[ausev] Open Garage - Sunday June 11 @ 3:00 -- calling all cars

[Chris Robison]

Oops -- I intended to keep this on the list, not just send it to Rush. 
For whoever's interested...

---------------------------- Original Message ----------------------------
Subject: Re: [ausev] Open Garage - Sunday June 11 @ 3:00 -- calling all
cars From:    "Chris Robison" <eeyore at phototropia.org>
Date:    Fri, June 9, 2006 2:37 pm
To:      "Rush" <Rush at ironandwood.org>
--------------------------------------------------------------------------

Hey Rush ...

The heat issue is something I'm going to have to monitor carefully.  I
plan to do this with temperature feedback (likely via a thermistor) to the
control system, which I'm currently trying to design. The elements are
separated from the thermoplastic airbox (which, surprisingly, is not at
all heat resistant despite having housed the stock heater core) by being
mounted on a sheet of "G10" composite material, often referred to as a
type of phenolic though I'm not sure that this is correct.  I bought it
from a local plastics house, back when I thought that it was the same
thing as "FR4" which is used in circuit boards. Though I don't think it's
going to be a problem, if I were doing it over I'd use FR4 as it is
actually the same material for the most part but has a fire retardant
added to the resin from which it's made.

The control system I'm designing is a bit of a gamble, but I'm pretty
certain at this point that it's going to work.  I'm building a PWM
controller to feed a controlled amount of power to the ceramic heater
elements. The conventional wisdom is that this won't work because the
ceramic elements are PTC (Positive Temperature Coefficient) meaning that
they draw more current as their temperature decreases. However, I've found
that they are not PTC in nature until very close to their normal operating
temperature, and in fact have a "minimum" resistance below which they
actually switch to an NTC behavior.  Because of this, I'll be able to
control them; the important issue remaining is that the ratio between PWM
duty cycle and power output won't be linear.  But, that will be a software
problem.  :o)

To answer your question, it will draw from the pack directly.  This will
be part of the design challenge, since the input voltage will swing from a
little over 310V (dead) to well over 450V while being charged.  But since
it will be feedback controlled (whether from the vent temperature or the
cabin temperature), that shouldn't matter.

I will use AC. The current plan is to drive the existing compressor with a
separate motor. I have a ~2HP 260V permag motor that hopefully won't blow
up if I overdrive it a "little."   :o)  We'll see.

  --chris


On Fri, June 9, 2006 12:35 pm, Rush said:
> Chris-
>
> I'm converting an S-10 and am getting into the heater part... your
pictures are extremely helpful, thanks. How did you solve the heater
next to plastic problem? I'm only going to use 1 heater coil, pretty
warm up here even in the winter time, mainly for defrosting use. Do you
plan to hook up the AC? Are there any things that you would have done
differently? Are you using a DC/AC converter or hooking the heaters
directly to your dc?
>
> Lots o questions.
> Thanks.
>
> Rush
> Tucson AZ
> www.ironandwood.org
>
>
> ----- Original Message -----
> From: "Chris Robison" <eeyore at phototropia.org>
> To: "AustinEV announcements list" <ausev at austinev.org>
> Sent: Friday, June 09, 2006 9:16 AM
> Subject: Re: [ausev] Open Garage - Sunday June 11 @ 3:00 -- calling all
cars
>
>
>> Sorry for not getting in on this thread earlier.
>>
>> I'll be actually working in my garage for the entire weekend trying to get
>> it cleared and cleaned and get the truck to at least appear respectable
(if that's possible given its current stage of disassembly).  Anytime
during the weekend that anyone wants to stop by, if I'm not there I'm
probably out nearby, buying something.  My phone number is
512-743-8362; call me if you want to make sure I'm there (or harass me
if I'm not).
>>
>> Hopefully in the meantime I can come up with something worthwhile to
actually *do* while the video is shooting.  For those not familiar
(which
>> should be basically everyone, since I haven't updated my site in
months) is that the truck is almost fully disassembled, and I'm trying
to work out
>> how I'm going to make changes to the frame to support the suspension, and
>> also the very high torque of the motor I'm using.  Mark Farver has
suggested lifting the cabin box off the frame, and that is starting to
look like a very attractive option.  Shouldn't take more than four
people
>> to do it, as the cabin box is now almost entirely stripped.  I may even
hoist it up from the ceiling...    I'm also working out a control
system for the electric heater, but that's not exactly exciting
visually.
>>
>> Pictures of the project are here:
>>
>> http://ohmbre.org/gallery
>>
>
>