ELECTRIC VEHICLES Archives

WATER VERSUS CONVECTION COOLING — WHAT’S THE DIFFERENCE?

CHOOSING THE RIGHT COOLING SYSTEM FOR YOUR APPLICATION

For applications relying on an electrical drive system, such as those in the marine and automotive sectors, overheating poses serious risks to equipment performance. Employing an appropriate cooling system helps to safeguard equipment, but knowing what to look for can be tricky. Here, Mike Torbitt, managing director at resistor manufacturer Cressall, explains the differences between water and convection cooling and how to determine the best-suited system.

When engines operate significantly above their optimum working temperature for long periods of time, they are at risk of engine failure due to overheating. Excessive heat not only reduces the ability of lubricants to protect engine parts from wear and tear, but it can also lead to thermal shock. This phenomenon occurs during rapid temperature changes, causing application components to expand and contract at different rates, resulting in cracks and fractures.

There are several steps you can take to protect against overheating. Firstly, it’s important to understand that optimum operating temperatures differ between applications. For example, the ideal temperature for car engines ranges between 75 and 105 degrees Celsius, while for boats this can vary depending on engine type. Selecting dynamic braking resistors (DBRs) with insulated components can help to prevent thermal shock, but employing an effective cooling system is also essential in avoiding overheating.

However, with both water and convection cooling options to choose from, it can be difficult to select the right cooling system for your resistor. So, what’s the difference?

CONVECTION VERSUS WATER-COOLED DBRS

While both options require minimal maintenance and are cost-effective to run, there are several key differences between air and water-cooled resistors.

Convection cooling, also known as air cooling, refers to the transfer of heat into the ambient air using airflow. There are two types of convection cooling systems available: natural and forced convection.

Natural convection relies on the buoyancy effect to cool the application. Since warm air is less dense than cool air, it naturally rises upwards away from the heat source and is replaced by cool air. Natural convection is therefore able to generate a consistent air flow without the need for ventilation mechanisms in applications where the ambient airflow meets thermal demands.

However, where increased heat transfer is required, forced convection cooling is preferable. Since forced convection uses fans, more air can be moved through the system in the same amount of time.

Despite generally being more effective than natural cooling, forced convection also has its limitations. Fans can be noisy and take up a lot of space, meaning they are not well suited to compact applications.

Consequently, water cooling often provides a more effective solution. Not only does the water-cooling method use less space and energy than convection cooling, but it is also better suited to applications with higher continuous power requirements. Since liquid has a higher density than air, it has a higher capacity for heat carrying.

MARINE COOLING

Water-cooled DBRs are especially useful in maritime applications. Cooling often proves difficult as the drive system is usually placed within the ship’s innermost parts and surrounded by heat-sensitive equipment.

To tackle this, most vessels use a chilled water system for machinery cooling and air conditioning. Adding resistors into systems such as the closed air/ closed water (CACW) is relatively simple and allows for up to 95 per cent of the energy from a DBR to be transferred to the ship’s water supply. This recirculation protects the equipment in the machinery room from detrimental ambient temperature increases.

Some marine applications also utilise a sea water cooling system. Provided the DBR is coated in a suitable material such as titanium to safeguard against erosion, this method is a sustainable way of reducing fresh water usage.
Cressall has several decades of experience in designing and manufacturing convection and water-cooled DBRs for applications ranging from automotive and railways to cranes and maritime. In addition to matching continuous power requirements of up to 1500 kilowatts (kW) for convection-cooled DBRs and up to 1800 kW for water-cooled DBRs, Cressall also offers custom options tailored to individual applications.

Safeguarding your application from heat is crucial but proves challenging without a thorough understanding of the different cooling methods available. Choosing a reliable convection or water-cooled DBR provides the assurance that your equipment is protected against overheating.

To discuss the right cooling system for your application, get in touch with our expert team.

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Are EVs too heavy?

ARE EVS TOO HEAVY?

THE IMPORTANCE OF LIGHTWEIGHTING ELECTRIC VEHICLES

In June 2023, the Institution of Structural Engineers published a report suggesting that the weight of our cars is too much for many multi-storeys built in the 60s and 70s. Known for being heavier, EVs have been the first to be blamed ─ but is this fair?

It’s clear that cars have come a long way in design and development over the past 50 years. But while their safety, range, and ride have improved drastically, there’s something else that has increased too ─ their weight.

Looking at some of the most prevalent vehicles of the 60s and 70s highlights the increase in weight. The BMC AD016 was Britain’s best-selling car for more than five years and had a kerb weight of just over 830 kg. Other popular cars included the Ford Escort at 867 kg, and the estate Ford Cortina at 940 kg. So, what’s the comparison to modern vehicles?

CARS IN THE 2020s

Let’s consider last year’s most popular car ─ the Nissan Qashqai. Comparing petrol and equivalent hybrid models within the range, such as the Acenta Premium, shows a weight increase of approximately 250 kg with the partially electric version. The 1.3L petrol comes in at 1348 kg, versus the hybrid 1.5L version at 1612 kg. While the slightly larger engine will contribute to the weight increase, it’s clear that the battery itself ─ even for just a hybrid ─ adds up to the weight. And the Tesla Model Y, the UK’s best selling electric car, boasts a weight of 1980 kg, with 771 kg belonging to the battery alone.

