Ceramic Heaters

[dabineri]

OK, I have a pair of ceramic heater elements for my 144V system.  Should
I mount them in series or parallel physically (NOT electrically).  I
have enough space to either line them up side by side OR one after the
other in the air stream.  '91 Celica conversion.

Any ideas as to which is better are welcome.

Dave

--
D. Abineri     dabineri@...

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev

[James Massey]

G'day Dave, All

At 06:43 AM 6/07/2008, Dave Abineri wrote:
>OK, I have a pair of ceramic heater elements for my 144V system.  Should
>I mount them in series or parallel physically (NOT electrically).  I
>have enough space to either line them up side by side OR one after the
>other in the air stream.  '91 Celica conversion.
>
>Any ideas as to which is better are welcome.

The answer to this question is highly dependent on airflow, as the
power capability (resistance) of a ceramic element is directly
related to how hot it is. The resistance falls fairly linearly to
about 150 degrees Celcius (at the element), above that temperature it
very sharply rises, to a point at about 180C the resistance is way
high and I had to stop the test as I couldn't drive enough into the
element to make it heat any further.

It was a couple of years ago that I did the test, and I haven't been
able to lay my hands on the data, so the temperatures and resistance
values may be a little out, but the graph looks a bit like this:


Resistance
ohms
    |                                        |
25 |                                        |
    |                                        |
20 |---___                                  |
    |      ---__                             |
15 |           --__                        /
    |               --___                  /
10 |                    --__             /
    |                        --__       _-
  5 |                            --____-
    |_________________________________________
   0        50        100          150      180
             Temperature degrees Celcius

So if your airflow is high, and keeps the elements down around 50C,
you'd be better with them in series, so the second one gets warm air
and can generate higher temperatures.

I'd connect them in parallel, as you can always limit the maximum air
speed through them to maximise the energy transfer to the air. It was
interesting playing with the airflow after I'd done my initial
temperature/resistance test, and see the power falling off as the
temperature 'knee' was passed, the air is still very hot off them,
but such a small amount of air was hardly an issue (as there is so
little energy in it).

Hope this helps.

Regards

[Technik] James

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev