NiCad FAQ - NiCad Legends

NiCad FAQ - NiCad Legends

Post by Lacroix Ma » Tue, 10 Oct 1995 04:00:00



Primarily to sci.chem.electrochem.battery

I send the following text as is, with some added notes..  They respond
to the first thread in this conference.  
I personnally believe the data from manufacturers (they DO tests), you only
need to give a phone call to get tech doc and the like.

The FAQ comes from :

ftp.armory.com in /pub/user/rstevew file nicad.faq.zip
or
ieee.cas.uc.edu/pub/electronics/faq/ftp.armory.com

I am preparing a revised version, but would like to include some tech data
from manufacturers, and computed results about energy densities,
charging, ...  So I guess it will be a good Christmas gift ...;-)

Here we go with the FAQ and the rest

Enjoy
Marc

========================= CUT with (NiCad powered)) Laser gun ================

NICAD FAQ, from Ken Nishimura

note :
1) Ken is known as KO6AF, HT's are Handheld Transmitters ...
2) this FAQ will be improved soon, but, as far as NiCad's are still DAQ's
(Daily Asked Questions) on the list and elsewhere, I thought this will fix
some 'legends', and give some answers.
3) this FAQ was initially posted on sci.electronics, and others  probably
4) I added some coments I sent to Ken who seems very busy at the time.  I
intend to help him getting a new FAQ out soon...

Marc

There we go, Ken speaking :

Quote:

> Greetings:

>   I have decided to write this diatribe due to the continuing Ni-Cd
> battery saga.  Yes, batteries are LOW tech -- they can't compare
> to the bells and whistles of our latest HTs, but... your new HT is but
> a paperweight (albeit an expensive one) without power from your batteries.
> This is not a response to any particular prior post, and is unsolicited,
> so in short, I'm not flaming anyone....  But, I thought it may be useful,
> so, without further ado, let us take a more careful look into
> NiCd battery management.

>                                            -Ken

> P.S.:

>   1)  The stuff below glosses over some of the more technical nitty gritty
> details.  I wanted it to be shorter than 50K Bytes!  

>   2)  I actively solicit corrections, both technical and editorial.  If
> you have information contrary to that presented below, please let me know.
> Flames, on the other hand, are summarily disregarded, as usual.

> -------------------------------------------------------------------------------
>                            Some Ramblings About NiCd Batteries
>                            Ken A. Nishimura (KO6AF)

> Credo #1:  Charge control is the key to battery management.

> More batteries are destroyed or damaged by bad charging techniques than
> all other causes combined.  Once a battery reaches full charge, the charging
> current has to go somewhere -- most often, generating heat and gases.
> Both are bad for batteries.

> Q:  How does a Ni-Cd battery work?

> A:  Let us answer this with another question.  How does a electrochemical
> cell work?

> First, a bit of nomenclature.  A cell is a single electrochemical device
> with a single anode and a single cathode.  A battery is a collection
> of cells, usually connected in series to obtain a higher terminal
> voltage.

> Batteries, whether they are primary (use once) or secondary (rechargeable)
> are devices which convert chemical energy into electrical energy.  In the
> case of the latter, they can take electrical energy and store it as chemical
> energy for later use.

> The key to electrochemistry are the processes of oxidation and reduction.
> Remember the phrase" "LEO (the lion) goes GER (grr??)" -- Lose Electrons
> Oxidation -- Gain Electrons Reduction.  When one oxidizes a material,
> it gives up electrons it becomes more positively charged, or
> enters a higher oxidation state.  Likewise, when one reduces a material,
> one is adding electrons to it and either making it negatively charged
> or reducing its oxidation state.

> Now, one can make a cell using two materials, say A and B and immersing
> them in a solution which can conduct ions, called an electrolyte.  (An
> ion is a charged atom or radical of a molecule capable of transferring
> electrical charge).  Now, let us say that material A is easily oxidized --
> it likes to lose electrons, while B is a material that likes to
> be reduced.  When these two materials are immersed in an electrolyte,
> and a circuit is completed from A to B, A is oxidized and electrons
> are released to flow to the circuit.  After performing electrical work,
> the electrons flow into B, where B is reduced.  The circuit from B to
> A is completed by the flow of ions in the electrolyte.  A secondary
> cell can be reversed by forcing electrons into A, and reducing the oxidized
> A to regain unoxidized A for use again.

