18 Replies Latest reply on Jul 17, 2020 4:03 PM by BigG

    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.

       

       

      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.

       

       

       

      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

       

      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.

       

       

      Any suggestions / ideas would be greatly appreciated.

        • Re: Hardware hacking an electric fan heater without burning the house down
          BigG

          I'm assuming the switch on the heater is a 4-way 2 pole switch, similar to this more robust version: https://uk.farnell.com/schneider-electric/k1f013qch/rotary-switch-2-pole-5-6a-230v/dp/3108333

           

          As such, I started looking at 4 way double pole power relays and I found that there are a few options available, such as this one:

           

          https://uk.farnell.com/schneider-electric/rxm4ab2jd/relay-4pdt-250vac-6a/dp/2056435

           

          Looking at the photo of the fan switch, it looks like there are two ratings one at 6A and the other at 15A. Now, if I went for a 4PDT relay rated at 15A, the price shoots up for that rated current and for the price of one 4PDT relay I could buy two fans.

           

          So I am wondering if I could craft my own hybrid relay circuit using a suitably rated DPDT or SPST power relay, where one is for 15A and the other one is for 6A. This could saves quite a few bob but the circuit wiring will need thought as I wouldn't want a case of two relays turning on at the same time.

           

          Any suggestions?

          • Re: Hardware hacking an electric fan heater without burning the house down
            BigG

            I've worked out a possible logic table for the fan and the two heater elements.

             

             

            So I think 2 x SPST (NO) 16A relays (not sure if this could be combined somehow) and then 1 x SPST(NO) 6A relay would work in this context.

             

            Would this be correct?

              • Re: Hardware hacking an electric fan heater without burning the house down
                shabaz

                It's hard to say, I'm not sure I understand the existing wiring unfortunately : (

                It might be two separate elements, but I've never taken apart a modern fan heater.

                Heaters are quite high-power, so might need some care if modifying, since wires could get hot.

                This is quite an advanced mod, not sure how it will be implemented, will the relays and circuitry be installed inside the heater? It could he hard to install everything in there.

                It could be way easier to use a remote controlled mains socket adapter, but it may take some of the fun out of the project too, if the aim was to modify the heater product itself.

                So, not really sure what to suggest : (

                  • Re: Hardware hacking an electric fan heater without burning the house down
                    BigG

                    I am still unpacking and tearing it down myself to understand the wiring and the rest.

                     

                    I've yet to sketch out a wiring diagram and it's quite hard to capture the key elements in photos.

                     

                    It looks like two separate elements to me based on the wiring.

                     

                     

                     

                    shabaz  wrote:

                     

                    Heaters are quite high-power, so might need some care if modifying, since wires could get hot.

                    This is quite an advanced mod, not sure how it will be implemented, will the relays and circuitry be installed inside the heater? It could he hard to install everything in there. Will the relays and circuitry be installed inside the heater?

                     

                    No the idea is to remove this top covering and then have the control hardware outside of the enclosure. Not sure just yet as to where to place. As you say, the wires can get quite hot.

                     

                     

                    It's actually quite neatly designed, in my opinion.

                     

                    {gallery:autoplay=false} Motor

                • Re: Hardware hacking an electric fan heater without burning the house down
                  colporteur

                  When I started reading you post I thought, why didn't I think of that. My initial response is how fail safe the mains using solid state components like triac verses relays. A logic device that monitors the environment controls the triac. The logic device gives me the advantage of creating doors to options that I can come back to and use when I need them. Unfortunately this type of design is not cost efficient and you wind up with project like a car block heater being controlled with a Raspberry Pi. It is cool but way to expensive.

                  • Re: Hardware hacking an electric fan heater without burning the house down
                    BigG

                    The part that has me perplexed is the mechanism behind the dial:

                     

                    What is this component called and how does it work. It looks to me like a beefy potentiometer with an on-off switching mechanism, but not sure has cannot confirm via google (and how did I survive before googling).

                     

                     

                      • Re: Hardware hacking an electric fan heater without burning the house down
                        shabaz

                        Hi Colin,

                         

                        I was looking at your photos earlier, and think that's a bimetallic strip (it bends when it gets hot, and self-disconnects). the rotary control just adjusts the point it occurs by moving it closer or further away by a fraction.

                        These were popular in older thermostats (nowadays it will be a semiconductor or perhaps a thermistor, and an electronic circuit, but the older (but quite reliable) designs had the bimetallic strip.

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                      • Re: Hardware hacking an electric fan heater without burning the house down
                        ralphjy

                        Very interesting teardown.  Always fun figuring out these electromechanical gadgets.  You've almost inspired me to hack an old thermostatically controlled window fan but summer is here and I use it all the time .  Plus have too many other projects - never enough time.

                         

                        I'll be watching to see what you come up with....   Have fun hacking.

                         

                        Also meant to ask - what is the meaning of the symbol in the picture?

                        • Re: Hardware hacking an electric fan heater without burning the house down
                          BigG

                          The awesome thing about element14 is the wealth of expertise and the documented lessons learnt... Automatic Dough Shaper - Blog #10 More Magic Smoke

                           

                          Yes, I'm exploring triacs! Thankfully, I've ticked that off the list - i.e. know your power ratings etc. So I basically just want to use one triac for now to remotely turn the device on and off. I decided to place the triac above the microswitch as shown (will be snipping that red wire).

                           

                           

                          That's the plan anyway. I'm working through element14 as there are plenty links on triacs.

                           

                          Now when looking at my design process, I've zoomed straight onto snubber capacitors (I have a habit of doing that... zoning in on something that's probably not necessary but just want to understand).

                           

                          And, while searching online I came across these guys. They are reasonable price wise but are they appropriate... and if so, how do you choose.

                          http://www.capacitorguide.com/mica-capacitor/

                           

                          Not sure what other bells and whistles are needed to look after the triac and the circuit for switching high loads. I'm basing my max load off 24A RMS (to cover the 6A + 16A).

                          • Re: Hardware hacking an electric fan heater without burning the house down
                            shabaz

                            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..

                              • Re: Hardware hacking an electric fan heater without burning the house down
                                BigG

                                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://

                                  • Re: Hardware hacking an electric fan heater without burning the house down
                                    shabaz

                                    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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