Testing and charging individual cells?

This is what I've found:
Prius Battery Photos

GOOD LUCK!
Bob Wilson

 

The basic chemistry of nickel metal hydride fixes all the basic answers for you. An individual NiMH cell has a nominal voltage of 1.2 volts. It can be a bit higher, 1.3 or so maybe, right after a full charge, and it's considered totally discharged if the voltage is down around 0.9 or 1 volt. There's a Wikipedia article on NiMH that explains the subtleties more, including why safely charging a NiMH cell is trickier than just watching voltage.

The reason these numbers don't match what you were seeing is that the rectangular plastic Prius part you keep calling an "individual cell" is really a "module" built with six individual cells connected in series inside. So you just multiply the individual cell voltages by six. A normal module is around 7.2 volts nominally, can be up around 8 or a bit more right after a full charge, and had better not get below about 5.5 or 6 volts, which is the point where it's officially totally discharged. One with a reading lower than that (like the 3.2 that you saw) is possibly beyond hope.

What you'll see in the many, many threads in this forum on this subject is people tending to invest in NiMH-specific smart chargers with a readout for the amount of charge put into or supplied by the module.
6.5 amp-hours was the as-new specification. You won't see that with dozen-year-old modules, but you'd want a capacity of at least a few amp hours. You might find the deadest one to have a capacity of pretty nearly zilch.

Hope this helps,
-Chap

 

Tail light, stop watch, and volt-ohm meter. If possible a second amp meter.

Bob Wilson

 

Yes if you charge module (or even whole battery) for long enough every cell will be charged to 100% in correct way. Just use small enough current since cells will be overcharged so they will use the extra charge by heat.

Cells that where charged opposite may be impossible to get working again so you should test those (modules) were good.

You can just test one module with 12V light.

You can test your modules against each other. You will then find your best and others should be close to that.

 

This is an example:

The safest approach is to get a computer controlled, RC battery charger. This one has a temperature probe, upper and lower voltage limits, and current control. It also handles charge/discharge cycles and records the capacity. These mean it can handle NiMH charge/discharge cycles without risk.

This is what can happen if a manual process is used and someone gets distracted:

The cells overcharged and bulged out fracturing the compression rods.

I am trying to discourage use of a 12V, lead-acid battery charger because:

• large lead-acid batteries can boil off electrolyte instead of generating gas and rupturing the case
• lack NiMH battery limiting circuits to prevent over charging, heating, and rupturing the case
• have no battery capacity measurement record

Of course it is your charger, batteries, and work area. Now to answer your questions:

For a brief instant in time as the charger will force the voltage but put any load on it and the voltage will drop like a rock. There will be no useful energy storage.

No, do one module at a time. The 12V light is a safe, load resistor that won't burn your fingers or melt anything it comes in contact. You can achieve the same result with a high-power, resistor but the heat is more concentrated. Still, Radio Shack carries them and you can find one to use. Be sure and use Ohms law and the rated power rating to keep the resistor from burning up.

Manually:

• Use a volt meter to monitor discharge voltage and stop when it reaches 5.9V.
• Use a current meter to measure the amps.
• Use a stop watch to measure the time.
• Calculate the Amp*Hour capacity of discharge.
• Avoid distractions and do not fall asleep.

Automatically, buy a computer controlled, RC battery charger designed to handle NiMH batteries. Key features:

• Voltage high and low limits
• Current range
• NiMH dV/dt stop charge detector
  
• Charge limits to avoid overcharge
• Temperature probe to stop if overcharging
• Recorded Ahr capacity on discharge
• Recorded Ahr capacity on charge, optional

Semi-automated:

• Use 12V charger as raw power supply
• Connect a +16-20V, electrolytic cap to filter the power supply
• Use two, adjustable voltage regulators, one for charge limit of 8.0-8.2V and the other as current limiter.
• Use two, adjustable voltage regulators, one for discharge limit of 5.8-5.9V and the other for constant current.
• Use a Darlington transistor to operate a single pole, double throw relay to power an AC clock to measure duration.

Bob Wilson

 

That's the approach I'd use if I still own my PiP when the battery fails. I'm assuming the bell-curve applies to the failure rates of individual cells, therefore, initially it might be 1 or 2 bad cells, then 4 or 6, which I hope to replace with salvaged cells from a discarded battery. This should work for a few years, then eventually the whole battery will have to be replaced. That seems to be the most economical approach.

