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eric, ni cads?

A

Anonymous

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Somewhere I thought I read about ni cads and how they could be reprogrammed once they have acquired a memory set. Is this so Eric? I sell integrated navigation systems and my clients are burning out their ni cads rapidly. Two or three charge discharge cycles or something to that effect, is this true? Can you please share your expert opinion? Thanks as always! ED.
 
This is Dave Emery, not Eric. I can answer this one for you. There are a lot of old wives tails about NiCads acquiring a memory. The story usually goes something like this "If a NiCad pack is only ever partially discharged, the pack will only be able to provide the same partial discharge". THIS IS UTTER CRAP.
The main killer of NiCad batteries are equipment manufacturers who make cheap chargers.
Sadly, I am referring to most equipment manufacturers including many power tool companies. The problem lies in the chargers. Everyone wants either a fast charger capable of charging the pack in a few hours or a trickle charger which will charge the battery pack overnight. Sadly, almost none of these chargers can be left plugged in for an indefinite period as is often claimed. The cells are damaged by heat which builds up inside them when they are left charging at the currents provided.
Have your customers disconnect the charger as soon as the pack is charged. Also contact the equipment manufacturer and let them know that they have a problem. A good rule of thumb is as follows: Q: Is the pack hot? No = OK. Yes = The pack is already damaged due to a poorly designed charger. If the equipment company has a problem with this you have my full permission to give them my e-mail address. I will be glad to pass on the pertinent info to them. All the best, Dave. * * *
 
On the internet I learned that nicad memory is a bit of a myth on earth but is real in satellites orbiting the earth at precise rates charged by solar panels at precise timings from daylight solar charging.
I also learned that when nicads are drained below zero the nicad reverses ploarity and becomes useless. I have opened up nicad packs and found faulty zero volt cells while the others were OK proving the latter. No memory just one or two dud cells.
It is I think the weakest link in the chain phenomenen with the lowest charge nicad getting to zero volts before the others and reversing polarity.
 
Hello John , a good tip it to solder a schottky diode in every cell (ej: 1N5821) , with this you will never had a dead o reverse cell between Good cell like you refer before.The cost is little compared with the cost of a pack .if your pack is of 12 cells you need 12 diodes ,OK.
Every time i thank all the people for this good forum.Alex
 
Ok everyone. For the full story go to : http://www.ssaclub.force9.co.uk/Reference/F_NiCd_Memory.htm
I think that this should be proof enough for anybody who can read that overcharging is the killer of almost all NiCads. Dave. * * *
 
Hi Dave and all,
Interesting posts. I've learned something here as I have always assumed that memory was a problem, although it could be reversed by a sequence of deep discharge and charge. I seem to remember that there was an article in Electronics World on this subject a while back. Will try to find it.
I have often brought dead cells (shorted) back to life by high current pulse charging. This burns out the little whiskers that form between the plates, that cause the short, and the cell comes back to life.
Eric.
 
Thanks Alex and Eric for a great forum, I am an electronics novice amongst experts and any help and advive is much appreciated.
Back to to second half of thje World cup, Bye.
 
Hi Eric have you ever seen the SunRay supercharger nicad - nmhi charger for recharging batterys in the field from cars power supply and home.
It uses negative slope charging . The unit also has a discharge feature that when drawing the battery down enough switches instantly to recharge mode . David T.
 
There is a nice handbook at the above URL. The handbook concludes that NiCads do have memory if the electronics don't dischange the battery deeply enough, and tells how to avoid memory problems.
 
Thanks everyone for your responses about the ni cads, as usual I have been educated by the many experts here in this forum.Again many thanks ! ED.
 
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