Is it possible to recharge a single bad module?

You can charge a module that is low.

But if it is bad (for example, shorted out) then you should not bother trying to charge it. Remove it and put a good one in it's place.

To charge a single module you do need to tear the can and battery pack down to where you have access to the individual modules. At this point you'll have the hybrid battery pack unbolted from the car.

Remove the nuts on either end of the module. Attach your NiMh charger.

Take time to correctly torque each nut on the HV battery and hv cable connections when you are done.

 

If a module is the first to go high when charging, and the first to go low when discharging, then I would dump it.

You can see this when using techstream or your OBDII + Torque app.

Now if during charging and discharging it is consistently higher than the rest, or consistently lower than rest, it *may* be worth trying to save.

Yes, you can charge just one module even though the buss bars are still attached.
WARNING: HIGH VOLTAGE WILL BE PRESENT.

 

Since each module contains 6 NiMH cells, anything less than 6vdc per module (1vdc per cell) is pretty iffy.

 

My understanding is that the modules need to be left in the HV battery when charging even then they are disconnected and charged separately, otherwise the cells expand and stay permanently deformed. I have read that some people have fabricated a clamp so that they can charge an individual module, but at the same time, allow airflow on both sides.

I have a different requirement. I've replaced all my modules with the NPB Kit and have 26 of the original 28 that appear to be serviceable. Has anyone tried trickle charging them in a way that doesn't require clamping? I'm not sure how long I'll have them sitting around, and don't know what the discharge rate would be if they are left disconnected. Just wondered if there was a way to keep them at a serviceable voltage.

 

There are several ways to tell bad modules, but one way is to spot modules (2 per 'block') that have 1.2 or so voltage lower than your other modules. I found that no amount of careful or aggressive charging would fix those. My bad modules registered 6.80ish V when my good ones were more like 7.90V. Actual voltages will depend on the 'state of charge' of your HV battery when you removed it.

I just had my HV Battery 'out' to replace just '4 modules' and do 'a bit of reconditioning' of the pack. This is a big job, be forewarned. It's not difficult, but there are lots of little steps and you have to work carefully (high voltage etc) and inform yourself before you fiddle around. Luckily PC and Youtube have great resources. To get the battery out, plan to have the right tools and sockets, ziploc bags or organizers for all the interior fasteners etc and about 2-3 hours. The assy itself is heavy and awkward and sharp - two people are better than one to remove it. Once out, it's not as simple as changing bad modules for used good modules. You'll need to review how to recondition and balance the modules and obtain the appropriate chargers - and, as above, do your charging/discharging cycles only in the provided rails/block assy. Reconditioning took me 2-3 weeks. The whole project took me a month, including 2-3 hours reassembly. If you skip reconditioning and balancing, cleaning the fan that cools the HV battery and cleaning the corrosion off the 'busbars' (why would you, since you'll have to spend another 6 hours of interior removal/replacement soon if you skip these steps?), You could do the whole thing in a couple of days with no mistakes and learning how to do everything ahead of time.

 

I have been using a SkyRC iMAX b6ac v2 charger in "Auto Charge" NiMH mode... the key for me was to also buy the temperature probe and set the Cutoff Temperature to just a few degrees above room temperature where I was charging. In my case that is 25 degrees celsius cutoff (which is about 77 farenheit). I have not had a module "expand" on me since I started using the temperature probe and temperature cutoff. I also have the other cutoffs set up, like milli-amp-hour capacity, timer limit, (and i think voltage?) just in case, but those are not always as exact and not as fool-proof, and the auto-charge feature doesn't always cutoff when it is supposed to ( I guess it has trouble reading the voltage fluctuation at end of charge cycle). I would not charge unattended. Note I am only using my old batteries in a little robot, im not sure of the long term effect of charging this way. I realize the Prius itself probably doesn't charge them the same way or possibly to the same fullness.

 

Bob Wilson has fabricated clamps and gone a little further, adding two layers of metal foil separated by plastic wrap to one of the clamp boards, making it a capacitor capable of measuring the pressure being developed in the charging cell.



It doesn't look like his clamp boards were especially designed for ventilation, but that could be added. I think the sides of the modules are already a bit dimply to allow space for air flow.

 

update for future surfers... ive been charging more modules on the skyrc byac v2 and i noticed that even at low current, like 1 amps, there is an ever so slight physical deformation of the pack. you have to hold it up at a certain angle to see it. It is definitely noticeable if you have a cold module next to one that is just charged at 1 amp.

in that picture above, you can definitely see the deformation. each of the 6 cells in that module has puffed up. That is not what they are supposed to look like. you can see in the way the light reflects off each one, they look like little mounds in the picture above and thats not how they would be inside a proper clamp.

I am no longer confident in this process and am not sure if it is doing damage to the cell. and if there is damage it seems entirely possible the cell could become dangerous while charging. The little text on top of the modules actually says "danger, do not recharge". Toyota / Panasonic probably invented that giant clamping system for a reason.

i would never charge one of these modules unattended and without a working temperature probe on the charger set to a low temperature, and i dont think i would stick one of these back in a car. I'm using a handful of them for farting around with hobby stuff where there is minimal danger. I used to think "Oh you can just pull these out and use them like giant rechargable NiMH cells" - but i now believe that is mostly wrong.

 

1 amp isn't a low charge at end of charge, it's a quite low charge in the middle. I think the idea of a temperature probe is great; which and where do we get? Here's a radical idea for non-in battery charging? why not always work in packs of three modules, securing them in your vice and only charging the middle one. Another innovation I've seen on PC: put balloons over the vent holes so that you can see / capture that nasty gasses that come out.