But is it fair to place all the blame on electric cars? It’s worth noting that, while electric and hybrid equivalents are likely to be heavier, there are still plenty of larger petrol and diesel cars on the upper end of the scale. New Range Rovers typically weigh upwards of 2400 kg, and the trend towards larger vehicles in general is another important factor in the weight debate.

Therefore, making more lightweight vehicles is likely to become a growing priority ─ not just in achieving higher fuel efficiency, but also to support older and aging infrastructure.

BUILDING LIGHTER EVS

When it comes to electric vehicles, the battery is likely to be an area of focus. Simply opting for smaller batteries won’t do; this will only negatively impact the range of usability of the vehicle. Therefore, if we’re going to make EV batteries lighter, a more sophisticated approach is required.

One option is the implementation of regenerative braking technology. Regenerative braking allows the surplus energy generated by braking to be directed back into the battery. This improved efficiency can extend the EV’s range by ten to 15 per cent, and even higher in optimum conditions. Therefore, by implementing regenerative braking technology, it becomes possible to slightly reduce the size of the battery, without a huge effect on range.

To safely implement regenerative braking technology, a dynamic braking resistor (DBR) is essential. The DBR dissipates any excess energy in the system, such as that generated when the car is braking on a full battery. Providing a safe way of dispelling this excess energy is crucial to protect the electrical components in the vehicle and to prevent overvoltages.

In line with lightweighting measures, it’s therefore important to choose a compact DBR. Here at Cressall, we have a range of lightweight DBRs available. Our flagship EV2 resistor is just 15 per cent of the weight of an equivalent air-cooled resistor, making it an ideal choice for EV manufacturers seeking to cut vehicle weight with no loss to safety or performance.

While there’s truth in that EVs are typically heavier than their petrol equivalents, it’s clear that the trend towards larger cars in general has contributed to the strain being placed on our infrastructure. But with EV uptake only set to increase within the next few years, making them lighter must be a priority. Regenerative braking is just one example of a technology crucial to improving EV efficiency and weight ─ and with new technologies emerging all the time, it certainly won’t be the last.

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Overcoming EV regulatory challenges

OVERCOMING EV REGULATORY CHALLENGES

THE SOLUTION TO MEETING EU REGULATION WITHOUT IMPACTING PERFORMANCE

The end of the road for internal combustion engine vehicles (ICE) has been on the agenda for a few years now, with many countries on track to meet their own targets for final sale. But the rollout isn’t without its challenges. Here, Simone Bruckner, managing director of power resistor manufacturer for the electric vehicle (EV) market, Cressall, explains the resistor solution to ensuring EU-compliant braking systems.

According to the European Automobile Manufacturers’ Association, or AECA, of the 1.9 million cars registered in 2021, the number of diesel car registrations represented 66 per cent less than in 2017. In the same time period, battery and hybrid EVs experienced a tenfold increase. However, while electrification seems to be progressing well for cars, challenges remain in other vehicle categories.

THE REGULATION

EU regulation relates to any vehicle belonging to category M3 — vehicles used for the carriage of passengers, comprising of more than eight seats in addition to the driver’s seats with a maximum mass exceeding five tonnes. Typically, these are buses and coaches.

Regardless of how category M3 vehicles are fuelled, they must be fitted with a secondary or endurance brake to safeguard the vehicle’s ability to stop. Category M3 vehicles brake differently to cars, as they do not purely rely on their service brakes to slow down. Instead, they also use an endurance braking system, which enables the driver to reduce the speed, or descend at a nearly constant speed, without using its service brakes. The benefit of an endurance braking system is that it doesn’t overheat as quickly on long declines and reduces the risk of fade or failure of the service brakes.

In order to comply with regulation, vehicles must pass the ECE R13 Type -IIA test, which requires the vehicle to maintain a speed of 30 kilometres per hour (kph) for 12 minutes on a 7 per cent slope without using its service brakes.

THE CHALLENGE

In the past, passing this test has proven difficult for EVs. The technical issue comes when the battery is fully loaded. The vehicle’s endurance braking system works on a regenerative braking model, meaning that when the vehicle’s brakes are pressed, the kinetic energy is converted into electrical energy, which is directed to the EV’s battery to recharge it.

When an EV’s battery is full, the vehicle’s kinetic energy cannot be converted into electricity and stored, meaning regenerative braking is impossible, and the endurance braking system cannot operate. So in order to pass the test, it’s important to ensure the availability of sufficient capacity in the battery, or create a separate outlet channel for excess energy to be directed into to keep the system operational and ensure the vehicle can pass the downhill test.

THE SOLUTION

One solution to ensuring sufficient capacity of the EV’s battery is to fit a dynamic braking resistor that removes excess energy from the system and dissipates it as heat. This heat takes the form of hot water within the EV’s own, existing cooling system. Removing energy from the system in this way ensures that the endurance braking system remains active by providing an outlet for excess energy.