 

"RC battery charger NiMH" turns up a bunch. I found at least 4-6 acceptable chargers on eBay ranging from $17-$50. Read the manuals and pick one that 'makes sense' to you.

In my case, an MRC 989 worked perfectly. However, other have been used and threads posted with their results.

I would recommend searching this forum for threads about rebuilding traction batteries. You'll find a lot of useful tips and experience.

In 2009, I upgraded our 2003 Prius traction battery, it had not failed, with a rebuilt using modern traction battery modules. It cost less than $1,800 and gave me confidence the better built, later modules would be worry free. That has turned out to be the case. I didn't have a failed battery or even weak but I wanted to get a good, professionally rebuilt battery and could afford it.

Bob Wilson

 

Hi everyone, after reading this post it got me wondering about my battery. I pulled out the HV battery to replace 2 modules and then tested every module which the lowest one at that point was 7.54V and everything else above 7.6V. I tested the full circuit by initiating the safety switch and read 213V. My car still gives me problems with the battery drain but would like to ask if the voltages seem right to you all? What should I expect to be a bad voltage?

If you could also please help guide me to a forum that explains why the hybrid battery drains when Im at a stop light. Oh, and yes I push the brake down hard enough. Thank you all.

 

Voltages are fine. But that doesn't mean that modules are. You need to mensure the voltages under load (and maybe charge and also check capacity) to be sure that they are good.

Hybrid battery slowly draining while the car is in ready and engine is not running is normal. Every function of the car takes its power from hybrid battery (when engine is not running). AC takes a lot of power so that drains the hybrid battery fast if it's hot and AC is running hard. If the hybrid battery drains too fast (with AC off) check that it has normal capacity. And maybe check that 12V battery doesn't have a shorted cell (it would have low voltage and get hot).

How fast does the hybrid battery drain?

 

I was testing the load only with Torque Pro app and read 16.3 V per block. If you're familiar with the app the display only goes up to 14 blocks. 2 modules per block. This is with the car turned on and lights on. No A/C running.

The 12V battery is brand new. Just a couple weeks ago I bought it.

The battery drains fast when I am on the street or parking lot. In can deplete within minutes down to 2 cells on the display sometimes 1 cell. When I am at a stop light I see the battery draining on the display as well. An it will drain a cell in about 2 mins. I'm going to check for error codes today at Autozone. Torque Pro is not receiving errors.

 

When the hybrid battery is draining fast with AC not running display doesn’t show any arrows to or from hybrid battery?

12V battery being new doesn’t really mean that it couldn’t be faulty but if the problem started before you have replaced it it’s probably not the cause.

What happens to block voltages when hybrid battery is loaded do they all go down about the same or does one go down a lot faster/more than others? If one goes down more than others then one or both of the modules in it are bad. Bad hybrid battery can goes to itself to drain fast as the bad module won’t have capacity and low capacity battery will drain fast.

 

The arrows do display a drain happening. The arrows are going from the hybrid battery.

Yes I don't think the 12V battery is a problem. I do have to repair the combination cluster that I do know. I wouldn't think that causes any drains from the hybrid battery.

The block voltages do reduce but not much. When sitting I noticed them at 16.8V and when driving slow they reduce to 16.3V but never really go lower. I have one or two blocks that are .2 or .3 V lower than the other.

I checked on the codes and only came back with P0171 error. That is an O2 sensor. I feel that is a bigger problem.

 

Where the arrows are pointing to? There shouldn't be any arrows when parked without engine running.

 

When parked it is charging the Hybrid battery.. it's when I'm in gear it's draining the hybrid battery. When I drive slow in town or a parking lot it drains too fast. I sometimes have to pull over in order to charge the battery enough to drive.

 

It is probably not the best that you cannot see what is happening on the last 5 blocks (10 modules). I'm not 100% sure, but I think you can modify the OID fie to add the PIDs for the missing block Torque Pro expert, please feel free to chime in and correct me if I'm wrong.

Have you checked the brake pedal switch is sending the correct signal to the ECU to tell it to cut the power?

What is the current draw displayed by Torque Pro?