Highest recommended voltage drop range to pair up modules?

Wow, that graphic looks amazing... Not sure what to make of it... Looks healthy... But I'm only familiar with one bulb, not four bulbs for load testing.

As for your error code, you need the subcode too... Dr. Prius app does that. Here's buyer's guide: Hybrid battery diagnostic and repair tool for Toyota and Lexus

Once we know the subcodes we'll be able to tell you next steps to fix... Looks like something minor, or at least that's the first impression.

 

I would use your car to gather some data. Use an app like Dr Prius or Hybrid Advisor to log HV battery voltages while performing accelerations; both heavy and light, and at low as well as high states of charge. Look at what you get and see what stands out.

Personally I didn't try to build my pack based on load test results but instead I used measured capacity. I load tested to determine if a module was bad. Also any modules that wouldn't "recondition" to above 5500 mAh were replaced. Then I matched capacity results to average out the blocks.

I think you will find that your "high voltage drop" modules have less capacity and are dropping more at higher load and at low state charge- and not in a linear fashion. I don't know what the"best" method is to DIY test your modules to prevent problems.

It is tougher for Gen3 owners as I understand that the limits programmed into the ecu are tighter than Gen2.

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Had a pack like this a year ago and just kept driving it in hopes of getting more info each time the warning lights came on... Was very strange. I'd have days where I'd clear warning lights 3 or 4 times and then I'd go weeks with none. Made no sense. Then I went on a long road trip for christmas a year ago and before I left I pulled the pack and put in a more reliable one. A year later after that pack was ignored as low priority on the shelf all that sitting time made the bad modules much easier to find and am ready to put that rebuilt pack back in my car for testing next week.

 

I dug up my notes from my rebuild a few months ago. I tested each module with a 20A load for 2 minutes. Almost all were within 100mV (0.1V) of each other. One was 110mV, but any module with a difference above that was replaced (two did hit about 240mV).

In daily use, the voltage difference varies from 130mV to 270mV. I've got one block that's always a bit high and another that's always low, so state of charge isn't perfectly balanced. It appears to be stable so it doesn't bother me enough to open it back up.

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I got the car because it had a shorted cell in one module- hence the rebuild. Initially the at rest voltages were fairly even but the capacities were all over the place. The load test results were after performing multiple reconditioning cycles- from 3 to 6 cycles. Took just over a month of weekends and evenings using several hobby chargers and a discharger. In all I replaced 4 modules.

Like I said, I paired up modules to average out the measured capacity. Seems to have worked decently.
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NOTE: as many people know, Block #1 is the furthest from the CPU and Block #14 is closest to the CPU. If you look at the wiring, notice the module furthest from the CPU is paired with the module closest to the CPU. Block #2 consists of the modules 2 and 3 (furthest from the CPU and so on). So when you pair the modules in your spreadsheet you should take this into account.

In your spreadsheet, module #1 and module #28 are paired together as Block #1 in the pack. Both happen to have low voltage drops, so they are not paired properly for balancing.

I am not an expert. However, my impression is the Prius module is rated at 6.5 amps. So load testing at 10 amps or 20 amps seems excessive to me and could harm the battery. I have about 4 months of experience learning and testing Prius batteries using the Sky RC iMax B6AC v2 chargers (I have two of them). Usually the modules do not get warm using the Sky RC iMax B6AC v2 charger. This charger can charge at a rate of about 5.2 amps and discharge at a rate of 0.6 to 0.8 amps. When discharging, I also connect one headlamp, which I "think" produces a total load of about 5 amps. I know this because when I charge the battery at 5.2 amps, it charges in 3 minutes, which is how long I discharge the batteries. Note: the SkyRC iMax charger does allow you to specify a Delta Voltage Drop value, however this charger charges for 29 seconds, and then stops for one second to capture the voltage and resistance. I suspect it is not looking for Delta Voltage Drop each second, so it cannot detect when the NiMH battery is fully charged. Also, it does not allow you to specify a max voltage when charging. Other than that, this is a good charger for individual modules.

I have two weak batteries. If I charge them up to 8.15 volts, when I apply a 5 amp load, it drops down to 7.70 volts in one second. My other batteries will drop from 8.25 volts down to 7.70 volts in about 2 to 3 minutes. The two batteries that drop so quickly do have 3 minutes of capacity between 7.70 volts down to 6.5 volts, but they are in a weaker voltage range. But since their useful voltage range is lower than the other modules, this causes a problem. The capacity range should be taken into account when pairing the batteries for the blocks (I just had this aha moment).

 

I’m having problems with my hybrid battery and trying to learn how to test and
replace the bad modules. I think I need to pair similar capacity and voltage modules together to make a good block so it won’t trigger the P0A80 code again. I believe the weaker modules don’t hold the charge well, the voltage drops under load and then the battery also heats up. I was looking at a few chargers, but will get the SkyRC B6AC v2 since it worked well for you.
Thank you for your very helpful notes.
I plan to begin this project during the holidays when I’ll have more time.

 

Oops! I was mistaken. After reviewing my HV battery, modules 1&2 are paired together, 3&4, and so on.

 

I have read that the module order for Prius Gen 1 is reversed compared to Gen 2. For Prius Gen 1, module 1 is closest to the CPU and for Gen 2, module 28 is closest to the CPU. I was mistaken about the pairing. Modules 1&2 are paired together (as block 1), 3&4 are paired together (as block 2) and so on.

