Comments on: Dash plans temporarily dashed http://www.ohmbre.org/blog/2005/12/25/dash-plans-temporarily-dashed/ an unusual story of a boy and his truck Thu, 28 Aug 2008 02:05:14 +0000 http://wordpress.org/?v=2.0.5 by: Chris Robison http://www.ohmbre.org/blog/2005/12/25/dash-plans-temporarily-dashed/#comment-9 Mon, 26 Dec 2005 01:30:51 +0000 http://www.ohmbre.org/blog/2005/12/25/dash-plans-temporarily-dashed/#comment-9 This is hard to say. PTC (Positive Temperature Coefficient) heater elements draw a varying current, depending on how hot they get. Resistance rises with temperature, and so they are self-regulating to a certain extent. So, if I have three instead of two, the current draw won't necessarily be higher for the same amount of heat output. They'll just be operating at a higher temperature, with less airflow needed for the same amount of heat. What I'd really like to do is make a simple PWM circuit to control them. It would be pretty simple as PWM circuits go -- with a simple resistive load the power wouldn't really have to be cleaned up at all. No inductors or caps on output, just pulse it right through. Bottom line is, I have no idea. Too many unknowns, including the behavior of the elements at half or 1/3rd my pack voltage. I may even use "between 2 and 3" elements, breaking apart the last element and only using one or two rows of its ceramics, instead of all 4. This is hard to say. PTC (Positive Temperature Coefficient) heater elements draw a varying current, depending on how hot they get. Resistance rises with temperature, and so they are self-regulating to a certain extent. So, if I have three instead of two, the current draw won’t necessarily be higher for the same amount of heat output. They’ll just be operating at a higher temperature, with less airflow needed for the same amount of heat.

What I’d really like to do is make a simple PWM circuit to control them. It would be pretty simple as PWM circuits go — with a simple resistive load the power wouldn’t really have to be cleaned up at all. No inductors or caps on output, just pulse it right through.

Bottom line is, I have no idea. Too many unknowns, including the behavior of the elements at half or 1/3rd my pack voltage. I may even use “between 2 and 3″ elements, breaking apart the last element and only using one or two rows of its ceramics, instead of all 4.

]]> by: vivek g. http://www.ohmbre.org/blog/2005/12/25/dash-plans-temporarily-dashed/#comment-8 Sun, 25 Dec 2005 17:55:12 +0000 http://www.ohmbre.org/blog/2005/12/25/dash-plans-temporarily-dashed/#comment-8 How will the current draw of three ceramic heaters affect your car's range/performance? From what I remember, ceramic heaters typically draw 10-15 amps. How will the current draw of three ceramic heaters affect your car’s range/performance? From what I remember, ceramic heaters typically draw 10-15 amps.

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