It is estimated that by 2030 there will be 220 million electric vehicles on the roads. EVs, however, are fuelled by battery power and overheating must be avoided. Steve Hughes, managing director of REO UK, looks into the benefits of using water-cooling resistors for automotive applications


emperature can have a huge effect on the performance of a product, with overheating, for example, not only reducing the

efficiency but also the lifespan of components. So, whether a product is subjected to environmental heating or cooling, or if it generates its own rise or drop in temperature, managing this temperature is critical. In many industries, such as the marine, renewable and railway sectors,

components often have to face extreme environmental conditions; and at REO we have found that many of the challenges faced in these sectors, like temperature, are also applicable to automotive manufacturers. Take electric vehicles as one example. The International Energy

Agency (IEA) aims to have 220 million electric vehicles (EVs) on the road by 2030. EVs, however, are fuelled by battery power and overheating must be avoided to ensure reliable and efficient operation.

THE OPTIONS Most manufacturers understand the importance of effectively addressing and understanding heat transfer considerations early in the design process, saving time and minimising prototyping costs. Despite this, many OEMs are unsure how to choose between the two main ways of regulating device temperature: air-cooling and water-cooling. Braking resistors are used to dissipate heat and slow down a mechanical system to avoid overheating. Brake resistors have relatively low ohmic values, a high power rating, and are typically encased in a frame to create a safe distance between surrounding components. To increase its dissipation capability, the resistor’s frames feature cooling fans or liquid coolants. Traditionally, air cooling has been most commonly used as it is

relatively inexpensive and requires little maintenance, other than filter replacement. This is because the fan technology is robust and able to undertake some degree of damage – if a single fin broke on the fan, for example, it would remain functional and safe to use. There are, however, limitations when it comes to air-cooling. Not

only does the integration of a fan mean that the device’s enclosure must, generally, be bulkier to accommodate it, but fans can create an additional source of noise. An alternative solution is provided by a water-cooling product like the REO braking resistor D 350. Suitable for integration in EVs, this

converts the excess electricity that is not needed for recharging the EVs battery into heat that can be dissipated safely, or as energy that can be regenerated into the vehicle’s power supply. An effective use of energy that would otherwise be lost, this also reduces the need for resistance heating using the battery’s energy, which can reduce the vehicle’s driving range. The benefit of using a water-cooling resistor in an application like

this is that they can be easily integrated into the existing cooling systems of the vehicle and are able to deliver cooling on the areas where fans often fall short. Water-based systems operate on a very simple principle of heat exchange

whereby pipes containing a liquid coolant circulate around an enclosure and out of the device to keep components cool. The excess heat generated during use is thermally conducted by the water in the pipes, which can then be transferred out of the device and regenerated for other processes. With EVs, automotive manufacturers aim to make driving as energy

efficient as possible. Not only are fans in air-cooling systems limited by their reliance on ambient temperatures to cool down overheating components but, depending on the size of the application, OEMs may need to integrate multiple fans as opposed to just one. In comparison, water has a high heat conductivity and only requires

a single pump to cool infrastructure, significantly lowering the overall energy consumption and cost of the cooling system. Another advantage is that coolant can be stored in the pipes below

the application’s ambient level for even faster cooling. Water-cooling is the only method that permits cooling below the ambient air temperature and is ideally suited to industrial applications. In addition to maximising efficiency, resistors like REO’s REOHM series

D 330 make an additional space saving of up to 88%. The use of a water-cooling system allows optimal temperature characteristics to be achieved, while the performance of the component is improved.


Available from Molex, the Coeur CST High-Current Interconnect System has a float design that accommodates pin to socket misalignment, allowing for ease of mating PCB to PCB, PCB to bus bar, or bus bar to bus bar without the risk of overstress damage to the socket contact system. Allowing for a mated board-to-board profile as low as 5.00mm, it delivers between 30.0 and 200.0A of current and offers a wide range of configurations to accommodate PCB, bus bar, and wire solutions. The wire-to-board and wire-to-wire Coeur CST solutions will include male and

female crimp contacts, single and multi-row housings. Molex


Omron Electronic Components Europe’s new D2F-5 microswitch measures just 5.7mm x 12.7mm and a has a height from 5.5mm. With a rating of 5A, these subminiature switches are said to be ideal for high current applications and have a minimum durability of 10,000 actions. The switch is available in variety of terminal variations

including self-clinching PCB, left angled, right angled terminals, solder terminals and compact solder terminals.

Omron Electronic Components Europe


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