Insulated resistance heating wire

[raptor1956]

I'm playing around with a project to heat an aluminum plate to no more than 50C and although nichrome wire is useful it is not usually insulated so bonding it to an aluminum plate would be a bit of a shorting problem.  Are there sources for insulated heating wire that would be suitable?  I know that anything you put over the wire to insulate it will reduce the thermal conductivity so the wire will run hotter than the plate but so long as that's not a huge difference and the insulation can comfortably handle the wire temp that shouldn't be a show stopper.  The other thing is the actual bonding of the wire to the plate so the the heat generated will be reasonably well transferred to the plate -- once again another intermediate surface will increase the thermal resistance but within reason should also not be a show stopper.  What kinds of materials are a good choice to effect the bond>

So, in summary, are there sources of insulted heating wire or preferred applied insulation that will prevent electrical shorting yet provide adequate heat transfer?  And, what are some good choices for bonding agents to affix the wire to the aluminum plate?  And just to be clear, I'm not talking a large or thick plate or large power -- I'm looking at a plate perhaps 1/8 inch thick by 12 inches by 12 inches with a maximum power to the wire of less than 50W and perhaps as little as 25W.

Thanks,


Brian

[Gyro]

You  might do better with an array of metal-clad resistors mounted to it depending on how even the heating needs to be.

[KL27x]

Mica is first thing that comes to mind. Good thermal conductivity, electrical insulator, and it can be made in very thin and flat sheets due to crystalline structure. Can be purchased in relatively large and thin sheets. At 50C, you can use the regular heatsink goop to couple the mica to the alum plate.

Not sure how to stick the wires to other side of the mica, though. A lot of commercial products use ceramics to hold the wires in place. Maybe there is some kind of clay you can buy which will fire at lower temps, say in a regular oven. I'm thinking you fire the whole mess in the oven, alum plate, mica, wire/clay. Then goop the mica side to the aluminum plate.

[Marco]

Any conductor with high temperature capable insulation is potential insulated resistance heating wire

[Mr.B]

Mica is also the first thing that comes to mind.

For the bond I use Thermal Epoxy in other applications.
It should work well in this application.

http://www.arcticsilver.com/arctic_silver_thermal_adhesive.htm

[ConKbot]

For only 50C, slap a kapton insulated heater on the back and call it done.
http://www.omega.com/pptst/KHR_KHLV_KH.html

Omega is a good source for expensive, reliable, and in stock items like, ebay or other places if you want it cheaper

[Sceadwian]

50C is nothing for insulation, any reason you can't just use an appropriately sized length of magnet wire? Screwing a plate over the top of the wire will give you all the physical bonding you need, you just have to avoid over driving the element.

[raptor1956]

You  might do better with an array of metal-clad resistors mounted to it depending on how even the heating needs to be.

Not long after posting the OP it occurred to me that a small number of power resistors could easily be bonded with some screws and thermal paste and they would be electrically isolated.  So, problem solved but thanks for the advise.


Brian

[Brutte]

At this benign conditions I would not even bother searching for a resistive wire. I'd use an enamelled copper wire for transformer windings. Just stick it with some epoxy to the plate. Connections made with thicker stranded wire would be a good thing.

[Sceadwian]

At this benign conditions I would not even bother searching for a resistive wire. I'd use an enamelled copper wire for transformer windings. Just stick it with some epoxy to the plate. Connections made with thicker stranded wire would be a good thing.

That's exactly what I was talking about, just gotta pick wire thickness vs length to get a desired number of ohms for your voltage source to heat just fine. I think even cheap magnet wire insulations is 100C

[edpalmer42]

At this benign conditions I would not even bother searching for a resistive wire. I'd use an enamelled copper wire for transformer windings. Just stick it with some epoxy to the plate. Connections made with thicker stranded wire would be a good thing.

That's exactly what I was talking about, just gotta pick wire thickness vs length to get a desired number of ohms for your voltage source to heat just fine. I think even cheap magnet wire insulations is 100C

The problem with using magnet wire is that to raise the temperature to 50C, you have to pump an inconvenient amount of current through it at a very low voltage.  With resistance wire, the current is lower, the voltage is higher and the power is the same, but in a more convenient package.

[Brutte]

Just use a thinner and longer wire.
You can also easily buy a thin enamelled constantan resistive wire (eBay). This one has a low tempco and is used for wire wound resistors/shunts. Overkill but available.

[penfold]

There is always heat-trace cable, come insulated, rated for high temperatures, if there is not a variety rated for exactly 50 degrees then you would have to go for a higher temperature and use some control

[raptor1956]

Well there are a number of alternatives but given the desire to run from 12VDC and limit the current to 4A and about 50W max magnet wire would have to be pretty thin to have sufficient resistance in the 3 ohm range so the simplest method looks to be the use of metalized power resistors bonded to the aluminum plate.  perhaps 6-8 resistors distributed to produce an more-or-less even heat/temp level.  No doubt nichrome would be cheaper but the insulation and bonding complicate the process.  I found a decent temp controller that will operate from and control 12VDC so that simplifies the upstream design a fair bit -- I can plug this into my car and run from the cigarette lighter port.

Again, thanks for the help guys...


Brian

[timb]

I have two large rolls of insulated nichrome heating wire, if you're interested in some let me know. I have way more than I'd ever need, so I'd be happy to send you as much as you want.

I bought them on eBay a couple of years ago to repair the ovens in some old test gear, which also used insulated nichrome.

[raptor1956]

I have two large rolls of insulated nichrome heating wire, if you're interested in some let me know. I have way more than I'd ever need, so I'd be happy to send you as much as you want.

I bought them on eBay a couple of years ago to repair the ovens in some old test gear, which also used insulated nichrome.

What's the ohms/meter of the wire?


Brian

[Sceadwian]

raptor, try working out the math on thinner gage magnet wire, I think you'll be surprised at how easy it is to tune the wattage and voltage requirements.

[salbayeng]

Professionally we would use "silicone heater mats" , just peel off the backing, and stick it on !
http://au.rs-online.com/web/c/automation-control-gear/temperature-control-process-heating/silicone-heater-mats/

Nowadays you can also buy heated bases for 3D printers, maybe something there would be helpful?

I have in the past made my own heating trace wire by slipping some nichrome inside very thin fibreglass sheath, you can only make about 2m at a time, the fibreglass braid sticks with most adhesives, we used super glue,you could position the wire in place, run about 6" of super glue over it, rub it back and forth a few times with a small ziplock bag on your finger (rubber gloves get stuck), then do the next 6 inches.

[Brutte]

If that is 50W then just use a 50W transformer. Tie primary winding to mains and secondary across backing aluminum plate. Solder guns work that way - secondary winding usually has only one coil and operates at mV levels.

[LaserSteve]

Cotronics.com

Steve