Author Topic: Maintenance of NiCd cells in Emergency lighting  (Read 565 times)
Ash
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Maintenance of NiCd cells in Emergency lighting « on: October 15, 2016, 11:50:51 AM » Author: Ash
I got a FL luminaire with emergency function and there is a NiCd battery. It is old but the battery is working and in good shape for its age

Asking whether the battery needs some maintenance actions besides charging to keep it in best shape, and whether permanent charge in the luminaire is best



Battery : GP 450DKT3A1P
3 cell 3.6V 4500mAh

EM unit : Gaash 14S
1 hour emergency rated (36W T8 at low power)
24 hour full recharge



Some measurements :

charger output open circuit 8.8V
charger output short circuit 240mA
permanent charge of full battery 4.1V 150mA

discharge (emergency) 2A
starting from 3.9V
going out at 3.2V and latching in off by some logic (empty battery jumps up to some 3.8V without load, if i disconnect and reconnect the battery it lights again for few sec downto 3.2V and latching off again)



Battery manufactured in 2003. I assume it was put to use not long after that and was mostly in permanent charge since, except the occasional outages

About 2 months ago the luminaire was cut off from power

I got it yesterday with battery at 0.05V. After overnight charge (12 hours, half of the rated time but i think most of the charging is allready complete by this time) it holds the lamp in emergency for 18min untill it cuts out, with the voltage/current measurements as above

Now it is in charge again
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merc
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #1 on: October 15, 2016, 01:29:11 PM » Author: merc
AFAIK, NiCd batteries are perfect for high drain applications (they can supply quite high currents).

They do suffer from the "memory effect" - if not discharged completely ("half discharged") and recharged again (repeatedly), they lose their capacity. But this can be fixed by maintenance cycling (like 3 times completely charged with a low current, 3 times completely discharged). Some rechargers can do that automatically.

They don't mind complete discharging (to ~0 V) unlike LiOn batteries.

For the best performance - I'd try those maintenance cycles and repeat them time by time.
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RCM442
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #2 on: October 15, 2016, 02:52:53 PM » Author: RCM442
AFAIK, NiCd batteries are perfect for high drain applications (they can supply quite high currents).

They do suffer from the "memory effect" - if not discharged completely ("half discharged") and recharged again (repeatedly), they lose their capacity. But this can be fixed by maintenance cycling (like 3 times completely charged with a low current, 3 times completely discharged). Some rechargers can do that automatically.

They don't mind complete discharging (to ~0 V) unlike LiOn batteries.

For the best performance - I'd try those maintenance cycles and repeat them time by time.
Going to add that if dendrite crystals have already started forming, they may have already punctured the seperator and might not be savable. Try what merc said first though
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #3 on: October 16, 2016, 12:35:02 PM » Author: jrmcferren
The 0.05V sounds like there is some drain after the light latches off (to operate the latch). While NiCd Cells don't mind going down to 0, packs should never be taken to 0 unless you can discharge the cells individually. If you discharge a pack to 0 what will happen is one of the cells will get a reverse charge (negative voltage), this is bad for most battery chemistries (Lead acid can in theory be recovered since they have no polarity until the first charge at the factory). Getting a 3 Cell NiCd pack should be easy (and can actually be a DIY project if you are willing).
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Ash
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #4 on: October 16, 2016, 01:15:05 PM » Author: Ash
The 0.05V was the voltage across the pack after the luminaire was disconnected from power for over 2 months. We can assume that first the EM pack worked down to 3.2V, then the EM pack cut out and the battery kept going down to 0.05V on self discharge alone. As self discharge is happening inside the cells, it is impossible for a cell to get reverse charged from self discharging
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #5 on: October 31, 2016, 02:19:10 AM » Author: Medved
The NiCd cells can handle quite well complete electrode discharge, but they get destroyed one reverse charged. And the reverse charging always happens, when you have multiple cells in series and you discharge the pack too low (the weakest cell got reverse charge from the remaining charge of the stronger ones). And when an electrode capacity asymmetry is build into the cell (that is with all sealed cells, allowing to handle reasonable overcharging currents), one electrode reverses when the cell voltage drops below about 0.6V (but that is by far not as damaging as the complete voltage reversal, so for a short time it is accetable). So to make the device "fool-proof" in that matter, you do need an over-discharge protection, which makes sure no cell may get reversed even when all the others have about 1V.
With 3-cell battery that means minimum voltage of 2V...

And the "memory effect capacity loss" is nothing else, than voltage depressing by about 0.1V at the point of the "memorised" discharge level. So if the device does work down to at least 0.9V/cell, you will never observe any "memory effect" (with a 3-cell pack that means minimum operating voltage below 2.7V).

