Martin Thermal Engineering just leased a new Tesla Model 3 and it’s no surprise that we love it. We also started the process of installing 18 solar panels on our home and depending on how well we can maintain a high outward flow of electrons to the grid during the day, and a moderate inward flow of electrons from the grid at night – we will have a payback of less than 4 years on the solar installation.

Ok, there’s nothing too surprising about all that. It’s green economics at its finest! But in the process of buying and driving our new EV, my brain was bombarded with a whole slew of surprising benefits. I’m sure our readers have considered at least some of these, but I will be surprised if anyone thought of all eighteen. Here goes…

1. Benefits of Electrons versus Fluids
a. No more messy oil changes – with all that waste motor oil to dispose of.
b. No more checking the coolant level and the automatic transmission fluid level with the engine warmed up and the vehicle on level ground.
c. No more stains on the garage floor because your oil pan gasket is leaking. No need for kitty litter to absorb the fluid leakage puddles.
d. No more adding 95 lbs of dead weight (fuel) every time you run out of chemical energy in the tank. (Tongue-in-cheek…electrons weigh a lot less per mole than carbon and hydrogen atoms. Yes, the EV batteries are pretty heavy regardless of their charge/discharge state – but the Tesla doesn’t drive like a heavy vehicle.)
e. No more worries about spilling a gallon can of gasoline in your garage, where the vapors might escape and get ignited by your water heater.
f. No need to bother with brand loyalty to a multinational petroleum company’s fuel (…even if their detergents and other additives were demonstrably better than the competition) because electrons don’t need detergent, octane improvers or knock inhibitors.
g. Never need to hang around a gasoline station where you are forced to breathe in gasoline vapors and the exhaust from other cars. Recharging at home happens without any other vehicles running nearby and recharging at a supercharging station means the nearby vehicles don’t have any gaseous emissions at all.
h. No worries about carbon monoxide poisoning if you forgot to turn off the engine. It doesn’t have an engine – only a motor/generator and a battery (+ electronic controls). And of course, there’s no tailpipe at all.
i. No more contribution to photochemical smog by emitting NOx and HC pollutants – and (if you charge the car with green electricity) no more contribution to climate change by emitting carbon dioxide and filling up holes in the greenhouse layer.

2. Benefits of the EV Driving Experience
a. No more sensing the “pause” when the automatic transmission shifts from lower gears to higher gears. For you manual transmission guys and gals – no pressing the clutch and maneuvering the stick shift.
b. No more pressing the gas pedal…no gasoline inside this puppy. (It’s still ok to call it the accelerator pedal.)
c. No more wasting potential energy by coasting downhill and braking or putting the engine in lower gear. Gasoline engines can “reduce” fuel consumption to nearly zero when you are coasting downhill – but they can’t defy entropy and convert the CO2 + H2O molecules back into C8H18 molecules. Regenerative braking does just that – it converts a good portion of your potential energy into battery storage as you travel downhill at constant speed.
d. No more overheating and warping your disc brake rotors because you are braking too much going downhill. The full power of regenerative braking is amazing – so much so that you almost never want to take your foot off the accelerator entirely – if you try that, you might find yourself slowing down more than you want to – even on a steep downhill grade.
e. No more replacing brake pads every 25,000 miles. Ok, I didn’t actually estimate how many miles the factory-installed Tesla brake pads will last, but on the highway, I never need to brake, and on city streets, I only brake during the last 5 to 10 feet before a stop. That’s all because the regenerative braking system causes the car to decelerate at up to 0.3 g, which means the regenerative stopping distance is 100 ft if the initial velocity is 30 mph and the final velocity is 3 mph. The best news – all 100 feet of deceleration happen without applying brakes at all.
f. No more wasting the front one-third of the vehicle on a 100-hp engine that takes up the entire front compartment and frequently gets too hot to touch. Now you can have both a front trunk and a rear trunk, and you can reach into both without getting grease stains on your hands and clothes.
g. No more worry about your radiator overheating on a steep incline – you don’t even have a traditional radiator (although there is a glycol coolant loop that rejects heat to a second refrigerant evaporator and absorbs heat from the inverter, battery and other electronic components). The cabin heat and the glycol heat are ultimately rejected to the environment through an air-cooled refrigerant condenser, but you can’t add water anywhere except the windshield washing fluid reservoir, and all the heat exchangers are out of sight when you open the front hood.
h. The ability to amaze your non-EV friends with the mathematics of a supercharger’s power as compared to the regular wall socket in your garage. The 120V, 12A circuit at home delivers about 1.4 kW of power and takes 54 hours to add 270 miles of range to the EV’s battery (approximately 5 “miles” per hour). Compare this to one of Tesla’s newer superchargers that delivers up to 130 kW of power and could potentially add 270 miles of range in just 30 minutes (nearly 500 miles per hour). Wow!
i. The ability to amaze your non-EV friends with the possible cost savings associated with buying electicity instead of hydrocarbons. Obviously, installing solar at your home gives you the best economics because your electron consumption is essentially “free” whenever you push electricity back into the grid while the sun is shining and you only consume grid power for vehicle charging at night when the buyback rate is cheaper. But even without solar, if you apply for an EV-billing rate from the utility, and if are diligent about only buying electricity during off-peak hours (varies by utility company, $0.138 per kWh for this example) you can buy a “tank of electrons” (let’s use 270 miles of range as the baseline) for a little over $10. Compare this to a gasoline vehicle that has a fuel efficiency of 25 miles per gallon and has a tank size of just under 11 gallons (a combination that gives the same driving range of 270 miles). Again, gasoline costs vary, but in California a price of $3.75 per gallon is pretty common. The price for that same tank of gasoline (giving a range of 270 miles) $40. Yes, driving habits vary, but how’s that for surprising?!

