Project Logs

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• Second Life for Batteries

  James Nee • 04/30/2016 at 01:24 • 0 comments

  A good friend of mine posited a few months ago about what will happen to all the lithium ion batteries after they've reached the end of their usefulness? These cells typically will be able to hold an 80% charge, which is good enough for many applications such as cell phones, laptops and the like - but is incredibly noticeable in an electric vehicle application, especially for the range anxious.

  That said, it is interesting to see that electric vehicles on the road today have not yet suffered a as much degradation in capacity as expected - http://www.csmonitor.com/Business/In-Gear/2015/0219/How-much-will-Tesla-Model-S-battery-life-decrease-over-time.

  The secondary market for lithium batteries is most likely to be grid energy storage. There is already a healthy amount of investment in the idea from multiple angles, such as Tesla's Powerwall, to Nissan and Eaton teaming up to recycle old Nissan cells (https://chargedevs.com/newswire/nissan-and-eaton-collaborate-on-second-life-ev-battery-applications-2/). I am excited by that because leveling the demand and supply of power will not only improve the efficacy of time dependent renewable energies like hydro, solar, tidal, wind, but also provide a useful end of life for the millions of lithium ion cells being produced. Additionally, with the modular and self-sufficient nature of the Power Pack module this is an easy transition from serving in a vehicle to serving the grid, without the need for labor intensive break downs or even the need to build new enclosures for the cells. The real question is the transmission voltages that these cells will need to support which may require some reconfiguration of the pack or multiple modules to achieve.

  Also - I am working on a scale version of the enclosure! Expect an update on that process soon.

• Adjusting to the times

  James Nee • 04/25/2016 at 21:07 • 0 comments

  I know that the submission deadline has passed so this log won't be seen, but this point is so important I just had to write it now!

  As a big proponent of electric vehicles I love reading about the industry and what's happening, and one of the big stories now is the rising cost of lithium and the implications it can and probably will have on the industry as a whole.

  Link to story - https://chargedevs.com/newswire/companies-scramble-to-secure-lithium-supplies-as-white-petroleum-prices-soar/https://chargedevs.com/newswire/companies-scramble-to-secure-lithium-supplies-as-white-petroleum-prices-soar/
  

  While electric vehicles themselves are clean, the processes to mine, extract, and purify the elements that go into build lithium batteries, currently the standard for powering millions of electronic devices, is incredibly damaging to the environment. It may be possible for these processes to be less detrimental, but for now it is not.

  This is why I believe diversity is so important. It is possible for users to have the ability to choose to use a the most pragmatic energy source for their situation and not be at the mercy of market fluctuations or dependent on next generation technology. For now it very well be that the most sensible fuel to use is some form of oil, but the hope is that as the arms race for better, denser, cheaper batteries accelerates everyone will be able to benefit.
  

• Gasoline Power Pack Calculations

  James Nee • 04/23/2016 at 22:32 • 0 comments

  Before going forward and designing the gasoline combustion engine module, I wanted to take a moment and think through the energy requirements and use that to drive the sizing of the engine.

  My working theory is that to maintain a cruising speed of 100 KMPH (roughly 60 MPH) on a flat grade would require something on the order of 30 KW with an "average" vehicle (drag coefficient, weight, rolling resistance). If that is true, then a 40 HP engine (roughly 30 KW) would be enough to power the vehicle. Now note this is to maintain a cruising speed. Acceleration is a separate case and needs to be handled by studying the expected duration and magnitude of acceleration and to size the engine and capacitor banks accordingly. That is a much more complex issue and will be looked into a future time.

  For now, I want to present a back of the envelope approach as to how I am viewing the issue and to see if my theory that a 40 HP engine will be sufficient to cruise at highway speeds.

  Weight of the vehicle - 1850 kg

  http://www.nytimes.com/2004/05/05/business/average-us-car-is-tipping-scales-at-4000-pounds.html?_r=0

  Drag coefficient of the vehicle - 0.35

  https://en.wikipedia.org/wiki/Automobile_drag_coefficient

  Rolling Resistance of tires - 0.03

  http://www.engineeringtoolbox.com/rolling-friction-resistance-d_1303.html

  Distance traveled per second is 27.78 meters/second (100 Kilometers per hour)

  Power consumed to overcome rolling resistance = rolling resistance * normal force * distance traveled per second

