Gen II Prius Individual Battery Module Replacement

Why only .7 amp? there is a reason or its because your charger can go higther?

 

It is a charger limitation. Most of these little RC chargers can only dissipate 5W which works out to about 0.7A. My charger (Supermate DC6) will not allow me to program more than 0.7A when discharging these batteries. (It will go higher for smaller cell counts/voltages.) That small discharge current is what makes the process so lengthy. The battery module under test could handle a much faster discharge. Even at 0.7A, I managed to burn out the current limitation in one of my chargers last week. (It shows "BREAK DOWN" which is apparently the message it gives when its thermal protection circuit is tripped.)

Presumably, the discharge current rate is one of the primary differences between the charger/balancers used by professionals and these RC chargers we are using. If I were designing a charger/balancer specifically for this purpose, I would try to use the discharge current to charge some other battery. For example, the discharge current could be used to charge the car battery if that is what is being used as the power supply (ensuring the car battery doesn't get overcharged). What would be very elegant is to design a multi-battery charger (e.g. configuration like the hitec quad chargers) that was timed to use the discharge from one battery to charge another battery. The big advantage of any of these schemes is that the charger would no longer be limited primarily by how much energy it could burn off (waste) during discharge via heat dissipation.

 

Your module voltages look good. You either have some connection problems in the battery unit (corrosion?) or have problems with your battery ECU. If its the ECU, I have one from my original 2004 battery that you could try.

JeffD

 

1st I want to say thank you all for your help. I'm new on Prius Chat but everyone is friendly and helpful. After disassembling the battery pack and cleaning each brass jumper by hand i was still at a loss. Each cell checked out great within .5v of each other. Nothing seemed wrong. So I looked at the 12V battery. It was the original battery from 2006. On a whim I took it out and had it checked out. It was low in cranking amps but wasn't horrible. I bought a new one just to be safe. Reinstalled the new 12V along with the hybrid battery with the cover off so when my information display was reading low I could check each cell. Drive about a mile till it was low pulled over and checked each cell (an interesting thing was I had a red triangle). Every cell was 7.5 +- .02V. So no problem there. After putting one service plug back in the battery I started it up and headed to home. Only thin time the red service triangle was gone and the bars weren't going to full fast. I decided to drive it on the freeway for a while. It charged up slowly and once it got to full didn't drop to 2 bars like it used to. Long story short all seems to be fixed and all it took was a new 12V battery. Here's my question. With all the techonalgy packed in that car Toyota couldn't have added a simple volt meter that would say "hey replace the 12V car battery or I will start to act up and give you all kinds of problems". What I take from this is I know have no reservations when it comes to working in the battery and will be rebuilding it down the road using gen 3 cells. I'm also curious as to how hard it is to add a second battery and what are the advantages?
Thanks everyone for your help.

 

That's crazy. I have never seen a weak 12V battery cause those symptoms but, I'm glad your problem is fixed. Good job!

 

There are no particular advantages to adding a second battery, except under very specific circumstances of terrain and typical trip length. Remember, this is a hybrid, which means that the overall efficiency of the car is not so dependent on battery size, but is just as much about aerodynamics, rolling resistance, weight, regeneration efficiency, and ICE efficiency. There are those that made plug in mods to their cars for mainly commute purposes (see the forums about that), but those batteries are generally much larger than the standard battery.

 

Offline and JeffD, thank you for all your very informative posts. I bought a 2003 Gen 1 with 2 bad modules diagnosed by Toyota and I have the battery out and verified the bad modules. I came across a second dead 2001 Gen 1 and got that as well for parts. I pulled that battery from the parts Gen 1 and it must have been sitting awhile because all the modules are discharged down to less than a volt. I bought this charger which has a power supply, I figure I only need one since I only need to charge up 2 modules: Thunder AC6 Smart LiPo Balance Charger/Discharger w/ AC Adapter for 1-6 Lipo/ 1-15 Nimh + USB to PC Software

This is different from the ones you two have and am wondering if it is okay? Also any recommendations on charging up the discharged cells?

