Re-hydrating the battery modules.

You could try with just plain water to start as this would show if it is necessary to use any chemical. If you have two modules open perhaps you could try one with and one without. This would be extremely helpful to be able to do a rough comparison between the two seeing what capacity gains there are and how it affects internal resistance. These are things I would do if I had modules to work with.

John (britprius)

 

No need to cut the top off another module. You could try my method with 2 holes for the plain water version so you will not have any risk from spillage when filling.
I used a 3 amp charge but you can use 5 amps if you wish, but charge long enough for the modules to feel warm (about 100F or so) . Charge minimum of 9000 mah
On the first discharge I discharged at 5 amps down to 5.4 volts, on the second discharge I did the same again, but at 5.4 volts I reduced the current to 300 ma and continued the discharge down to 3 volts.
I then charged the modules again then discharged at a regulated 10.5 amps down to 6 volts and timed to get the capacity. My discharge lasted 41 minutes. Calculation:- (41 X 10.5) divided by 60 = 7175 mah
I realize you will use a hobby charger to find the capacity, and may not be able to discharge at that high rate.

John

 

I would use the second version if you can set the charge and discharge to 5 amps for two cycles. At the end of the second cycle discharge to 3 volts at around 300 ma (you could use a car side lamp bulb for this if it is easier). Then set the charger to do another 5 amp charge and a discharge of 5 or 10 amps down to 6 volts for capacity check to suit yourself.

John
merged
I just appreciate your help. Work has to come first.

John

 

A number of people have asked about the type of screws to use. Any steel or plastic machine screws could be used, but avoid nickle plated or plated in general as any plating may react with the electrolyte as will possibly some forms of stainless steel with nickle as a component.
If in doubt leave a screw in some mixed chemical for a few days to see if any reaction occurs.
Even screws without heads such as "Allen" key driven grub screws could be used as it is not the screw head that is being used to seal the hole. Although I agree this could add to the sealing effect if some sealing compound or soft washer is used under the head.

John (Britprius)

 

External air pressure is generally considered to be 14.7 lbs per sq inch. This equates to approximately 1/3 of an imperial ton on both sides of the module with the module evacuated. The cell plates are tightly packed like a pack of cards between the module outer walls.
When the modules are stacked and clamped in the battery it is the vertical cell separator walls of the cells that take the clamping forces via vertical ribs on the outside of the module.
The outer side cell faces are almost supported against each other by almost pinhead size raised spots. If you peer down between two modules these raised spots do not actually touch, but have a gap of about 10/1000 inch. This allows the side walls to flex outwards about 5/1000 inch each when under pressure, and then support each other. A straight edge placed along the outside of a module will slide along the wall ribs without touching the raised spots unless there is pressure in the cells. These ribs can clearly be seen in the picture below borrowed from Roy's post.
Since all the cells in a module are connected by the vent mechanism all the cells in the module will be at the same pressure.
This structure allows for greater surface area and air passage for cooling.
.Gen 1 and 2 Battery modules 001.JPG

John (Britprius)

Roy if possible could you measure 10 ml of water and put it in one cell of the module with the top removed. This will give me a base line of how high this will fill the top of the cell.

John

 

There is another problem with only filling through one hole, and I am not trying to disparage the method only pointing out the possible problems.
You have no way of guaranteeing that all cells will be filled to the same level. An air lock at any point in the very small openings between cells will upset everything.
I thought of many scenarios trying to accomplish the same thing. This is why I have a home made vacuum tank sitting doing nothing as I was considering filling the modules in the same way as I used to fill printer ink cartridges.
You can by pulling a complete vacuum guarantee filling all the cells, but this is not desirable. You then find it is all but impossible remove equal amounts of fluid from each cell.
I am not saying you cannot do it by a vacuum method but is it worth the extra complexity given that all the equipment used must be capable of handling the caustic solutions involved to save one hole. This rules out brass zinc copper stainless, and aluminium. KOH even eats glass.

John

 

Back in the 50's I had some NiFe ex government cells. These were welded steel cases vitreous enameled with a center steel plug for topping up the electrolyte sealing the cell completely . They were filled with NaOH and had a voltage if I remember correctly of 1 volt. They were about the same size as a single Prius cell. They were virtually indestructible, but there energy density was very low.

John.

 

Thanks Roy that is just the sort of information we need. So 22 to 23ml would appear optimal.

John

 

Thanks for the warning on module venting. I think there are a number of likely reasons why this can happen, but also why I encourage the initial charging cycles with the modules still unsealed.
Likely reasons are:-
Over filling the cells. This will cause pressure to rise quickly,and when the module vents to vent fluid.
Charge rate to high particularly near the end of the charge cycle.
The third and most likely reason is a sticking safety relief valve "perhaps" exacerbated by over filling.

Something I notice when doing the pressure tests that I did not pay much attention to at the time was that when the stuck valves initially opened. There was a loud pop followed by a decaying hiss until the pressure dropped to 80 psi at which point there was no evidence the valve was venting apart from the fact that the pressure was being held steady with the compressor running. Subsequently when testing the pressure went up to 80 psi and just stopped rising. There was no "pop or hissing" the valve opened gently steadily releasing the pressure from the running compressor. The output volume from the compressor would be much more than the cells gassing.

Perhaps I should amend my post to make releasing the safety valves a mandatory part of the process. The alternatives are to charge cycle with the modules still open as suggested in my post. This also removes the need to clamp and eliminates any chance of bloating. If it is desirable for some reason to charge with the modules sealed " and this would apply even if the modules have not been "re-hydrated" to fit a hose to the module vent with the open end of the hose in a bucket of water. Thus greatly diluting any escape of fluid to a safe level, and capturing any small droplets stopping any risk of breathing them in.

John (Britprius)