  0.03*1823.9 kg *9.8 m/s^2 *27.78 m/s = 14896.37 J/s

  Distance traveled per second is 27.78 meters/second

  Power consumed by drag = 0.5*density of air (assuming 25 C)*velocity of the object (assuming still air)*area exposed to oncoming air*drag coefficient * distance traveled per second

  0.5*1.1839 kg/m^3 * (27.78 m/s)^2* 3 m^2 * 0.35 * 27.78 m/s = 17766.82 J/s

  14896.37 + 17766.82

  Overall power consumption to maintain 100 KMPH = 32663.19 Watts or roughly 32.6 KW

• The Sub-frame

  James Nee • 04/23/2016 at 22:32 • 0 comments

  One of the most critical components in this project is what I call the "sub-frame". It is essentially a cradle that sits inside the engine bay and seats each of the Power Pack modules. It is also the most difficult to standardize, and the prototype version will definitely be a one off, custom piece.

  Knowing that I wanted to make the design as flexible, and easy to construct, as possible. This piece acts as an interface between the existing engine bay, which was designed for a very specific footprint, and packaging scheme. The bottom of the sub-frame may be able interface with existing engine mounts which could increase the vehicle rigidity and allow for the weight of the modules to be distributed more evenly across the chassis, instead of through the ends of the 3 cross tubes which are currently intended to be welded to the chassis.

  Another element I have given a lot of consideration to is how to properly secure the enclosures. Using foam padding along the front plate and square tube support members will dampen road vibrations that will transfer through the structure and reach the module packs. To ensure that the modules will not fly out of the slots, however, I believe the best option is to use a rotary latch like the one shown below, produced by Southco. It can be electrically actuated to release the module, but also includes a manual override in case of emergencies.

  Image and product listing can be found at http://www.southco.com/en-us/r4-em

  One big area of exploration is how this addition will change the way the vehicle deforms in the case of a crash. If the cradle is filled with lithium modules, the weight in the engine bay will far exceed that of a normal combustion engine. In that instance, this will dramatically change how the vehicle behaves in a crash scenario and may cause sever injury or death to the driver and/or passengers. Before proceeding further I definitely want to think about how to do scale tests and how the design of the cradle can be done to mitigate or prevent any problems.
  

• Questions Going Forward

  James Nee • 04/23/2016 at 19:37 • 0 comments

  This weeklong sprint has been really helpful in building up the design and getting the idea to a point where at least I can communicate what I hope it will do. That said, the journey ahead is still long and there are plenty of other unforeseen questions to answer. In meantime, however, there are plenty of questions I know to ask and it would be good to post them up here for future reference.

  1. Charger - will there be a charger in each module or one for the whole vehicle? My current thought is that one per vehicle is the way to go. Having a charger separate from the module is cost efficient, but can make the wiring more complex. Additionally, given that there will be a junction box where all the modules connect, that traction box could be design for selective bi-directional current flow, using relays to disconnect modules that are not designed to receive current (i.e. internal combustion engines). This also h
  2. Climate control - AC and heater systems are pretty standard in vehicles, but do not use standard parts. Each vehicle will have it's own condense, pump, and compressor set-up and attempting to re-use existing parts may be unfeasible. While it would certainly be ideal to use existing hardware to minimize prototyping costs, in the long run it would be best to have it included in the add-on frame (more on that in the next project log). This way the entire engine bay can be cleared and the add-on frame includes all the optional features like heating, AC, 12V accessories, and so on.
  3. Attaching the sub-frame - I realized that I have not created a post on the sub-frame design so I will be posting that in the next project log, but a necessary element of this platform is a way to seat the modules in the engine bay! Currently, the sub-frame is relatively straightforward design; a specialized rack that will seat 3 modules and specialized additions like AC or heater units. The issue is how does the sub-frame attach to the vehicle chassis? Is it welded, bolted, or bonded? Additionally, further investigation should be done to determine the effect of this addition on frame stiffness and corner weights and think about the impacts on vehicle dynamics, because why build a car that handles worse than it's original design?

  These are a few questions that I still have rolling around in my mind, but have neither the time or energy to answer fully at this time. As the project progresses, I definitely will dive deep into exploring these topics and evolve the platform accordingly.

• Checkpoint #1

  James Nee • 04/23/2016 at 07:59 • 0 comments

  With the deadline for Design project entries fast approaching, I have decided to stop design and begin polishing my work for the contest - generating renders, going over the numbers on the cost estimates, so on and so forth.

