Best location to hook up an accessory heater?

[tstclr]

I picked up a 12volt ceramic heater on Ebay. I plan to use it as a rear window defroster for my "pseudo daily-driver" 64. I want to eliminate the cigarette lighter plug. I'm going to mount it on the package tray and attach the ground wire to the body under it. I then want to run the postive wire to an under-dash mounted toggle switch. Where is the best location to run the main feed from it without over taxing the wiring? I want it to only work with the key on. Should I run it off the ignition switch?
Thanks
Todd


63 Lark 2dr Sedan
64 Daytona 4dr Sedan

[tstclr]

There were no amperage ratings, only "150 watts". That's a good idea-hooking it up to the blower switch feed. I'll run larger guage wire and I'll try a 15 amp fuse to start.
Todd

63 Lark 2dr Sedan
64 Daytona 4dr Sedan

[John Kirchhoff]

Here's how to calculate amps, watts/volts=amps. If your heater draws 150 watts and your battery is charged up, you're driving down the road and the charging system is putting out 14.2 volts, the heater is going to require close to 11 amps after figuring in the voltage drop through the wiring. If you're at a stop sign idleing with the lights, heater, etc, on, your electrical system will probably be down around 11.5 volts and the heater will then draw 13.5 amps at around 11 volts at the heater.

You'll probably have about 10 feet of wire from the dash area to the heater, so you probably won't want to go any less than a 10 guage wire. You'll end up with a voltage drop of around 2.1% which is acceptable. Were it me, I prefer to run an 8 guage wire from the solenoid up by the battery, through a 15 amp fuse, through a switch under the dash or where ever you prefer and then back to the heater. 18 feet of 8 guage wire would have a voltage drop of around 2.5% which is ok. I'd put the heater on its own circuit because for comparison, the heater is going to draw power equal to two modern headlights on high beam and three running lights. If you're afraid of forgetting and leaving the heater switch on and running the battery down, you could include a solenoid on the 8 guage wire. A small wire drawing just a little juice would run to the ignition switch so the only time the circuit would be hot would be when the ignition switch was on. I agree with hotwheels, running another 13.5 amps through the ignition switch is probably asking for trouble sooner or later.

[gordr]

quote:Originally posted by John Kirchhoff

Here's how to calculate amps, watts/volts=amps. If your heater draws 150 watts and your battery is charged up, you're driving down the road and the charging system is putting out 14.2 volts, the heater is going to require close to 11 amps after figuring in the voltage drop through the wiring. If you're at a stop sign idleing with the lights, heater, etc, on, your electrical system will probably be down around 11.5 volts and the heater will then draw 13.5 amps at around 11 volts at the heater.

You'll probably have about 10 feet of wire from the dash area to the heater, so you probably won't want to go any less than a 10 guage wire. You'll end up with a voltage drop of around 2.1% which is acceptable. Were it me, I prefer to run an 8 guage wire from the solenoid up by the battery, through a 15 amp fuse, through a switch under the dash or where ever you prefer and then back to the heater. 18 feet of 8 guage wire would have a voltage drop of around 2.5% which is ok. I'd put the heater on its own circuit because for comparison, the heater is going to draw power equal to two modern headlights on high beam and three running lights. If you're afraid of forgetting and leaving the heater switch on and running the battery down, you could include a solenoid on the 8 guage wire. A small wire drawing just a little juice would run to the ignition switch so the only time the circuit would be hot would be when the ignition switch was on. I agree with hotwheels, running another 13.5 amps through the ignition switch is probably asking for trouble sooner or later.

John,

I concur with you just about 100%. But I think a headlamp relay rated at 20 amps would suffice in place of a solenoid, and would be cheaper and easier to mount. And I agree, I would NOT, under any circumstance, put that much load on an ignition switch. The car might become very warm indeed, ONCE.[}]

And the best place to mount an auxiliary heater? Inside a nice warm garage, of course. It's a b**** doing it outside in the cold.

Gord Richmond, within Weasel range of the Alberta Badlands

[tstclr]

Thanks for the input guys. The factory wiring on the unit is only 14 guage(!)Of course, it's only about 3 feet long. It's loud enough that I shouldn't have a problem remembering to turn it off. I figure I'll mount the switch in the area between the hood release and vent cable. There seems to be enough room there and it's out of plain sight.

Todd


63 Lark 2dr Sedan
64 Daytona 4dr Sedan

[tstclr]

Thanks to everyones advice, I got the "defroster" hooked up correctly tonight. We had the relay and socket in stock at work. It took me 3 hours as I wanted to do it right (soldered the connections, used heat shrink tubing, routed the wires out of sight etc). Both the feed circuit and the switch circuits are fused and everything works great. Now on to my seatbelts(which arrived today), washers, and rear brake drum. Speaking of the rear drum, I forgot to mention CanadianStudebaker had an NOS drum in stock! It should be here tomorrow.

Todd

63 Lark 2dr Sedan
64 Daytona 4dr Sedan