An Interview with Tesla Battery Hacker [wk057]

We covered [wk057] and his Tesla Model S battery teardown back in September. Since then we had some time to catch up with him, and ask a few questions.

You’ve mentioned that you have a (non hacked) Tesla Model S. What do you think of the car?

It’s the best car I’ve ever driven or owned, period. Not to get too into it, but, I love it. I’ve put almost 20,000 miles on it already in under a year and I have no real complaints. Software feature requests… but no complaints. After almost a year, multiple 1700-miles-in-a-weekend trips, and an overall great experience… I can never go back to a gas vehicle after this. It would be like going back to horses and buggies.

A salvage Tesla Lithium battery had to be expensive compared to a Lead Acid setup. What made you go with the Tesla?

Actually, if you consider that the Model S battery is already pre-setup as a high-capacity pack, contains the wiring to do so, and the modules are much more energy and power dense than any lead acid battery bank, it’s actually almost cheaper than a comparable lead acid bank and all the trimmings.

I haven’t officially weighed them, but the modules from the Model S battery are roughly 80 lbs. 80 lbs for a 5.3 kWh battery is around 15 lbs per kWh, which is impressive. For comparison, a decent lead acid battery will have a little over 1 kWh (of low-rate discharge capacity) and weigh almost the same.

Also, the Tesla pack is much more powerful than a lead acid bank of the same capacity.
Generally a lead acid battery bank would have a capacity that would only be realized with slow discharges, so, 1/20C. Much over that and you sacrifice capacity for power. 1/20C for an 85kWh pack is only 4.25kW, barely enough for a central air unit and some lights without losing capacity.

Now the Tesla pack can be discharged (based on how it does so in the vehicle) at up to 3.75C for short periods, and at 1/2C continuously without really affecting the overall capacity of the pack. That means I can run 10x more power than lead acid without a loss in overall charge capacity. Leads to a much more flexible battery solution since the loads will, in reality, always be so low that this will not even come into play with the Tesla pack, but would almost always be a factor with lead acid.

Charging is also somewhat better with the Tesla battery. Charge a lead acid battery at a 1/2C and it will boil. Charge the Tesla pack at 1/2C (42kW) and it might warm up a few degrees. Oh, and the charging losses at high rates are much less than lead acid also.
Overall, without continuing to yack about the technical aspects, it’s just a much better battery, takes up less space, weighs less, and has more power available.

There are likely decent arguments for other solutions, but the rest aside, this one won out because it was definitely more interesting.

Click past the break to read the rest of our interview with [wk057]!

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An Arduino power inverter

inverter

If you’ve got a few solar panels lying around, or even if you want some 120/230 V AC power from a few 12 Volt batteries, you’ll need a power inverter. Sure, you can drop on down to any big box store and pick one of these up, or you can be like [Michael] and build your own (Danish, translation).

[Michael] found himself in the possession of a few halogen light transformers and decided to make use of them by building a DC to AC power inverter. The inverter is fairly simple – just the transformer, a few MOSFETS, and an ATMega0168 for software control that includes a ‘soft start’ feature that prevents power surges on startup.

The circuit is simple enough to etch at home, although a soldermask and a nice insulated enclosure would probably be ideal for this application.

Laptop backlight converted from CCFL to LED

ccfl-to-led-backlight-conversion

[Lee Davison] acquired an Acer laptop that didn’t have a display anymore. He had enough parts on hand to add in an LCD panel and give it a CCFL backlight. But when he started looking for an inverter to drive the backlight he couldn’t find one. What he did have on hand were some smashed screens that had LED backlights and so the CCFL to LED backlight conversion project was born.

He tore into the LED display and found the driver board. Unfortunately he didn’t locate the datasheet for the exact LED driver, but he found one that was similar and was able to trace out the support circuitry on the PCB. This let him cut away the unneeded parts of the board without damaging the driver. He didn’t want to pull out the CCFL tubes until he was sure the LED conversion would work so he tried it out on another smashed panel (where does he come up with all these parts) and it worked great. Once he got everything in place he was very happy with the results. The only drawback to the system is that he doesn’t have the ability to dim the backlight.

Headphone light show

Seriously, nothing says ‘Look at me!’ like these headphones. [Yardley Dobon] added a rainbow of colored electroluminescent wire to his headphones and made them pulse to the music. The video after the break shows the headphones bumping to the tunes. This is one of two versions of the project, the other runs the EL wire along the headphone wire itself. We’re a bit surprised that the high frequency from that parallel run doesn’t inject noise into the signal. We do enjoy seeing these in action, but in practice observers unfortunately won’t be able to hear the tunes to which the lights are pulsing.

It took us a little while to figure out that [Yardley] didn’t roll his own VU hardware. The inverter driving the EL wire is designed to bump to the music. But he did hack it to use an audio line rather than a microphone. He mentions that this has other uses, like allowing carefully crafted sound clips to precisely control the inverter.

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Driving your home appliances with hybrid power

This system of hybridizing your home’s electric appliances is an interesting take on solar energy. It focuses on seamlessly switching appliances from the grid to stored solar energy as frequently as possible. There’s a promo video after the break that explains the setup, but here’s the gist of it.

Follow along on the pictograph above. We start on the left with solar panel. This feeds to a charger that tops off a 12V battery. When that battery is full, the charger feeds to the inverter which converts the 12V DC to 110V AC power. This is fed to a pass-through which is in between the appliance (in this a case a lamp) and the wall outlet. The pass-through will switch between mains power coming from the outlet, and the 110 coming from the inverter. The homeowner won’t know, or care, which power source is being used. But sunny months should result in lower energy bills. The real question is how long it takes to cover the cost of the system in saved electricity.

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Pedal-powered 32-core ARM Linux server

Sure, it’s probably a gimmick to [Jon Masters], but we absolutely love the pedal-powered server he built using a group of ARM chips. [Jon] is an engineer at Red Hat and put together  the project in order to show off the potential of the low-power ARM offerings.

The platform is a quad-core Calxeda EnergyCore ARM SoC. Each chip draws only 5 Watts at full load, with eight chips weighing in at just 40 Watts. The circuit to power the server started as a solar charger, which was easy to convert just by transitioning from panels to a generator that works just like a bicycle trainer (the rear wheel presses against a spin wheel which drives the generator shaft).

So, the bicycle generator powers the solar charger, which is connected to an inverter that feeds a UPS. After reading the article and watching the video after the break we’re a bit confused on the actual setup. We would think that the inverter would feed the charger but that doesn’t seem to be the case here. If you can provide some clarity on how the system is connected please feel free to do so in the comments.

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Arduino rover evolves to a trike design

[Eduard Ros] wrote in to show off the latest version of his Arduino powered autonomous rover (translated). You may remember seeing the first version of the build back in June. It started with a remote control truck body, adding an Arduino and some ultrasonic sensors for obstacle avoidance.

The two big wheels and the pair of sensors look familiar, but most of the other components are a different from that version. The biggest change is the transition from four wheels to just three. This let him drop the servo motor which controlled steering. At first glance we though this thing was going to pop some mad wheelies, but the direction of travel actually drags the third wheel being the larger two. The motors themselves are different, this time depending on gear-reduced DC motors. The motor H-bridge is the same, but [Eduard] used a simple transistor-based inverter to reduce the number of pins needed to activate it from two down to just one. He also moved from an Arduino Uno to a Nano to reduce the footprint of the controller.