RECHARGEABLE BATTERY | MODEL CONSTRUCTION

Sealed alkaline nucleotidase (NiCd) and Nickel-metallgidridnye (NiMH) batteries are finding increasing application not only in industrial devices but also in home appliances, replacing batteries size AA and AAA. But these batteries, like any other, eventually “emptied” and require charging. To recharge, as recommended by the instructions for use and marking of the batteries themselves, through them must pass through the current ICT = 0.1 mA from the numerical value of the nominal capacity C for 12 — 16 hours.

But what if a suitable current or “smart” electronic charger and a simple transformerless available charge current differs from the value of batteries? To estimate the charging time is definitely unlikely to succeed. And if you define it by eye, when incomplete charging capabilities of the batteries will be limited but if excessive shortens the life and even the possibility of their explosion!

So that when you use not native charger, in which the charging current Iz is different from the standard (0,1), we offer a charging time t s to determine using a special formula. At its conclusion based on the following main points:

1. The charging time t s (h) is inversely proportional to the charging current I (A or mA) and is directly proportional to battery capacity (Ah or mAh).

2. The charging current should not be more than that allowed for “fast charging” IB. If not specified, then make it equal to 0.25 of the numerical value of capacity. (Before you use the charger, measure the current “de facto” — it can differ from the nameplate values).

3. When servicing of the battery is the main part of the current goes directly to the charge — electrochemical processes, and the other part is spent on support work and related phenomena: the movement of ions, heat and other losses.

It follows from the foregoing that the theoretical “ideal” charging time can be determined by the formula:

t s=C/I (1).

Considering losses, we introduce a correction factor To

t s=K*C/I (2),

where K = 1,2 when “fast charging” (IB = 0.25) and K = 1.4 to 1.6 at standard (ICT = 0.1). These values of the correction factor derived from the characteristics of most batteries.

Formula (2) is already accurate enough and acceptable for practical use. But the values you can specify.

Express To using a linear relationship of the type y = ax+b (3).

Then the General formula will look like:

t s=(C/I. a+b)*C/I (4).

Knowing the capacity and the recommended value of the charging current standard and “fast” charging and the appropriate charging times for specific battery to calculate the coefficients a and b.

For example: Nickel-cadmium battery capacity of 300 mAh, standard current of 30 mA time t s = 16 h, and “fast charge”: 16 = 75 mA and t s = 5 h.

Substituting this data in formula (4), we get two linear equations with two unknowns. After solving the system we get:

the time factor a = 17,15 h

the dimensionless coefficient b = 1,017.

Knowing these coefficients can easily be calculated by formula (4) charging any batteries the charger.

For example, if the current available charger is 50 mA (0,17), then the calculated charging time will be 8.2 hours (8 hours and 12 minutes).

For practical use the following is a table of coefficients a and b depending on time standard charge indicated on the battery.

the selection table of the coefficients a and b

Note. The charging time should not exceed 20 — 24 hours.

For small Iz, when the value of t s is measured in tens of hours, your best bet is probably to use a single simplified formula

t s=t s.cm.C/10 Iz

A. IGNATIEV, S. Osinovka, Bashkiria

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