Show All ItemsMake yourself a cheap heating pad! Ecological and financial benefit : you don't get to heat your room, just yourself. This pad cost me about 15-20$ to make (I already had the AC adapter and the mosquito net), way cheaper than the one you find in the market. Electrical consumption isn't much (like a laptop): less than 3 cents/night (for this price, you will get a sauna in you bed!) I check it, there is no health issues with the magnetic field: http://www.cancer.gov/cancertopics/factsheet/Risk/...Easy to fix on a chair, an arm chair or/and in a bed (put it under the bed sheet, if you move a lot, you can tie it with a small string)!!! It's very important that the heating cable doesn't touch itself, in no point: this could create a short circuit and the cable could become cherry red and start to burn. Some cable have a coating but the coating of the one I bought is very symbolic: a simple scratch and it is off. The length of the cable should be long enough to generate enough resistance (otherwise your AC adapter will burn down) but at the same time, the shorter the cable is, the warmer it will be... but it should not be too short because of the AC charger , but if the cable is too long, the cable won't be warm enough...
Well, the tricky part of this project is to find the right length according to your adapter: cf Step 5Advantage over an electric blanket:Much cheaperhygienic: there is no real need to clean it but you could immerse it in water if you want (since the pad is just made of plastic and metal wire). Much safer and durable: the cable have less risk to touch itself or to be twisted (and then break), so technically it should be usable forever (it's not the case for electric blanket since you need to wash them and since when you move the blanket, the wire get slowly twisted (which is very bad for the cable especially hen it's hot) Very light and not cumbersome: a very important feature for people who move a lot. I have a nomadic life and I can't afford to move with a lot of stuff when I move from one place to another : warm blankets are too heavy and voluminous. This pad is perfect since I can even use my computer's AC charger during the night and if for some extreme reason I cannot carry it, it's fully recyclable.
Step 1: What You Will NeedTo make the pad:50x40 cm pvc coated fiberglass mosquito nets for window (or you can use an old blancket to sew the wire on it) sewing thread and needle a heating wire: The difficult part is to determine the type of heating cable and the length you will need.(for other cable cf Step 6)The lenght I choose: for one pad 6m for my first (hot) pad, 7 m for the second (8 or 9 would have worked). The length influences the heat generated by the cable... to make sure you use the correct lenght it all depends on you power source (for me my AC adaptator). Heated mattress pad induced AC voltage Tursiops_GTechnoidMVMjoin:2002-02-06Norwalk, CT said by Tursiops_G:Well the reversed Hot/Neutral is pretty likely, this house was built in the 50's from a Montgomery Wards kit. The ground is open since I know there are only two wires to that outlet.However, the mattress pad only has a two prong plug not three prong. Optimum OnlineARRIS TM1602TP-Link TL-WDR4300 The fact that there appears to be a connection with the "hot" side of the line with the switch in the OFF position, suggests a Hot/Neutral reversal...
Is the outlet and cord both Polarized?Old Electrician's saying: "White to White, You're All right. White to Brass, Shocks Your @$$"... -Tursiops_G. cmslick3join:2004-05-24Joliet, IL to Tursiops_Gsaid by Tursiops_G:"White to White, You're All right. White to Brass, Shocks Your @$$"...I like that and I'm going to use that in the future.The outlet is polarized, and there is a power strip plugged into the outlet. The strip is a cheapie, but polarized as well with built in safety covers. The plug for the pad I'm not sure about, something makes me want to say it is not polarized. I guess what you're going to suggest next is that I reverse the plug and see what happens?said by cowboyro:It's normal and expected.I'm not quite sure this should be an expected experience... But I do understand your point. The thing that bothers me is that my wife's side does not do this. Also, I believe this is a recent development and we've owned the same pad for over a year now.What I don't quite understand is how much voltage would have to be running through the coils to induce 40VAC on my body?
Since is has to jump the gap of padding and sheets between the coils and myself I would think it should be a considerable voltage. cowboyroPremium Memberjoin:2000-10-11Shelton, CT75.3 5.5· said by cmslick3:What I don't quite understand is how much voltage would have to be running through the coils to induce 40VAC on my body? Since is has to jump the gap of padding and sheets between the coils and myself I would think it should be a considerable voltage.It really doesn't take much. You're making the mistake of looking at voltage, not current. In this case the voltage is almost irrelevant, what matters is the current - which is very small. Think of it, all you have is a capacitive voltage divider. If you get on a chair and you hold an insulated wire in your hand, you will have ~60V between you and the ground (equal capacitors between your hand and both hot and neutral). Will a meter register 60V between you and the ground? Highly unlikely, since the internal resistance, even extremely high, will be a almost a shunt compared to the reactance of the capacitors your hand forms with the wires... cmslick3join:2004-05-24Joliet, IL
cowboyroPremium Memberjoin:2000-10-11Shelton, CT75.3 5.5· said by cmslick3:The skin contact closed the circuit and allowed a small current to flow between us which is why we felt a little tingle. But the current was kept low because I wasn't in direct contact with the wires, correct??Correct - all you had was capacitive coupling and the current is somewhat small at 60Hz... Had it been 6000Hz it would have been a different story though SmokChsrWho let the magic smoke out?Premium Memberjoin:2006-03-17Saint Augustine, FL to cmslick3Call me weird, but I like that feeling. This particular effect I can create any time in the kitchen, by simply grabbing the fridge and touching someone at the sink.As coyboyro said it doesn't take much, and you are measuring with a very high impedance meter. If you were to measure it with an older VOM that actually used a meter movement, you would likely only see a slight deflection if anything at all.That's part of the reason that some of us experienced techs like to keep a true "analog" (sorry, Luthful ) meter around, because in certain (Hi-Z) cases, the newer meters can deceive you into thinking something is good or bad when it really isn't.
to cmslick3said by cmslick3: didn't do really well with capacitance in school. Assuming the heating element is powered directly from the AC line one end of the element will be a 0 volts - relative to Earth ground and the other side at 120 volts.As mentioned the amount of voltage depends on capacitive coupling and how each body is coupled to the heating element. Worst case is that one person is at the low end and the other at the high. That being said because frequency is low - 60 Hz and so is capacitance (not a lot of area and pretty far away from the element) the amount of energy coupled is very small. As mentioned modern DVMs have very high input impedance resulting in high voltage ready even for very small current flow.Sounds like each side is powered separately. Are the plugs polarized? If not you ought to be able to change the voltage/current between persons by reversing the plug on one of the heaters. Try the different combination and see if that changes the amount of current between you and your wife.
said by cmslick3:Something that I failed to mention is that the pad has digital controls, with 10 levels of adjustment.Even with digital control off should be "off." With a digital control there is a snubber across the Triac or back to back SCRs that passes a tiny amount of current even when off. That can sometimes be a problem if the load is extremely low but not with an electric blanket. If you are able to measure the voltage at the element in the off control position it should be extremely close to zero volts.Out of curiosity are both blankets in the same orientation on the bed - cord comes out the same place? Do they plug into the same receptacle? If the sides are connected to different receptacles it is possible there is 240v between them rather then 120. They would still work fine but the induced current will be higher./tom alphapointeDon't Touch MeMVMjoin:2002-02-10Columbia, MO to cmslick3said by cmslick3:With both sides plugged into the outlet there was 40VAC between my wife and I based upon measuring from skin to skin, with 15uA of current.