Working time: How long can I work with my battery powered rescue equipment?
Even though we only very recently launched a new line of hydraulic rescue equipment with a unique and specially developed battery platform, we are already receiving many of the same questions from users. Every time we give a demonstration or training with the new Pentheon tools, one question always arises, and it is also often the first question to be asked. This blog attempts to provide you with an answer to the question most frequently asked about our Pentheon tools:
How long does the tool work on one battery?
It is easier to ask this question than it is to answer it since this depends on several factors, such as load, ambient temperature, proficiency of the user, etc. Because of this, we are unable to specify the exact working time in number of minutes.
Technical highlight: What is battery capacity?
Battery capacity is the amount of electrical energy that fits into a battery. This is indicated in ampere hour (Ah). The battery capacity is measured by evaluating how much electricity is able to flow through a battery in a certain period of time. This is calculated by discharging the battery using a specific current intensity.
For instance, 7 amperes can be drawn from a 7 Ah battery in one hour. An ampere is the unit of electrical current. However, electrical current in itself is not the only thing to consider. It is a combination:
The voltage in a Pentheon battery varies between 20 V and 29 V, depending on how full the battery still is. We therefore calculate using a nominal voltage of 25.2 V over the battery's entire range (from full to empty). In the case of Pentheon, the calculation is as follows: 25.2 V x 7 Ah = 176 Wh
The tool uses a maximum of 1000 watts. When we use the battery at its full power of 1000 W, it will be empty in 10.56 minutes. For example:
From a technical point of view, however, one could state that a battery can be used for almost 11 minutes at full capacity. This may not seem very long, but... the battery is actually rarely used at full capacity. The following examples will explain this more clearly.
Example 1: Candy
Compare it with a large bowl of Smarties or Skittles.
We have put 1,000 pieces of candy in the bowl, and 100 pieces of candy fit in your hand at one time. When you want a candy, you can opt to take one at a time. But you can also decide to grab a whole handful in one go.
Imagine taking a handful of candy out of the bowl every minute. After 10 minutes, you'll have reached the bottom of the bowl (1,000 pieces / 100 per handful). You could also take one piece of candy per minute, which means that it would take you 1,000 minutes to get to the bottom of the bowl. Or, perhaps, after five handfuls of candy you might be getting full and decide to take only three at a time after that. In short: The amount of time it takes to get to the bottom of the bowl depends on how many pieces of candy are taken out of it each time.
Back to our battery. The example in the box assumes that we continually take the maximum number of candy pieces out of the bowl (i.e., use the battery at full capacity), while during the designing of our new cordless tools, our aim was to make them as energy-efficient as possible and still offer maximum power. In other words, we don't take a whole handful of candy at once, but as few as possible. We only take 100 pieces of candy at once when it is really necessary.
If you search on the internet, you will find numerous websites that, by calculating the number of amperes, attempt to explain how long you can work with a battery. These calculations are complicated and often raise more questions than they answer because, in ideal circumstances, this can certainly be calculated. But situations in which the battery is used are not always the same and are surely not always optimal. It is impossible to always work with your tool at a temperature of 20 degrees and with an equal load. It is therefore a good idea to actually put your battery and tool to the test in practice to see how they react under various conditions.
Factors that affect the working time
While developing the Pentheon battery, it was therefore essential for us to conduct field tests – in particular to enable us to gain insight into the working time of this battery for its users. Tests were carried out under conditioned circumstances with the factors that affect the battery's working time most significantly:
Extremely low or high temperatures affect the working time. In the test phase, we exposed our batteries to extremely high and low temperatures in order to get a good idea of the effect this had.
Using battery tools on new car models requires higher working pressure. To achieve this, we need more power in the engine, which uses more battery capacity. This decreases the working time.
Extremely skilled operators may achieve the same result with fewer cutting or spreading actions, thus sparing battery capacity. We can assume that the training of extrication techniques has a positive effect not only on the action speed of the tool operator, but also on the battery's working time during a rescue operation.
Is the battery fully charged and stored under the most optimal conditions? On-tool charging ensures that the battery is always charged and ready for use. The batteries are installed in the fire truck and are almost always stored under ideal conditions in the fire station.
Example 2: Driving a car
Compare it to driving a car. Why does the number of miles or kilometers I can drive on a tank of gas differ with each trip?
To put it simply, the distance a car can drive depends on two things: the capacity of the fuel tank and the car's fuel consumption. A large, heavy car generally consumes more than a small, light car. The surroundings and driving style also affect fuel consumption. Are you driving in the mountains or through a flat countryside? Do you have a sporty driving style – with a lot of accelerating and braking – or do you drive in a more defensive way, often letting the car slow down by itself? The heating and air conditioning also consume energy and therefore have an effect on fuel consumption. So, it's easy to see that it's not only the size of the fuel tank that determines a car's range. When we translate this to rescue equipment: The capacity of the battery (volume of my fuel tank) is not the decisive factor for the total working time (range) of my rescue equipment.
Various car manufacturers are producing cars that are increasingly energy efficient and, like them, we have done our utmost to ensure that Pentheon tools use their available energy more economically. After all, this also affects the working time of your rescue equipment. The automatic start/stop system is one example of this economical use of energy. This feature ensures that the motor stops when the tool is not being operated and also when it has reached its maximum pressure, thus eliminating the unnecessary use of energy. The battery is also kept in top condition while it is being discharged and charged, thanks to the Battery Management System (BMS).
Back to the field tests
We have conducted a number of cutting tests in order to ascertain how many cuts a battery can make. This turned out to be approximately 40 cuts. We carried out the test using tools that had been stored for longer than 12 hours at -20º Celsius, but also with tools that had been exposed to +45º Celsius for 12 hours. We performed cuts on new cars as well as on older ones in order to gain as much insight as possible into the practical 'range' of Pentheon tools.
So, what can we conclude from all these tests? If you need to use a tool to remove the side of a car and this will require, for instance, 15 cuts, the cutter's battery will not be empty and you will be able to complete the job using a single battery. If 15 cuts are also needed on the other side of the car, this adds up to 30 cuts but, even then, the battery will still not be empty. The two sides have been removed and, with the capacity left in the battery, the roof can also be removed.
Just as the volume of a fuel tank does not define a car's range, a battery's capacity does not tell us everything about the working time of the rescue equipment. There are many factors that affect how long a battery will last. Therefore, an important question to ask yourself is the amount of time you need to remove two sides and the roof of a vehicle. This might not be about the number of minutes you are able to use the tools but, instead, the effective working time; in other words: am I able to do what is necessary to extricate my patient. And we can assure you: That is possible with Pentheon tools J.
We welcome your feedback in the comments.
Ronald de Zanger & Marinus Verweijen
Holmatro Rescue Consultants