Author Topic: Renewing Block Nicads (Read 2925 times)

jimh · « **on:** February 06, 2007, 08:25:25 AM »

I had acquired some block nicads a couple months ago and have done several things to get them "up to speed". When I picked them up, they were mostly dry of electrolyte (which I heard is a no-no), so I added some electrolyte (20% potassium hydroxide and water). I put each battery (5 cells x 1.25v each) on a 20 amp charger for about 4 days, thinking to "decrystalize" them. Not knowing their amperage rating, I just stuck with the maximum output of my charger. Then I connected them all up and charged them as a group. When the voltage got around 13.5, they started gassing. I stopped and threw my inverter on and sucked 1KW for 7 hours. Then the voltage dropped below 10.5 and the invertor gave the sign to shut down. Not satisfied with the output, I got some reconditioning tips from the following website:

http://www.nasa.gov/offices/oce/llis/0644.html

It writes:

1. Discharge at C/2 constant current rate until the first cell reaches 1.0 v/c.

2. Drain each cell with a 1 ohm resistor until each cell's voltage is less than .03 V/C.

3. Short each cell for a minimum of 4 hours.

4. Recharge battery at C/20 constant current rate for 40 hours (+- 4 hours).

5. Repeat steps a, b, and c.

6. Charge battery at C/10 constant current rate for 16 hours ( +- 4 hours).

7. Repeat steps a, b, c, and f.

I recharged them up, again at 20 amps (about 14 volts). Then I discharged them. Where the draining was needed, I put them up against 3 x 300w resistors. When I got the voltage low enough, about .2, I shorted them. Then I recharged them again. I did this 2 more times, but the performance hasn't improved. Is there something I should be doing or am I expecting too much? Did I do something wrong? I don't have any information on these batteries. If someone knows what they are capable of, please say.

JimH

Flux · « **Reply #1 on:** February 06, 2007, 02:20:02 AM »

All I can say is that although everyone else tells me they last forever, the ones we had at work were very ineffective after 20 years, the job they did wasn't very demanding and they needed almost continuous charging. They were never run short of electrolyte, but never had it regularly changed.

It is CO2 that kills them and I suspect that if never let dry and the electrolyte is changed every few years they may well last a very long time.

If they have dried out and been exposed to CO2 in the air you may have had your lot.

You seem to have done everything right to revive them, but the previous owner did the thing that you must never do ( let them stand dry).

Yours seem very modern and most modern batteries are not made as well as the old ones, although in relative terms they are much cheaper.

Good luck. perhaps Nando can give you some help.

Flux

WindChopper · « **Reply #2 on:** February 06, 2007, 05:05:15 AM »

IMHO - I think that you are one block short in your setup ....

Not a nasty comment - Physics ....

Nominal "Full Charge" per Cell for a NiCad is 1.4 V

Discharge curve For a NiCad @ C/20 Discharge

Starts at 1.4V - Drops to ~1.25V in maybe the 1st 15% of the curve

"Flat" discharge from 1.25V to 1.20V for maybe 75% of the curve

Rapid Drop to 1.0V for the remaining portion of the curve.

I have always used 10 Cells for a "12V" NiCad Pack.

Your current ( no pun ) setup ....

(+)---[+ -]---[+ -]---[+ -]---[+ -]---[+ -]---[+ -]---[+ -]---[+ -]---[+ -]---(-)

Should be ....

(+)---[+ -]---[+ -]---[+ -]---[+ -]---[+ -]---[+ -]---[+ -]---[+ -]---[+ -]---[+ -]---(-)

At 10 Cells

~14V is Full Charge

Flat Discharge is 12.5V to 12.0V

Final stage is 12.0V to 10.5V ( Your Cutoff )

At 9 Cells ( your setup shown in the photos )

~12.6 is Full Charge

Flat Discharge is 11.25V to 10.8

Final stage is 10.8V to 10.5V ( Your Cutoff )

Try rewiring each block for "6V" and running two Blocks in series.

You may get more usable discharge curve range.

You will end up with 1 extra block but your overall discharge range may be better.

Russ

Flux · « **Reply #3 on:** February 06, 2007, 08:00:59 AM »

Good point, I never considered how many cells you are using in a string.

NiCd's are not compatible with lead acid voltages they have a grater rang of volts from gassing to flat.

