Well, either you're trying to troll me again, or the approach you would apparently take if you had to solve that problem would be to calculate how much heat would be produced in an extension cord shorted across your car battery.

Since I don't think even you would take such a backward approach, I'll conclude that you are just doing your usual trolling.

Please do everyone a favor and just stop.

It was in no way a trolling. It was a request to further explain your post to the OP that, as the first step, she must determine the amount of heat she NEEDS and then design around that. I just started you off with an example and asked you how you could help the OP follow through on your instructions. Apparently, I was right since you didn't follow through.

I am expecting, however, that you will come up with some explanation of why you didn't follow through and eventually minimize the importance of knowing the amount of heat NEEDED.

 

No, not trolling. Didn't know I did it before and if you think I did, I'm sorry, but I didn't do it purposely, so I think you must have misunderstood my previous intentions.

What I'm doing is trying to build a small heater with what I have on hand. I'd like it to heat slowly if possible. It is going to be wrapped around a pipe and needs to heat what is inside it. The temp inside needs to be from 100 - 160F depending upon pressure inside the vessel (it varies between liquids and how much vacuum can be applied at a constant rate - which is more difficult than it sounds with evaporating liquids).

The pipe or glass bottle has a flat bottom and a coil of wire will be tightly wound in a spiral and then up the side of the pipe or vessel.
In another application, the wire will be inside the liquid and allow for better contact with the solution during evaporation.

I have a lot of low ohm resistors from 3, 5, 10, 15 & 20 watt resistors and .22, .47, .56, .62, .68, 1, 1.5, 2.2, 4.7, 5, 6, 10, 15, 30, I could easily get 9-10 ohms from these at whatever wattage is needed and use these at the base of the pipe or bottle (or mount them to an aluminum plate).

The heat from a resistor works just like the heat I calculated for a wire. If you use reasonably sized wires for 3A loads (18 - 24 gauge, for example), almost none of the energy will be dissipated by short lengths IF YOU USE RESISTORS as your heating elements.

Use the formula: power (W) = V*V/R

Where R is the TOTAL resistance (load) on the power supply. And V is the voltage you measure when your power supply is connected to the load. NOTE: most power supplies drop voltage if they are trying to deliver near the maximum rated current.

 

I'm trying to figure out what temps I can get and how wire gauge and length effect temp. I need a low temp heating element anything from 25 - 100 C.

You may have locked yourself into the wrong approach before you even got started. It sounds to me like you need a controlled-temperature heat source where the amount of heat supplied can vary widely as needed to maintain a temperature "window", for instance to supply a lot of heat as a liquid is evaporated and then very little to just maintain. Trying to dial in a single wire, that you can apply a single power supply to, will not accomplish that goal. You need a thermostat.

One thing I'd recommend is to consider a controlled, heated bath containing water or oil (depending on the temperature you need). Use a recirculation pump and a heat exchanger to move the heat into your vessel, or simply immerse the vessel in the bath. A standard laboratory hot bath will give you high capacity and tight, accurate control.

 

Many years ago I needed a small fish bowl heater & assumed 5W would be enough. On a 6 in. Al disc , glued 30 ea. 220 ohm 1/2 W Rs, 2 in series for measured 35 ohms operating from 12 V DC. A thermistor was used to set temperature to 80 deg. F. Worked well for a few years until B's died.

 

Worked well for a few years until B's died.

B's?

 

B's?

Thought crossed my mind also, what is or are the Bs? However, my condolences on their passing.

Ron

 

Many years ago I needed a small fish bowl heater & assumed 5W would be enough. On a 6 in. Al disc , glued 30 ea. 220 ohm 1/2 W Rs, 2 in series for measured 35 ohms operating from 12 V DC. A thermistor was used to set temperature to 80 deg. F. Worked well for a few years until B's died.

Bettas?

 

It was in no way a trolling. It was a request to further explain your post to the OP that, as the first step, she must determine the amount of heat she NEEDS and then design around that. I just started you off with an example and asked you how you could help the OP follow through on your instructions. Apparently, I was right since you didn't follow through.

I am expecting, however, that you will come up with some explanation of why you didn't follow through and eventually minimize the importance of knowing the amount of heat NEEDED.

