[Tom]

EDN has an interesting article: Automobile electronics seek to plug power leaks, by a Product Manager at Linear Technology. It has some tidbits on LED headlights: "The main roadblock preventing solid-state lighting in cars is the cost. HB-LED-production numbers will have to grow to cause the price drop necessary to include them in Chevrolet models as well as Cadillacs. In addition, temperature changes strongly affect LED-light output, with output varying by as much as 50% over the automotive-temperature range of subfreezing temperatures in the winter to triple digits in the summer" and Switching Regulator sleep states.

There is also some information on both the Volt and Tesla, e.g. "EV manufacturers, such as Tesla, are working on alternative methods for cabin heating, such as relying on seat heaters for localized heat, as well as PTC (positive-temperature-coefficient) heaters for general cabin heating."

 

[DaV8or]

Seat heaters alone ain't gunna cut it. What in the world is positive temperature coefficient heating??

 

[LyleL]

That was a very informative article, thanks Tom.

 

[Koz]

I'm reasonably familiar with LEDs. We actually have a sample case from an LED manufacturer showing how there heat dissipation technology keeps the output higher by keeping the junction cooler. For amber LEDs the output drops significantly once the junction temperture gets above about 120f. White LEDs aren't as bad but they suffer from this issue too. Life is shortened as well with high temperatures, but for automobiles the shortened LED life is not an issue since it is still plenty long. Since there is so much cost pressure from the core propulsion technologies of the Volt, I hope they are not planning to use LEDs in the first generations for the headlamps. Daytime running lamps and most other lighting in the car are well suited for LEDs, however.

I do hope they consider in-seat air conditioning to lessen the cabin conditioning load. Heating and cooling the occupants directly is a lot more efficient then through cabin air ducting. I'm a little biased though, since we use a lot of A/C in Florida.

I wish the car makers would provide hot climate models that had special built in window shading (like some luxury cars have). This option could also include the in-seat air conditioning, perhaps an extra coat of clearcoat, and solar cover-ready features. I think in roof solar would have to be way too expensive to do even a little bit. A solar cover seems more practical. The Volt would need a(some) lock down point(s) and an interface along with programming to allow cabin cooling and battery charging.

 

[Tom]

What in the world is ...

What in the world is positive temperature coefficient heating??

It generally is implemented in such a way that when the temperature exceeds a given setpoint then the amount of heating from a (typically secondary) heater is reduced. As a result of valence electron scattering, all metals (thick layers) between room temperature and melting temp have a positive temp coefficent of resistivity, but it is relatively small. A second mechanism must be added for additional positive TC.

 

[DaV8or]

It generally is implemented in such a way that when the temperature exceeds a given setpoint then the amount of heating from a (typically secondary) heater is reduced. As a result of valence electron scattering, all metals (thick layers) between room temperature and melting temp have a positive temp coefficent of resistivity, but it is relatively small. A second mechanism must be added for additional positive TC.

Umm... I'll try this again. What in the world is a positive temperature coefficient heating system and how does the mechanism work as it relates to automotive application? How does it make someone riding in the car warmer? It just sounds like a fancy electric heater with a thermostat so far.

 

[Tom]

For info on PTC applications in EVs look at the article "PTC Thermistors as Auxiliary Heating Units for Automobiles." The key ideas are that EVs generate little heat and need aux heaters. PTC heaters are small, self regulating, and can be located close (head rest, seats) to the occupant.