  This is what I have so far:

  • A rough first draft of the Power Pack module specifications
    
    • The footprint was determined by taking a 2 sigma deviation from the standard values described in a scholarly article related to hood sizing
    • High power, communication and coolant connectors were determined based on the use case
    • Sealing the enclosure is dependent on the energy source - batteries are completely watertight, whereas engines are ope
  • A conservative budget for a path to prototyping a full scale, working vehicle based on the Power Pack concept
  • Preliminary designs for a Power Pack based on Panasonic NCR18650B cells, as well as on based on a Briggs & Stratton 10 HP gasoline engine
  • Gallery sketches and imagined use cases

  I don't know if it's enough to merit entry into the contest, but at the very least I am excited to get feedback on my work, and even if I don't move forward in the contest I plan on continuing to develop, test, and mature this idea.
  

• Thinking about the User

  James Nee • 04/22/2016 at 01:30 • 0 comments

  Design of the battery enclosure continues, but I wanted to take some time to think about the end user. Am I working on something that only I would find useful, valuable or interesting? If that is the case, it wouldn't be the end of the world but I do want this project to reach an audience greater than one.

  So I decided to think outside myself, and envision what other situations there would be that the Power Pack platform would be useful. Granted whatever I came up with is not backed up by extensive user research or surveys, but I like to think that the use cases are reasonable, and describe a large portion of car owners and operators in the US.

  The following are three completely fictional accounts of what I imagine are a few archetypal users of this product.

  Jon - young urban professional

  Jon lives in an apartment in Santa Monica, and would love to drive an electric car, and while his commute is only 40 miles a day, he cannot charge his car at night. That and the fact that his office has no electric vehicle charging yet, it’s logistically difficult to drive electric. He does live near several hydrogen refueling stations and it is convenient for him to refuel there. Instead of buying a dedicated hydrogen vehicle, however, he likes the modular aspect so that if he decides to move to a place where hydrogen refueling is not convenient, he can switch to battery electric, or gasoline if necessary, and it is relatively easy to sell his hydrogen module.

  Sandra - rural pragmatic traveler

  Sandra lives in the northern reaches of Montana and she has both a biodiesel and gasoline option which allows her to travel for hundreds of miles without refueling, as well as utilize used vegetable oil to power her vehicle, which she gets from local diners and bars that she frequently rolls through. What makes the Power Pack module appealing to her is that it’s easy to perform maintenance on the system without needing to go to a mechanic, and if a problem is really severe, it’s just a matter of ordering another engine module instead of buying a whole new vehicle. The electric motor also has some handling advantages. With the instant torque, moving off road up steep grades is much easier. Without a supercapacitor bank Sandra can’t really maintain a high acceleration, but for now this what she has is sufficient.

  Arthur - performance driven amateur racer

  Arthur is a gearhead living in modern times. He is part of the National Auto Sport Association (NASA), and wants to race electric. At the moment there are no standard class where he can race electric, so he has converted his ‘vintage Porsche 911 to have a fully electric drivetrain. What’s great about the Power Pack system is that he can race all weekend without needing to worry about recharging or downtime. He keeps a several spare modules fully charged at all times, and quickly swaps them out between races. Additionally, since he does like using his Porsche for scenic drives, he has two different battery chemistries - one that cannot deliver as much power, but has more energy so it can go for longer drives. When racing range is not as much of an issue, but when he darts in and out of corners being able to source a lot of power from the modules is key.

• Costing It Out

  James Nee • 04/21/2016 at 03:34 • 0 comments

  In parallel to the enclosure design I wanted to get a sense of how much this project will cost me. The goal is to get a donor vehicle, convert it to electric, and then use that as a test bed for various module types.

  Realistically I would not go from 0-60 right away, but would test the components piecemeal - build a scale version of the enclosure to test the design to see where things could improved. Such unknowns like the epoxy bond, the EPDM bulb seal, anchor points for the enclosure, and more need to be tested before a full scale version is built up.

  Additionally, the cost of building a full scale prototype is not realistic at first. The current goal is to operate at roughly 375 V, which is similar to what other OEM vehicles operate at (BMW, Nissan, Tesla) meaning their electric motors and inverters are designed for those voltages and should lead to a lower cost price point for power electronics at that voltage range. Unfortunately, not being able to operate at the economies of scale available to OEM manufacturers, building a lithium ion based battery pack to that voltage would cost around $18000 USD before shipping (for a 30 KWHr pack based on Panasonic NCR18650B cells - 28 cells in parallel per group, 100 groups in series). This could be certainly be made more cheaply with used Nissan Leaf cells which could be had for ~ $10000 for a 30 KWHr pack.

