In-car ceramic 12v heater...

Discussion in 'The Projects Forum' started by gbrennan, Aug 6, 2012.

  1. gbrennan

    Thread Starter New Member

    Aug 6, 2012
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    Hey guys, first thing is to say I have the same electrical knowledge as a spoon, however, any help or advice would be appreciated beyond the realms of the said spoon's emotional spectrum.

    I want to start a little project, geared around the fact that I hate getting into my car in the winter as its freezing. I would like to set up a remote heater in my car. I haven't yet decided on how it will be remotely activated, possibly infrared, maybe even get my raspberry pi involved or my phone, but thats further down the line.

    I want the system to be independent of the car, so that it could be transferred between vehicles and in the event of selling the vehicle, I get to keep my genius contraption (which you are all about to tell me won't happen).

    Ignoring the idea of remote activation, just concentrating on powering the device, I would like to use a solar trickle charger to connect to a rechargeable battery that would power a 12v ceramic heater.

    This is the heater: http://www.maplin.co.uk/in-car-ceramic-heater-48775

    Here is a solar trickle charger? http://www.maplin.co.uk/solar-powered-12v-12w-battery-charger-217850

    The thing I have absolutely no idea about is amps, watts, volts etc.

    So would this solar charger successfully power a battery (throughout the day before) - that I could use to run the ceramic heater and what sort of battery would I need as I know that the ceramic heater runs off of 12v but I don't know about the amps or the wattage.

    Hopefully this is enough of an initial explanation. Thank you for any help and please forgive my ignorance.
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Biggest problem is that because you only have 12V, it takes HUGE amounts of current to get any appreciable heat. I had a rear window defroster that drew something like 20A it eventually burned up the cigarette lighter outlet it was plugged into.. Bottom line, if you do install a heater large enough to do any warming, it will kill your battery pretty quickly. The car's heater derives it's heater from the hot water running through the engine.
     
  3. gbrennan

    Thread Starter New Member

    Aug 6, 2012
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    presumably I will only need about 5 minutes of heat to get the job done? How big a battery would I need and what kind?
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    The actual current draw of the heater is not posted, however, it is listed as having a 15 amp fuse. The solar charger is listed as 12 volts and 12 watts. Now, the heater will draw something less than 15 amps, and the solar panel will put out something (probably a lot) less than 12 watts (which is 1 amp at 12 volts.) In addition, there are efficiency figures that are unknown. But if the heater actually drew 15 amps and the solar panel actually put out 1 amp, then the battery would need to charge for 15 times as long as the heater is running. In actual practice, it will probably be more like 30 to 1. So, for a rough approximation, you can assume that for 5 minutes of heat, the battery would have to recharge for 150 minutes. In addition, the battery would have to be able to provide 15 amps for 5 minutes without going below about 12 1/2 volts at any time.

    Also be advised that 15 amps at 12 volts is only 180 watts of heat, which is not much. By comparison, a hair dryer on high puts out about 1500 watts.
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    Good analysis.
    That heater takes 150W.
    With over 12A from a cigarette lighter outlet, the outlet and cord will get hot.
     
  6. gbrennan

    Thread Starter New Member

    Aug 6, 2012
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    Well the solar charger would just be left on the dashboard most of the day (8 hours) so hopefully that would provide sufficient charge. With regards to the battery, would this one do the trick...

    http://uk.farnell.com/panasonic/lc-ca1215p/battery-12v-vrla-15ah/dp/1769784

    It has a pdf data sheet on the page and if my interpretation is correct, it can run for just shy of 15 minutes at 15 amps.

    Thanks for all the help guys, especially tracecom, very informative.
     
  7. MrChips

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    Oct 2, 2009
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  8. #12

    Expert

    Nov 30, 2010
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    You could get a long electric cord for that price.
     
  9. BMorse

    Senior Member

    Sep 26, 2009
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    or, just install a remote start module, so you can "pre warm" your car before you get in?? Less likely to kill the battery or catch any wiring on fire :)
     
  10. gbrennan

    Thread Starter New Member

    Aug 6, 2012
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    I hear what you're saying about the remote start module, but I want it to be independent of the car. Ok so would that setup work, with the solar charger, the battery and the heater? Plus how do I remove the possibility of setting my car on fire via hot wires/connectors?

    I appreciate your collective genius.
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    Cut off the cable from the heater and rewire the heater with heavy duty wire and connectors to the battery and controller.
     
  12. wayneh

    Expert

    Sep 9, 2010
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    If the strategy is ultimately to warm the car with sunlight, it would be FAR more efficient to do this directly if you could find a suitable method. The PV panel is maybe 10% efficient at best and using battery storage loses half of that. So maybe you'll get 5% efficiency of storing solar energy for later heat.

    Is there a passive way to do better than 5%? I wonder if you could "recharge" a sodium acetate heat pack by laying it on the dash in the sun.

    Another thought is to just warm the seat, not the entire interior. I can tolerate a very cold car as long as the seat is comfy. Maybe you could slip your heater under the seat, to get the biggest bang from those precious watts.
     
  13. MrChips

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    Oct 2, 2009
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  14. crutschow

    Expert

    Mar 14, 2008
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    You have ignored the point about the low heat output of your battery powered heater. 150W will have only a very minor effect on the internal temperature of the car, especially if left on for only 5 minutes or so. Try a hair dryer in you car on the low heat setting and measure the temperature rise (and that likely still puts out several hundred watts more than the car heater).
     
  15. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Bullseye. It will do basically nothing.
     
  16. gbrennan

    Thread Starter New Member

    Aug 6, 2012
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    Thank you for all the comments. So how come the heater is allegedly effective running off the car 12V socket and battery, but if I do it this way, it won't really have any benefit?
     
  17. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Look at the ad for the heater, and read the evaluation comments. Most users are only trying to defrost the windshield, and it apparently doesn't even do that well. It doesn't put out enough heat to raise the temperature in your car more than a degree or two in five minutes. I have a similar unit that I bought to disassemble in order to study the ceramic heating element; mine is not much more than a toy.
     
  18. BillB3857

    Senior Member

    Feb 28, 2009
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    I use the ceramic cube heaters found in most retail stores (wal-mart, etc) and just run a heavy duty extension cord. The unit I have has a thermostatic control and keeps the frost off the window and the inside nice and toasty on a very low setting.
     
  19. #12

    Expert

    Nov 30, 2010
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    The way I would go at this is similar to the idea from crutschow. Measure first, design second. My day job is about human comfort due to temperature. I work in the 10,000 to 100,000 watt range. I would start with "how cold is the worst outside temperature?". "What temperature would be comfortable to you?" A bit of math and the answer comes up in watt-minutes. When you have that, you can get an answer that will work.
     
  20. crutschow

    Expert

    Mar 14, 2008
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    The key word is "allegedly". Welcome to the world of Madison Avenue. ;)
     
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