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Please help me determine the amount of current at 9 or 12 volts i need to warm a wire and melt ice.

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MikeT1982

Wed Jul 27 2011, 09:27PM

Registered Member #621 Joined: Sun Apr 01 2007, 12:37AM
Location:
Posts: 119

Hi guys, i wasn't quite sure how to title this, but here is the deal. I just got done being creative and making a hopeful defrosting wire. I had to plumb a sump pump with about 6 ft of 1.5" pvc pipe out of my basement. About 3 feet of it is underground and may freeze in the winter. It always drops below freezing here in PA. I drilled a small hole in the pipe inside the house and snaked a doubled up section of 24 gauge solid conductor wire that i braded. I took a 12 ft section of wire and doubled it over at the halfway point making a 6 ft section. I then twisted it into a braid. I placed epoxy over the hole through which it passes as not to leak. The wire snakes all the way through the pipe and protrudes slightly from the opposite end. It makes it though any areas where water may pool and freeze inside the pipe.

I would like to connect it to a 9v or 12v transformer say, either an ac stepdown or a wallwort, and select a resistor to limit the current to just enough to warm the wire enough to keep ice from forming abd blocking off my sump pump.

Do you guys think this will work, and how can i determine how many amps (or milliamps) to pass at 9-12v to warm the wire slightly!

Thanks a ton ahead of time guys!!

- Mike T

Ash Small

Wed Jul 27 2011, 09:44PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Is it copper wire that you've used?

I think it's usual to use ni-chrome wire for this.

The wire from an electric heater (maybe a fan heater) may be suitable.

I've also obtained some good results using stainless steel wire (rigging wire from a yacht)

The resistance of the wires I've mentioned is quite high, so the resistor value required would have to be worked out after you've measured the resistance of the wire used. (I'd use 'trial and error', one of my favourite scientific methods

MikeT1982

Wed Jul 27 2011, 10:24PM

Registered Member #621 Joined: Sun Apr 01 2007, 12:37AM
Location:
Posts: 119

Shoot, i didn;T know about that type of wire. My wire actually has insulation too and is double conductor, so i twisted both together at each end, resulting in basically a double run so the current runs through two 24gauge wires for 12ft. :-/ Hopefully all of this is okay arghh. So i'll measure the resistance of the wire and possibly if it is high enough to not yeild the the maximum current of my transformer, i'll be okay? I may expiriment with another duplicate of the wire outside the pipe and feel it, and as long as its warm but not melting it should work no? hehee, trial and error i love!

Oops just looked it up! It is PVC insulation covering the wire.

Forty

Wed Jul 27 2011, 10:30PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

they make a heat tape for putting around pipes that does exactly what you want. it's some sort of nichrome/high resistance ribbon that you plug in. lowes or home depot may have it.

Ash Small

Thu Jul 28 2011, 12:01AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Forty wrote ...

they make a heat tape for putting around pipes that does exactly what you want. it's some sort of nichrome/high resistance ribbon that you plug in. lowes or home depot may have it.

This was pretty much what I was doing. The best I came up with (when I was building a 12V shower that ran off batteries) was to wrap (wind) SS wire around multiple parallel small-bore ceramic (or glass) tubes.

This application (preventing pipes from freezing) would probably work with a low current through a high-resistance wire wrapped around the plastic pipe, but would probably also work with un-insulated wire inside the pipe, as the resistance of the wire will still be orders of magnitude less than the water, even if it is contaminated.

MikeT1982

Thu Jul 28 2011, 02:13AM

Registered Member #621 Joined: Sun Apr 01 2007, 12:37AM
Location:
Posts: 119

Hmm. Yeah i was wondering if the heat tape would work on the outside of plastic pipe. Thanks for the headsup on that! I didn't feel like digging the pipe back out to wrap it as i glued it as i was laying it :-/ So then i spent a good amount of time snaking the wire through the pipe last night and she's ready for hookup. I know that there is insulation on it, but i've seen the cord of my vaccuum cleaner which has insulated wire inside of a rubber tube and it gets pretty hot to the touch after running for a bit. So that's what i was hoping to duplicate, a water tight insulated wire that stays warm. I am not sure if my idea will really work out though! I just found a wallwort from radio shack that will push 2 amps at 3-8 volts. So maybe i'll ohm my wire, and if it's around 0, i'll put a 4 ohm resistor which would pass the 2 amps at 8 volts...and start at 3 volts which would pass .75 amps and see if that warms it enough.... Gosh i hope this works LoL!

klugesmith

Thu Jul 28 2011, 02:28AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

The heat tape we're talking about has resistive material with a large positive temperature coefficent, similar to the stuff in polyfuses. It's intended to be connected directly to mains voltage, and draws very little current until it's so cold that the pipe is at risk of freezing. Then the tape produces a lot more heat, with intrinsic temperature regulation.

MikeT1982

Thu Jul 28 2011, 02:35AM

Registered Member #621 Joined: Sun Apr 01 2007, 12:37AM
Location:
Posts: 119

Oh wow...that's really interesting that it adjusts it's current draw based on temp. Shoot i guess there is a better solution than the path i'm trying to take LoL...I love this forum i always learn new things from ya's!!!

Chip Fixes

Thu Jul 28 2011, 02:57AM

Registered Member #3781 Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701

I don't know what they are called or even how exactly they work but you could get one of those (thermal switches?) that open when they hit their rated temperature. For example: I had a 12v seat warmer that had this little (thermal switch?) wired in series with the heating wire that opened the circuit after it hit 100 degrees

Ash Small

Thu Jul 28 2011, 09:17AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I remember back in the 'seventies one of the 'popular' hobby electronic circuits was an Ice 'warning light' for your car.

There must still be copies of it on the net. It was basically a circuit that switched on a warning light when the temperature dropped to O degrees C.

A similar circuit could be used here. Instead of switching on an LED it could be used to switch a transistor that turns on the current to the heating wire.

EDIT: Schematic is here:

and here:

You'll only need half of the circuit, as this one also warns of low lighting to remind you to turn the lights on.

You could probably coat one of the wires I mentioned above with enamel paint/varnish, or similar to insulate it.

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