 supermate DC6 DC multi-function balance chargers ($30 a piece) Dynam Supermate DC6 DC Multi Function Balance Charger/Discharger 1-6 cell Lilo/LiPo/LiFe, 1 to 15 cells NiCd NiMH.
• linemens gloves
• A basic volt meter

• Metric sockets
• Common Sense (This will help prevent you from electrocuting yourself)
• Electrical Tape
• 10 feet of stereo wire

NOTE: Make a post on Facebook to see if any of your friends have these battery chargers. I bought mine only to find out a few friends already owned what I needed. These battery chargers are commonly used to power R/C cars, planes, and helicopters.

Basically you will need to disassemble the back of your prius in order to get to the battery pack so you can remove it.
There are quite a few videos out on how to safely remove the battery pack. From there you disassemble the battery pack itself by removing the top casing and both bus bars that are under the plastic covers. Use extreme caution when doing this. The batteries are wired up in series.

Label your battery modules with a permanent marker. 1 through 28. You use the voltmeter to test the voltage of each individual cell. Record your results on a sheet of paper or excel spread sheet. All of them should be within .05 volts. The modules with abnormally low voltage are usually the cause. In my case I had two modules go bad. It is a good idea to load test the battery as well. I used a 55 watt halogen bulb with some alligator clips. If you are unsure which modules are bad, post your results here on priuschat. The forum is very helpful.

Once you determine your bad modules
It helps to mark the culprit module with an "X" or something to help you remember what to replace.You must replace them. You can order used replacement modules from ebay. They are generally $30 to $50 a piece. You will have to remove the battery modules one by one until you get to the bad battery. Each module is held in by one screw at the bottom of the case.

Balancing the battery pack:
IMPORTANT NOTE: Leave battery modules compressed in the case when charging. Otherwise they will swell.
It takes about 1.5 days to balance a single battery module. So 8 NiMh balancers will allow you to balance all 28 of your batteries in about 6 days. I figured 8 chargers was a good time to cost ratio. If you have 14 charger it will take only 3 days. If you have 1 charger it will take 42 days. (1 charger not recommended)
Because your battery pack is wired in series each module should have almost an identical voltage and charge. This is where your expensive chargers come in handy. You will need to discharge then charge each individual module three times. Set to NiMH.

Settings:
Charge at 5 amps up to 7250mAhr
Discharge at .7 aMhr down to 6 volts
DSCH<CHG for 3 cycles.
Other settings: I set the timer limit to 720 minute cut off. I also set the cool down period to 5 minutes.

As you balance your modules, record the 3 cycles of data the your chargers have given you. If you notice one of the batteries is not charging to full capacity, run another cycle. If it still is not charging to full capacity you may need to order another module from ebay. After all your modules have been balanced by your chargers, check and record the voltage of each one. They all should be within .05 volts of each other.

Final balancing:
This is where it is a little tricky and time consuming. You need to create a wiring harness to connect all your modules together in parallel. This means all of the positive terminals are wired together and all the negatives terminals are wired together. Positive to positive, negative to negative. DO NOT TOUCH THE POSITIVE TO THE NEGATIVE!!! You are basically creating one large 7.2 volt battery. Doing this will equalize the voltage difference between the batteries. Leave it like this for about 6 to 24 hours. It took about 6 hours for my batteries voltage to equalize.

Do a final voltage check to all your battery modules. At this point they should be identical with a .01 to 02 volt difference. Remove your custom harness you made and reassemble your battery casing. Installation is reverse of removal. Before putting all of your interior pieces back together take your Prius for a test drive.


I literally put my prius back together the day I left for my epic road trip and it has been working ever since. Thank you everyone here for all your help!!!

 

Haha you are welcome! Just be careful and use common sense. If you have problems/questions create a post. I am working on a detailed write up so hopefully it will be up before you get started.