Charging nicad batt pack with variable voltage current limited bench power supply

When I do that with a battery pack I set the current to about 1/20th of the rated drain current. You should see the current drop off on the meter as the batteries charge. If I need the battery quickly then I turn up the wick. 10 minutes at 1 amp usually gives me enough to finish what I need to do. The pack gets warm at this current but not enough to cause undue concern.

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Best Regards:
                     Baron.

I started out at 2 amps, never got warm. I have no idea of what the rated drain current is. How far above nominal voltage do you charge at?

Thanks,

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

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14 volt pack = 12 x 1.2 volt batteries = 14.4 volts.

end of charge voltage is 1.4 volts/cell

12 * 1.4 = 16.8 volts

Set the power supp;y output to 16.8 volts. Set the current limit to 200 ma (0.2 Amp). Charge the battery overnight, then use it to determine the level of charge. Adjust the current up in 100 ma (0.1 Amp) steps until you get a full charge in 10 hours. If the battery pack has an amp hour rating, divide that by 10 to get the proper charge current.

This is trickle charge, not fast charge, because you don't have a way to monitor the pack's internal temperature and turn off the power supply when the battery reaches maximum charge. Overheating a NiCd during charge can cause high internal pressure, which causes a vent to open (releasing the pressure and usually some electrolyte) and rendering that cell (and thus the entire pack) unusable.

John

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Is this your battery pack?

If so it is 1.5 AH. a C/10 charge rate would be 150 mA, and a 20/C would be 75 mA. Does your charger state how many hours it took to fully charge your battery pack? B&D has discontinued the Firestorm line, so there will be lots of that line hitting the yard sales and flea markets before long.

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You can\'t have a sense of humor, if you have no sense!

You can perfectly well charge batteries with it, but you cannot automatically detect full charge on NiCd or NiMH batteries.

You must use the "constant current" charge method, which means you must know the battery's charge state before you start, and then charge with a known current for a specific amount of time.

checking

Unlike lead-acid and Li-based batteries, NiCd batteries can't be reliably charged using a fixed voltage. There are just too many factors influencing the voltage of those batteries.

I have seen NiCd batteries close to 1.6V at full charge (while still charging). Your battery is 12 cells, which means you must set your charger's voltage to at least 20V. Higher is OK, but don't go to the extreme, because then you'll get some nasty sparks when connecting the battery.

Here's the procedure:

1. Make sure your battery is fully discharged.
2. Set your power supply voltage to 20-30V.
3. Set the current limit to your desired charge current.
4. Calculate how long you need to charge. If you are charging slowly, add 40-50% to compensate for charge inefficiency. If you are charging quickly, add less.
5. Set your alarm clock.
6. Connect the battery.
7. When the time is up, disconnect the battery.

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RoRo

John put it much better than I would have done.

But to answer your question, I don't bother monitoring the voltage at the outset ! The current is by far the most telling parameter. If you set a reasonable charge current you should find that the voltage will be about a 1.0v to 1.5v above the pack voltage.

--
Best Regards:
                     Baron.

14.4v charger or

died. I had a

current. That

it and after

drill works.

I've read

not checking

This is a _generally_ safe strategy for charging a drill battery pack, Set your supply to 20 volts. Then use this:

1N4001 +---------|Batt -

That will deliver ~150mA to the pack - the rate recommended for an ovenight (~14 hour) charge, based on the battery Mike Terrell mentioned.

Far better would be *knowing* the mAh capacity of your pack. You can then design a circuit that is closer to guaranteed safe. Furthermore, you can add a TL431 on the output to steal current when the full charge voltage (1.43 volts per cell) is reached, thus reducing the current going into the pack. That way, if you forget to remove the pack from the charger, it won't cook at the higher current.

Ed

The pack is 1400 ma/hr if I can trust what I found on the net.

Thanks for the diagram!

Wes

Ok, in that case, change the 47 ohm resistor to 100 ohms. That will set the charge current to ~137 mA, very close to the recomended C/10 (140 mA) rate. If you want to add the TL431 circuit:

+20-------Vin[LM317]Vout---+-----+ Adj | | | [10R] [100R] | | | 1N4001 +----+-----+-----+------>|--->Batt + | | | | [220R] [2.2K] | | | | +---[LED]---+ P | 5K o---/_\\ TL431 t | | | Gnd -----------+----+----------------------->Batt -

To adjust: monitor the pack as it charges. When it reaches 17.16 volts, adjust the 5K pot until the LED just turns on. The TL431 circuit will draw a little over 3 mA when the LED is off with the battery voltage below the 17.16 volt set point. When the voltage reaches the set point, the circuit will draw about

87 mA. The LM317 continues to deliver ~ 137 mA, but the battery will "see" only about 50 mA after the set point is reached, charging at roughly the C/30 rate.

Ed