The purpose of “Investigation Anecdotes” is to inform our readers about the intriguing field of engineering investigations. We hope you are instructed by this content, and we encourage you to contact us if you seek additional information.

P.S. If (a) reading this blog motivates you to buy a Tesla and (b) if you are a friend or colleague of Martin Thermal and (c) if you don’t know anyone else who owns a Tesla and (d) you are asked by the Tesla sales person if you want 1,000 miles of free supercharging – please consider giving them Dawn’s name as a referral. Contact us if you want further information.

When a consumer product fails thermally, customers may get “steamed” and demand their money back.  When the failures are frequent enough that the Consumer Product Safety Commission receives dozens of complaints about “melted plastic” and “first degree burns” a few weeks after the initial launch of the product, they may require the seller to pull the offending product from retail shelves and issue a “safety recall” notice to all consumers.  If you consider a product that is being sold at a rate of 100,000 units per month, it is easy to see how quickly the recall costs could add up.

However, the matter could become even more problematic if the supply chain involves multiple entities (e.g. a product designer, a contract manufacturer, and a marketing entity).  When the recall costs are tallied up, the manufacturer and designer could find themselves in a legal battle to determine whether the thermal failures were caused by “design defects” or “manufacturing defects”.

One particularly challenging aspect of an engineering failure investigation is to understand why only a small percentage of all the shipped products fails prematurely.  By carefully examining the failed units, an engineer may be able to identify the correct failure mode(s), but inspection alone likely will not be sufficient to determine whether the root cause was a bad design or low quality manufacturing.

After the failure mechanism is identified (e.g., loose connection or excessive current draw) the engineer should examine and test a large number of “new-in-box” units to see if there is a correlation between parts that are “out-of-spec” and parts that fail when used normally.   If brand-new parts meet the dimensional and functional requirement of the design, it’s pretty obvious that the design wasn’t adequate to prevent the overheating.  On the other hand, a finding that many of the parts don’t conform to the design dimensions (and other requirements) doesn’t definitively prove that manufacturing defects were the cause of the safety problems.

In a recent investigation of a recalled consumer electronic product, this author discovered that 80% of “new-in-box” samples did not meet the design specification…but less than 3% of the samples failed thermally when first used.  Tellingly, we also found that 9% of the samples were not only “out-of-spec”, but “grossly-out-of-spec” and that each of the samples that failed thermally fell into the “grossly-out-of-spec” category.  (Conversely, none of the 20% of the “in-spec” parts failed when used normally, which provided validation that the design was adequate.)

Using “statistical inference” we concluded that it was virtually impossible (48 chances in a billion) for all of the failed samples to come from the “grossly-out-of-spec” population if only random forces were at play – hence there must be a “causal link” between the “grossly-out-of-spec” condition and the thermal overheating result.  Statistical methods proved extremely helpful in illustrating that the manufacturing “nonconformances” were indeed the “defects” that caused the safety recall!

The purpose of “Investigation Anecdotes” is to inform our readers about the intriguing field of engineering investigations.  We hope you are instructed by this content, and we encourage you to contact us if you seek additional information.