I didn't "follow through" because you are trolling. Of course, that's based on the notion that not even you would believe that the design of a heating system doesn't need to take into account the amount of heat that it needs to provide. Apparently you want us to believe that you would do exactly the same thing if you were trying to design a resistive heater to heat a cup of coffee or trying to heat the water in a boiler to heat an apartment building. If that's not the case, then you are trolling by complaining about someone trying to get the TS to consider estimating how much heat they need for what they are trying to do.

If I wanted to design a heater to cook a turkey, I would most definitely start out by determining, at least roughly, how much heat energy would be required to cook a turkey and, from that, how much heat power would be needed from the heater. There are a number of ways to estimate it. For a very, very crude lower-boundish estimate you could consider the amount of energy needed to raise an equivalent weight of water from room temperature to the final meat temperature. Then give a generous factor for insulation loss. But this doesn't take into account the energy associated with the changes in the meat as it cooks. A simple Google search found many sites that give values for the energy per weight to cook meat and other foods. If you are designing the cooking chamber, too, then it is relatively straightforward to estimate the energy loss as the temperature in the chamber rises. Then I would consider the energy needed to raise the air in the chamber to the desired oven temperature.

What I would NOT do is start my design by asking how much power I get by putting wire of a certain effectively random size across a voltage source without any idea of how much power I need. I could be orders of magnitude off in either direction and just wasting my time.

 

I didn't "follow through" because you are trolling. Of course, that's based on the notion that not even you would believe that the design of a heating system doesn't need to take into account the amount of heat that it needs to provide. Apparently you want us to believe that you would do exactly the same thing if you were trying to design a resistive heater to heat a cup of coffee or trying to heat the water in a boiler to heat an apartment building. If that's not the case, then you are trolling by complaining about someone trying to get the TS to consider estimating how much heat they need for what they are trying to do.

If I wanted to design a heater to cook a turkey, I would most definitely start out by determining, at least roughly, how much heat energy would be required to cook a turkey and, from that, how much heat power would be needed from the heater. There are a number of ways to estimate it. For a very, very crude lower-boundish estimate you could consider the amount of energy needed to raise an equivalent weight of water from room temperature to the final meat temperature. Then give a generous factor for insulation loss. But this doesn't take into account the energy associated with the changes in the meat as it cooks. A simple Google search found many sites that give values for the energy per weight to cook meat and other foods. If you are designing the cooking chamber, too, then it is relatively straightforward to estimate the energy loss as the temperature in the chamber rises. Then I would consider the energy needed to raise the air in the chamber to the desired oven temperature.

What I would NOT do is start my design by asking how much power I get by putting wire of a certain effectively random size across a voltage source without any idea of how much power I need. I could be orders of magnitude off in either direction and just wasting my time.

have you ever specified equipment for anything? If being off by an order of magnitude concerns you, take a look at an electric oven.

3700 watts

20 lb Turkey (9000 grams)
Cook from 4C to 74C for heat demand of 630kcal (or x 4.184 to get joules)= 2.5M joules

My turkey should be done in about 12minutes.

Or conversely, if I want it to cook slowly and want it done in 4hours, why do they give me a 3700 watt oven 8nstead of a 200 watt oven?

Think about your order of magnitude statement.

And remember, me calling you out on your BS answer to an OP is not trolling - it is simply calling you out on a BS answer!

And to @RogueRose , generally heaters are really bad at heating things unless they are well insulated or submerged in the liquid they are heating. Also, if you want tight temperature control, use a heater that can supply 10x the power into the medium Than you think you need but, uses a heating element with low thermal inertia (is light weight) so you don't keep over shooting your target temp. Thermostats help but A PID controller or Fuzzy Logic controller also helps because no heating element has zero thermal inertia. You can always reduce the energy input with PWM and other power control methods but, once built, it is hard to add more power later.

Cheers.

 

Bettas?

I like that answer. Let's see what Bernard says.

β

 

And to @RogueRose , generally heaters are really bad at heating things unless they are well insulated or submerged in the liquid they are heating. Also, if you want tight temperature control, use a heater that can supply 10x the power into the medium Than you think you need but, uses a heating element with low thermal inertia (is light weight) so you don't keep over shooting your target temp. Thermostats help but A PID controller or Fuzzy Logic controller also helps because no heating element has zero thermal inertia. You can always reduce the energy input with PWM and other power control methods but, once built, it is hard to add more power later.

I want no part of your fight with @WBahn, but I agree wholeheartedly with the advice quoted above.