An inverter designed for lead acid will either trip on over volts or shut down on low volts depending on the number of cells in a string.

It is unlikely that you will be able to run the inverter during the charging phase if you have enough cells to take you to flat at the inverter low volts limit.

Remember Nicd's can be run flat there is no need for the 50% discharge nonsense.

Maybe you have more capacity than you thought.

Flux

jimh · « **Reply #4 on:** February 06, 2007, 09:21:09 AM »

Great! I will see what the rewiring does. Be back soon.

JimH

Nando · « **Reply #5 on:** February 06, 2007, 11:26:03 AM »

NiCad in reference to the Lead cell, several companies have produced a pack of 2 cells ( 2.4) to replace one Lead cell -- so for a 12 volts, YOU DO NEED 10 Cells for 12 volts and the charger has to be profiled for 1.37 Volt/cell at float charge. and for new cells 1.47 volts/cell for bulk charging -- for Edison ( Ferro Nickel) the voltage is 1.57 volts/cell.

Unhappily, when NiCad are not used for long time, due to atmospheric pressure changes the electrolyte water "evaporates" leaving the KOH solid ( powder Inside).

If new KOH is going to be added, then the battery needs to be washed to remove the KOH that has been "affected" by the CO2.

There is another chemical solution, unhappily, I have been trying to remember it for years, to wash and Re-new the batteries to almost 100 % with new KOH and Lithium.

If you have excess KOH, why don't you experiment with some cells, remove the KOH, wash the plates with distilled water, apply low current for about 24 hours ( 2 to 4 %) of the cell amp-hour, then wash them again and fill with the regular KOH and Lithium and charge normally.

It may do the trick.

Nando

jimh · « **Reply #6 on:** February 06, 2007, 12:29:32 PM »

Nando,

"wash the plates with distilled water, apply low current for about 24 hours ( 2 to 4 %) of the cell amp-hour"

I don't want to sound stupid (politically correct would be abuntantly confused and uneducated in the field) , but it sounds like you want me to charge them dry. Or does "rinsing" mean to fill them with distilled water only. Can you detail your thoughts for me?

Also, I don't know the cell amp-hour. I was hoping someone could identify these animals for me to tell me that.

When I researched the electrolyte used for Nicads, I didn't find anything that said to add lithium. If I need to do that, does anyone know where I can get it and at what rate do I add it to the electrolyte?

JimH

Talking slower still doesn't mean I'll understand

Flux · « **Reply #7 on:** February 06, 2007, 12:55:59 PM »

No don't leave them dry for many seconds.

I think Nando means to charge them when filled with distilled water. This is similar to lead acids when you are trying to remove sulphate with EDTA added.

The basic idea is to get the old KOH and K2Co3 into solution so that you remove it on the next flush. This should get you back to something like the correct electrolyte sg and will at least attempt to remove the carbonate that causes the trouble.

Difficult to judge from the pictures but generally NiCd are significantly larger than lead acid of the same capacity ( try half capacity as a guess).

The volts will fall very quickly if they are cold so bear that in mind when deciding on the discharged point

Flux

Nando · « **Reply #8 on:** February 07, 2007, 08:49:55 AM »

I do not have a lot of time available, so I try shortcuts and I write meaningless phrases.

You wash, pour, wash, you,(rinse well), you fill H20, you charge, 24 hours, wash, pour, wash, pour, ( Rinse well), electrolyte fill, charge, CHECK.

Lithium is OK for NiCads, though I do not know if yours require or not require Lithium, Lithium reduces the discharge current, some use photographer quality and it is expensive.

Nando

jimh · « **Reply #9 on:** February 08, 2007, 01:29:28 AM »

Yesterday, I took 2 batteries off my bank and hooked up the cells series to make a 12 volt bank (out of 2 batteries). Shortly after that, and before I started charging, the cells were bubbling on their own and the bank started losing voltage steadily. Overnight, they went from 12.6 volts, down to 5.5v and still dropping. Has anyone hooked these cells up in series (within the same battery) and been able to keep the voltage? I would jump to the conclusion that I had a short in one or more cells, but crossed that off as a possibility since I don't lose voltage when they were all hooked up previously (like in the picture above). Also, I did not have a drastic voltage difference before (from cell to cell), but now, the cell voltages are all wacky. I'm more perplexed than I was before.

