Size, Length and Wire Resistance

If the temperature is being controlled by a temperature sensor and input settings, then it would seem like you do not have a problem. (Unless the sensor controls only Max and not Min temp).

If not, the larger wire will be less resistive... if the same current is drawn, it will be colder. Then your guys will get slow and unhappy. (similarly, if it is smaller, it might cook them )

If you can identify the type / make of the wire, you should be able to get specs on it from the maker's web site. Presumably larger wire = less resistance, and thus less heat. I'm not sure it would be feasible to compensate by making the wire longer. (It depends on the size and properties of the 'closest' wire.)

Does that help any?

Thanks JCase.

The thermostat does control the temps, so in that regard, yes it will compensate some. I want to make sure that I can achieve the maximum output of 150 degrees or even a little higher would be OK.

If I can find say a 35 gauge or 31 gauge wire, can I use a formula to determine what length wire will compensate for the difference in wire diameter? Or is this not feasible?

I forgot the mention, the panel is rated at 30 watts.

Yes, to get the total resistance the same is fairly simple.

Just take the per unit of length resistance of the wire you have * the length,

Rtot = Rperunit * length

then do the same for the other wire;

Rtot (you know now) / Rperunit = length of new wire you need.

The trick is to make sure you know the resistance of each of the wires / wire types involved that you are working with.

Alternatively, you could measure the R with your meter of your existing wire.

The important thing here is the power. The formula is power P=I²xR, with I=V/R (I current, V voltage, R resistance).

If you keep the resistance (more-or-less) the same, all will be well. Thinner wire - shorter, & vice versa.

I'd go on, but I'm nackered - so have a look at this site.

Not difficult,

Regards, John.

BIG SAFETY EDIT: You mentioned "insulated wire" - if you're connecting this directly to a mains electricity supply, it'd better be dam'd well insulated. I think that unless you know exactly what you're doing (which, without disrespect, you don't), you'd be better off going for the insulated heating tape or wire available from various outlets.

Try googling "heating tape" (it may work, haven't tried) - or looking at RS Components, or Farnell (to name 2). Just try to do the sums so you have about the same power over the same area, & you'll be OK. Avoid bunching wire/tape up causing hot-spots.

I think maybe it would be cheaper and easier to just start with a heating pad. You know, the kind you use when you have a backache? The problem you may run into (other than the safety issues) with buying the wire is that the wire may be some alloy that affects the resistance and durability properties. Do you know exactly what the commercial panels you have are constructed with?

Hi, heat losses in wire is I²R losses , and resistance=(sp. resistivity)_Ni-Cr*(length/area). Temperature to be attained, thickness of wire, specific resistivity of wire are theand radius of the wire are the things you know. So you can do the maths, vary the length and get the amount of heat.

May be you should use a copper wire with a digital temperature controller. I think its worth a try.

Try finding some old broken hair driers or heaters and strip the nichrome wire out.Electric blankets are a source for the insulated types. Alternatively i used to use an incandescent lamp and a protective barrier to prevent burning. Another idea is to cement the wire between two slate tiles useing tile adhesive and drop the voltage to 6-18 volts (so you dont shock the poor critters) or yourself regulate the temp buy adjusting the input voltage

Thanks for the replies.

John, no offense taken, I will be very careful.

I measured the resistance of the commercial unit at 349 ohms and the wire is approximately 22.5 feet long. That gives me an ohm/ft value of 15.51.

I bought some 34 gauge NiChrome wire that is rated at 13.37 ohm/ft according to the chart they sent me. So using this I am going to need 26.1 feet of my wire to achieve the approximate performance of the commercial unit. Does this sound correct?

I will probably start with about 30 ft just to see how hot it gets and shorten it from there until I reach my maximum operating temp of 150 degrees.

Larry

Your figures are fine.

Any chance you could run it through an isolation transformer (at least during testing)? - then I could sleep easier .