heating element

[ghostman11]

i need to make a heating element and i am unsure what gauge of nichrome wire to use.
also can someone check i havnt messed me maths up
i need a 230W heater the line voltage is 240v.
so if im right that means i need wire with a overall resistance of 250R?
this should pull around 0.95A?? am i correct so far?
so what gauge wire would i need? obviously i dont want the wire burning out and i dont want 100's of meters of it
any sugestions?

 

[Mosaic]

V=IR:

R=V/I = 240/.95 =252 ohms.

You need to know how long you wire must be. Are u heating a room? A Water pipe? A window defroster?

Once u know the length needed u select wire based upon its resistance/unit length. And go with the closest option, which of course dictates the gauge.

 

[ghostman11]

what i need to know is what is the smallest gauge i can use without it melting? then i can choose based on lengh etc
the heater is for incubators btw

 

[Wp100]

Hi,

You are calculating your wire gauge which is only a small consideration in the making of a heating element.
The core, and / or outer sheath and electrical safety at 240v are much more important.

If its anything other than a bench test experiment then go to a good pet shop where you will find a vast array of heaters both in terms of wattage and encapsulation, eg fish tank glass heater, reptile heating lamps, heating pads and heating cables etc etc.

 

[ghostman11]

Hi,

You are calculating your wire gauge which is only a small consideration in the making of a heating element.
The core, and / or outer sheath and electrical safety at 240v are much more important.

If its anything other than a bench test experiment then go to a good pet shop where you will find a vast array of heaters both in terms of wattage and encapsulation, eg fish tank glass heater, reptile heating lamps, heating pads and heating cables etc etc.

i have used many types of comercial heaters but all the equipment here is custom made. the reason why i am building one is because i cant buy in a suitable heater that will fit.
the element will be wound onto a ceramic core similar to the core in a fish tank heater. the heating element is isolated in its own housing (hard to explain without a pic) safety has and is always a priority for us. hence why i am asking about wire gauge etc.
theese arge comercial incubators holding approx 1200 eggs, we have looked exstensively for a heater that would fit our design and have no luck so now i would like to custom make one

 

[Wp100]

Hi,

Well if its housing that many eggs it cannot be very small and you will need a reasonably sized fan and housing to distribute the heat around.
I know heating lamps are often used instead.

As you say without actually seeing it its hard to say what will suit, but there do seem many choices, a bathroom towel rail heater element from Screwfix, a 250w Ceramic or Quartz heater plate from RS.
There are a couple of UK firms who actually make heating elements and would do one offs etc - might be worth searching out.
Heres one my work mate has used for a custom element
**broken link removed**

 

[ghostman11]

thanks for the sugestion........but it is going to be easier to build one myself. maybe once i have that sorted and know exactly what we want then i can look into getting them made. so back to the origanal question does anyone have any idea what the thinist gauge of wire i can use is?

 

[colin55]

You have to work out the wattage being dissipated for the area you are creating. As the area reduces, the wire will glow brighter and brigher and this will limit its life.
In addition you have not provided any details of the method of extraction of the heat.
You are really way over your head.

 

[BrownOut]

No idea whatsoever. Look at some commercial heaters and see what wire gauge is being used. Honestly, how hot do you plan on the wire getting? The melting point of Ni-Chrome has to be in the thousands degrees. My little electric heater at home gets red hot, and the wire doesn't melt.

You can do a rough calculation for temperature if you know the specific heat of the wire material, the heat transfer between the wire and surrounding material ( which is what, by the way? ) the watts per unit length, etc. Clearly, the wire gauge depends on a number of factors.

