Charging NiCads

Ferrarimx5

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Will this work?

Batteries:
Five sub D Cells per pack
Two packs in series

Charger:
12 volt wall-wart charger that reads 16.5 volts on a multi meter
1 amp out put

Batteries are 2500 mah 6 volt each in series (So, 5,000 mah at 12 volt?)

The batteries are the resistors.

I am taping the batteries together in series and taping the stripped wires of the wall-warts to the terminal ends.

is this bad?

Fully discharged batteries so how long should I charge them? 5 hours?
 

MikeSalt

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5 hours wouldn't be enough, because there are some losses associated with the charging process. However, determining the charging end-point is tricky and Ni-Cads don't take too kindly to being overcharged.

I would get a proper delta-V charger and attach magnets to the ends of the wires and charge each pack separately.
 

fivemega

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Batteries are 2500 mah 6 volt each in series (So, 5,000 mah at 12 volt?)
Your batteries are 2500 mAh 6 volt each in series (So, 2500 mAh at 12 volt)
When you charging NiCad batteries, your charger must be constant current controlled at certain current.
Connecting such a battery to wallwart (without current control) may undercharge, overcharge or over current and finally damage the cells.
 

Ferrarimx5

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5 hours wouldn't be enough, because there are some losses associated with the charging process. However, determining the charging end-point is tricky and Ni-Cads don't take too kindly to being overcharged.

I would get a proper delta-V charger and attach magnets to the ends of the wires and charge each pack separately.

Thank you!
Now that I understand how a Delta V charger works
I will modify one of my cordless drill NiCad chargers (designed for 7.2 volts) to work with an individual battery pack.

This should provide a much faster charge rate without my having to do any math or guesswork.

 

magellan

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Thus thread caused me to reread the Wiki article on NiCads. I thought this section on the "jelly roll" of NiCads vs. the bobbin construction of alkalines was interesting:

"NiCd batteries usually have a metal case with a sealing plate equipped with a self-sealing safety valve. The positive and negative electrode plates, isolated from each other by the separator, are rolled in a spiral shape inside the case. This is known as the jelly-roll design and allows a Ni–Cd cell to deliver a much higher maximum current than an equivalent size alkaline cell. Alkaline cells have a bobbin construction where the cell casing is filled with electrolyte and contains a graphite rod which acts as the positive electrode. As a relatively small area of the electrode is in contact with the electrolyte (as opposed to the jelly-roll design), the internal resistance for an equivalent sized alkaline cell is higher which limits the maximum current that can be delivered."

Apropos of The topic of this thread, the article also mentioned that it's important to have a quality and not a cheap charger for NiCads as the cheap ones tend to damage the cells over time (see the section on "Overcharging").
 
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sbj

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...Fully discharged batteries so how long should I charge them? 5 hours?
About 3 hours and twenty minutes.
At the end of the charging time, feel that the batteries are getting warm. Then they are full.
 

Ferrarimx5

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About 3 hours and twenty minutes.
At the end of the charging time, feel that the batteries are getting warm. Then they are full.

Changing my charging procedure.
I have a maglite charger (14 volt)
I do not have the actual cradle attachment that this wall wart would plug into.

Can I charge the single 7.2 volt battery pack by attaching the leads to each end of the battery pack?

apparently this is the same as attaching the flashlight to the cradle and plugging in the wall wart, right?

Just trying to be safe and efficient.. Still have not ordered the proper cradle.. but have both the charger that plugs into the cigarette lighter/accessory plug and the 110/120 volt charger made and supplied by Maglite. My plan is to attach the positive lead to the positive terminal on the battery and the negative to the negative side.

Will charge for 5 hours..

Does this sound right?
Seems like the cradle is just a holding place for the flashlight and does not change the output voltage. Does the cradle house special electronics to regulate the charging rate?

Charging a 7.2 volt pack at 14 volts does not sound correct, but seems to be how it is set up.

Previously I have been stacking two battery packs to help match the voltage.
 
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Ferrarimx5

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No,

I burned up the Maglite Charger in two hours..
Battery pack did get a good charge and did not get hot.

Seems like it needs the cradle.
 
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