Questions Regarding Pocket Type Filled NiCad Batteries

The excessive crystal formation probably due to outgassing caused by overcharging....bad cell in bank, ok till changeout...

Overcharging how? The charging voltage is 147Vdc, same as for other banks, while charging current less then 0.1 Amp. And crystal formation is not only in one cell but in 50% of the cells out of 104.

Even if the reason is bad cell so do you mean just one bad cell or several? and how do i determine that which cell(s) is/are bad? per cell voltages of each cell 1.4Vdc, specific gravity of the cells is between 1180 & 1220 and electrolyte drop does occur in the cells which we check every month.

The crystals are formed from the electrolytic fluid....This is most common due to overcharging where the fluid is boiled out, and may be an intermittent occurrence.....I would explore the possibility of replacing the charger, if it is a real problem... In a battery bank such as this, the single bad cell is ok to leave until battery changeout, it will not effect the other cells...

http://www.davidsonsales.com/docs_pdf/NCPPO&Manual.pdf

What i thought was the reason for recurring crystal formation was the absence of rubber seal around the vent caps. Most of the vent caps are missing these rubber seals or some of them have it broken. Now what i think is that the electrolyte vapors evolving escape through the broken or absent seals and convert to carbonate on exposing to air and deposit around the caps. If the seals were there intact, the evolving electrolyte vapors would try to pass through the vent caps instead of opening thru the seals. These vent caps have plastic particles in them which would stop the electrolyte from further passing and send it back inside the cell to rejoin the electrolyte body. Only H2 and O2 would escape.

About the charger replacement, what fault could it have when the charging voltage and current levels appear constant?

I thought that NiCd cells needed to be discharged quite far before recharging them, or else they developed a "memory" that would "let" them discharge only partly. In other words, not suitable for trickle-type charging.

(Unless I am confusing these with another battery type or am out of date.)

I thought there was no such thing as 'memory' of battery, not that the manual says anything like that a...anyway, the batteries are not on recharge. They're tested once a year on load till their voltage drops to 1.0V/cell. Then they are put on boost charge till completely charged. For the remaining period the bank is on float charge on 147Vdc charging voltage and less than 0.1 Amp charging current.

What about my second query about the damaged cell at 0.45Vdc. Is it okay to be connected in the bank or should it be removed to protect the remaining cells in the bank?

Lyn your correct on memory. In the 1st post I noticed that they are refilling Ni cads with electrolyte? Never heard of Ni-Cads that need this? They are normally sealed as far I as know.

The NiCad chemistry isn't limited to sealed batteries. and wet chemistry cells don't have the same charge/discharge limitations that small, sealed, paste type do, especially the memory effect. Take a look at these:

Well as I have said many times in the past, your never to old to learn something new. Thanks RAMConsult

Refilling NiCads with distilled water, not electrolyte!

Does that mean that the batteries should deep discharged and that too frequently to avoid the memory affect? But the manufacturer manual does recommend float charge.

And as i said, these are tested once a year till discharged to about 1 volt per cell and they seem to be performing satisfactorily.

Question on using the clamp meter for measuring current. Are you using a clamp meter that can measure DC current. Most clamp meters can only measure AC current. In my 40+years in the electrical trade, I have only seen 1 clamp meter that could measure DC current, and then it was used to measure larger currents. Most good multimeters have a 10 amp DC current function, but this has to be inserted in the circuit. If some of the cells are shorted, then the voltage across the other cells will be higher. I would check the voltage across each cell individually to check for overcharging.