Nichrome (Kanthal) wire loop against a fan

I bought some nichrome wire (actually Kanthal A1) for heating purpose. I did not realize when I bought it that there was no electrical insulation on the wire, hence, I cannot simply make a loop on the intake side of a fan in order to have some hot air flowing from the fan. How do I solve this without too much... kludge ? I can think of several solutions, but it generally involves some kind of structure to hold the loop.

I tried to form a spring-like shape with the wire but it's too thin to hold and it will possibly make self contact, decreasing the resistance, leading to too much heat.

Antoino: ...... in order to have some hot air flowing from the fan. How do I solve this without too much... kludge ?

Well......you could buy a fan heater. :D

OldSteve: Well......you could buy a fan heater.

That would arguably be the more sensible approach as your naïvety suggests you are not sufficiently experienced in such projects.

If you study such appliances; fan heaters, hair dryers or toasters, you will see that the heating elements are supported on mica cards. Or custom-designed ceramic assemblies.

Insulating a heating wire is a problem as you don't want to thermally insulate as well. Typically heating wires are protected inside a cage to let air through but keep fingers out.

And insulated wires can still burn even if they can't electrocute. Cage is the simple answer.

Insulated support might be something like a piece of old ceramic tile?

Hi,

What voltage do you want to use on the heating wire, what power rating are you expecting?

Thanks... Tom... :)

TomGeorge: Hi,

What voltage do you want to use on the heating wire, what power rating are you expecting?

Thanks... Tom... :)

I'm aiming for a 35 C /38 C air temperature inside an enclosure, so I'm trying to heat the nichrome wire to a slightly greater temperature. I have measured 6 ohm for 60cm of wire, with a 18V DC power supply, this would draw 3A of current and 54W of power.

OldSteve: Well......you could buy a fan heater. :D

I'm trying to heat a box, not a room. Not a solution unless I can find a 8cm x 8xm x 2cm fan heater.. Also I'm in the 30/50W power range, not 2kW

Antoino: I'm trying to heat a box, not a room. Not a solution unless I can find a 8cm x 8xm x 2cm fan heater.. Also I'm in the 30/50W power range, not 2kW

Coincidental you mention that, as a 1 kW 110V fan heater element operated at 18 V would draw 27 W and a 1.5 kW element would draw 40 W.

They seem to like advertising "micro heaters" with elements about the size you cite, or the element out of this.

Antoino: think of several solutions, but it generally involves some kind of structure to hold the loop.

Yes its largely a mechanical arrangement. Plastic that can withstand the temperature with a hair dryer. Spacing with a kiln.

Given the temperature , would an incandescent light bulb do the job ?

Paul__B: Coincidental you mention that, as a 1 kW 110V fan heater element operated at 18 V would draw 27 W and a 1.5 kW element would draw 40 W.

They seem to like advertising "micro heaters" with elements about the size you cite, or the element out of this.

Wait.. Are you suggesting that I power this kind of heater with just a 18V C power supply ?

Boardburner2: Yes its largely a mechanical arrangement. Plastic that can withstand the temperature with a hair dryer. Spacing with a kiln.

Given the temperature , would an incandescent light bulb do the job ?

Yes it could, but I'm trying to replicate a design that I know give good results (with the manufacturer implementation of course). I don't need light, bulbs are too fragile and will fail, and I need something dimmable / PWMable, without thermal inertia. Nichrome wire was suggested here according to this specification, and as it's widely available (Vape Nation !! ) I'm going to give it a try. I would like to have a uniform temperature inside that box, and I think a bulb with make some kind of temperature gradient. I have ordered a lot of Dallas temp sensors, and I will do measurements. The advantage of the nichrome wire, as I see it, is that I could heat the box not from a single point in space, but from a line, which should lead to a more uniform temperature.

What you might try doing is to take a PC fan (no bigger than 120mm), and create a couple of brackets from PEEK plastic that can be mounted on opposite sides of the fan via the mounting holes.

The brackets should have a number of evenly spaced holes for bolts/screws to be threaded into the them.

Put these brackets on the downstream/outflow side of the fan.

Then take your wire, and on one side, at the first screwhead, snug the wire between the head of the screw and a nut - make sure it is tight enough to clamp the wire, then draw the wire over to the next screw, around it, then back to the next screw up on the opposite side, around it, etc - until to get to the last screw. Again, snug a nut to hold the wire in place - draw the wire tight (a bit of tension on it) then tighten the nut to hold the wire. Make sure the wire has some space between it and the fan body (don't want to melt the fan!).

Crimp your power wires to the ends of the heater wire (you can not solder to this wire - also, your power wires should have heat-resistant insulation, like silicone or similar).

The contact points on the bolts are small enough that they won't heat up so much as to melt the plastic brackets and come loose (PEEK is high-temp capable plastic anyhow). Plus, the size of the bolts compared to the wire will make them effectively a heat sink; there just won't be much thermal conduction happening. Finally, the plastic brackets keep everything insulated (electrically and thermally).

Let me know if that isn't clear - I can draw you up something to visualize it better.

:)

Hi,

Antoino: I cannot simply make a loop on the intake side of a fan in order to have some hot air flowing from the fan.

No you can't, you would be pulling warm air over your fan motor. You need to put the heating on the outlet of the fan, one reason is as just stated, so you don't cook the fan motor. The other is, you will get better air flow efficiency by moving cool/cold air with the fan, rather than heated air, due to the air density. How quick do you want the control to respond to changes in temp, you could use an array of power resistors, the type that have fins and mounting lugs. Just a thought.. Tom... :)

How big is the box? Is it well insulated? Whats the temp outside the box? 50 watts is about 170 BTU / hr, that would heat a pretty big box to 38 C.

Now the interesting thing about the hot air gun that I suggested - or an equivalent hair dryer - is that the fan motor actually operates from something like 12 Volts.

So a dirt cheap 1500 W hair dryer would adapt perfectly to this requirement of 40 W operation from an 18 V supply. :grinning:

Paul__B: Now the interesting thing about the hot air gun that I suggested - or an equivalent hair dryer - is that the fan motor actually operates from something like 12 Volts.

So a dirt cheap 1500 W hair dryer would adapt perfectly to this requirement of 40 W operation from an 18 V supply. :grinning:

It probably would, but you would have to take the hair dryer apart, and wire the motor separately from the heating element, as the way the voltage is dropped is usually by using the heating element as a very large resistor with the motor placed in series (IIRC).

Other than that detail, it would probably work fine.

With a lower heater power, the fan need not run as fast, or as noisily.

Sometimes the motor (with its bridge rectifier) is in series with the "low" element but even 500 W at 110 V implies 4.5 A and the motor requires nowhere near that, so it is tapped on the element. The element is certainly not a very large resistance, 4.5 A at 110 V is 24 Ohms.

Since the intention here is to provide an alternate power supply and control system, it is a "given" that you would take the appliance completely apart and re-wire the pieces.

My opinion is that maybe grabbing a heat-sink (to wick away the cold side), a Peltier device a fan and a LOW voltage high current supply would have been a better starting point.