I would add that, in my (limited) experience, fuzzy logic is much, much easier to dial-in for fast response and minimal overshoot when you're dealing with sudden, dramatic changes in temperature. PID is great when things are a little more stable and slow moving. Others may disagree.

 

have you ever specified equipment for anything? If being off by an order of magnitude concerns you, take a look at an electric oven.

3700 watts

20 lb Turkey (9000 grams)
Cook from 4C to 74C for heat demand of 630kcal (or x 4.184 to get joules)= 2.5M joules

My turkey should be done in about 12minutes.

Or conversely, if I want it to cook slowly and want it done in 4hours, why do they give me a 3700 watt oven 8nstead of a 200 watt oven?

Think about your order of magnitude statement.

And remember, me calling you out on your BS answer to an OP is not trolling - it is simply calling you out on a BS answer!

So apparently you DO want people to believe that if someone asked you to design a heating system you wouldn't even want to consider whether they were heating a cup of soup or the boilers on the USS Missouri, since you believe that even suggesting that the heat requirements of the intended objective might have an impact on the design to be BS.

Your attempts to confuse the issue by pointing out that multipurpose systems are designed to meet the most demanding requirements and are then throttled to meet their other requirements is just a pure red herring. Unless you would use that same oven heating element to heat design a system to heat a thimble full to 100 deg F or to heat an skyscraper's office spaces. I had previously tried to give you credit by assuming that you would not do this -- but you seem adamant about insisting that you would. So fine. Go right ahead. I will no longer give you the benefit of the doubt by assuming you are a troll as opposed to something worse. But it really doesn't matter because there is no point in carrying on the discussion further.

 

So apparently you DO want people to believe that if someone asked you to design a heating system you wouldn't even want to consider whether they were heating a cup of soup or the boilers on the USS Missouri, since you believe that even suggesting that the heat requirements of the intended objective might have an impact on the design to be BS.

Your attempts to confuse the issue by pointing out that multipurpose systems are designed to meet the most demanding requirements and are then throttled to meet their other requirements is just a pure red herring. Unless you would use that same oven heating element to heat design a system to heat a thimble full to 100 deg F or to heat an skyscraper's office spaces. I had previously tried to give you credit by assuming that you would not do this -- but you seem adamant about insisting that you would. So fine. Go right ahead. I will no longer give you the benefit of the doubt by assuming you are a troll as opposed to something worse. But it really doesn't matter because there is no point in carrying on the discussion further.

No, but seems to have taken you 300 words to say, "I know nothing about designing a heating system." I'm done here.

 

I will no longer give you the benefit of the doubt by assuming you are a troll as opposed to something worse.

Something worse? Like accuracy, correctness? I guess times, they are a changin'

 

No, but seems to have taken you 300 words to say, "I know nothing about designing a heating system." I'm done here.

I can only HOPE you are done here. History does not bode well for such hopes, however. Please surprise us all.

 

I can only HOPE you are done here. History does not bode well for such hopes, however. Please surprise us all.

If you can't admit you are wrong, at least stop talking!

I think this comment says it all...

I want no part of your fight with @WBahn, but I agree wholeheartedly with the advice quoted above.

I would add that, in my (limited) experience, fuzzy logic is much, much easier to dial-in for fast response and minimal overshoot when you're dealing with sudden, dramatic changes in temperature. PID is great when things are a little more stable and slow moving. Others may disagree.

 

If you can't admit you are wrong, at least stop talking!

I think this comment says it all...

Well, no surprise that you weren't actually done like you claimed.

Did you notice that the comment that says it all underscores the very recommendation I made from the very beginning. In fact, YOU said, "use a heater that can supply 10x the power into the medium." How can the TS possibly use a heater that can supply 10x the power? Ten time what power? Gee, seems like they would need to have at least some idea of how much heat/power they need to accomplish the goal before they can have something to multiply by ten.

So, once again, it is apparent that your whole problem with me suggesting that they might want to start by figuring out how much heat they need is nothing more than you wanting to troll me.

If you still claim that you aren't trolling, then please explain how someone can follow YOUR recommendation and use a heater than can supply 10x the power into the medium if it is BS to suggest that they should determine how much heat/power they need to accomplish the task?

 

Eventually, you will say to yourself...

Spoiler

 

@GopherT Like many threads here, when the "experts" are confronted they claim "TROLL". And it always seems to be the same group of "experts".