Typical concerns around the use of a resistor for this application centre around a possible negative impact on weight and cost. But Cressall’s EV2 water-cooled DBR is designed specifically for EV applications, providing the high reliability, mechanical simplicity and low weight required. The EV2’s unique patented design means it is typically ten per cent of the volume and 15 per cent of the weight of the inequivalent air-cooled DBR. It can also be integrated into a vehicle’s existing overall cooling system, removing the need for a separate cooling circuit, further reducing weight additions.

The shift away from ICE vehicles is well underway, and despite no solid targets for the end of the sale of ICE buses and coaches, their electric counterparts are proving popular in Europe, with sales expected to quadruple by 2030. But for uptake to have as much success as anticipated, it’s crucial for automakers to consider how to ensure their braking systems are compliant to keep the EU’s roads safe.

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Electrifying agriculture

ELECTRIFYING AGRICULTURE

HOW EV TRACTORS CAN SUPPORT THE SECTOR’S SUSTAINABLE SHIFT

The electrification of the on-road transportation sector is well documented. What’s less discussed, however, are the off-road applications that can also benefit from electrification. That includes agricultural equipment. Here‘s how the agricultural sector can electrify, and the echnologies that can help.

According to the UK Government’s Department for Environment, Food, & Rural Affairs’ Agri-climate report 2021, in 2019, agriculture was the source of ten per cent of total greenhouse gas emissions in the UK. The sector was also responsible for 68 per cent of total nitrous oxide emissions, 47 per cent of total methane emissions and 1.7 per cent of total carbon dioxide emissions.

However, despite these figures, it seems the farming community is seeking change. The 2021 Farm Practices Survey indicated that 67 per cent of farmers consider recognising greenhouse gases to be either fairly or very important when taking decisions about their land, crops and livestock. One method of reducing emissions is to electrify equipment that traditionally runs on fossil fuels, such as tractors.

A NECESSARY CHANGE

Modern agriculture depends on a fleet of heavy-duty vehicles, from pickup trucks and small utility vehicles to massive tractors and combines that can weigh several tonnes, plus attachments. This machinery is commonly powered by diesel engines, mostly due to their higher torque and dependability. And here is where an electrification challenge may lie.

The electric sceptics of the agricultural industry claim that the largest problem with electrifying tractors and other heavy vehicles is that battery-powered options don’t have the energy density of a diesel model required to do long, hard work in the field. As load impacts on battery life, pulling a piece of heavy equipment would drain power fast. Using diesel, therefore, means a farmer won’t have to worry about filling the tank for 10 to 12 hours while out on the job.

Battery technology, therefore, needs to be developed in order to withstand the heavy loads of agricultural vehicles and supply a lasting and reliable source of power. Some manufacturers have produced compact, swappable batteries to extend the length of operation. Another option, developed by John Deer in 2019, features a long power cable that’s only available for farmers who are able to produce their own electricity via the use of solar panels, manure digesters or windmills.

Right now, despite its challenges, attempts to electrify farming vehicles are well underway. The work is being done, and given the mounting pressure to decarbonise all areas of industry, it won’t be too long before electrification becomes more accessible to the masses. In addition to the battery itself, manufacturers must consider the other components that make electrifying possible.

DYNAMIC BRAKING

Resistors will play a role in electrification, to support the process of regenerative braking. As part of regenerative braking, excess kinetic energy is used to recharge an EV’s battery. It is able to do this because the electric motor in an EV can run in two directions: one, using the electrical energy, to drive the wheels and move the vehicle, and the other, using the excess kinetic energy, to recharge the battery.

When the driver lifts their foot off the accelerator pedal and steps on the brake, the motor starts to resist the vehicle’s motion, “swapping direction”, and begins putting energy back into the battery. As a result, regenerative braking uses the EV’s motor as a generator to convert lost kinetic energy into stored energy in the battery.

Regenerative braking can support the ongoing dilemma of electric tractor battery range. However, to work effectively, other technologies are needed to make the process safe and effective. If the vehicle’s battery is already full or there is a failure, regenerative braking cannot happen as the excess energy has nowhere to go and must be dispelled safely. If not dissipated, it won’t be possible to slow down the vehicle, resulting in braking failure. To make electrifying agriculture safe, resistors are used to collect excess energy and dissipate it safely.

Cressall’s EV2 dynamic braking resistor converts excess kinetic energy during the braking process into heat that can be dissipated or used in other parts of the vehicle, like to heat the tractor’s cabin. It is a high-power density, lightweight and compact resistor that has proven to meet all major shock and vibration standards, suitable for all automotive applications, not just on-road vehicles.

While electrifying on-road vehicles has become well recognised, the same attention must be paid to other areas of the automotive industry. The agricultural sector is beginning to wake up to the prospects of decarbonising, and positive steps are being taken towards electrification. To make it happen, agricultural vehicle manufacturers need to consider the technology that can make agricultural EVs more efficient, and safer.