> This, of course, is an oversimplified view, as only certain combinations
> of materials and electrolytes provides useful and practical batteries.

> Oh, one more bit of nomenclature:  The cathode is where reduction takes place,
> and the anode is where oxidation takes place.  So, in a battery which
> is producing current, the positive terminal is the cathode, and the negative
> terminal is the anode.  Yes, this is counterintuitive from our understanding
> of diodes, where the cathode is negative with respect to the anode...

> Now, the NiCd system itself:

> When the cell is fully charged:

> The cathode is composed of Nickelic Hydroxide.

> Now, nickel is one of those elements that has multiple oxidation states --
> it can lose a different number of electrons per atom, depending on how hard
> it is coerced.  Nickel is usually found with oxidation states of 0
> (free metal), +2, +3 and +4.  The +2 state is referred with a -ous suffix,
> while the +3 and +4 states are referred with a -ic suffix.
> So, nickelic hydroxide is really NiOOH (the nickel has a charge of +3) or
> Ni(OH) (the nickel has a charge of +4)
>       4

> The anode is composed of free cadmium metal (zero oxidation).

> The electrolyte is usually a solution of potassium hydroxide (KOH).

> When one connects a load to the cell, as explained earlier, the anode is
> oxidized and the cathode is reduced.  Electrons leave the anode where
> the cadmium is oxidized and forms Cd(OH) , plus 2 free electrons.
>                                    2
> These two electrons go to the cathode where they reduce the nickelIC
> hydroxide to form nickelOUS hydroxide or Ni(OH) (where the nickel has
>                                           2
> a charge of +2)

> This reaction can take place until the materials are exhausted.  In theory,
> cells are manufactured so that both anode and cathode are spent at
> roughly equal rates.

> Q:  OK, so what happens when cells are charged?

> A:  Well, in a nutshell, the inverse of the discharge.  To charge, one
> is forcing current back into the cell (opposite of discharge current).
> Here, electrons are being taken out of the positive terminal, and forced
> into the negative terminal.  This means that the material at the positive
> terminal is being oxidized (hence is now the anode -- confusing, eh?) and
> material at the negative terminal is being reduced (now the cathode).

> In the NiCd system, the cadmium hydroxide is being reconverted into cadmium,
> and the nickelous hydroxide is being reconverted to nickelic hydroxide.

> Note that the electrolyte in both charge and discharge is a means to move
> the hydroxyl (OH-) ions around.  Unlike the lead-acid system, the electrolyte
> really doesn't change in composition too much between the charged and
> discharged state.

> Q:  OK, so what's so tricky?

> A:  The easy part of charging is reconverting the spent material on
> the plates to the charged condition.  The hard part is knowing when
> to stop.  Let us take a moment to think about what happens when
> we overcharge the battery.  Once all the nickelous hydroxide is
> converted into nickelic hydroxide, and in theory all the cadmium
> hydroxide is converted into cadmium, the charging current has to go
> somewhere.  As the energy of the charging current cannot go into
> more chemical energy, it goes into splitting water (water is
> still the major constituent of the electrolyte).  Just like the
> age old chemistry experiment of splitting water into hydrogen and
> oxygen, a fully charged NiCd cell does the same thing.  You are
> forcing oxidation at the positive terminal and reduction at the negative.
> When one oxidizes water (actually the OH-) ion, one produces oxygen.  Likewise,
> at the negative terminal (now the cathode), one produces hydrogen.

> This of course is bad.  Oxygen + hydrogen = BOOM.  Cell manufacturers,
> or at least their lawyers, frown on this from happening.  So, they cheat.
> During manufacture, they deliberately oversize the negative plate, and
> they partially discharge it.  That is, they put a fully charged positive
> plate, but put a slightly discharged, but bigger plate of cadmium in.
> The amount of free cadmium in the oversized plate is matched to discharge
> in step with the amount of nickelic hydroxide provided in the positive
> plate.

