It has been a while since my last post, but I have been busy with school starting again and other obligations. I have made progress, however, and have a lot to report.

St. Louis has cold winters, so I decided while waiting for the battery charger to come in from Belktronix in CA to do some work on the heater.



The 1500 watt heater and it's control circuitry has been completed. It gets very hot quickly, but posed some challenges getting it to run properly. The core is made from a "Titan" brand heater that cost $19 at Walmart. After doing some testing on the plastic it was mounted in, I decided to cut out a piece of acrylic referred to by many as Corian (tm). They make countertops from it and I have made a lot of the insulators and other components from it. It has a higher melting point than the frame the heating elements are mounted in, so no problem there. The photo shows the Saab heater core on the left and the all electric version on the right. The heater is ceramic, and puts out more heat as more air blows through it.

The Saab uses a sophisticated environmental control system that regulates by temperature rather than the simple knob type heat/AC control, so I had to design a circuit that would control the heating elements and prevent them from being on if the fan was off or running too slowly. A set of relays, under the hood, (also installed now) will switch on the 144 volts to the heater and the controller on the side of the heater box will take care of the rest.

For the techno types out there, I used an LM339 quad comparator to monitor the fan voltage and shut down the relays if the speed of the fan is too slow. Due to the design, the voltage is zero when the fan is at full speed. At about 6.5 volts I have it adjusted to shut the heater off. It keeps the heater box from melting if little or no air is blowing. The motor that used to open the air mixing flap now trips a microswitch to turn on the heater. The piece holding everything is also machined from acrylic and is bolted to the side of the heater box on the passenger side. I have some options open with the circuit to include some temperature regulation as well at a later time. It all works as predicted. If all else fails I incorporated a thermal limiter on the heating element.
So it was one of the more inexpensive
parts of the project to do.

Currently I am designing a frequency to voltage converter to restore the tachometer. I should have something to report on that soon.

I promised in my last post to include a photo of the Kenwood/Sirius satellite radio I got off Ebay. I am really pleased with how it works and all it does. I have less than $50 in the whole rig and it even gets the satellite broadcasts when I hook it up! I have to pull the dash front out to install the volt meters and it will be put in at that time.


Above: The control interface

Left: The Ceramic Heater installed in heater box. The wiring runs through the old heater core tubes out to the front of the firewall.






Kenwood Sirius Radio/CD Unit


With the arrival of the battery charger Tuesday, things are getting close now!

With a battery pack and a bit of luck I will soon be going down the road.