1 (edited by caswal 2013-01-15 14:17:44)

Topic: Homemade Nichrome heat mat

I really liked danny's nichrome heat bed he made. To me it had a major advantage, although the silicone heat mat from qu-bd is awesome, I didn't have a power supply around that could deliver that kind of current at 12v. But I do have a universal laptop adaptor that can do 5 amps and 24v, 100 watt limit.

So by my maths I needed to make a 6 Ohm heating element, and make a new mosfet circuit to run it. I also wanted this to be as fully reversible as possible. So I found some wafer thin (0.5mm) silicone matting, and brought myself the other components. So the plan was/is to have it laid out Alu / Silicone / Nichrome / Silicone / Glass.

I needed to work out what nice paths I can make for the nichrome, that would get me the resistance I wanted. So pen and papered a couple of designs, until I got the length and runs needed. Then design a loom jig to form the nichrome into the correct shape.

Here is the jig:

https://lh5.googleusercontent.com/-VlPlZEVEG5c/UPVSFcrqrjI/AAAAAAAABAU/DTHJ6_XAtJQ/s1024/IMG_6994.JPG

I then placed some kaptop tape, to stick and hold the wires down:

https://lh3.googleusercontent.com/-QgCKRN8hsmw/UPVSX87KMcI/AAAAAAAABA4/JhGbVkvrLCk/s1024/IMG_6996.JPG

Then do the other runs:

https://lh3.googleusercontent.com/-84UdSmCuf08/UPVSnj1PWNI/AAAAAAAABBI/lA2pvgLONzs/s1024/IMG_6999.JPG

https://lh4.googleusercontent.com/-ylhWjSSPfog/UPVS3b25hBI/AAAAAAAABBg/Cy2TGXLj3LM/s1024/IMG_7001.JPG

The lift it off, and stick the tape to the silicone:

https://lh3.googleusercontent.com/-z6urvebQNs8/UPVS3NFVhMI/AAAAAAAABBY/25Ddy9WGDJk/s1024/IMG_7002.JPG

Add some extra kapton, stick the edges down to the opposite side of the silicone, twist the ends up of the nichrome up, solder and heatshrink the cables on, and forget to take any more pictures. Until testing:

https://lh6.googleusercontent.com/-MajPePWMWrI/UPVS3a7PoGI/AAAAAAAABBc/AsZwFH4r9HE/s1024/IMG_7003.JPG

I use this in conjunction with the stock heater, giving me about 150 watts of heating in total, and also a more even heating area, which I hope should lead to less warping. I believe that as the heat element is at the centre of the bed, the circular drop off of heat to the outside exasperates the warping.

I have soldered a signal wire, from the gate pin of the Sanguinololu to signal my mosfet, both grounds of the power supplies are common.

Lead Programmer & Co-Owner of Camshaft Software - Creators of Automation - The Car Company Tycoon Game

2

Re: Homemade Nichrome heat mat

You must really hate hairspray.  tongue

Seriously looks great, I love the loom!

3

Re: Homemade Nichrome heat mat

The loom for wiring is awesome. Wish I'd thought of that

4

Re: Homemade Nichrome heat mat

Loom is beautiful. I'm stealing that idea smile.   I intend on running 110V AC, so I need a fairly long amount of nichrome to hit 25-30ohms without using too thin of wire.

The loom is great too, because it makes it easy to avoid certain sections.

5

Re: Homemade Nichrome heat mat

Clever construction!

Seeing how neat you have it make me wonder about using a casting silicone over and around the wire to make your own heated mat. Would likely get a really neat result.

6 (edited by cckens 2013-01-15 22:45:05)

Re: Homemade Nichrome heat mat

How about a cut down silicone baking mat as the over-layer?  Pretty cheap for a bed warmer.

Kapton for the adhesive on the mat would probably work just fine.

7

Re: Homemade Nichrome heat mat

lawsy wrote:

Clever construction!

