Engineering Roundtable - DIY Heated Seats


Usually for our Engineering Roundtable video series, we enlist one of our industrious engineers to build a project on camera and describe their process for you.

Fortunately, there are many people at SparkFun with a lot of craaaazy ideas, so every now and then we give the engineers a break and let someone else take the spotlight. You may be familiar with Nic, our enigmatic motion graphics designer. In addition to possessing a wide range of facial expressions, Nic possesses a dream. That dream is to outfit his second red, 1990 Honda Civic wagon with heated seats, and we’re all about helping people realize their dreams.

So here, without further ado, is Nic showing us how he turned his car into a glorious mobile chamber of cold-impervious opulence.

If you’d like to replicate Nic’s project on your own, you can see his product wishlist here (wagon not included). As always, leave questions or comments below, and we’ll see you for the next Engineering Roundtable soon!


Comments 33 comments

  • FUSE!

    What will happen is the solder joints on the heating pads wear through the electrical tape (use shrink wrap), short together, and you then have several hundred amps going through the positive wire, which will catch fire, and so will the car. And you will have a bad day.

    Don’t fool around on this one.

    You want the fuse next to the battery, not for convenience, but because shorts between the battery and the fuse will not blow the fuse, so you want to avoid that extra little bit of cable run. Notice the car maker puts their fuses close to the battery too.

  • Nic! He speeketh! {g}

  • 1) Yes, Fuse.

    2) Yes, feed from the switched Aux circuit, so it goes off when the key is turned off.

    3) MOST IMPORTANT - If you are going to run these so far out of manufacturers spec (12+V instead of 5V) Then get yourself a handful of Thermal Fuses and put one in series with each pad and in physical contact with each pad. For example: http://www.amazon.com/Microtemp-Thermal-x2103-Cut-off-Skywalking/dp/B00EC83QES -About $1 each. Opens at 142C (288F) and will shut down the pad in case it goes above that temp. (They come in all different temperature ratings, so use one thats some degrees above your expected max temp. They do not reset, but must be replaced if tripped. What do you want for a buck? At least not a burnt up seat.) Other then that! Nice project, nice video. Nice wiretwist with the drill :)

    • Dumb question.. If he put one pair of parallel connected pads in SERIES with the other parallel connected pair, then each set of pads would be dropping 6v, right? Would this be better if they’re rated for only 5v?

      • Yes, putting 2 in series would drop 6V across each. In this case though take a look at the product video they made for the pad. They tested it at a number of different voltages to see how much heat each would produce. They did run it up to about 16V i recall when the pad started to damage itself. Its all a trade off between how much heat you need, the life expectancy of the pad, and safety. There are a number of other factors that could come in to play: How hot can the seat material get before taking damage? And the cushion underneath. Is the pad being wrapped in some material to help it spread its heat over an area or just stuck inside the seat cushion, etc. In the end, as long as you make sure the pad is not getting to a temp that will damage it or the material around it it is likely ok. Adding a thermal-fuse is just an additional safety measure.

  • A thermostat might be a good idea to keep yourself from having to switch it on and off all the time like window wipers… Fuses are always a good idea, Putin a normally off relay in there connected to the accessory side somewhere (cig plug or radio) is good so you don’t kill your battery if you forget to turn it off.

  • You could even go a step further and add a microcontroller to the setup. Readings from a temperature sensor could cut power to the pads as required to keep the seats from getting too toasty. You could even go as far adding a switch with different heating levels (temp selection + temp sensor readings = heating pad temp).

    • If you’re putting a microcontroller in there anyway, then you DEFINITELY need the coolness factor of a pressure sensing (butt sensing) switch to turn it on.. You could even identify different drivers by their weight and set a target temperature based on their preference! ;-)

    • Or separate heat zones like many cars have. Butt / Butt + Back / Back / Off

  • Kudos to Nic for putting this project up, and risking everyone’s comments about fuses. I woulda made the comment too if it weren’t for all the others. Additionally you crushed the price of the kits for this exact thing you find on ebay.

    • thanks man! i originally shot the tutorial using a fuse tap from Auto Zone. I couldnt get it to work, so I had to cut all that footage out. If someone is confident in using a fuse-tap they have 2 fuses built in, which is cool. I think what my problem was is I only put in one fuse when it must have needed both.

  • First thought is “where’s the fuse?”. You really should have even had the fuse in line when you first tested. (Can you say “sparks flying”?)

    Second thought: Beware the airbags! If you read the car repair manuals, they say to always disconnect the battery when you’re doing things like taking off the console cover or anything around the dashboard. I don’t believe the airbags will go off if you have the battery disconnected. If you were to set them off, it would be a “very bad day”. American airbags come out with a lot of energy.

    • removing the connectors to the seats can sometimes trip the SRS computers and require you to do a reset procedure through the ODBII connection, it depends on the model and where the pre-tensionors are. That’s ESP true with a car that has airbags in the seats. In most cases, if the connector goes to an airbag, there’s a little shorting wire in the connector that drops in on the airbag side to prevent static discharge and erroneous signals when they are unplugged.

  • Definitely add a fuse. And how well are the 5V heaters holding up to 12-14V?

    • A fuse is a good idea for sure. The pads are holding up really well. In the product video they are in, Rob tested them to stand up running for 6 hours at a time with no insulation. They didnt have any problems till 16V, uninsulated, so I figured I’d be safe to use them.

      • Just FYI: I don’t know 1990 Honda electrical systems, but I’ve seen foreign cars of that vintage run charging voltage (15.6v) in their nominally 12v electrical lines. I don’t know if that was by design or some problem with the individual cars' voltage regulator circuits, but since you said “no problems until 16v”… well, 15.6 is awful close

        • A couple of related points: in Amateur (Ham) radio, we realize that typically “12v” batteries at full charge are more like 13.8v, and that’s the number we usually use.