 

[ghostman11]

the element will be wrapped onto a ceramic square 4x5 inchs, there is a fan dissipating the heat through a duct to a array of 12 fans where the air flow to the incubator is controlled. the heater i use at present is 220W and is ok, but due to a redesign is now too big. i need a fairly gentle heat rather than a white hot wire.
i would like to use 41 gauge nichrome it works out around 109ohms per meter so i wouldnt need miles and miles of it but my gut feeling is that its too thin.
19 gauge wouldnt melt but its only around 1.4ohms a meter so would take a couple of hundread meters?? if i am aiming for 252 ohms.
i think best thing to do is emmail the nichrome people and see what they sugest.
origanaly i was using "toaster ribon" from a local company but they went bust and i never found out exactly what it was. it wasnt standard nichrome so i have no way of sourceing it from somewhere else. plus it was a little too dificult to bend to the heater ceramic former

 

[colin55]

Your best option is to buy a $5.00 light dimmer.
You really don't have a clue about anything you are suggesting. I suggest you leave it alone. A little knowledge is a dangerous thing. Especially in your case.

 

[ghostman11]

Your best option is to buy a $5.00 light dimmer.
You really don't have a clue about anything you are suggesting. I suggest you leave it alone. A little knowledge is a dangerous thing. Especially in your case.

what exactly do you mean by especialy in my case?? you are making way too many assumptions about me. you are correct i dont know anything about making heaters from nichrome wich is why i have asked some questions.
i see no reason to patronise people looking for answers.

 

[BrownOut]

Look at this chart. It shows how much current is required for a guage of wire to reach a specified temperature ( which you still haven't specified ) I'm no heating expert, but I'll guarentee you that you dont' want to fool with hair thin, delicate wire that will break before you ever get it to work. I would just use something that will be rugged, like say 16-22ga wire, and use a controller to prevent overheating. If you don't want to control it, then I don't have a good solution.

There is also a new product called "positive temperature coefficient" heat wire, or PTC wire. A few feet of it would be in the wattage you're looking for, and it has a sort of build in self-regulation.

 

[ghostman11]

thanks for the info brownout. the tempreture of the incubator is 99.97F wich i normaly reach in the space i use with around 200-250W, i might have to go back to the drawing board as 16 gauge is going to be too long at around 0.5ohms a meter! but i do take your point about thin wire wich was the main reason iasked as i had a ugly feeling it wasnt going to be easy. maybe i need to look at diff wire

 

[ghostman11]

i guess the best thing to do for now is contact a heating wire company and take it from there. is too many variables at the mo, but thanks for the info i will have a read and see if i can come up with some answers. the heater isnt always on its controlled by a pic via a realy

 

[ghostman11]

ive had a chance to read a little on the ptc heaters, very interesting stuff. and deff worth looking into a bit more.

 

[Diver300]

I think that 50 or so of these:

MULTICOMP|MCPRW0AWJW47JB00|RESISTOR WIREWOUND, 4.7OHM, 10W | Farnell United Kingdom

would be a lot easier to use than heater wire.

 

[ghostman11]

yes they would be easier in one way but wont fit the shape of the former. at the moment i am reading up on what i need to do to pwm the heater with zero crossing etc so plenty to keep me busy lol thanks for all the sugestions is always nice to learn the options!

 

[BrownOut]

yes they would be easier in one way but wont fit the shape of the former. at the moment i am reading up on what i need to do to pwm the heater with zero crossing etc so plenty to keep me busy lol thanks for all the sugestions is always nice to learn the options!

That will probably be your best solution. It eases many tough challenges.

 

[ericgibbs]

yes they would be easier in one way but wont fit the shape of the former. at the moment i am reading up on what i need to do to pwm the heater with zero crossing etc so plenty to keep me busy lol thanks for all the sugestions is always nice to learn the options!

hi G11,
Hope you are feeling better..
A technique that can solve some problems is the use of say a 2A mains rated diode in series with any heating element you may construct from off the shelf elements.

eg: if you get a 500W wound heating element, hair dryer or some of the older style of 500W bowl reflector heaters, by adding a diode you have a 250W heater, use an SCR to control the half voltage to the heater.

EDIT:
you could buy spare new heating element coils that can be rewound to suit your heating area.

EDIT2:
This circuit would give you a mains isolated zero crossing detector.