If you have a device that will be in storage for a long time, and needs incredible reliability when it is used, then a rechargeable battery probably isn’t going to be the solution you are looking for. Other chemistries are happy with being over charged without transforming into a rocket engine. Lithium based batteries are sensitive about how they are charged, and can cause a fiery disaster if not treated well. Having charging circuitry in your device can be very convenient, but it can also come with significant regulatory requirements and safety approvals. When looking for a battery, you need to consider whether a rechargeable battery is the right choice or not. It goes to show that despite a lot of testing, edge cases of battery behaviour can come out to bite you if the situation is just right. I’ve crashed dozens of aircraft testing new hardware/firmware, this was the first time one ended up catching fire. The fire may not look like much, but if this had happened at the far end of it’s flight area over by the trees in the distance this would have been a huge disaster by the time we were able to drive to it. I needed the energy density of a lithium secondary cell, but not the ability to cost millions in fire damage liabilities. From then on, we only flew LiFePO4 cells, as they do not exhibit this cascading failure mode, and are much more stable. We were lucky we had a firetruck on hand for this eventuality, or it could have been a major disaster. This cascaded through the other cells until the venting gasses caught fire and set fire to the surrounding grass. The large 4 cell lithium ion polymer battery was crushed, and one cell started to fail. The crash was in the middle of a field which had not seen rain for 6 months, on a 42☌ (107.6☏) windy day. If you have high current demands for motors, bright LEDs, or processing power, you could rule out many chemistries immediately.Īs an example of these considerations, I had an experimental autopilot crash a small unmanned crop photography aircraft some time ago. Some batteries are capable of very high currents, and others may struggle to produce much at all. Closely related to voltage is of course current. If you require multiple cells to achieve a voltage that is practical for your project, the pack might become too bulky or impractical. The voltage of the battery might also play a significant role in your choice. Hearing aids are a great example of this, as you wouldn’t expect to see a lead acid battery in a hearing aid, at least not in one meant for human use. If your product is going to be portable, the volume and weight of the battery may play a significant role in the choice. Such high temperatures can cause some chemistries to fail in fiery ways. In the Australian example, a black box in the sun can easily reach over 70☌. Batteries are based on chemical reactions, which slow down at -40☌, if the electrolyte doesn’t freeze completely and stop the battery from functioning. When you’re testing the product in your room temperature lab, all looks good, then the product ends up in Canada exposed to -40☌, or in Australia experiencing +45☌ ambient and all of a sudden, the batteries don’t perform as expected. If the product is going to be used outdoors, or in an industrial environment, you might find it exposed to temperatures that are far lower, or higher, than some chemistries can handle. These disadvantages may outweigh any benefit you gain from either of those battery types.Īnother consideration that is often overlooked is the environmental conditions present where the device is used. But shipping batteries is not just regulations, a lead acid battery for example is very heavy and could incur significant costs for delivery due to the weight. With shipping regulations for Lithium based batteries, it can be hard to get a product with lithium polymer batteries to your end user by mail. One often disregarded aspect of battery choice by engineers is how the product will be delivered to the end user. However, is that really the optimal choice for your device? Let's take a look at the vast array of options out there, as well as other considerations when it comes to battery choices. If you are developing a product that needs a portable power supply, you might immediately jump for a popular lithium polymer battery or simple AA battery.
0 Comments
Leave a Reply. |