Seeing how neat you have it make me wonder about using a casting silicone over and around the wire to make your own heated mat. Would likely get a really neat result.

That did cross my mind, sandwiching it between 2 sheets of glass, with silicone from a chalk gun in between. It is hard to keep the nichrome holding its shape, it took my several attempts to get this all to work. Relying on kapton to hold it steady.

I did wander if using a heat gun on the nichrome would get it to hold its shape better when removed from the loom.

cckens wrote:

How about a cut down silicone baking mat as the over-layer?  Pretty cheap for a bed warmer.
Kapton for the adhesive on the mat would probably work just fine.

That would work, but I wanted to make this paper thin.

Lead Programmer & Co-Owner of Camshaft Software - Creators of Automation - The Car Company Tycoon Game

8

Re: Homemade Nichrome heat mat

I was thinking more like a two part silicone that you mix and then pour over the top with a rectangular frame to contain it. Should set flat, thin and with the wires nicely protected and insulated.

Another question: how quickly does it heat up from cold to print ready?

9 (edited by caswal 2013-01-16 09:50:42)

Re: Homemade Nichrome heat mat

lawsy wrote:

I was thinking more like a two part silicone that you mix and then pour over the top with a rectangular frame to contain it. Should set flat, thin and with the wires nicely protected and insulated.

That should work, if you use my jig design, you would get peg holes, but they could be filled in later, or not bothered with.


lawsy wrote:

Another question: how quickly does it heat up from cold to print ready?

Looking at the graph in Repetier, it seems to climb at around 20-25 degrees per minute.

Lead Programmer & Co-Owner of Camshaft Software - Creators of Automation - The Car Company Tycoon Game

10

Re: Homemade Nichrome heat mat

sorry for asking this noob question, but what is the silicone's purpose? to hold wire in place? or make the surface even? or some unknown reason?

Solidoodle2 with Ceramic tile heated bed http://www.soliforum.com/topic/2544/my- … eated-bed/
"1kg should last for an while" is a lie!

11 (edited by caswal 2013-01-16 15:11:14)

Re: Homemade Nichrome heat mat

RavensCrest wrote:

sorry for asking this noob question, but what is the silicone's purpose? to hold wire in place? or make the surface even? or some unknown reason?

There are never stupid questions! Don't apologize.  Better ask then let something go wrong or break. smile

This silicone mat, is sold as being heat conductive to sit between heat sinks and heat sources (such as processors/electronic chips). So it helps to conduct and distribute the heat more evenly. It fully wraps around the nichrome wiring, contacting more surface area.

If there was no silicone the nichrome would be pressing directly against the glass and the alu bed, resulting in a very narrow contact patch, which brings along the second reasons. Electrical Insulation, I have the Kapton tape side down, facing the aluminium bed acting as an insulator. But also the silicone itself acts as an electrical insulator. Otherwise the nichrome wire would just short through the bed, not heat up and worse blow my power supply/mosfet switch.

The one long term safety mod I will do, is add a 7.5 amp fuse in series with the nichrome mat.

The third reason is as you state, to act as a shim/give some play and squish between the bed and the glass,.

Lead Programmer & Co-Owner of Camshaft Software - Creators of Automation - The Car Company Tycoon Game

12

Re: Homemade Nichrome heat mat

Hello Caswal,
I was wondering. what is the nichrome wire's gauge for this build?
if each one of your wire is about 55inch,are you using 26-28 gage Nichrome wire?

Solidoodle2 with Ceramic tile heated bed http://www.soliforum.com/topic/2544/my- … eated-bed/
"1kg should last for an while" is a lie!

13

Re: Homemade Nichrome heat mat

I used this stuff: http://www.jaycar.com.au/productView.asp?ID=WW4040

Size 28, Resistance of 13.77 ohms per meter

Lead Programmer & Co-Owner of Camshaft Software - Creators of Automation - The Car Company Tycoon Game