$3000 Hybrid Aftermarket Kit?

By Bill Moore

Posted: 18 Aug 2012

I love the work Charles Perry and his colleagues are doing at Middle Tennessee State University. They've come up with a way to replace the rear wheel hubs on your average front-wheel drive car with a pair of electric motors that can propel the car at speeds under 40 mph, purportedly for upwards of 35 miles. It will, they believe, improve your around-town fuel economy from 50-100%, which would be very cool, especially if you could install the system for the $3,000 being reported on the Internet.

But as much as I like the idea, it's the three-grand price tag I have issues with. I am not convinced it can be done for that amount of money. Maybe you can buy the twin rear wheel motors for that price, but a battery pack large enough to move a car 35 miles, not to mention all the supporting electrical and electronic components?

Do the math here. The EPA rates the Chevrolet Volt, with a 16kWh battery pack that weighs around 400 lbs and runs the length of the passenger compartment, and then some, at being able to propel the car 35 miles in EV-mode. And the Volt is significantly more aerodynamic than the 1994 Honda Accord wagon Professor Perry and his team used for their development 'mule.' So, right off, the 35 miles range sounds unrealistic. Maybe 3.5 miles might be a better number. Here's why.

Consider the Toyota Prius generation two (model years 2004-2009). It has a 1.3 kWh NiMH battery. It too can be coaxed to travel about a mile or so on its battery if the speed is kept under 35 mph, but it has to be on very level ground and a downgrade would help a lot. Given a protective SOC buffer of say 30% - 10% at full charge, 20% above full discharge -- that leaves about 910 watt hours of energy to move the car one mile. But NiMH is a relatively low energy density battery compared to lithium. Toyota's PHV plug-in version of the Gen III Prius has a range of about 12 miles in EV-mode at highway speeds. It's lithium ion battery pack is rated at 4.4 kWh. Seventy percent usable state-of-charge equals 3,080 watt hours, or 256 watt hours per mile; and in actuality, it's probably higher than that.

I wasn't able to find any information on the size of the MTSU battery pack or type of chemistry, but lets assume they're using lithium. We're also probably safe in assuming they paid around $500 per kilowatt hour, and probably higher. At this price, the 16kWh pack in the Volt will run $8,000. The 4.4 Prius PHV pack will be $2,200; and that's just the cells, not the battery management, charger, inverter, electronic controls, etc. Now, for the sake of argument, lets further assume that these needed components will likely run somewhere around $1000 dollars, and I am guessing that is way too low. So, you've got the two wheel motors, the battery pack, whatever housing it has, plus cooling system, as well as all the necessary cable harnesses, control systems, etc. There just isn't anyway this is going to come in for $3,000, but I am certainly willing to be proven wrong. If I am wrong, then that's good for all of us, really.

However, if I am right and we're probably talking something closer to $7500-10,000 for the complete system, then we shouldn't get people's expectations so high. And, of course, we've not even addressed the question of how much money do you put into a 'clunker' before you start throwing good money after bad? Now, that's some math I'd love to see analyzed.

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