DIY Silicone Heat Blanket

[Robertking]

I recon just turn it on for an hour before you go to bed and that would do me

[MadRussian]

I have a questions on the resistance wire layout.
Why resistance wire crossing over one bus to get to another?

I not sure if this is the best way of resistance wire layout. Silicone could burnout or wire press through and short-circuit entire blank.

Why not to do layout differently?

I made couple drawings of two possible alternatives wire layouts.
Number one bus located side-by-side.. Number two design like a toaster where one bus on opposite side of the blanket. This particular one would be a lot easier to make.
I spoke with electrician and he said either one should work also he said number two design better because if one wire break it will be only one wire affected not whole section of the blanket

[troublemaker]

All groups of wires need to be the same length/resistance. For a 120VAC mat shoot for around 10.5 total ohms and for 240VAC 26 ohms.

[MadRussian]

All groups of wires need to be the same length/resistance. For a 120VAC mat shoot for around 10.5 total ohms and for 240VAC 26 ohms.

aaahhhh now make sense.
This eliminate #1 wire layout. How about #2. Still make sense.
If I use 3.3 ohms/ft wire and blanket 7.5' long each wire will make about 25 ohms resistance 15 wires will make total resistance on the blanket 375 ohms. too much? Too little? I'm rusty here how much Watts Amps it will draw?

I like my number two wire layout because it easier to make. only need proposal figure out wire size.

[chrismp]

I like your second wire layout!

There was a posting in this thread where I mentioned links to online calculators that make it easy to calculate the wattage of the blankets with a certain resistance...here's the link to the page: http://www.skibuilders.com/phpBB2/viewt ... c&start=15

[MadRussian]

I like your second wire layout!

There was a posting in this thread where I mentioned links to online calculators that make it easy to calculate the wattage of the blankets with a certain resistance...here's the link to the page: http://www.skibuilders.com/phpBB2/viewt ... c&start=15

I spent all afternoon yesterday trying to figure out numbers. Couldn't figure out.... my head hurts

[tufty]

I like your second wire layout!

There was a posting in this thread where I mentioned links to online calculators that make it easy to calculate the wattage of the blankets with a certain resistance...here's the link to the page: http://www.skibuilders.com/phpBB2/viewt ... c&start=15

I spent all afternoon yesterday trying to figure out numbers. Couldn't figure out.... my head hurts

P = IV
V= IR

Working from a desired wattage to get a resistance, by substitution we get R = (V^2)/P

So let's say you want a 2kW blanket, that gives a total resistance of 28.8Ω (That will mean a current draw of around 8.5 amps).

For parallel equal resistors (your drawing 2), total resistance Rt is given by R/N where R is the resistance of each element, and N is the number of resistors.

So if you want to use 15 elements, each one will need to be around 430Ω. At 3.3Ω/foot, that's a 130 foot blanket, should do you a few pairs of skis at once. :)

So either you need more resistance, or less elements, or to run the elements back and forwards a bit, or possibly a bit of all 3.

[MadRussian]

P = IV
V= IR

Working from a desired wattage to get a resistance, by substitution we get R = (V^2)/P

So let's say you want a 2kW blanket, that gives a total resistance of 28.8Ω (That will mean a current draw of around 8.5 amps).

For parallel equal resistors (your drawing 2), total resistance Rt is given by R/N where R is the resistance of each element, and N is the number of resistors.

So if you want to use 15 elements, each one will need to be around 430Ω. At 3.3Ω/foot, that's a 130 foot blanket, should do you a few pairs of skis at once.

So either you need more resistance, or less elements, or to run the elements back and forwards a bit, or possibly a bit of all 3.

With some help of my wife, I came to conclusion for this type of design I need different material, more gauge, 35-38, which give me more Ω/foot . Using wire with approx. 130 ohms/m I can do 2.5 m using 15 pc. and get very similar results for power calculation-wise, about 2240 watts.

IMO, optimal should be close to 50 ohms/m wire.

[chrismp]

A blanket with 15 pieces of 2.5m wire with 50 ohm/m would result in a total wattage of 6350 watts, which is a lot! I'd shoot for something around 2-3000 watts. That is plenty!

My blankets have approx. 2100 watts and get to 100°C in about 15 minutes. The highest temperature I ever achieved was around 200°C!

How wide are your blankets going to be? 15 wires sounds very little...I have 40 in my blanket spaced approx. 1 cm apart from each other.

[MadRussian]

A blanket with 15 pieces of 2.5m wire with 50 ohm/m would result in a total wattage of 6350 watts, which is a lot! I'd shoot for something around 2-3000 watts. That is plenty!

My blankets have approx. 2100 watts and get to 100°C in about 15 minutes. The highest temperature I ever achieved was around 200°C!

How wide are your blankets going to be? 15 wires sounds very little...I have 40 in my blanket spaced approx. 1 cm apart from each other.

Made a mistake on conversion, not 50 ohm/m but 50 ohm/ft, or 125 ohm/m..

Saw a general perception of 1 wire per 1 inch, not per 1 cm, my calculations on number of wires were based on that.
If to run 1 wire every 1 cm, need 40 pcs for approx. 16"x90", or 0.4m x 2.3m blanket. So I'll have to work with wire in the area of 95 ohms/m.

[twizzstyle]

Pshh, units... those don't matter.

http://en.wikipedia.org/wiki/Mars_Climate_Orbiter

[MadRussian]

finally starting to understand all this stuff.
how much power blanket should be? I see numbers all over from about 1500 W to 4000W.
I want to make blanket under 8 A or 1750 W 240 VAC. is that enough?

[MontuckyMadman]

Depends how fast and at what pressure u want to laminate.
We have 1400 watt blankets they draw 12amps each at 120v.
We press at 60 psi but laminate pressure is higher. It takes about 15 min to get to 180f if we start at 80f and then 30 min to cook the laminate.
If you press at a higher psi, you may want to cook the laminate faster to avoid pressing out too much resin.
It all depends on the viscosity of your resin sytem and the glass transition of your resin. And speed of cure.
You can press a ski at 125psi if you cook the whole thing in 15min flat, but i wouldnt recommend it in yoir home.
Around 2-3 watts per inch is very suficient for your blanket, 2000 watts will do very well.

[Richuk]

How much power? You need enough power to reach the final cure temperature. A ramp rate of between 1 and 2 degrees C/ minute appears to be OK. Ramp up too quickly and depending on where your temp probe is located, the body of the ski may start to over-heat or the tips may lag behind. The goal is an even cure, so above a rate of 1.5 degrees C/per minute and you may need a cooling system or a press design that compensates for this issue or both.

Tg isn't part of the equation. G S Springer states everything we need in the first couple of pages and again during the summary:

http://141.213.232.243/bitstream/handle ... sequence=2

MR - It sounds like you are making just the one blanket and the guys are quoting in terms of two. I think Falls uses one blanket, so it's worth checking his journal.

[Misha]

I made the heater by the second version of the picture. the first option at inclusion is deformed. wires start being attracted to each other)
I use the heater 1,5kWt/~ 220/230V