          Also, in cars, you have this HUGE inductor called a “starter”, and when you release the starter button, there can be a spike of up to about 70v in the system. Although it’s very brief, and so probably won’t affect things like resistance heaters, it can do a number on electronics. (This is why most cars cut off things like radios and computers when “cranking” - they actually use a “break-before-make” switch arrangement for the accessory power.) If you do decide to add a computer, either use a regulator that can handle the big transient, or go to powering it from something on the accessory line.

        • ah! thanks for the heads-up.

          • Oh, BTW, instead of wiring the pad pairs in parallel, wire them in series. This may limit current in some failure modes, and will also mean that each pad sees 6v (worst case 8v) instead of 12-16V. That’s much closer to the pads' rated 5v.

            • Great idea- I second the ‘wire them in series’ thought. Run them for an hour that way and see how warm you get.

              Adding a layer of high temp silicone material could keep them from bending too much and breaking from flexing too much (especially on the seat).

  • An easier and safer way to wire the Heater is to use an unused fuse in the fuse box. Look at the user manual. It should list what fuses are used for what. There are usually two or more unused locations you can wire the heater to and put a fuse for the amp rating of the heater. In line with the wires wire the switch. Most foreign cars either have the fuse box located near the drivers side door or inside the hood near the battery box.

  • What you did was dangerous. No fuse, Not hooking up to the switch side of the ignition And paralleling the heating pads, Is definitely dangerous. As others have said, The use of a fuse is absolutely Essential.. Also as others have said, it should be hooked to the ignition side of the switch, So if something does happen it will happen when someone is around. Not when it’s setting in your garage in the middle of the night when everyone is asleep. There should be a junction point under the dashboard to connect power to your device. Paralleling the heating pads is also a bad idea. It is one thing to run these pads on 13.5V+ on the bench. They have open-air to displace the heat. Putting them in a seat insulates them. The heat builds up quicker and could catch the foam padding on fire. A related example is when they used to use Knob and tube wiring In houses. 14gauge would carry a 20 amp circuit. When they started Insulating the wires there was no place for the heat to go so they had to increase the Size of the wire to 12gauge in order to keep them from overheating and catching the house on fire. Also you should not use solid core wired in Any automotive application. Vibration can cause the wires to break and short out. And the movement of the seat can cause it to break as well. Also do not twist the wires. Lay them as flat as possible and keep them from rubbing against each other when you sit down. When running it through the seat do not stretch the wires. Route them In a curve type pattern so they can move when you sit down. I have been doing this type of work since the 70s and if you were working in my shop you would be fired for doing that kind of work. There have been several incidents involving cars catching fire in garages and burning down the house and maybe killing the occupants. Keep your family safe and disconnect this garbage and do it correctly.

  • When I saw the thumbnail for the video, I saw the reflection on the insulation for the heating pad and it looked like little flames, or at least that’s what my brain immediately went to :D

    The charging voltages people have mentioned in foreign cars, my Honda also spikes up to 15.5 when I rev the engine. It went to 18 when the regulator opened up and the alternator nearly fried itself. It tripped my SRS computer, and I had to do a reset procedure through the OBDII connector.

    Thermostat, YES! Or thermal fuse! Running them in series (in two parallel groups), good idea, that makes for safe failure if one shorts (but not if two short in the same string).

    Also, cement those pads to a fabric or rubber (neoprene?) that can handle the heat, AND keep them from distorting from getting in and out of your car! Your movements could, over time, grind up the heat tape or the connections to the wires and then you’ll get a short for sure.

    Otherwise… you’ve got me thinking… ;)

  • fuses are nice….most importantly is to find an aux power supply…not directly from the battery…then when you turn off the key the power will turn off to the heat pads as well….it really sucks getting into a cold car only to find the battery is dead….

  • I know it has been said by many others but it is important, FUSE. I would have taped into the power distribution box (let the manufacture tap to the battery). I would also have looked to tap into a circuit controlled by the ignition. I would make for a bad day trying to start your car and no power because the seats were left on.

    Anyone ever tried a Peltier? heated and cooled seats?

  • While everybody is throwing up “fuse”, let me drop a question: would the female quick connects(https://www.sparkfun.com/products/11461) work on a standard ATO fuse? I know I prefer the 90° connectors with the ends insulated, but has anybody tried this?

    • Yes, I’ve done this several times. They work well. I’ve taken a bit of random plastic and some electrical tape to tie them together to make things more manageable when swapping out the fuse.

  • Next up, heated steering wheels so you don’t have to wear gloves! Also, for summer, chilled seats if your car happens to be facing the sun while parked without a windshield visor :)

  • Very cool Nic, very industrious also. I would have approached it with a seat pad that fits over the seat so I would not have to remove the car’s seats…..I am generally kind of on the lazier side of car projects. And +1 on adding a fuse especially on a heating circuit directly connected to your car’s battery.

  • Always add a fuse ! You can get inline fuse holders from auto parts shops. They normally come with about 6" of wire on either side of a molded fuse holder with cap for water proof. I normally crimp a lug on one side to connect to the battery, and then connect the load on the other side. Next to the battery, it makes it easy to see to remind you that that is where you put the fuse, but also that you actually added on in the first place.

    • Thanks man. I’ll do that for sure. I just need to watch Dave Stillman’s video on how to use a multimeter first so I can figure out what size of fuse to use ;)


This Week

This Month

Heartbleed

Happy Arduino Day!