Batteries overheat in test of portable fans from mainland

July 20, 2015 14:58
Four mainland-manufactured portable electric fans with their Li-ion rechargeable batteries were tested. A fan (inset) exploded during charging last year. Photos: Ming Pao Daily, Headline Daily

Safety concerns emerged in a test of portable electric fans made in mainland China, Ming Pao Daily reported Monday.

Four different brands and models of such fans with their lithium-ion (Li-ion) rechargeable batteries were selected for testing.

The newspaper invited Lo Kok-keung, an engineer in the department of mechanical engineering, Hong Kong Polytechnic University, to conduct a test of the batteries' ability to prevent themselves from overheating and even exploding in the case of a short circuit within the fan.

The temperature of a Gold Quality battery in a Lileng fan reached 108 degrees Celsius in three minutes and 43 seconds.

Its plastic wrap melted off and white smoke was emitted.

The temperature of the other three battery samples reached between 42.7 C and 55 C.

However, these three samples gradually cooled down, and no white smoke was emitted during the test.

Lo said that the ability of all four batteries to protect against a short circuit was limited.

An object at a temperature of 50 C can already burn the skin of a user, he said.

The battery in the DreamTree fan reached 55 C in the test. It did not have a mechanism to protect against excessive current or a short circuit.

A manager surnamed Chan from the fan's manufacturer told the newspaper the safety mechanism is installed onto the fan instead.

Professor Eric Cheng Ka-wai from PolyU's department of electrical engineering said that the four tested battery samples were of the 18650 Li-ion type.

It is a low-cost type of battery, so the quality of its protective mechanism is limited.

Under normal circumstances, if a battery short-circuits, the protective device inside will prevent the overheating of the battery so that it can return to normal use.

However, with a less effective protective mechanism, high temperatures can be reached, damaging the battery and the safety device itself, so the battery can no longer function.

The Customs and Excise Department said Li-ion batteries and portable electric fans are regulated under the Consumer Goods Safety Ordinance.

The department tested 44 Li-ion battery samples collected from 2013 to July 2015.

Only one sample failed to meet the labeling requirements, 36 samples did not violate the general safety requirements, and the remaining seven samples are still being processed.

Lo suggested that a user of a portable electric fan should pay attention to whether the battery overheats while it is being charged.

If so, the user should immediately stop charging the battery.

A user should guard against overcharging the battery and, in particular, avoid charging it overnight.

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