Not having a clue as to what is happening, I was thinking of a way I could keep them all in series as before, and somehow get the additional 1.25 volts like several of you said I need. Unless this phenomenon is explainable, could I use 4 of the 5 cells blocks in series, then parallel the 5th cell? Check the photo.

Thanks,

JimH

jimh · « **Reply #10 on:** February 08, 2007, 01:32:40 AM »

Sorry, the photo didn't come too clear. I hope this links to it. The photo is in my files.

http://www.otherpower.com/images/scimages/7188/Nicads_3.JPG

Bruce S · « **Reply #11 on:** February 08, 2007, 09:18:42 AM »

JimH;

With both dry NiCds and wet ones, if they are left sitting too long, they have the possibility of reversing their polarity.

I think that having redone your setup you may have found that one of the cells could be hosing the whole thing down.

With them setup the previuos why to others where able to overcome this one cell by "covering" for it.

At this time, it would be a good idea to seperate the blocks let them set for a day and see which one is going bad on you. If you have one trying to reverse it polarity it can be a disaster waiting for the worse possible moment. Mine did and it was explosive, luckliy they were in a safe plastic environment.

The pic may still be up in my diaries:-(

Setting them all up in series will again hide a bad cell's voltage problem, but it will show up later.

I generally set my dry cell NiCds up in Parrallel to get the voltage where I want it and then in series for the Amperage.

Hope this helps;

Bruce S

WindChopper · « **Reply #12 on:** February 10, 2007, 03:28:56 AM »

JimH

For what it's worth ....

If I understand your hook up for the two battery test, and the comment regarding discharge ( you seem to indicate that you had no load on the rewired pack when the problem happened ) .... then you have problems.

While NiCads have self discharge characteristics, they do not usually exhibit them in the manner that you indicate !

It sounds like you have cell to cell leakage across the cells within a "Block".

With the way the original pack was configured, cell to cell leakage would be masked as all (-) and (+) connections in a given block are essentially in parallel.

When you rewired the cells you seem to have unmasked that sort of problem.

I would:

1) Remove all links between cells in a "Block".

2) Measure each cell to see if it was the correct polarity and a reasonable voltage.

3) Within a "Block" test from each (-) and each (+) to all other

(-) and (+) connections

You should only show voltage from a given cells (-) to its (+).

If you show a voltage from a given cell's (-) or (+) to any other cells (-/+) then you have a problem with cell to cell leakage within that "Block".

I looked closely at the photos of your original setup and it does not look like there are internal cross connections within a "Block" that would prevent you from rewiring its cells in series.

I realize that it's a pain in the butt, .... but you need to remove all the cross links from all the "Blocks" and test each of the battery blocks.

You may have just had a lucky find and hit the only "Block" that had a problem or you may have problems in several blocks.

A bailout may be to go back to the original configuration and locate an additional "Block" to make up the required 10. This is however, just masking the original problem which will eventually come back to bite you.

Normally you should be able to wire a "Block" in series.

A Google search indicated that NIFE still seems to be around - you may want to snail-mail them a letter requesting info on those blocks. ( I never found an internet site for them. )

From an EPA site that Google found a NIFE INC. ref. in, I found two variations on an address:

NIFE INC

GEORGE WASHINGTON HWY

LINCOLN, RI 02865

Wish you the best on the project - glad its you and not me having to "un-link" all those blocks and test them.

Russ

WindChopper · « **Reply #13 on:** February 10, 2007, 03:33:29 AM »

DUHHHH ....

From an EPA site that Google found a NIFE INC. ref. in, I found two variations on an address:

NIFE INC

PO BOX 100

LINCOLN, RI 02865

NIFE INC

GEORGE WASHINGTON HWY

LINCOLN, RI 02865

Wish you the best on the project - glad its you and not me having to "un-link" all those blocks and test them.

Russ

jimh · « **Reply #14 on:** February 11, 2007, 09:15:39 PM »

Russ,

Thanks. I will do some testing to see what I can find for cell cross leakage. I appreciate the detailed directions, since I believe to be a bit...let's say, challenged. One more question though. I posted a photo link above, which I found some evident problems with. But my thoughts were to go back to my original battery layout, but use the last cell in the group of batteries to give me the 10th battery. In theory, can this work, or will it throw my whole group off balance? If someone feels this could be done, please help me with a connection diagram.

Thanks,

JimH

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