# Car heater power?



## dimitri (May 16, 2008)

I think it should be fine, but more importantly it depends on duty cycle, i.e. how often will elements be turned on and how long will they stay on. Are you planning manual control or thermostat based control or both?

If using thermostats, pay attention to AC vs DC ratings and use appropriate relays to avoid welding thermostat with DC current.


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## Woodsmith (Jun 5, 2008)

I will aim at thermostatic control but I will need to think about where to install it/them. Thanks for the tip on using relays, I had read about that already hence a little nervousness on anything else that may differ due to using dc.

I am also looking at ensuring that the fan and the heating is linked so that I can't have heating without the fan running and can't have higher power heating without the fan being on a higher setting.

The elements have a thermal cut out, I will try and isolate them to operate on the supply relays.


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## dimitri (May 16, 2008)

I would use one appropriately rated DC relay to control the power circuit from the main contactor to the heaters. Then any control elements such as thermostat, fan switch, manual switch, etc. can be connected in series to control the relay, using 12v low current circuit. When any one of those controls open the circuit, heater is off.


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## Woodsmith (Jun 5, 2008)

That sounds like a good and simple way to wire it.
Thanks.


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## tomofreno (Mar 3, 2009)

I recently installed an electric heater in place of the original heater core. I used a heater relay kit from KTA. It has 12V coil, and connects the main pack to the heater through 20A fuses. I replaced the fuse holders in the kit with in-line 20A ones as the kit ones looked more like 10A. Like you I wanted the fan on if the heater was on so I pulled 12V from the heater blower motor to another switch in series to turn the heater on/off. I have no thermostat.

Tom


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