The "famous" satellite, where the "memory effect" was killing its performance was designed wrong in that manner (the fear of cell reversal brought the designed cut off voltage to about 1.1V/cell) and with that it yields the real reduction of the usable battery capacity. Unfortunately it was not possible to remotely reconfigure the cut out level, so the craft was "cursed" with that reduced battery capacity till its end of life.

But in any case it was a design error, quite well understood very short time after it was observed, but as no correction was possible, it "gave birth" to the "The memory effect causes capacity reduction" myth...
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #6 on: October 31, 2016, 03:33:09 PM » Author: hannahs lights
One trick you can use to revive sick nicads or just to rid them of there memory is to get a capacitor of a few thousand micro farads charge it to about 12 volts and discharge it across the sick cell I've tried it and it does work. Needless to say be careful when trying this?
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #7 on: November 01, 2016, 03:31:56 AM » Author: Medved
One trick you can use to revive sick nicads or just to rid them of there memory is to get a capacitor of a few thousand micro farads charge it to about 12 volts and discharge it across the sick cell I've tried it and it does work. Needless to say be careful when trying this?

For the "memory" it is way enough to once discharge them to really 0.9V/cell and charge back, then it is completely gone (the "memory effect" is in fact a border in the structure of the charge containing layer; once you discharge it completely, you etch that away and the new recharge will form a completely new, fresh layer, obviously without that border).
The capacitor discharge (or more energetic and so risky a high current jolt from a car battery,...) is treating just the dendrites. But usually the separator remains damaged there (where the dendrite was), so it is very likely they form rather soon again...
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #8 on: February 26, 2017, 01:28:21 PM » Author: Lodge
What size are the cells in the pack are they a sub C size nicd battery ? because those are commonly found in older style drill battery packs and can be obtained for free if you take them from the battery recycling box at most hardware stores / ikea/ office supply stores (you might need to ask permission, from the staff but I've had pretty good luck) and split the pack open to remove the cells, they are all tabbed cells so they are easy to solder into a smaller pack and most packs will have a few good cells left in them, if not take them back so they get recycled and either reassemble the pack or tape the cell contacts so they don't short out in transit,  or if you need a new pack look at some of the R/C sites they offer a large array of newer NICD battery configurations and the costs aren't that high and they are normally fresh cells.. 
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #9 on: February 26, 2017, 01:53:03 PM » Author: Ash
The form factor of the cells is not very important, as anything would fit in there (just make an isolated pack out of it and attach to the mounting tabs with a zip tie). Most of them are either Sub C or 1/2D

I dig batteries from the recycle box all the time. Its mostly AA NiMH's that the users throw out after single use out of ignorance, but drill batteries etc are usually dead to the point that the cells from them are not very usefull even for an emergency light (capacity sufficient maybe for 1 minute run)
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #10 on: February 26, 2017, 02:22:28 PM » Author: Lodge
I've found several with just a fuse that's gone, because someone is to lazy to recharge it and keeps on working till the drill stops spinning,voltage drops current draw grows and fuse blows, or they stall the motor ending the fuse pretty quick, maybe I got lucky but if they are free and you have some time sometimes you will get lucky as well..

I also love the free AA/AAA Nimh batteries you can just take home and recharge...

Ive had pretty good luck with Lithum Ion packs for 18650 cells as well because they will shut down if there is an imbalance, making the pack inoperable,  but if you play with Li cells play it safe and don't try recharging them unless you have a proper charger with all the safety features, and take care disassembling the pack because if you short a cell it can get pretty interesting real quick...   
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Ash
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #11 on: February 26, 2017, 03:50:54 PM » Author: Ash
Not a fuse - The cells just have useless capacity left in them. Sometimes along with the electrolyte crust starting to get out near the terminal

The Li i have no proper charger, but there is another thing i done with older cell phone batteries (Li Ion single cell) : Setup a voltage divider from the output of a 7805, so its voltage is about 3.7V..3.9V. With high value resistors. Leave the cell connected to that and see what happens

If the cell got an internal short it will be bad.. Therefore i leave it on the concrete outside

If the cell gets up to this voltage, then connect it back in the device and let the device take care of it from this point
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Re: Maintenance of NiCd cells in Emergency lighting « Reply #12 on: March 01, 2017, 10:51:19 AM » Author: Medved
Sometimes along with the electrolyte crust starting to get out near the terminal

That means the seal had failed and the cells are going to dry out rather quickly (the H2/O2 gasses escape instead of being recuperated into water). The gas recuperation requires certain pressure to build up during overcharge, without that they just escape, so water gets lost from the cell.
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