  Instead it would probably be wiser to go for a lower voltage, and a measly range. 144V is common voltage among motors used by the DIY community, and by virtue of needing less cells in series to achieve that voltage is much cheaper to build.

  Finally, I wanted to keep the big picture in mind as well. Though I passionately believe in a pure electric future, I completely expect automobiles to be powered by fossil fuels for a long time yet. Through the budget planning process I began looking into a gasoline powered module, built from readily available single cylinder, four stroke engines. As expected, it is significantly cheaper to run on gas. :(

  More on the gasoline module, and the associated super capacitor module, soon!

• A Well Engineered Box

  James Nee • 04/21/2016 at 03:17 • 0 comments

  I began designing the PowerPack Lithium Battery enclosure. I developed the form factor rather arbitrarily based on averages from an article that looked at Pedestrian Crashes - A Methodology for the Geometric Standardization of Vehicle Hoods to Compare Real-World Pedestrian Crashes. That set the footprint that I wanted to achieve with this enclosure. I started with the a lithium battery enclosure because I felt that would be the most difficult to do. I would be packing as much as 2700 cells (100 groups in series, 27 cells per group all in parallel) in this pack if I want to achieve a ~30 KWhr pack. With the current fitment I was able to get to 80 cells, but that was with a rather conservative cold plate design that can definitely be slimmed down. The cold plate could be a whole project in itself, but at this time I am just taking a dead simple approach that I know can work.

  The key features of this stage in the design was the attempt to make it water tight, ideally IP68 but with this approach to sealing further testing is required to verify that, and easy to construct. The enclosure is large, so would require a rather large press brake or a box and pan brake, but the intent is to epoxy the edge together. This was chosen over riveting and welding because of several reasons. The enclosure is made from 5052-H32 aluminum, which is great for folding, but, like many aluminum alloys, undergoes a significant change when welded, to the point where the welded joint is significantly weaker than the un-heat affected metal. That coupled with the fact that it's cheaper and easier to epoxy the edges together than to rivet and epoxy or weld, made it a clear choice. It must be said, however, that this does increase the overall manufacture time for the enclosure depending on the epoxy cure time, and also would probably require some jig to hold the enclosure while the epoxy cures.

  The lid is fastened using quarter turn fasteners which primarily function to compress the weatherstripping seal. The weatherstripping meets ASTM E283 which actually focuses on air movements in buildings, but does have a test method for water access as well. That seal, plus the design of the enclosure, should ensure a watertight enclosure to store sensitive items like lithium batteries and electronics.

  Finally, a breather vent was added to equalize the humidity inside and outside of the box. This vent is waterproof, but still allows air to pass from within the box to the surroundings to ensure no condensation will form inside the enclosure. This could also serve to help with rapid pressure changes, but that is unlikely to happen, and it uncertain if the breather vent is large enough to exchange the air quickly enough.

  A preliminary fit test. As of now I can only fit in 80 modules in series (each module has 27 cells in parallel). The goal is to get to 100, which would require a reduction in the cooling plate size.

• Sketching It Out

  James Nee • 04/19/2016 at 04:45 • 0 comments

  I started sketching some ideas of what the finished product might look like.

  The hope is to eventually design and build the whole vehicle from the ground up so that I could define the suspension characteristics, weight distribution, and surround sound system, but for now It only makes sense that to get a nice donor car and convert it.

  Thankfully, many others have converted traditional gasoline vehicles to be electric, and based on the experience of others a I would be looking at a Chevy S10, or a Honda Civic. A Porsche 911 would also be a great choice, but definitely out of my price range.

  The idea in itself is relatively simple - clear out the engine bay, and replace it with a mounting rack for Power Pack Modules.

  One of the ideas that I played around with was also the concept of a hood alternative. There is definitely a lot to be said about the aesthetics and aerodynamic qualities of a single, stamped hood, but do cars without sensitive moving components in the engine bay need to be shielded as robustly?

  With the S10, it is probably that the mounting rack would be in the bed itself, improving weight distribution, ease of access, and time to replace modules.
  

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