How low will NiCd cells discharge to?

[treez]

Hello,

I am doing an emergency LED light unit. It obviously has a microcontroller in it which runs off the battery.

I am just wondering , if the mains is OFF for several months, then the microcontroller and the control circuitry will keep draining 50mA from the battery (battery is five 5000mAh NiCd cells in series)

Here is the cells used:
**broken link removed**

......how low will the battery discharge to?

....surely an individual NiCd cell will not discharge to less than 0.9V/cell?...even if the micro tries to draw a constant 50mA from it?

Supposing the Nicd cells discharge to less than 0.5V/cell...............how do you recharge such depleted cells, or are they damaged forever?

 

[BradtheRad]

how low will the battery discharge to?

Batteries will discharge into a resistive load until they are down to 0 V.

If the load has a threshold V, the batteries will not go below that.

if the mains is OFF for several months, then the microcontroller and the control circuitry will keep draining 50mA from the battery (battery is five 5000mAh NiCd cells in series)

At 50mA drain, 5000mAh batteries will last 100 hours.

Supposing the Nicd cells discharge to less than 0.5V/cell...............how do you recharge such depleted cells, or are they damaged forever?

Rechargeables do not like to be drained completely. They do not like to be left discharged for long times. Each occurrence of these is liable to cause them to decline in capacity. However they can still be recharged and used.

For best performance charge them as soon as their volt level drops to 1 V or so.

 

[treez]

If a NiCd cell goes down to 0.5V or less, then can it be recharged by just flowing a C/10 current into it?....or do you need much higher charging current to get it charging when its been discharged to such low voltages?

 

[BradtheRad]

Yes, nicads are designed to take a certain amount of abuse, because they are marketed to the population at large. That means you and me.

The C/10 figure is commonly recommended as a safe charge rate for most batteries. Some can take more. Nicads are able to.

However not all types of rechargeables can take too fast a charge, or can take continued charging after they are fully charged.