Re-hydrating the battery modules.

When done on a car's cooling system, it's usually done through just one hole. A connector with a 2 or 3 position valve is stuck on the filler neck, the valve is turned to the vacuum source until a good vacuum* is pulled. Valve is turned to the 'neither' position to see if the vacuum holds, then turned to the hose running from the coolant jug, and the coolant gets slurped in.

-Chap

* where "good vacuum" is sort of relative ... A/C shops need a motorized pump that can draw within a few microns of absolutely no air; cooling-system tools usually use a shop-air venturi capable of drawing maybe 27 inches of mercury or so.

 

Yes Chap you are right, only one hole would be needed - when I pull a vacuum with my motorized pump on my car's AC I only attach to the connector on the low side of the system.

My concern might be the amount of vacuum to pull so as to not collapse the cell inward. (using my air conditioning motorized vacuum pump). The hand pump that I use to pull a small vacuum to test vacuum operated valves might do the job using a 3 way valve to direct fluid into the cell.

To illustrate the power of vacuum, here is a true story.

I worked in a shop that filled large (very high 13.8 KV voltage) transformers
(10 ftx10ftx10ft) with oil under vacuum. The transformer tanks were made with very heavy plate steel and you would pull a vacuum to draw moisture out of the electrical windings before filling with oil. We had a round tank about 15 foot long and 5 ft in diameter that we would pump the oil from the transformer into temporarily while doing a repair inside the transformer. One day we pulled a vacuum on the empty big round tank to prepare it for an oil transfer and forgot to shut off the pump - we heard a very big bang and found the big round tank buckled in the middle like a pop can that had been squeezed in half.Scared the hell out of us, we thought the shop had blown up.

Roy from Canada

 

Good idea about resin screws.
The level in the modules must originally been above the level of the terminal screws,on the inside of the module the terminal is a button that touches the top of the cover - for them to leak the level must have been near the top - what gap would you think is appropriate to leave at the top. I have cut one very close to the top so I could fill a chamber with water and measure the volume when the level is near the top and give you my result if that would help.

Roy

 

25 to 35% would leave the level below the battery terminal so the possibility of leaking would be low.
Roy

John- I have a module cut off right at the top - exposing the 6 cells. The cells are bone dry - on each side of the battery in each cell is a space about 1/16 in wide that will hold a bit of solution unless the plates expand when hydrated with the new solution.

Roy

 

Will try that

Roy

Putting a new roof on my garage so will be busy for a while - will check for messages to-night.

Roy

 

Roy, any chance you could post a pic because you know the old saying.......

Very curious about this experimenting and would love to try something similar myself.

 

I will try but my skills in the computer area are poor and I may not suceed.
Roy

 

I'm thinking the situation is different enough to allay that concern. The modules are built to be under enough compression to hold their shape with internal pressures to +120 psi or more. With the right compressors you can get positive pressures as high as you want, but for some reason nobody ever manages to pull more vacuum than about -14.7 psi no matter what kind of pump they use. That probably represents around 300 pounds of inward force on the wide flat sides of the module, which I expect is well under what they normally see from the compression plates in the battery case ... and they're not empty tanks, they have plenty of internal structure to resist collapse.

Your empty round tank had a surface area around 39,574 square inches ... pull that down to -14 pounds per square inch, and it's feeling a lot of pounds.

Here's what I'm vaguely thinking (altogether untested, of course):

1. Build a battery rotisserie. Copy the one in your crazy uncle's garage full of classic car restorations, only scaled down to the size of a traction battery.
2. With the battery on the rotisserie up-side-up, make one small 'ole in the top of a module and insert the (snugly-fitting, vacuum-tight) fill proboscis.
3. Open valve to vacuum source until module is maximally evacuated. Close that valve.
4. Spin rotisserie up-side-down. Open valve to jug of (water or weak solution) located at or above rotisserie height, allowing fluid in to fill module. Close that valve. At this point the module is probably full or near-full.
5. Open a valve to a clear evacuable container, located below the rotisserie, marked for the desired volume of fluid to draw back out of the module, leaving proper space for expansion. Six cell volumes should equalize as the module is upside-down with the intercell openings at the bottom.
   
6. Close that valve, spin back right-side-up and remove the proboscis. Air will enter to fill the expansion space. Drive in the sealing screw.

Agreed. What seems to be certain is that the Gen 2 terminal seals are better than the Gen 1 versions - only the Gen 1 versions required a service campaign to inject sealant between all the positive terminals and the bus bars. There was an old "Murphy's law corollary" that said any expensive semiconductor downstream of a fuse would protect the fuse by blowing first. That seems to be exactly what Gen 1 terminal seals would do to protect the relief valve. Maybe if the relief valve is exercised, though, and brought back to an 80 psi operating threshold, it would be better? No sé.

For that to work, I guess it would have to be possible to pressurize the module to the point where the relief valve unsticks, even if that is above where the terminal seeps, and it would have to be true that breaching the terminal seal that way once does not leave it permanently compromised. I don't have any evidence one way or another on that either.

-Chap

 

Dont you think drilling 6 holes and letting them fill by gravity would be a lot faster and easier and could be done without removing the battery from the car. However I like doing things the hard way and will probably byild a spit to turn the battery on

Roy

 

6 holes * 38 Classic modules = 228 possible places to leak

 

Yes I think you are right.

Maybe be better to pull a vacuum after all.

Roy

 

Do you guys see any indication (a lot of plastic parts have a code stamped in somewhere) of what kind of resin the module housings are molded from?-Chap merged Also, do you have a figure for the resin thickness at the top of the module, where the screws are to be inserted? That should be easy for Roy to get with a cut-off top and a micrometer. John, what was the thread pitch of the screws you used? Did you tap the holes in a separate step, using a thread-cutting tap? Or a thread-rolling tap? Or just use a self-tapping (or a thread-rolling) screw? Did you determine what seemed to be a safe limit to tightening torque?

-Chap

 

Here are some pictures and dimensions of the Gen 2 module with the top cut off.
The thickness of the top is 11/64 inch (4.4 mm) the total depth from the top of the module to the top of the battery below is 17/32 (13.49 mm).

This is a correction of a measurement I made in the top of the module --- the thickness of the top is only 2,2 mm thick, I give Alex credit for pointing this error out. My measurement included a lip on the top cover that cannot be seen in the pictures. This points out how small a surface the screw has to seal the cell after hydration. Some sort of flexible sealant may have to be used if leaking eventually occurs when the modules are installed in a working battery. John uses fine thread screws and I used course thread self tapping screws. He has pointed out the fine thread gives a better sealing process and may be all that is needed to prevent leaking. I used self tapping for speed of the work as I did 38 modules with 6 holes each with the battery in place in the car. I later had to seal the screws because of leaks.


Roy from Canada