Re: How Things Work?

Before proceeding, please be sure you will is up to date and your
significant other(s) know where you have hidden your important papers.

>
> I am thinking of using a discarded (good) electric controller from an
> electric blanket as a controller for a nichrome wire foam cutter. Can
> anyone gibve me a general idea how electric blankets work. Pointed in
> the right direction I can use a multimeter to check out the wiring and
> see if I can use it for controlling a foam cutter.
>
> There are two controllers. The controller I where I snipped off the
> insulated power wires has a regular two prong plug (2 wires) for the
> wall 115 Vac outlet. Inside the controller is a heating "zig zag" wire
> assembly next to a 3/4 turn moveable knob contact for adjusting the
> blanket's set temperature. I would believe the "zig zag" wire heats
> up to cut off the power supply at set point. This "zig zag" part is
> an independent 3 wire circuit but must be connected to the 115Vac
> power source somewhere.
>
> Since I don't have the blanket any more I am a bit puzzled as to how
> things are wired up. Also I can't imagine 115 Vac running though the
> blanket's embedded heating coils as any fracture will be a fire hazard
> or a shock hazard. Yet there is no transformer to step down the
> voltage and not much by the way of safety cut-offs in the controllers. >
>
Reply to
Tom
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There was as ad on TV tonight for a service that allowed you to create a will for $63 - perfectly legal. If buying a real controller is less than this - buy one, if its more, make a will, then modify your blanket control but please let your wife know how to list things on ebay.
Val Kraut
Reply to
Val Kraut
: : There are two controllers. The controller I where I snipped off the : insulated power wires has a regular two prong plug (2 wires) for the : wall 115 Vac outlet. Inside the controller is a heating "zig zag" wire : assembly next to a 3/4 turn moveable knob contact for adjusting the : blanket's set temperature. I would believe the "zig zag" wire heats : up to cut off the power supply at set point. : What you are describing sounds more like a rheostat than a temperature control. If you have a multimeter, it should be easy enough to set it to the voltage sacle and measure the out put from the controller.
There are several articles describing how to build one of these things on the net. googleing "nichrome cutter" led to more articles than I care to count. :-)
Bruce
Reply to
Bruce Burden
If she knows how to use a computer, just have her Google wills. She will find a plethora of sites, some of which are free.
Reply to
willshak
Having seen the results (*) from a broken electric blanket, I'd still have to say be very careful, and I really do hope it works out for you.
*
- A destroyed bedroom - $5,000.00 - Clean up and airing out the rest of the house - $1,000 - Having at least one wag claim thet someone forgot to put out the post-coital cigarette.... =2E - Priceless
Reply to
The Old Man
I do not recommend this. Your intentions are good but you're a bit misguided.
Here is what I know about electric blankers (form my own observations):
*YES*, there is 120V AC going applied to the heating coils of the electric blanket. It does not use any type of a voltage step-down device. The heating element is well insulated. I gather that manufacturers think that it is safe for use.
Some newer blankets have a sensing circuit in the controller which cuts power to the heater the instance there is a break in the circuit. They also use a polarized plug so that the heating coil will not be on the live side of the circuit once the safety cutoff occurs. Older blankets did not have this feature.
The "controller" that you've mentioned is nothing more that a simple thermostat circuit. It is actually more like a cycling timer and thermostat Very simple design using an adjustable bi-metal switch. All ti does is to cycle the full power off and on to the blanket. The cycle time is controlled by the value dialed on the knob and also affected by the ambient temperature.
The on/off ratio is the lowest at the lower settings and fully "on" at the highest setting. The ambient temperature offsets this a bit (the colder it is the more "on" time you get).
I do not see how that could be useful for hot wire cuttter. Best way to control hot wire cutter would probably be a low voltage variable transformer. Or some sort of Triac controlled circuit (similar to standard dimmer switches). The "dimming " circuit could either be used on the high or low voltage side of the transformer.
Peteski
Reply to
Peter W.
I suspect electric blanket elements are high impedence low current, high voltage devices.
Foam cutters are very low impedence, hence use high current, low voltage. Most of the cutters I have seen use six volts or lower. On mine I used an adjustable battery charger/eliminator, and it worked fine, but it was a fifteen amp device and I was using about ten amps of it.
I think you would be much better off using a low voltage device, and you can easily use manual control rather than automatic. Much safer, too.
Reply to
Don Stauffer in Minnesota
I thought that I explained it well enough but I guess not. Electric blaket's controller is purely either fully on or off. The overall blanket's temperature is the product of the average of the "off" and "on" time of the controller. But the cycle time is relatively long (off for about a minute and on for 10 seconds or so in the low settings). Noting that can be used to control a hot wire cutter. Hot wire has a very low mass and even if you wanted to control its temperature by controling the duty cycle of the voltage, the cycle would have to be much faster (few times a second). The electric blanket controller is just not a proper device for this application.
A triac-based dimmer would be perfect for this application. Just note how well it can control the brightness of a light bulb. A hot wire cutter's thermal inertia is more like a light bulb than an electric blanket.
Peteski
Reply to
Peter W.
I normally build aircraft in 1/48 and 32nd scale. But every now and then I'll build a piece of German or Soviet WWII armor in 1/35 scale. I'm also a sucker for the realism for the Friulmodel metal tracks. Long evenings were spent assembling these links one by one, I knew there had to be a better way. Well there is: I found the Trakmaster 01 track linking tool on the Mission Model website, I purchased one and finally got around to trying it out on the tracks of a PZ IV last night.
The reason for this email is to announce to all you armor fans that Trakmaster is a positive joy to work with and is everything Mission Models declared it to be. All of a sudden the stack of unbuilt Panzers is looking good. (Incidentally, instructions state that Sherman tracks can not assembled using the Trakmaster). I even leave the assembled tracks in the jig after inserting the wire in order to apply super glue.
I rarely praise a product and I've never praised a product on email before, but the Trakmaster's ease of use really grabbed my attention.
Dick...
Reply to
Dick's News

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