deep cycling NiCad N cells

[db (martinez, ca.)]

i use nicad n cells in my 41s and just got a new storebought charger. i have 4 individual cell holders from my old-time-used-to-be homemade charger that i'd like to use to deep cycle drain them. what would be a good way? i was thinking of connecting a light bulb to each one and draining them seperatly till the lights go out. does anyone else have a more scientific idea?

[William R.]

A penlite bulb is a excellent lo-tech load ( I have used 28V aircraft landing lights to load-up linear power supplies for test ) I have used a lamp that is of the same voltage but slightly lower amperage than the original device (less up-front hit on the cells) I hate it but Radio Shack seems to be your source for parts. I would like a confirm on the load rating (in the mA range) Some small lamps have a real punch and will take all they can get. (for ex- 1137 12v auto lamps will drain a car battery) Good luck!

[db (martinez, ca.)]

Thanks for the reply William. I looked at all the batteries and none have the ma rating on them. I once thought they were only 150 mah for some reason but they could be up to about 200 i guess. I'm nowhere on electricity, i only know the formule i had to know for the LSIT and some stuff that Ellis Esaly and Katie taught me. I can barely turn on my stereo. Since you think a bulb is a good enough way to drain the batts i'll do it. Is there an optimum rateing i should go for? I guess i want something i can see a glow in. Or, if you want to channel Norm: should i go for BIG LEDs? They might be slower but i would have a finer "guage" with them.

You the expert man. I'm just the monkey with the soldering iron here. What do you think? thanks - d

[Trent Moseley]

db,

You mentioned Norm and the red LED's. Don't forget the 34C.

tm (Redwood City)

[Dave Shaffer (Arizona)]

LEDs might be more interesting, but they don't actually pull much current - at least if you put in the correct (unless you want a real brief, real bright red flash!) current limiting resistor. A single radio-shack bought LED will want 10-20 mA (check the back label - some might want a bit more), so use a 100-200 ohm or so resistor in series (for a single cell) with the LED. Otherwise, just use a single-cell flashlight lamp (or 2 or more in parallel if you really want to pull the juice from your batteries in a hurry).

If you don't care about a glow, just use a 10 to 50 ohm resistor by itself.

[William R.]

Those big red LED's are good. I would have to look up the specs on them. You mentioned the mA/ current of the batteries, that is kind a max load or limit. What you want to look at is the current requirements of the calc. This goes to the issue with LED's.. electronics. LED's need a simple circuit to limit the voltage or amperage during operation. Your calculator will draw a sligtly different load (current) depending on how hard you hammer it. Yes, it is nothing like a Laptop etc. but it does matter.(micro level) Basicly your batteries could produce max 300 mA under load, but it is more important what your calculator will draw under max and normal load, it should be quite lower. At max load batteries will die quickly,
This is all really not that complicated, train the batteries to be one with the calculator. Oh yeah,,,, you want to train the batteries to mimic the calculator needs, I still say stick with a low current lamp. ??? I may have missed somthing, use the calculator to train the batteries ???

Edited: 10 Feb 2007, 12:55 a.m.

[Richard Ottosen]

Quote:

---

LEDs might be more interesting, but they don't actually pull much current - at least if you put in the correct (unless you want a real brief, real bright red flash!) current limiting resistor. A single radio-shack bought LED will want 10-20 mA (check the back label - some might want a bit more), so use a 100-200 ohm or so resistor in series (for a single cell) with the LED.

---

A red LED will not draw any significant current from a single NiCad or NMH cell. A red LED takes about 1.65 volts before it starts to draw even a few milliamps. A NiCad or NMH cell is only 1.25 volts when completely charged.

You could put two cells in series to get enough voltage to turn on the LED. You would then need the current limiting resistor. A 43 ohm resistor would give 20 milliamps of current -- the maximum current a typical LED is specified for. A one amp/hour battery would take about 50 hours to discharge. With the 2 cells in series there is the danger that one of the cells would get reverse charged. This is very bad. The bottom line: Don't use LED's to discharge NiCad or NMH batteries.

Quote:

---

Otherwise, just use a single-cell flashlight lamp (or 2 or more in parallel if you really want to pull the juice from your batteries in a hurry).

---

This would be my choice. But... Be aware that even a low brightness flashlight lamp will draw on the order of half an amp to an amp from the battery. You do not want to discharge the battery faster than its amp/hour rating.

-- Richard

[db (martinez, ca.)]

William & Richard;
So i want to get a lamp of some sort that will draw around 150ma? If R.S. doesn't have it i'll check at Zackit in Vallejo.

Richard; Any new RPN calcs in the pipe?

[Richard Ottosen]

Quote:

---

William & Richard;
So i want to get a lamp of some sort that will draw around 150ma? If R.S. doesn't have it i'll check at Zackit in Vallejo.

---

That should work OK. It will, however, take over 6 hours to discharge a one amp/hour battery.

You might find that you can't get a lamp that draws as little as 150ma of current. I am guessing that your batteries are rated for at least one amp/hour. If so, you can us a lamp that draws nearly an amp.

Quote:

---

Richard; Any new RPN calcs in the pipe?

---

I have been doing some work but there is nothing to report yet.

Were those your pictures of the DIY-RPN on the Web? Very nicely done!

-- Richard