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Hardware hacking an electric fan heater without burning the house down

BigG

I recently purchased a 2kW electric fan heater for $12 (it was on sale). This was an offer too good to refuse, especially as the latest Project14 competition is hardware hacking.

 

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These fan heaters, like any other personal heater, are great for the winter months.

 

However, as I have on the very odd occasion left an oil heater on over night (it is very easily done), I certainly wouldn't want to do the same with an electric fan heater.

 

So I want to add in some "smarts" or electronics to ensure that it can automatically turn off if I leave the room etc. and it would also be handy to remotely adjust heat and fan speed.

 

The nice thing about this particular fan heater is that it has a safety cut off switch, should it tip over. I thought that this would be my starting point for my project, as this part can be readily enhanced.

 

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The part I am struggling with is how to or what electronic options could I use to hack the heater settings switch, which is mechanical. How could I do this electronically, bearing in mind we are dealing with mains voltage.

 

{gallery:autoplay=false} Heater Settings Switch

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And the other question is what options are out there on how to hack the fan speed controller... this also is mains voltage, so I'm out of my depth in terms of using a digital potentiometer, for example.

 

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Any suggestions / ideas would be greatly appreciated.

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  • If you really want to control it, unfortunately the cost will be much higher than the amount spent on it : (

    Triac circuits are not safe to build without a dedicated PCB. SSRs are not cheap (there are low-cost ones but some can burst into flames). Both of these options need heat-sinking too, and you don't have anywhere for that - and it's another problem you're creating for yourself to do that externally and then having to worry about earthing any exposed metal or screws.

    If you're ok with just switching the individual elements and fan off and on and don't want to try to control the amount of power more granularly than that, then relays might be the easiest option, for instance one relay per element, and one to control the fan. It won't need 24A capability, because the max will be 13A (UK mains).

    This finder relayfinder relay seems nice - it has spade connections which will be less awkward than PCB pins, and far easier to crimp on the connections although there will be effort to design and make up your wiring harness. It's a reliable brand too. I used a different relay in their range to power on/off a waste disposal unit (maybe 500W motor) and it's been functioning for 12 years like clockwork.

     

    I hate to say it, but personally I wouldn't hack this project, due to the cost and complexity to keep it safe. I don't want to be negative : ( but equally don't want to be too positive to mistakenly give you give the impression that it's something moderately achievable either, and then struggle with it. Hope you understand..

  • in reply to shabaz

    Hi Shabaz

     

    Thanks for all your valid comments.

     

    Yeah good point. It should've been rather obvious now that I think about it... "It won't need 24A capability, because the max will be 13A (UK mains)."

     

    And yes, yet another good point, re "then having to worry about earthing any exposed metal or screws.". I was wondering about this especially as there is no earthing via the mains plug being two prong (L and N wires only). So keeping this in mind for sure.

     

    Regarding design.

     

    For now all I plan to do is have an electronic switch for ON/OFF and leave the other controls alone as too costly/complex/dangerous/etc. Hence, the decision to just add the electronic switch (whether relay or triac) just after the microswitch.

     

    Regarding your point "Triac circuits are not safe to build without a dedicated PCB."

     

    Yes that would certainly be the intention, even if it just becomes a paper learning exercise for now. The part I'm still trying to understand is the energy loss via heat generated from the triac. Then the other part is the heat sink, especially if the heat sink was placed inside the fan heater enclosure near another large heat source, namely the heater element.

     

    So, lots to learn.

     

    Any comment on what are these "mica" capacitors.

     

    C://

  • in reply to BigG

    Hi Colin,

     

    It might be worth listing benefits/disadvantages of each approach. For this particular use-case I can see which of the approaches can be rapidly ruled in or out, but I forget that sometimes it's nice to do the exercise to validate it.

    Regarding thermal calculations, this Philipx NXP triac doc will be useful. Mica capacitors use Mica (mineral, comes as thin sheets) as the dielectric. It's generally for either high voltage use (since Mica doesn't break down as an insulator except at very high voltages) or for stability, so the datasheet would need to be examined.

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  • in reply to BigG

    Hi Colin,

     

    It might be worth listing benefits/disadvantages of each approach. For this particular use-case I can see which of the approaches can be rapidly ruled in or out, but I forget that sometimes it's nice to do the exercise to validate it.

    Regarding thermal calculations, this Philipx NXP triac doc will be useful. Mica capacitors use Mica (mineral, comes as thin sheets) as the dielectric. It's generally for either high voltage use (since Mica doesn't break down as an insulator except at very high voltages) or for stability, so the datasheet would need to be examined.

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