> Now consider what happens as full charge is achieved.  Oxidation of
> water starts at the anode, but since the cathode is oversized, and has
> excess hydroxide, the current continues to produce cadmium metal instead
> of hydrogen.  At the same time, the separator (the material used to prevent
> the plates from shorting) is designed to allow oxygen gas to diffuse through,
> from the positive to the negative plate.  The free oxygen then oxidizes
> the cadmium metal to form more cadmium hydroxide to prevent hydrogen
> from being formed.  Voila -- a safe battery.

> Q:  OK, so it looks like batteries are well protected.  Now what?

> A:  Not so fast.....  this scheme will work only as long as the overcharging
> current is limited to a value such that the rate of oxygen liberation at
> the anode is less than or equal to the rate of diffusion across the separator.
> If the overcharging current is too high, excess oxygen is produced at
> the anode, and since not enough oxygen can diffuse across to make up for
> the

...

read more »

 
 
 

NiCad FAQ - NiCad Legends

Post by Jim Thom » Mon, 16 Oct 1995 04:00:00


Warren, I have had an Alpha 4 for about a year, and wouldn't give it up for
the world.  It now happily tends to all the battery chores of a full season
competition flyer, with 3 transmitters, 4 extra TX batterys and about 20
various planes and RX packs.  The keypad and alphanumeric interface aren't the
most sophisticated, yet they work like they need to.  The sophistication is in
the design and electronics.  This baby does it all.  Go for it.
Jim Thomas

 
 
 

NiCad FAQ - NiCad Legends

Post by Dick Burkhalt » Mon, 16 Oct 1995 04:00:00


Quote:

>Warren, I have had an Alpha 4 for about a year, and wouldn't give it up for
>the world.  It now happily tends to all the battery chores of a full season
>competition flyer, with 3 transmitters, 4 extra TX batterys and about 20
>various planes and RX packs.  The keypad and alphanumeric interface aren't the
>most sophisticated, yet they work like they need to.  The sophistication is in
>the design and electronics.  This baby does it all.  Go for it.
>Jim Thomas

I gather from the ads that this rig only works off house current, is
that right?  I've also been considering getting one, but it would be
nice to have it to take to the field and charge my e-power packs.
However, if it does all the things it says it does and you're
obviously happy with it, I may just buy one for the shop anyway.

Dick

Dick Burkhalter

Kapaa, Kauai, HI

 
 
 

NiCad FAQ - NiCad Legends

Post by Jim Thom » Tue, 17 Oct 1995 04:00:00



Quote:

>Subject: Re: Litco ALPHA-4 (was: NiCad FAQ - NiCad Legends)
>Date: 15 Oct 1995 16:15:42 -0700


>: >Warren, I have had an Alpha 4 for about a year, and wouldn't give it up for
>: >the world.  It now happily tends to all the battery chores of a full season
>: >competition flyer, with 3 transmitters, 4 extra TX batterys and about 20
>: >various planes and RX packs.  The keypad and alphanumeric interface aren't the
>: >most sophisticated, yet they work like they need to.  The sophistication is in
>: >the design and electronics.  This baby does it all.  Go for it.
>: >Jim Thomas
>: I gather from the ads that this rig only works off house current, is
>: that right?  I've also been considering getting one, but it would be
>: nice to have it to take to the field and charge my e-power packs.
>: However, if it does all the things it says it does and you're
>: obviously happy with it, I may just buy one for the shop anyway.
>No...  I have one too and like Jim, I wouldn't trade it for anything.
>It runs off 12v current, and for at-home use, there is an included "brick"
>power source.  All the connectors are .1" phono-plugs, and the maxiumum
>current drain is about 1 amp; so you can easily run it from your car
>lighter jack by rigging up a lighter plug with a phono-plug.  I have a
>box-o-pigtails for every odd different way I might use the charger, and
>there are LOTS of ways.  :)
>--


Steve is exactly correct.  The Alpha 4 will run off 12 V, with the added
feature that you don't have to worry about polarity, it will sense it and take
care of business for you.  Nice touch.  Jim Thomas