Timer for electric heater

[SameGuy]

I started a different thread here http://forum.expeditionportal.com/threads/176773-12-volt-heater-thoughts and got some good ideas regarding heating the topper on my Tundra. At present I think I am going to go the electric route and probably end up using one of the DC Thermal 12 volt electric heaters. A propex or Webasto would be the cat's meow, but I'm still not even sure if sleeping in the back of the truck is going to be the direction we go so I'm trying to keep this experiment as cost effective as possible. I plan to use the heater to warm the topper before we go to bed, and before we get up, and only while the motor is running to prevent running down the house battery unnecessarily. My tundra has a 170 amp alternator so I don't imagine it will see any strain with even a 600 watt heater pulling 50 amps. I may be wrong on that, but we will see.

I know a heater will eat battery very quickly so I wanted to make the system as idiot proof as possible. I plan on having the heater on its own circuit to the topper wired directly to my house battery. That house battery is wired to my starting battery through a Blue Sea 7622. I will have an anderson connector which will allow me to unplug the heater completely from the battery, and I am planning to install a 30 minute timer
https://www.amazon.com/Intermatic-S...059187&sr=8-3&keywords=30+minute+timer+switch
to the heater. I realize this timer is meant for 120 volt but I don't see why it wouldn't work just dandy for my 12 volt application.

The specs read as follows:

[FONT=&quot]CSA certified. Resistive (heater): 20A, 125 VAC, 10A 250/277VAC. Tungsten: 7A 125 VAC. Motor: 1 HP, 125VAC, 2 HP, 250VAC. 50/60 Hz.

Am I correct to assume 20A @ 125 VAC for a resistive heater would give me plenty or headroom with a 600 watt heater @ 12 volts = 50 amp draw?[/FONT]

 

[SameGuy]

Thank you for the heads up. I haven't found a mechanical timer switch that would handle that kind of amperage so I may just go with a simple toggle switch rated to the amperage I need. I know there is a switch on the DC Thermal heater but I still want a backup switch in the circuit for safety. I may try to use a mechanical breaker in place of a toggle, just have to do some more research.

 

[herm]

The specs read as follows:

[FONT=&quot]CSA certified. Resistive (heater): 20A, 125 VAC, 10A 250/277VAC. Tungsten: 7A 125 VAC. Motor: 1 HP, 125VAC, 2 HP, 250VAC. 50/60 Hz.

Am I correct to assume 20A @ 125 VAC for a resistive heater would give me plenty or headroom with a 600 watt heater @ 12 volts = 50 amp draw?[/FONT]

NO!.

Amps is what you are after here, and the switch is only rated for 20 amps. I would not want to run it at even that at 12v as stated above. You could use the timer to trip a relay with sufficient current capacity for your heater and thus you would be using the timer at a low current.

watts = current x voltage Current is always your major factor when sizing wire, switches, etc.

 

[john61ct]

Kemo M113A plus a quality solenoid (relay) switch, IMO rated for double+ your device peak pull.

 

[rayra]

Time and again we keep seeing people trying to go with electric heat off a vehicle battery. It's a non-starter, pun intended. What's so hard about a decent sleeping bag?

 

[Nd4SpdSe]

You could always cheat and run a relay/solenoid to engage the heater circuit. You could use any timer since the solenoid will draw just a few mA of current.

 

[SameGuy]

I'm not planning on running the heater when the engine is not running but even with a 600 watt heater I 'could' run it off the house battery for close to an hour without going past the 50% mark on my house battery. I do like the idea of the timer attached to the solenoid, but I think I may keep things simple and install a high amp toggle switch in the circuit. If like the results the Kemo M113A plus a quality solenoid sounds like a fantastic option.