Introduction
As a Roadster owner, long time Tesla follower and even longer time engineer with experience of batteries and power systems, I thought I put together this little guide on the Tesla batteries and how to care for them. Hopefully this will be useful to the new influx of Tesla owners both as the Model S goes on sale and the Roadster reaches more affordable second hand prices.
Before spending serious money on my cars, I researched as much about the technology and the manufacturers as I could. In fact, I think I’ve probably spent more time researching this topic in the last decade than I have on any other subject, ever!
Nevertheless, as a systems engineer I have to be a bit of a jack-of-all-trades. There are probably specialist power engineers out there that have a more in depth knowledge about the topic than I do. I doubt this is exhaustive and I’d very much encourage feedback from other owners.
I've had to make this post multi-part due to the 6 pictures per posting limit.
Background
I’ve been involved with satellite systems engineering for over a decade. Specifically, back then I was systems engineer for the “bus” (service module) of the Surrey Satellite Technology Ltd GMP satellite platform, including the high level engineering of the power system. SSTL is a pioneer of using commercial technologies in the space field including batteries and Elon Musk was a 10% shareholder at the time.
The batteries that SSTL used were made from off the shelf Sony 18650 lithium ion cells and supplied by ABSL. Hundreds of cells were procured, tested, characterised by their performance and those deemed acceptable were assembled into strings, bricks and then battery modules of various multiples of series or parallel to get the voltage and capacity required. These modules would have their own internal safety and monitoring electronics. Battery modules might range from tens of cells up to several hundred and multiple modules might be used on a spacecraft. Such 18650 batteries have flown on Mars Express, Rosetta (the comet chaser recently in the news), Galileo and many other NASA, ESA and commercial spacecraft.
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The process of testing and building Li-ion 18650 based batteries (c) ABSL
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Rosetta (launched in 2004) is an example of a long duration mission using 18650 Lithium-ion batteries (c) Airbus DS
Those of you paying attention may have noticed this sounds familiar. Yes – it’s pretty much exactly the same way that a Tesla battery, or Energy Storage System in Tesla parlance, is built. So back in 2006 when a friend introduced me to Tesla, I was intrigued – and not entirely surprised – that they were taking the same kind of architecture we used and putting it in a car.
When you are designing spacecraft, you are very much aware that components have a performance at Beginning of Life (BOL) and End of Life (EOL). Some of the most important of these on a spacecraft are the solar arrays and the battery, both of which drop off appreciably in performance over the mission lifetime. The solar arrays will generate less power due to effects like radiation damage and the batteries will drop in capacity due to aging and repeated cycling. We design the power system so that the mission objectives can be met with EOL performance, meaning that at the beginning of the mission there is usually a surplus of power available.
It is important to note that different missions will see a different number of charge cycles – for example, in the case of a low earth orbit spacecraft like the International Space Station, this will be about 5000 cycles a year. Engineers of any electronic system powered by batteries know that there is a non-linear relationship between the Depth of Discharge (DOD) used and number of cycles the battery will last until the capacity reaches it’s EOL state (often 70% of new). They also know that the battery has to be kept within a set of temperature parameters for both storage and use to minimise aging. We were taught this at university: My copy of the satellite engineer's bible, Space Mission Analysis and Design, was published just as lithium ion was coming into use for spacecraft, but the principles are the same whether you are using NiCad, NiMH or Li-ion (see figure 11-11).
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As a Roadster owner, long time Tesla follower and even longer time engineer with experience of batteries and power systems, I thought I put together this little guide on the Tesla batteries and how to care for them. Hopefully this will be useful to the new influx of Tesla owners both as the Model S goes on sale and the Roadster reaches more affordable second hand prices.
Before spending serious money on my cars, I researched as much about the technology and the manufacturers as I could. In fact, I think I’ve probably spent more time researching this topic in the last decade than I have on any other subject, ever!
Nevertheless, as a systems engineer I have to be a bit of a jack-of-all-trades. There are probably specialist power engineers out there that have a more in depth knowledge about the topic than I do. I doubt this is exhaustive and I’d very much encourage feedback from other owners.
I've had to make this post multi-part due to the 6 pictures per posting limit.
Background
I’ve been involved with satellite systems engineering for over a decade. Specifically, back then I was systems engineer for the “bus” (service module) of the Surrey Satellite Technology Ltd GMP satellite platform, including the high level engineering of the power system. SSTL is a pioneer of using commercial technologies in the space field including batteries and Elon Musk was a 10% shareholder at the time.
The batteries that SSTL used were made from off the shelf Sony 18650 lithium ion cells and supplied by ABSL. Hundreds of cells were procured, tested, characterised by their performance and those deemed acceptable were assembled into strings, bricks and then battery modules of various multiples of series or parallel to get the voltage and capacity required. These modules would have their own internal safety and monitoring electronics. Battery modules might range from tens of cells up to several hundred and multiple modules might be used on a spacecraft. Such 18650 batteries have flown on Mars Express, Rosetta (the comet chaser recently in the news), Galileo and many other NASA, ESA and commercial spacecraft.
The process of testing and building Li-ion 18650 based batteries (c) ABSL
Rosetta (launched in 2004) is an example of a long duration mission using 18650 Lithium-ion batteries (c) Airbus DS
Those of you paying attention may have noticed this sounds familiar. Yes – it’s pretty much exactly the same way that a Tesla battery, or Energy Storage System in Tesla parlance, is built. So back in 2006 when a friend introduced me to Tesla, I was intrigued – and not entirely surprised – that they were taking the same kind of architecture we used and putting it in a car.
When you are designing spacecraft, you are very much aware that components have a performance at Beginning of Life (BOL) and End of Life (EOL). Some of the most important of these on a spacecraft are the solar arrays and the battery, both of which drop off appreciably in performance over the mission lifetime. The solar arrays will generate less power due to effects like radiation damage and the batteries will drop in capacity due to aging and repeated cycling. We design the power system so that the mission objectives can be met with EOL performance, meaning that at the beginning of the mission there is usually a surplus of power available.
It is important to note that different missions will see a different number of charge cycles – for example, in the case of a low earth orbit spacecraft like the International Space Station, this will be about 5000 cycles a year. Engineers of any electronic system powered by batteries know that there is a non-linear relationship between the Depth of Discharge (DOD) used and number of cycles the battery will last until the capacity reaches it’s EOL state (often 70% of new). They also know that the battery has to be kept within a set of temperature parameters for both storage and use to minimise aging. We were taught this at university: My copy of the satellite engineer's bible, Space Mission Analysis and Design, was published just as lithium ion was coming into use for spacecraft, but the principles are the same whether you are using NiCad, NiMH or Li-ion (see figure 11-11).
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