IUoU is an DIN

Din

DIN or Din or din can have several meanings:* A din is a loud noise.* Dīn, an Arabic term meaning "religion" or "way of life".* Din is one of the ten aspects of the Ein Sof in Kabbalah ....

-designation and acronym for an automated, three phase procedure to charge a lead-acid battery

Lead-acid battery

Lead–acid batteries, invented in 1859 by French physicist Gaston Planté, are the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, their ability to supply high surge currents means that the cells maintain a relatively large...

 by means of a battery charger

Battery charger

A battery charger is a device used to put energy into a secondary cell or rechargeable battery by forcing an electric current through it.The charge current depends upon the technology and capacity of the battery being charged...

. The three phases are: I-phase, constant electric current

Electric current

Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...

; Uo-phase, constant over-voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

;
U-phase, constant voltage.

The term 3-Step Charge Profile refers to the same procedure but is not part of the DIN terminology. At least one equipment manufacturer refers to the three phases as Bulk Phase, Absorption Phase and Float Charge.

The purpose is to fully charge the battery in a relatively short time without reducing its life span and to indefinitely keep the battery charged as long as the charger is connected. The three phases (or stages) have no connection with three-phase electric power

Three-phase electric power

Three-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by grids worldwide to transfer power. It is also used to power large motors and other heavy loads...

.

I-phase

When an IUoU charger is connected to an empty battery, it will enter the I-phase and provide a constant current. The current is determined by the charger and possibly its settings and should be in a reasonable relation to the battery's capacity. For longest battery life, the current would not exceed one tenth of the battery's capacity (C/10), although many battery specifications allow for a fast charge with a higher current than C/10. As a result of the current, the battery absorbs the charge and its voltage rises. The charger limits the maximum voltage to Uo, a constant or temperature-dependent maximum, typically 2.4 V to 2.6 V per cell. As soon as Uo is reached, the charger enters the Uo-phase.

Uo-phase

In the Uo-phase, the battery is continued being charged at a constant voltage, but the charge current is decreasing. The decrease is imposed by the battery. The voltage in the Uo-phase is too high to be applied indefinitely but it allows charging the battery fully in a relatively short time. So it is important that the end of the Uo-phase is detected reliably. Depending on the charger, the Uo-phase is concluded when the charge current goes below a threshold, typically 0.8 times the rated I-phase current and the U-phase is entered.

U-phase

In the U-phase, the voltage is decreased to typically 2.3 V per cell. This phase is intended to first fully charge the battery and to keep the battery charged, if desired indefinitely. The charge current decreases to a value much lower than C/10 and compensates for the self discharge.

Special cases

When an IUoU charger is connected to a full or partially full battery, the I-phase and Uo-phase are brief and the U-phase is entered quickly.

A bad battery will have short I-phase and Uo-phase, but there is a risk of gassing, further damaging the battery.

If a battery is connected to a significant load during charging, the end of the Uo-phase may never be reached and the battery will gas and be damaged, depending on the charge current relative to the battery capacity.