 

I need to update my comment above, however I do not see how to edit it, so I am reposting.

For Prius Gen 2, Block #1 is the furthest from the CPU and Block #14 is closest to the CPU. I hear that for Gen 1, the block order is reversed. I do not know the order for Gen 3.

My impression is the Prius module is rated at 6.5 amps. So load testing at 10 amps or 20 amps seems excessive to me and could harm the battery. I have about 4 months of experience learning and testing Prius batteries using the Sky RC iMax B6AC v2 chargers (I have two of them). Usually the modules do not get warm using the Sky RC iMax B6AC v2 charger. This charger can charge at a rate of about 5.2 amps and discharge at a rate of 0.6 to 0.8 amps. When discharging, I also connect one headlamp, which I "think" produces a total load of about 5 amps. I know this because when I charge the battery at 5.2 amps, it charges in 3 minutes, which is how long I discharge the batteries. Note: the SkyRC iMax charger does allow you to specify a Delta Voltage Drop value, however this charger charges for 28 seconds, and then stops for two seconds to capture the voltage and resistance. I suspect it is not looking for Delta Voltage Drop each second, so it cannot detect when the NiMH battery is fully charged. Also, it does not allow you to specify a max voltage when charging. Other than that, this is a good charger for individual modules.

When rejuvenating batteries, I no longer let a battery voltage drop below 6 volts. I have tried discharging them down to 2.4 volts, however I think this does more harm than good. For batteries with a low capacity, to revive them, I will charge the batteries @ 5 amps up to 8.0 volts. I will then charge them for 20 minutes @ 1.0 amps until it reaches about 8.58 to 8.66 volts. It is likely the Delta Voltage Drop occurs around 8.6 or 8.7 volts, which may prevent them from being charged any higher. This seems to increase their capacity. For bad batteries, I may do this once every 4 months or so.

To test the batteries, I charge them up to about 8.15 volts, and then use the Sky RC charger to discharge them at 1.0 amps (the most it can actually discharge), and also connect a headlamp (which is about 5 amps). I use this combination as I like using the timer on the charger. I will then discharge each battery (one by one) for 2-3 minutes. After the discharge, within one second, I will note the voltage which immediately starts to increase on its own. After testing all the modules, I will then calculate the voltage drop, enter this in a spreadsheet, sort by voltage drop, and pair the battery with the lowest voltage drop with the battery with the highest voltage drop, and so on until all batteries are paired. This is how I attempt to balance a pack.

Keep in mind some batteries have high resistance which reduces the voltage drop, so the voltage drop will be less, giving you the false impression they are good. These batteries are not releasing energy fast enough and you may wish to remove them from the pack.

 

Ummm.. Volts = Current * Resistance
High resistance at same current means high voltage, not low.

 

Block 1 in all Toyota/Lexus hybrids is at the negative terminal. In Gen 2 Prius the negative is the furthest away from the battery CPU and therefore block 1.

 

Does anyone check voltage rebound after the load test?

 

I have roughly observed that the voltage of the module rebounded after the load test. I discharged it with about 8A and charged the module to 8.5v. When the charging was stopped, the voltage would slowly fall back to about 8.1v. After discharging to 7v or 6.95v, the voltage will slowly rise, and finally it will stabilize around 7.5v. There will be a little difference between different modules. I found that the voltage rise of the module with a larger capacity seems to be smaller, probably above 7.35v, and the capacity is small. The rebound is more, basically above 7.48v. If the discharge time to 7V is less than 15 minutes, that module will be eliminated, because the capacity is already less than 2Ah, and the fault light may be lit again soon.
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UPDATE: Note: this information above is incorrect.

For Prius Gen 2, Block #14 is next to the CPU and Block #1 is furthest from the CPU. Also, after further examination, module 1 is not paired with module 28. It is simple... module 1 is paired with module 2 (block 1), module 3 is paired with module 4 (block 2) and so on. Module 27 is paired with module 28 (block 14).

 

The max load on the whole pack is about 100 amps. This value divided by 28 modules is about 4 amps. So applying a load of 20 amps seems way too strong, and the modules may perform differently than if a 4 amp load is applied.

One headlamp is 3.5 amps and an IKEA 12 V 20 W halogen is 1.5 amps. I used these in parallel with a load test, which provided a little less than 5 amps. A 3.5 amp load may be a normal load.

I suggest charging the batteries up to 8.25 volts and let them drift down to 8.10 volts. Then do a load test with 3.5 - 5 amps for 2 minutes. This should give you a good idea of which batteries are stronger. I suggest testing this higher range because I noticed my modules many times are charged up to 8.59 volts, which is where the Delta V drops, preventing the battery from being charged higher than this.

Replacing the modules that have more of a voltage drop seems like a good strategy to weed out the bad modules.

 

Incorrect, if the pack is drawing 20 amps, EVERY module, in a series connected pack, is being loaded to 20 amps.

Your math is correct for a PARALLEL connected pack, in which case, the LOAD is SPLIT between all the ,modules
But then you would a have a massive 182 amp hour 7.2 volt battery suitable for powering, i dont know, something that wants 7.2 volts at 182 amps for an hour, or a flashlight for several weeks months.