Thanks

 

The gen1 modules are not as good as the gen2, and are pron to leaking.
The modules consist of 6 cells at a nominal voltage of 1.2 volts making a total of 7.2 volts for a module.
A module that is discharged down to less than 1 volt would mean each cell within "if evenly discharged" would have a voltage of around 0.15 volts and would most likely be scrap. There is no harm in trying to revive them, but I think you are on a looser.
Please try to keep to the terminology of a "module for 6 cells" and as single cell within a module as a "cell". This is to avoid confusion when talking about voltages of the various components that make up the HV battery.
Try charging modules at 5 amps for 1 hour then let them rest for a couple of hours. Check the voltage after standing using a headlamp bulb as a load. Possibly good modules will hold at leased 7.2 volts for a few minutes. Let them stand a further 24 hours and check to see if they hold the voltage.

John (Britprius)

 

Thanks for the quick reply John. While I wait for my charger to arrive I have a regular car battery charger. The options are 6V/10amps, 12V/10amps or 12V/2amps. Which would be best to try?

 

If you put two modules in series (making 14.2 volts) the 12 volt 10 amps should be fine. Most lead acid battery chargers put out about 14.4 to 14.6 volts on the higher settings, but limit the charge time to 30 or 40 minutes. Measure the voltage from the charger off load and let me know. You could monitor the charge current on the charger amp meter (if it has one) or with a DVM.
If you are charging the modules still mounted in the complete battery fine, but if they are removed you need to put them side by side with timber supports on either side in a vice or G clamps to stop them swelling. Do not try to charge them without side support as they will swell and burst.

John (Britprius)

 

On one 40 min charge I was able to get 2 modules in series up to 6.5V.

 

Is that 6.5 volts per module or 6.5 volts for two modules in series. If it was for two modules I do not hold out much hope, but for single modules under load they "may" be salvageable. Try another pair and monitor charging voltage and current if you can. If you can only monitor one parameter monitor charging current, and let me know.

John (Britprius)

 

It was 6.5 for each of the 2 modules. I will try another pair and monitor.

 

This time I charged it for and hour and 15 minutes and got 2 modules up to 6.9 and 7.0. The voltage while charging was about 14.5 and I measured 10 amps. The other 2 modules I charged the first time have discharged to 2.17 and 2.47.

 

Things are not looking good if the voltages are dropping that much. At a charge current of 10 amps all the cells within a module should be fully charged and the module voltage will over 7.2 volts. It may be worth continuing just in case there are some good modules. The only thing you have to loose is time spent.

John (Britprius)

 

So I am looking for modules that will charge to over 7.2V with how much time charging? And then within a day discharge to what level?

Thanks.

 

Each cell within the module has a capacity of around 6.5 amp hours (AH) at 1.2 volts nominal. Slightly higher voltage when fully charged and down to about 1 volt when fully discharged.
This adds up "because the cells are in series" to 7.2 volts or as high as about 9 volts fully charged for a module at 6.5 AH.
A charge current of 10 amps for 1 hour ignoring any losses would be 10 AH. The cells would not absorb more than 6.5 AH so the last 3.5 AH would be given off as heat this should be avoided as much as possible. That would be the last 21 minutes of charge at 10 amps.

Actual charging time should be 39 minutes at 10 amps (39mins divided by 60 minutes x 10 amps = 6.5 AH). The charging time would be slightly longer than this because of losses say 10%.
The voltage will fall after charging over 24 hours, perhaps as much as 1 volt per module from around 9 volts + to
8 volts +, but should then gradually slowly fall over a period of many months.

I hope this helps explain the basics of charging the modules. Over charging the module slightly, and slowly is ok, as this helps to balance the charge levels of all the cells within a module. Over time some cells become more discharged than others, and over charging allows these cells to catch up as the other full cells give off the excess charge as heat.

This is the reason we overcharge the modules then discharge them 3 or more times checking each time the discharge capacity of the modules to show any improvement in capacity. The capacity of a module cannot be more than the lowest capacity cell within that module, and the lowest capacity cell is also the capacity of the complete HV battery.

John (Britprius)

 

Thank for taking the time to explain this John. I will continue to try to find good modules and in the meantime I have ordered a couple in case I cannot find any. My strategy is to get one of the cars going then sell it and replace the other with a Gen 2 pack.

 

Good luck with your plan. Do things methodically, and take plenty of notes. You will make mistakes as we all do, but learn by them, and you will win in the end. Above all work safely with the obvious shock and fire risk from short circuits.

John (Britprius)

 

I got one of them running by replacing 2 bad modules. I am getting a P3030 code. I think I might have damaged one of the sensors when I took everything apart and put it all back together. Especially since I took the bus bars out and cleaned them up. Also do you know where this goes?