Hi,

I have some question that turned up during a charing procedure.

I have a battery pack with 20 nicd cells. I read The manual which tells
you to charge it for about 16h at 200ma using a 25ohm resistor and regulated voltage 32-36v.

Usually i do have nicd charger. Here i have a normal power supply (regulator).

First question, why do we always charge nicd with constant current? Is it a bad procedure using ccv instead and why.

Second: if we connect a 25ohm resistor and charge with 200ma constant current. Wont The voltage be limited to 0.2A * 25 ohms = 12.5V ?

Third: The Dont tell you which voltage The battery pack should be When it fully charged. How do i know this? Lets say i charge with 1amp instead, The battery would be charge before 16h so i cant charge it for 16h instead i have to charge it to The voltage lever i guess?

Fourth: how is it possible to charge for 16-24h with really low current and not risk overcharging, while charging with high current There is always a Max voltage level or a specific time like 1h maximum described.

 

First question, why do we always charge nicd with constant current? Is it a bad procedure using ccv instead and why.

We don't always use constant current. Charging with constant voltage is more typical.

Second: if we connect a 25ohm resistor and charge with 200ma constant current. Wont The voltage be limited to 0.2A * 25 ohms = 12.5V ?

How many batteries are you charging? What is their capacity? What is the charger voltage?

I wouldn't charge multiple batteries in series if I had a choice.

Third: The Dont tell you which voltage The battery pack should be When it fully charged. How do i know this? Lets say i charge with 1amp instead, The battery would be charge before 16h so i cant charge it for 16h instead i have to charge it to The voltage lever i guess?

A fully charged NiCd battery will have a voltage of around 1.45V.

Fourth: how is it possible to charge for 16-24h with really low current and not risk overcharging, while charging with high current There is always a Max voltage level or a specific time like 1h maximum described.

NiCds tolerate overcharging better than most batteries. If you charge at 0.1C for 16-24 hours, you're less likely to have any problems.

 

20 cells(battery pack) im charging. idk their specs..

using a power supply set to 200ma cc charging method. i increased to 1a, charge the battery pack (20cells) to 29V, then i had to turn off because i had no more time that day to continue the charge.

 

We don't always use constant current. Charging with constant voltage is more typical.

Not true.
Most battery chargers charge with a constant-current to limit the maximum charge current, which can exceed the batteries max rating otherwise.
Then, depending upon the battery type, it may finish at a constant voltage.

 

I have a battery pack with 20 nicd cells. I read The manual which tells
you to charge it for about 16h at 200ma using a 25ohm resistor and regulated voltage 32-36v.

Second: if we connect a 25ohm resistor and charge with 200ma constant current. Wont The voltage be limited to 0.2A * 25 ohms = 12.5V ?

In my books, 0.2A x 25Ω = 5V
This is the voltage across the resistor, not the charging voltage.
You still need charged battery voltage + 5V to fully charge the battery.
Assuming 1.45V per cell,
20 x 1.45V + 5V = 34V

As the battery approaches full charge, the current will decrease.

I usually charge ni-cd batteries with a 100Ω 3W resistor.

 

NiCad batteries are usually charged at a constant current and have the voltage monitored. The battery voltage begins to fall when the battery is fully charged. That is when the charge is terminated or converted to a trickle charge. There is nothing wrong with trickle charging a battery but it takes a much longer time. The best fast chargers use pulses rather than straight DC.

 

More importantly, you need to know the capacity of the battery. From this you can select the appropriate charging rate.

For example, if the battery capacity C is 2000mAh, then 1C charge rate is 2A for about 1.5 hours. This is a fast charge rate and the charger must have an automatic stop using combinations of time, temperature and negative voltage drop (NDV, negative delta V).

Charging at 1/10 C would be charging at 200mA for 16 hours. The charging time and temperature should be monitored.

 

Please tell us the battery voltage and capacity.