Re-hydrating the battery modules.

sounds good keep us posted.

I previously years ago had success in getting h20 into a dead battery using my harbor freight vacuum pump through the relief valve, i only inserted water knowing it would do little and i was right lol

 

My research into the NiMH failure modes as it relates to hydration specifically has led evidence that use of NaOH as an augment/replacement to the KOH electrolyte has benefits to the cell electrochemistry in a significant way.
Have a look at this electrolyte refinement data for NiMH cells:

 

Further, I will be employing ultrasonic pulse charging with custom made gear to distribute the NaOH homogeneously and assist the electrode repair as per this analysis:

 

Wow, very high tech way to get the cells back into a usable condition, but I'm not knocking it at all.
How do you plan to flush out the detritus from each cell so it doesn't simply build up in the cavity at the bottom of the cell and end up recirculating through the plates?

As long as there is an escape for excess electrolyte and a circulation system employed and the return to the storage reservoir was piped to the bottom of the module, it would flush out the detritus .... I just need to double check if the bottom of all the cells is linked, but from memory it is ..... but I'm getting old and memory isn't something I tend to rely on these days :lol: A filter system and an electrolyte cooling system could replace the need for the fan/air cooling or even utilise this area for a liquid to air heat exchanger.

I like the idea of the plastic fittings replacing the plastic plug screws, easy enough to slip a piece of hose down through a barb fitting at one end of the module to reach the sump and the electrolyte fed in at the other end, the flow would gradually move and detritus to the drain end and be removed from the cell.

Are you sure the pulse charging would really be needed? The original charge/discharge current the pack suffers during normal operation is quite high, surely that would dislodge any build up if there was a method to wash that build up out of the cell. The problem is dispensing the clean cooled electrolyte across the top of each cell to flush the rubbish out and cool the plates .....

T1 Terry

 

AC pulsation can recombine some dendrite material into the electrolyte

 

The cells are like AGM cells, they are not really awash in liquid. Thus the 'detritus' cannot be flushed. If the detritus is very significant then the cell is at end of life anyway and will fail shorted from the build up at the bottom or would have low capacity and not be suitable for re use.
My understanding is the crystalline KOH forms due to loss of H2O via venting, resulting in increased cell impedance, increased heating and more venting etc. Thus once sufficent H2O is reintroduced and the electrolyte is homogenized via the ultrasonic pulsing and cavitation, the module is cycled 3 times and rerated for decent AH capacity and an internal resistance of sub 10mΩ.

I am designing for commercial sustainability so once I have ascertained the optimum parameters for module renewal I will document it.

 

All 6 cells in a module share a common atmosphere channel, if they didn't, they couldn't vent.

They vent through a pressure relief valve, leaking and disposing of valuable contents that lead to cell damage.

Why does this vent process even exist

There is no reason that I can see that all 168 cells cant share a common atmosphere, with one single vent. If 6 can, then why cant 168 ?

Perhaps the risk of conductivity at a high voltage between modules from one end of the hv pack to another ?

If there is no conductive issue, a single atmosphere would have stopped many of these issues with the cells. IMO

Even if there is a HV risk, a common atmosphere between a number of banks could have proven helpful and reduced any conductive issues ?

 

I imagine it's safer to handle low voltages cells with a removable circuit breaker stacked in series for serviceability and assembly. So low voltage cells with local vents.

 

Here is my thinking, using good cells, we will pretend we can get nice new cells
We drill out the pop off valve
connect all of them to each other for a common atmosphere
Place a low pressure relief valve (cause we now have a lot of places for excess pressure to run to in those other cells).

 

Why go thru all that ?

 

This is exactly what crossed my mind a long time ago...

On a side note, Gen 4 NiMH modules do not have the relief valve/vent. The round fitting is still on the top of the module, but there is no valve inside. Good, fully tested modules are available all day long for $30. How much effort is worth saving 30 bucks..

 

Well...just swapping out a few modules is not enough to rebuild the HV battery. In fact placing very good modules among mediocre modules will cause the ECU to throw a code. So it is best to rebuild aged packs with modules of reasonably similar capacity and impedance. Thus not only the weakest link causes failure, the strongest link also causes a different failure.

 

1- to prevent the escape of the gases from the battery system
2- allow all the cells in all the modules to stay more chemically balanced with the hv pack

 

correct, i can fill a pack with mediocre cells and run it all day long

 

quote
I tested the amount of pressure the modules are likely to operate at. It was found with the modules clamped in a vice the pressure relief valves stick somewhat after a period of non use. The pressure required to open them was 120 psi + or - 5 psi measured with both a mechanical, and an electronic digital gauge. After the initial opening this fell to a constant retest figure of 80 psi. This gives a module sidewall load of 1.7 tons imperial at the lower pressure.

OK, THERE IS NO WAY THIS ANYWHERE NEAR ACCURATE.

When I charge the module goes to delta end voltage, it swells, it gases
To prevent loss of gas I take a Q TIP, place saran wrap around it, place it in the vent hole seated fully down.

THERE IS NO WAY A Q TIP IS STAYING IN THAT HOLE AT 80 PSI LOL

If I remove the Q Tip 30 seconds after end of charge, it can gas out for 5 seconds, a LOT OF GASSSING.
You have to wait for the pack to unswell, 15 minutes or so, to allow the pressure to drop and the vent to close.

THERE IS NOT ENOUGH VOLUME IN THAT MODULE TO SUPPORT A 5 SECOND GAS AT 80 PSI MUCH LESS 120, NOT TO MENTION THE QTIP WOULD BLOW OUT LIKE A 223 ROUND LOL

 

It would be great if you could use the quote function correctly so we can see who it is you're quoting.

 

Hmmm. Never thought about that. I'll have to look into it. Not sure if I 100% believe it.

 

THANKS, NEXT YOU CAN CORRECT MY GRAMMER AND SPELING

 

I don't understand why you believe this "swelling" and "unswelling" is acceptable, and you use these in customer's cars?

 

So the latest NiMH modules lack a pressure vent?
That makes for a dangerous situation if an overcharge happens.