Ni-Cd batteries

Constant voltage chargers used to place a stiff voltage across a cell or battery for charging. Stiff means that the voltage changes little under load. True, or ideal, constant voltage means no change in voltage regardless of the load (not attainable in practice).

I said "used to" as these are not popular these days. Now, you find more constant current current chargers with temperature and voltage sensors to cut the charge back at an appropriate time.

A constant voltage charger is also called a taper charger as the charging current tapers off as the cell or battery charges up. The charging current tapers off with time ... again, not much used these days.

The ideal charger does not exist but the modern units come close. They use a constant current or a pulsed current and measure temperature and voltage as they do their thing. The little beasts often have computer chips built in.

A trickle charger is a very slow (low current) charger, and that might be what you are interested in?

orvillefpike wrote in news: snipped-for-privacy@w5g2000hsg.googlegroups.com:

NiCds get charged by CURRENT,not voltage;for a 1000mAH cell, a slow charge would be C/10,or 100 ma. NiCds last longer with fast charges,IMO.

--
Jim Yanik
jyanik
at
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Thanks

--
Panasonic used to have a really good Application Note on battery charger 
circuits for various chemistries. I just looked and couldn\'t find it 
anymore. You may want to do some more thorough digging on their website. If 
I recall correctly, Ni-Cd batteries were the only ones which would decrease 
in temperature (approx 10degrees) while charging, and increase if charged 
while full. This made it really easy to detect when the charge was done. 
Ni-Cd is very sensitive to over temperature and according to the A.N. heat 
was the #1 cause of premature failure. As far as fast charging, it depends 
on the Ni-Cd chemistry. Some can be quick charged and some not.

It was actually an interesting read, wish I could find it again...

Chris

** Groper Alert !!

** There is no such thing with Ni-Cd cells. ** Different animal.

Ni-Cd "fast chargers" pump in current until the battery gets hot and then shuts off the current. I think that this is the perfect recipe to ruin the battery quickly. I know that if you leave a lead-acid battery connected to a charger that delivers 2.3 Volts per cell, you can leave it on forever and it won't ruin the battery. That's the way it's done with alarm system and good quality batteries can last up to 15 years. I assume it could be the same with Ni-Cd batteries if they where "slow charge".

** You assume too much.

....... Phil

You know, you could have said that consant-voltage charging is unideal for NiCds, but of course you HAD to put in a groper in there somewhere...

In the greater scheme of things, this is relatively rare. Very few use Delta-t to detect end-of-charge. Shame actually, it's the more reliable and safe (albeit more expensive and inconvenient) way of doing it.

Shame actually, it's the more reliable and safe way of doing it.

Yes, they're pretty much all constant voltage type chargers.

Yes, with Lead/Acid, or SLA, that's pretty much the ONLY way it's done. With a few exceptions on certain time-critical applications, there are at least temporary exceptions to the "rule", but for the most part, they're all constant-voltage chargers.

Sorta kinda, but not really. On the El-Cheapo (TM) NiCd chargers. After the primary charge cycle, they use a constant voltage source via a current limiting resistor to feed each cell. (or each cell block if they're really cheap). The resistor is chosen as a best compromise over the selection of NiCd sizes that fit in that slot that will overcome natural NiCd discharge and not overly heat the cell(s) via wasted energy. It is deemed the heating and overcharging is insignificant to the overall life of the cell/battery.

Sheez, he's just asking a question.

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Linux Registered User # 302622

See:

For battery info.

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People. You can\'t live with \'em and it\'s illegal to hunt them...except in 
Texas.

Highfields Amateur Radio Club: http://highfields-arc.co.uk

NiCad chargers come in a variety of flavours, and they are virtually all constant current (or close to it).

Slow charge on a NiCad is C/10 or lower, but my preference is C/20 where C is the nominal capacity. Some high temperature batteries will get destroyed eventually at the C/10 rate. You can approximate this with a resistive feed from a voltage source, of course.

The terminal voltage of a NiCd is nominally about 1.2V, but can range from 1V to 1.5V depending on it's internal temp and state of charge. Don't let the terminal voltage exceed 1.5V, by the way, unless you are interested in pyrotechnic displays.

Cheers

PeteS

My question comes from the fact that, according to what I read, heat is the enemy of lead-acid batteries. If you charge them at more than

2.3 Volts per cell, they overheat and die quickly. I have a charger for a Makita drill that charges the 8 cell battery (8 x 1.2V = 9.6V) at around 15 volts and the battery have a thermistor in them, so when they "overheat" the charger shuts off. I thought that heat would also be detrimental to NiCd batteries also. I guess I'm wrong, that's why I am asking on this forum.

Thanks

Heat is detrimental in the sense of self leakage, particularly in NiCads, and also in the sense of overheating.

NiCads have a constant current charge regime, and at C/30 (in the correct ambient conditions) you can trickle charge them indefinitely, which is not true of other chemistries.

The most efficient charge controllers for NiCads depends on the chemistry involved (which varies widely for various manufacturers)

Cheers

PeteS

"orvillefpike"

** They can be damaged even at 2.3 volts per cell, unless the charge includes current limiting.

You have not read nearly enough to hold an opinion on the mater.

** Nonsense - it does no such thing.

With flat pack, the voltage will commence at around 10 volts, then rise over the charging period to around 12 volts.

Once all the cells are charged THEN they produce heat instead of storing the electrical energy as charge.

....... Phil

If the charger is regulated at 2.3 V and the cell is charged to 2.3 V, there is no current in one direction or the other, so how can it damage the cell. My NiCd charger has a transformer, a diode bridge, a relay and a capacitor so how can it go to 10 V then go up to 12 V when there is no electronics to regulate anything.

Thanks

"orvillefpike"

** ROTFL !!

Go away - IDIOT

** Gotta be a desperate attempt at a TROLL.

No one born is that stupid.

So maybe it wasn't.

...... Phil