Field of invention

The present invention relates to electrical devices using a power source with a need to optimize power consumption. The invention applies in particular to electrical devices which may enter into contact with water.

State of the art

Time life of a battery is one of the most sensitive limitations for on the go medical devices like insulin pumps. This limitation is amplified by the user need of small and light devices.

Zinc-air batteries provide a very attractive power source, due to their large content of energy versus volume. However, this type of battery requires oxygen to deliver its power. If oxygen availability is reduced, for instance when the battery is immersed in water, then battery power is also reduced. A complete power interruption may even occur if the level of oxygen is too low, involving the end-of- life of the battery cell.

Monitoring the status of a battery, for instance in an implantable medical device, is disclosed in US patent application US 2005/01 02005.

Prior art devices however do not disclose a way to detect a reduction of oxygen around a battery which requires this type of substance to function.

General description of the invention

One of the objectives of the present invention is to limit the unnecessary power consumption related to a device, for instance a device including a wireless communication system. An example of such a situation is, for a portable device, to reduce the wireless communication function while it is immersed into water (e.g. while the user would be swimming). It is obvious that under such circumstances there is limited or even no need for a portable device to operate and/or communicate wirelessly to a remote control or any other device. In addition, it is most probable that the communication would not be effective under such conditions, so that it makes a lot of sense to limit the energy consumption related to such wireless communication.

Another objective of the present invention is to extend the life time of batteries, in particular metal-air batteries (including but not limited to zinc-batteries), when the device is fully or partially immersed in water. To this effect the invention relates to an electrical device comprising comprising a water detecting means and power consumption reduction means, said power consumption reduction means being arranged in a way as to be activated when water is detected by said water detecting means, said water detecting means comprising an interface sensor.

In a preferred embodiment the interface sensor is an optical sensor which, advantageously, may be adapted to measure variations of the refractive index.

In another embodiment the interface sensor is an electrical sensor which, advantageously, is adapted to measure the variations of the resistance between two immerged contact points.

Other embodiments of the invention are defined in the dependent claims.

Detailed description of the invention

The invention is discussed below in a more detailed way with non-limitative illustrated examples shown in the following figures :

• Figure 1 represents a general view of an embodiment of the invention

• Figure 2 more precisely illustrates a way to detect water

• Figure 3 illustrates one example of electronic circuit for resistance measurement · Figure 4 is a graphical representation of a voltage drop during an anaerobic use of a zinc-air battery.

There are several ways to detect the presence of water. One of the most interesting ones with the present invention is the detection on the external surface of the device.

Water detection must be preferably accurate enough for differencing the fact that the device is surrounded or only sprinkled by water (e.g. difference between a drop of rain and a swimming activity) and/or in a prolonged or brief exposure to water.

The detection of water on the external surface of the device is discussed in a more detailed manner below. Two parameters have to be taken into consideration for the measurement:

• Most favourable location for measuring the presence of water

• Most efficient way to measure the presence of water

In this example these two parameters are defined in accordance with a zinc-air battery, but their definition can be extended to any type of battery cells, requiring oxygen or not.

Detection point

In general this location is defined with respect to the specific points on the external surface (if any) which may be affected by the presence of water.

For instance, if a zinc-air battery is used, an air inlet is required. This inlet must prevent the ingress of water, which could alter the electronic. For this reason, a hydrophobic membrane is used. The surface of the membrane represents the last location that will be covered by water and then, is the most favourable location for detecting the presence of water. Detection method

The detection method must preferably take two parameters into account:

• Low power consumption

• Ability to differentiate the fact that the device is immerged into water or only sprinkled.

One of the most cost effective solutions to detect the presence of water is to measure the resistance of a gap between two immerged contact points.

Water detection method & equipment

If an air-zinc battery is used, one preferred configuration consists in implementing two electrical contacts on the fixation ring of the air inlet membrane.

The resistance value can be measured using a dedicated circuit. A voltage or potential divider coupled to the contact points on the fixation ring for example offers a range of measurement over several orders of magnitude and is thus very appropriate.

If the device has an RF link with a remote controller, this link can be used for determining when the device is immerged, because the surrounding water decreases the power of the link or even cut it. This effect of surrounding on the RF link is especially efficient for the typical wavelengths that are used for RF transmission, like 2.4 GHz.

The decrease of power of the RF link is measured by emitting after a given while, which could be typically a few minutes, a connection request to a remote control that is associated to the device. When receiving this request, the remote control will acknowledge it with an information of the transmission power of the link. The device can also confirm the measured transmission power when receiving the acknowledge from the remote. The feature for controlling the transmission power of the RF link is available in several standards of RF protocol like Bluetooth. The present invention uses different approaches for detecting the presence of water surrounding a device. For zinc-air batteries, the presence of water may stop the inhalation of air. Such a situation may result in a partial or total dysfunction of the device. For preventing/slowing down this drop, the device can disable or reduce some power consuming activities and limits the function to the essentials, what will request less power. Ultimately, if the battery reaches a predefined minimum threshold, the device can stop all its activities / functionalities. The normal operation starts again only when the inlet of air is reopened and battery voltage is above the minimum threshold. Thus, the ability for detecting the presence of water will allow the device to control its power consumption and adapt it for saving its battery cell in order to avoid killing it.

Alternatively or in addition, the reduction of power consumption related to the unnecessary wireless activity while the device is immersed can help increase the power available for the device and increase its usage period.