Interior Pre-Heater/Cooler

Last Updated:12/23/01

Note: This was a project I came up with for my Jet 007 Omni conversion.  My Civic EV conversion uses a different system, with an add-on 900 watt AC powered heater and an electrionic timer.  I don't preheat using battery power, as I now have access to an outlet at work.  You can find these preheaters on the web.
Last Updated:01/28/98

My car is heated by a ceramic type electric heater powered by the main 120 volt battery pack. While these heaters are very capable, they don't put out nearly as much heat as a conventional car heater. (Most conventional car heaters put out almost as much heat as a home furnace! That is waste heat from the engine, so now you know where all that money goes.) Many commercial electric vehicles have a system to pre-heat or pre-cool the car. I wanted to add such a system to my car, but finding the proper timer proved rather difficult. What I came up with sounds a little "Rube Goldberg" but it does work. 
I used a mechanical 12 hour timer designed for household attic fans. I got mine at Home Quarters for about $20. It is a nice timer, but it is designed to close a circuit (stay on) for the set period of time and then switch off. I needed it to stay off for a set period of time and then turn on. The solution was to use the timer to control a 12 volt 30 amp normally closed relay. The system works like this; When I park the car in the morning I set the original heater blower controls to the desired setting, either heat or defrost, and select the fan speed. Next, I switch the mode switch to timer and select the desired time delay, usually 8 hours. The timer closes the circuit to energize the relay coil for the selected time. When the time expires, the timer opens the circuit, the relay closes and the blower fan and heating element powers up. Yesterday, when I came out to my car the interior temperature was a very pleasant 73 degrees. (The outside temp was in the very low 30s with a nasty wind chill.) One nice feature of this set-up is that it will also operate my air conditioning in the same way. All I have to do is set the heater/air conditioner controls to the proper setting for a/c. 

circuit diagram

Parts List

TIMER          S.P.S.T. 120 vac 10 amp Mechanical Fan Timer
MODE SWITCH    D.P.D.T. 12 vdc 30 amp Toggle switch  
RELAY          S.P.D.T. 30 amp universal automotive relay  
If you have any questions about my car please e-mail me. Send e-mail to Mike Chancey at:

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