# "I cant think of an electronics joke CURRENTly" however I could use some help on a project.

#### mfult0n

Joined Jan 1, 2018
8
Thank you thank you. I know hilarious.
I was hoping I could get some questions answered. I have a project I'd like to create and can't seem to find the direct answers to my questions online (or perhaps I'm just not smart enough to pull them together) so I thought I'd come here.

The Project: Id like to create a large heat mat, lets say 12x20ft. The heat doesn't need to be high at all, but would need to keep a temp of around 50 degrees regardless of the ambient influence.

It seems that Nichrome is a great resource for sending heat down a wire. My biggest question, how can I go about calculating how to keep a temp around the 50 degree mark based off of the determined length of wire and it's gauge?
I'd also like to utilize a battery to generate the power if possible.

Thanks and any feedback, opinions, guidance would be hugely appreciated.

Thanks,
Mike

#### panic mode

Joined Oct 10, 2011
1,918

#### Audioguru

Joined Dec 20, 2007
11,249
You are creating a large heat mat.
What will you cook on the mat?
How will you reach the cooked stuff without burning yourself?

You did not ask any questions so I did.

#### mfult0n

Joined Jan 1, 2018
8
Haha sorry guys, I hit the "post" button accidentally before I finished my rant. Should be updated by now. Thanks so much! And why would you cook when you can smoke

#### philba

Joined Aug 17, 2017
960
Unless the ambient temp is constant, there is no way to keep the mat at 50 without some sort of feedback. What's this for, a pet?

You could just go buy an electric blanket.

#### panic mode

Joined Oct 10, 2011
1,918
50 what? Kelvin, Rankine, Fahrenheit, Celsius...?
what is the ambient temperature?
what are you heating with it?

#### mfult0n

Joined Jan 1, 2018
8
Unless the ambient temp is constant, there is no way to keep the mat at 50 without some sort of feedback. What's this for, a pet?

You could just go buy an electric blanket.

ambient temp will vary from 10-32 degrees F.
So what would be a cheap way to provide feedback to regulate the temp?

#### mfult0n

Joined Jan 1, 2018
8
50 what? Kelvin, Rankine, Fahrenheit, Celsius...?
what is the ambient temperature?
what are you heating with it?

farenheit. I'd be heating a concrete floor inside a garage.

#### GopherT

Joined Nov 23, 2012
8,012
Have you tried a heated blanket? If one is not enough power, set a second one on top of it (or a third). You might need four to cover the area and then two or three thick. They have a power switch but I am not sure they have a simple triac dimmer vs a thermostat.

#### panic mode

Joined Oct 10, 2011
1,918
until the blankets get wet when car returns from rain or snow

#### mfult0n

Joined Jan 1, 2018
8
Have you tried a heated blanket? If one is not enough power, set a second one on top of it (or a third). You might need four to cover the area and then two or three thick. They have a power switch but I am not sure they have a simple triac dimmer vs a thermostat.

There are a number of reasons keeping me from using an electric blanket unfortunately.

Thanks

#### GopherT

Joined Nov 23, 2012
8,012
until the blankets get wet when car returns from rain or snow
I'm sorry, I missed the part where he said car.

Joined Jan 15, 2015
6,211
You can try starting with a Google of for example: Flexible Silicone Rubber Fiberglass Insulated Heaters which will start you with some interesting results. They can be sectioned. There are also other floor heating mat solutions along these lines as another example. You will need to do a little study on watt density to figure out exactly what you need or want. This includes solutions laid before concrete is poured or tile laid. Finally even a copper pipe retort can be matrix into a concrete floor and a heat exchange fluid or oil heated and ran through it.

Ron

#### Janis59

Joined Aug 21, 2017
1,357
As everywhere at thermal systems, just apply the equations to evaluate the all three thermal loss components, the radiation, the leading and the convection. When all those You have put into the Excel like function of temp by a power, then just read the power You need.
If want enormously accurate, just apply a Ansys or Comsol, or Lisa v8.
If want know with a warranty, make a physical model and measure temp by some IR device.
If want just approximately, and want that OBJECT has 50C, then forget the wire diam and apply what have in the shelf - any is good enough if at realistic length has a resistance what at chosen voltage gives chosen power.
If contrary, want that the WIRE temp be 50C, then apply a radiation formula if it is staying mostly in free air, and apply a thermal leading equation if it is in hard contact with matt what is severally cooled some times and some places.
However, if only You are not inhabitant of Siberia, all over the Planet other places has habit to use a kanthal wire instead. Cheaper, less oxidizing, longer serving, higher temp.
If need to spiralize, apply a d/D in the interval 5...20. See handbook http://www.cyfronika.com.pl/art145/kanthal-nikrothal.pdf
Element surface load in the interval 2-25 W/cm2 and wire surface load ought be 2...4 fold higher.

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#### Janis59

Joined Aug 21, 2017
1,357
RE:""I'd be heating a concrete floor inside a garage""
Why You not started with that statement. Then the advice is diametrically another - CONDEMN THE WIRES like nichromium or kanthal AND APPLY THE STANDARD building engineering solution. It is those red or orange flat-style resistivity cable (isotherm etc) what is DESIGNED to be zig-zag mured-in the cement, anything is well calculated, well insulated, approved, calibrated, sweared, licenced, accreditated etc etc and Tmax is about 50C. Let go to the appropriate shop and ask for that, and when cement had been hardened, just plug in the socket and forget.
Shops? Have no knowledge about other half of Planet, but here some of them are magachains like ByggMax, KRauta, Depo, ABC, Biltema, OBI and many many more.
However, knowing that 50C is much, and shop-boy probably will choose the most economic not most powerful cable type, just approximate the needed power with time function. If cable gan make a cold start in some 15-30 minutes, it has VERY large power reserve. Mass of cement be heated multiply to beton heat content and T difference something laike 40-50 C, divide to that chosen time (seconds!!) and voila - thats your power in Watts.

#### philba

Joined Aug 17, 2017
960
For what it's worth, He said 50F. That is 10C or so.

#### KMoffett

Joined Dec 19, 2007
2,918
There are a number of reasons keeping me from using an electric blanket unfortunately.

Thanks
What are the "reasons"? No point in us making suggestions, just to have you say "that won't work for me".

Ken

#### GopherT

Joined Nov 23, 2012
8,012
What are the "reasons"? No point in us making suggestions, just to have you say that won't work for me.

Ken
Maybe his pet pig doesn't like electric blankets.

#### ebeowulf17

Joined Aug 12, 2014
3,282
I don't have any great insights on the best heating method, but here's some math on the battery question.

In your best case, you say you've got 32F ambient and 50F target, so you need to increase 18F (10C.) All of the energy in a typical car battery could only heat about 5 liters of water (~1-1/4 gallons) by that amount. So, if your garage floor has more thermal mass than just 5 liters of water, it would take more than a car battery to warm it, even in your best case. Obviously it gets worse if it's 10F starting out.

You're going to need a real power source, unless you're talking about some serious, serious batteries!