Restoring G1 Drive Batterys

Hi Roy,

Is the 6.48V module restored to the point where you feel comfortable putting it back into service? If not, to solve the immediate problem of replacing the one bad module, perhaps Bob Wilson would be willing to sell you a used good replacement.

As I understand your post, the eBay battery that you purchased contained only bad modules? Are the module serial numbers in sequential order? Did that seller cheat you?

 

I've got a lot of chores to work this weekend so I won't be able to participate much. However, here is a list of my battery experiment photos. I plan to add text to explain what is going on but that takes a little more effort:

Prius Battery Photos
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You may find the last two photos from Eric's work in Florida doing an in situ refurbishment especially interesting. Eric recently achieved vehicle operation and we are now in the electrode activation phase. By installation in and operation of his Prius, Eric is at the leading edge.

Bob Wilson

 

I've updated the battery photo web page with some brief text:

Prius Battery Photos
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Bob Wilson

 

Hi Bob,

Thanks for such an informative presentation. In your NHW11/20 module comparison pics, I see that the NHW20 really is about 10mm longer terminal-stud-end to terminal-stud-end. (I don't see the double terminal connections I read about on the Panasonic site, but maybe that's an internal construction feature where I assumed they meant extra terminal studs.)

Something I've been wondering (posted for you on an earlier thread but you may not have seen it): have you actually tried populating an NHW11 battery case with NHW20 modules and determining the clearance from the terminal stud ends/busbar modules to the inside of the steel cover? Seems like a Very Good Thing to Know....

-Chap

 

I have a spare, unused NHW11 traction battery and have been thinking about either module refurbishment versus NHW20 modules. Of the two, I want to first try complete module replacement so we can continue to recycle the NHW11 batteries. But during the process, I will check my NHW20 module for fit.

After I test the refurbished modules, I may take a serious look at the NHW20 modules as a full pack replacement. This is not a trivial test and requires attention to detail.

Bob Wilson

 

Hi Bob,

Looking through your picture sequence again, I saw the disappointing result with the heat-sealed stainless tee nut, and wondered whether, as another maintenance-friendly modification idea, it might be worth testing whether you can just drill a hole in the top and tap it, and just directly insert a screw (either stainless or nylon, both easy to get in the hardware store) with a sealing washer. The plastic top looks thick enough to cut at least 3 threads if using a tap in the fine-thread series, and I would not be surprised if it would hold a screw securely enough to resist the internal pressure.

I'm not a materials guy, I don't know about the compatibility of either stainless or nylon with KOH, or which one has the closer expansion coefficient to the plastic used in the case.

My experience in the past with tapping holes in plastic material is that the holes recover a little after cutting, and end up being fairly tight fits for a standard screw (think: the feel of a nylok nut), which in this application is a benefit.

Just an extra thought if you haven't tried it already.

-Chap

 

It measures 2 mm., pretty thin. However, you're thinking the right way.

Now I've been looking at the 'safety vent' and believe it to be 'too tight.' I would be more interested in a reworked safety vent and that provides a lot more material to work with. But this is tricky stuff.

Bob Wilson

 

By too tight, do you mean it relieves at too high a pressure? (Out of curiosity, what do the normal range of pressures and the valve's relief pressure seem to be? I've been at a loss to estimate what the pressure must have reached in the overcharged battery you pictured - is that torn steel I see in the lower right corner?)

An M3x0.35 tap (it seems only right to use metrics ) could cut ~5 full threads in 2mm of material, if the material is plastic enough to cleanly cut a thread that fine - I'm not sure what the pullout force would be, but the screw would present only about 7 mm^2 of area to the pressure.

-Chap

 

I've pulled a vacuum of 25-28" and it didn't open up. I plan to test it with high pressure but I need to rig up a pressure fitting.

Yes and fairly recent. I've included the photo to try an impress on folks we are playing with powerful forces. I am not one to try and scare folks but make them seriously consider the importance of the right tool for the right job.

The problem is threaded hole cut in a flat surface that goes under pressure would tend to 'bow out' and thus increase the diameter of the hole under strain. The stress looks more like a blow-out plug.

One thought is to fabricate a small cylinder with a center, threaded hole. One end of the cylinder would expand in a cone into a thin disk. These cylinders could be rapidly spun and inserted into a beveled hole and friction heating weld the disk to the battery top. When the disk reaches the top of the battery it would brake to a stop and the weld is complete.

The advantage of this approach is a through weld and a threaded cylinder that the pressure would 'force closed.' As the pressure increased the cylinder would more tightly grip the threaded fastener. But this leaves the problem of leakage around the terminals.

My thinking is I need pressure testing not only of the relief valve but also of the terminals at higher temperatures, 40-50C. The pressure relief valve set point needs to be less than the terminal leakage pressure so the KOH solution won't bubble out and eat the copper bus terminals. This is not a trivial problem.

Bob Wilson

ps. The temperature probe hole would be an ideal, threaded cylinder but it is located in the wrong location, a center cell.