Choosing the right battery system for your robots is essential because each type requires a different type of battery. Some require smaller sized ones while others could require larger ones. And then we talk about the varieties of batteries. Here’s a detailed guide on the types of battery systems for robots.
Types of Batteries:
Our main focus will be rechargeable batteries and the first name that probably pops into your head is ‘lithium batteries’; the most commonly used rechargeable batteries. If you wish for something under budget then lead-acid batteries would fit the bill, or you could go for Lithium-ion or Lithium-polymer batteries. (Non-rechargeable batteries are quite pricey in the long run either ways.)
1. Lead-Acid Batteries
Lead-acid batteries are usually cheap and come in large capacities too. You can find them in larger platforms that don’t require tremendous power but need lots of energy capacity. You’ll find them in solar power systems, UPS, etc. However these are only available in increments of 6V and 12V, are super heavy and have low capacity per weight unit. They also take longer periods of time to charge and lose capacity if left in storage.
2. Nickel Metal Hydride Batteries
If you want to go for a cheaper option but lighter than lead-acid batteries, nickel-metal hydride batteries are the ones for you. They’re quite popular for their low internal resistance and the good power-to-weight ratio and are far safer than Lithium-based cells. You’ll find them in airsoft guns, cheap toys, AA/AAA replacements, digital cameras, etc. Disadvantages include a higher self-discharge (around 50% higher than NiCd). They also have a limited service life and do not absorb over-charge well.
3. Lithium-Ion Cells
Lithium-Ion Cells are relatively safe and have a higher energy density so they are suitable for electronic equipment that requires longer time between charges while still consuming more power. Their rates of self-discharge are also low and are very lightweight. They’re used in powering electronic gadgets such as mobile phones, laptops, and tablets etc. However, one major disadvantage to them is their cost i.e. they can be quite costly and they will also suffer from aging. Plus they require extra protection from being overcharged and discharged.
4. Lithium Polymer Batteries
Lithium polymer batteries are usually lightweight and come in packaged form, a collection of single cells with a balance plug and the main power plug. They are available in a wide range of voltages as well according to the required usage. You’ll find them in combat robots, RC airplanes, and drones, laptops, and phones even.
Keep in mind however that they can be very dangerous if not handled with care. They should be properly stored and maintained. They can also be quite pricey.
Now we’ll discuss some battery specifications you should know about.
All batteries will come with a list of voltage ratings and capacity ratings in amp-hours or milli-amp hours. Some will also come with a discharge current rating (C-rating) or burst current rating.
5. Lithium Polymer Battery Ratings
- Voltage/Cell Count:
LiPo batteries include series (S) and parallel (P) cells. The basic ones are labeled as 1S, and if not labeled they’re automatically assumed to be 1S i.e. a single set of cells in series. The nominal voltage of a LiPo cell is 3.7V and so if a cell is “2S” i.e. two cells in series, its voltage would be 7.4V. Similarly, it would be 18.5V for a 5S pack.
- Capacity and C Rating:
Capacity refers to how much power the battery can hold whereas ‘C rating’ refers to the measure of how fast a battery can be discharged safely without harming the battery. Most batteries you’ll find today come with two C Ratings: A continuous rating and a burst rating (the burst rating is only applicable in 10-second bursts, not continuously).
Let’s say you have a 1000mAh battery pack labeled as 25C/40C. It has the capacity to handle 25A continuous or 40A bursts (usually for a couple of seconds up to 10 seconds). These ratings tend to drop at larger capacities. C ratings above 50 are common for batteries less than 1000mAh. Usually, a 500mAh 75C/150C battery can handle 37.5A continuous and 75A bursts.
What Voltage, Capacity, and Current, do you require?
You will have to match the voltage of the battery system to the voltage at which your motor will be running. Capacity simply helps to determine battery life. And the discharge capacity or current is basically the total sum of the current drawn by all of the motors under a load.
Batteries for Stationary Projects
There are several reasons why you should opt for batteries rather than AC supply of current even if your project is stationary.
- Electrical Noise:
This wouldn’t usually happen with a supply of clean power but if you’re working on a DIY project you’ll definitely run into background noise interfering with your project. Batteries, on the other hand, will provide you with a clean, steady supply of DC power. Plus you also won’t have to deal with any unregulated voltage drops.
- Current Capacity
Let’s say you want to get a 12V AC-DC supply for a 50A motor, you will require a much larger supply than 50A. And even a bigger supply that could handle 75-100 amps for a small period of time even if your motor will then only operate at a fifth of that. Instead, you could opt for a LiPo battery rated with bursts of over 110 amps along with a cheaper power supply.
- Power Limits
Power limits vary from country to country. In the USA, for example, at 120V power, most wall outlets are connected to a 15A breaker bringing the peak power from the socket to 1800W. On the other hand, appliances are generally limited to 1500W of continuous power supply.