resistor heater to heat a 10 cu/ft box to 100 degrees

[Menticol]

Remember that Hair dryer resistance needs an airflow to avoid overheating and burning up. The toaster is a magnificent idea, or the light bulbs

 

[user_88]

Hopefully the o.p. will come back with a report on his experiment with the 32 gauge wire.
It is difficult to be certain that everybody is on the same page. That is, talking about the correct material .... units ... dimensions ....

His resistance measurement corresponds to the Nichrome A material ... @ 32 AWG.

No ... not actually sure it will work at this point.

 

[Sceadwian]

Menticol, a thermal monitor loop already has to be in place just put it near the heating element, with a thermal fuse for safety, that's all hairdryer makers do, and my idea was to use AC dimming to adjust the heating of the heating element whatever it ends up being. The fan should always be running.

user88, 1.2 watts per centimeter of 32 gauge wire. It will melt unless it is extremely well coupled to something that's cooling it. IE not air, since it's a resistance heating element it can't be wrapped around a metal heat pipe..

 

[zipdogso]

The questions that i have are first, how many resistors and what ohms could i use on a continuous basis and in what configuration. I don't need instant heat it can have warm up time. typically we turn on the incubator 2 or 3 hours before setting in the eggs. It will however have to be able to sustain the heat in the box at all times and from time to time the box must be opened to refill the water tray for humidity. So it will have to recover about 20 degrees in about 5 minutes max. There are two small lovers allowing fresh air into the box so that will have to be accounted for and there is a fan in the box that will circulate the air. I would probably set the resistors in front of the fan. The fan constantly runs. I was hoping to get away with 50 watts. however i can go higher if need be. But the lower the wattage to better the unit in my opinion. i like efficiency. Any help or suggestions would be most appreciated. Thanks!

Do they ensure viability of the eggs ?

 

[Boncuk]

Hi cbiblis,

I do not recommend to use radiation heat in an incubator. Depending on the relative position between heaters and eggs the eggs being closest to the heater will fry.

Use a normal household heater (like in a toaster) and blow circulating air over the heating element to distribute it using guides.

For the air intake use an adjustable sliding door to mix internal air with fresh air.
(Just using internal air the eggs rot before hatch.)

Boncuk

 

[cbiblis]

thanks for the reply all. What I'm looking for is the wire in a hair dryer. i am mass producing incubators, so i don't want to waste money on a hairdryer just to get the wire out of it. i would like to by about 100' of it and cut it to size for my application. i have yet to come across a site where they sell it by the foot so if anyone knows where i can purchase it let me know.

 

[user_88]

thanks for the reply all. What I'm looking for is the wire in a hair dryer. i am mass producing incubators, so i don't want to waste money on a hairdryer just to get the wire out of it. i would like to by about 100' of it and cut it to size for my application. i have yet to come across a site where they sell it by the foot so if anyone knows where i can purchase it let me know.

**broken link removed**

 

[Mr RB]

...
Mr RB's solution seems pretty straight forward and easy to scale up as high as you want. If you're worried about radiated heat from the bulbs put a heat shield in front of the bulbs and blow air across them to circulate in the incubation chamber. For reliable heating control you'll want some kind of forced air anyways.

Thanks. I've built a few incubators over the years. Light bulbs are good because when you open the door to inspect, the temp drops a couple degress and the bulbs come on full so you can see what you are doing.

Also you get to keep the wiring up high so the thing can be cleaned, etc, especially with eggs which are very conductive (and horrible to clean up once they dry). The last thing I would suggest is heating wire under the egg tray. Keep the bottom half of the thing totally free from wiring so you can clean and/or slide trays out etc. Put some light bulbs in the top in standard light sockets with a 4" 120v PC fan (the old style). Even a little fan will circulate the air well and give even heating. You can change and inspect heaters by just unplugging the light bulbs, or even reduce number of bulbs or change bulb wattages etc. Who wants to mess with fine heater wire and mains voltages??

 

[user_88]

ok, i hooked up the nichrome wire and 8 feet seems to put off plenty of heat at 70 watts. problem is when its heated it expanded a lot, to much actually. they will almost touch. i tried tightening the wire to the isolators when it was electrified then when i removed the heat , Snap, it broke. Does ne1 know of a source where i can buy the type of Resistance wire found in space heaters, hair driers, etc. the coil type about 18 gauge it looks like? i want to buy by the foot.

The 8' length of 32 AWG allowed too much current to flow, @ 120 V.
You might try a longer length of 32 AWG wire. Maybe a 12' length would add a sufficient amount of resistance, in order to reduce the current, and energy density, to the point that a critical temperature in the nichrome wire would be avoided.

Note that reducing the current by 1/2 causes a 1/4 reduction in electrical power. ...(P=I²R).

The previous statement is incorrect. If the original power was P=I²R, and you then decreased the current by doubling the resistance, then the new power would be
P=(½I)²(2R)=½I²R
That is, the power would be reduced by ½, not ¼.

 

[Sceadwian]

It's still gonna spring all over the place from thermal expansion, even with the reduced heat. I'm not sure why they'd even sell 32 gauge nichrome wire except for perhaps using in e-matches.

Where did you purchase your nichrome wire from, and do they have a wider slection of material types?

 

[MOSFET KILLER]

You can use nichrome wire, it is inside hair dryers. Just buy a cheap hair dryer, unwind the heating element (nichrome wire). For power control you can use PWM from an LM555 to drive a large transistor. Find out how many amps the transistor needs to be rated for by looking at the wattage on the hair dryer. Also, the heating element will work just fine with rectified DC which is what you are going to need for the transistor. The thermostat will be the duty cycle control on the LM555.

 

[cbiblis]

i got the wire off of ebay it was the biggest gauge they offered in 100'.

 

[mneary]

You could buy a hair dryer and just use the element.and fan (just take off the pretty plastic case. or not.). Get a 220V unit, it will operate at 1/4 rated power on 120. You can get cheap "travel" units for as little as $6.

I would be a little concerned about motor reliability, but at 1/2-1/4 speed it might be satisfactory.