battery question

[AaronR103]

Sorry. I was bit unclear. The dreaded "memory effect in Ni-Cads is effectively a myth. The conditions required to induce true memory are almost impossible to produce in the field.

This hasn't kept people promoting other chemistries from claiming their favored battery was "memory free". While technically true, is misinformation all the same. When I see people engaged in this type of misinformation it calls into question their motives.


Tobin

Can't speak for NiCd in lights (obviously) but I used to run into the memory problems all the time in radios working EMS and in the army.

A

 

[cool_hardware52]

Can't speak for NiCd in lights (obviously) but I used to run into the memory problems all the time in radios working EMS and in the army.

A

Aaron,

You need to do a bit of homework. Ni-Cad memory is a disproven myth. True memory refers to a loss of capacity at a specific point in the discharge curve, i.e. where the battery was last discharged to.

Batteries can have all kinds of problems, and "memory" has become the catch all for any battery that failed to perform as expected, regardless of cause.

You may have had unexpected results with Ni-Cads, but it likely wasn't due to "Memory"

The single most certain way to shorten the life of any rechargeable battery, including Ni-Cads is to deep-cycle them. Intentional discharges, in some useless attempt to avoid a mythical memory problem just damages the battery faster.


From Nickel-Cadmium Battery Application Handbook, Gates Energy Products, 3rd edition (1986), section 4.5.3:

The effects of elevated charge temperature on the immediate cycle capacity of the cell have been discussed in Section 3.2.1 and 4.3.3.1. Cells exposed to overcharge for very extented periods of time, particularly at elevated cell temperatures, may develop an additional shortcoming called voltage depression. This phenomenon is one in which the cell voltage is depressed approximately 150 mV below the normally expected values which were calculated on Figure 4.19. This depression affects Eo and is independent of discharge rate. This depression effect initially appears on the discharge voltage curve near the end of discharge. With extension of the overcharge time (non-discharge) of the cell, this depression progresses slowly toward the mid-point and beyond. Accompanying this effect of depression in the voltage dimension of the curve is an actual slight increase in the capacity dimension as illustrated in Figure 4.21.

Note that to induce a memory one must subject the battery to shallow discharges and very long overcharges at elevated temps.

This simply is not the use profile for most consumer goods. Far more likely is damage due to deepcycling. Why? Because most consumer devices are furnished with barely enough battery for the application, almost assuring frequent deepcycling.

If you are experiencing reocurring problems with batteries today, I'd look at the % capacity used per cycle, and check to see if the chargers are heat sources for the batteries. Many "Cradle" type chargers place the battery directly over the transformer, assuring you cook the battery while charging.


Regards,


Tobin