How an electric heater works?

[Sparky_s]

I'm starting in electronics and I want to build an electric heater to increase the temperature in liquids.

The basic idea is to know how an electric heater like this works:
**broken link removed**

I want to know also how the temperature can be regulated. Changing voltage or current?
And also if that thing works on DC or AC or both.

Thank you very much.

 

[Reloadron]

In real simple terms an electrical heater works on a principal of pushing an electric current through a heating wire (element) of a high resistance. The element is generally a high resistance wire like nichrome wire. The high resistance opposes the flow of current and the end result id heat. If you look into a toaster or hair drier you can see what happens. This link provides a good overview of heating elements.

Heating elements come in all sizes and designs. A Google of Heating Elements will bring up hundreds of hits and information.

The image posted uses a plate generally made of metal. Below the plate is a heating element. Heat from the element is transferred to the plate and from the plate to whatever is on the plate. That is one way of heating a liquid placed (in a beaker) on the hot plate. Another method of heating liquids is the use of immersion heating elements that are placed in the liquid. There are many ways to heat liquids using heating elements, those are but a few. The idea being to transfer thermal energy (heat) from an element to some medium.

Control is done using a sensor (there are many sensor types) that measures heat and converts it to an electrical signal. That signal can be used to control the temperature. There are a number of ways this is done.

Yes, increasing or decreasing the current in a heating element will increase / decrease the heat it produces.

What I mention here barely touches all of it but should give you an idea.

Ron

 

[Sparky_s]

Thank you so much Ron. I have got an idea about how an electric heater works.
1. Use a high resistance material like nichrome
2. An electric current in a high resistance material will produce heat
3. Depending the amperage, more or less heat will be produce.

But I have other question...
This works on DC, AC, or both?
If I connect a wire from the + pole in a battery, to the - pole of a battery it will produce a short circuit, so what is the changes needed to produce a wire that produce heating without producing a short circuit?

I will make a google will you or something else answer.

 

[BrownOut]

Heating wire, as already mentioned, has high resistance, so there would be no short circuit if you connected a heating wire from + to - on a battery. That said, DON"T CONNECT A HEATING WIRE FROM + TO - ON A BATTERY!!! The result could be catastrophic! If you want to know more about making a heater, make darn sure you get all the warnings and precautions before preceeding.

 

[Reloadron]

Oh yeah, my bad as you asked about AC/DC. A heating element is purely resistive. Therefore, for example, if we apply 120 VAC RMS or 120 VDC it matters not.

The trick is when building an element they use high resistance wire (I used nichrome as an example). The resistance of the wire is a key player in making heat. If for example I take a few feet of AWG 12 copper wire and place it across a car battery the wire will get hot real quick and likely melt. Now if I place several thousand feet of that wire across my battery it will just warm up. Higher resistance! I don't suggest placing anything across an automotive battery but as an example. I also did not look up the resistivity of a few thousand feet of AWG 12 wire. However, if we have a known voltage and current source we can use rules like Ohms Law to calculate the current for a known voltage across a known resistance. From there we can calculate the power as expressed in watts.

There can be much more to all of this so we are keeping things real simple.

Ron

 

[BrownOut]

I"ll just add: a real simple way to make a heater is to use a power resistor. For example, if you have a 5-watt, 10 ohm resistor, and you connect it to a voltage source, you can use some simple euqations:

P=V^2/R

If you use ~7V for V, then P=49/10 ~= 5W. The current is given by:

I = E/R = 7/10 = .7A. So your battery must be capable of providing .7A or 700mA. That's actually alot of current for most batteries, so that's why batteries are't used often for heating applications.

 

[Reloadron]

I"ll just add: a real simple way to make a heater is to use a power resistor. For example, if you have a 5-watt, 10 ohm resistor, and you connect it to a voltage source, you can use some simple euqations:

P=V^2/R

If you use ~7V for V, then P=49/10 ~= 5W. The current is given by:

I = E/R = 7/10 = .7A. So your battery must be capable of providing .7A or 700mA. That's actually alot of current for most batteries, so that's why batteries are't used often for heating applications.

Now that is a great example. If you were to mount a few (depending on how much heat you need) power resistors to the bottom of a metal plate you would have a hot plate similar to the image originally posted. Eventually things like watt density come into play but using a few power resistors is a good start.

BrownOut also makes another good point in that to make heat, especially high temperatures requires considerable current so batteries aren't always the best solution.

Ron

 

[Mosaic]

Using a peltier junction as a heater is more efficient than just resistance wire or resistors. However, u must not over heat a peltier.

 

[KeepItSimpleStupid]

High resistance is a relative term Any resistor gives off heat. P(Watts) = I^2(R). The trick is to find a material whose Resistance is such the material won't melt at a specific voltage while dissipating a given amount of power.

Ni-Chrome is one such material.

 

[Sparky_s]

I'm understanding it more, thanks

BrownOut also makes another good point in that to make heat, especially high temperatures requires considerable current so batteries aren't always the best solution.

Ron

Of course, I won't use batteries as power source.

Using a peltier junction as a heater is more efficient than just resistance wire or resistors. However, u must not over heat a peltier.

Yes, of course! I have purchased a couple of peltier junctions, but the maximum temperature that I can get with the peltier junction I ordered is 67ºC (aprox 150ºF).
With that temperature is enought to start, but I think I could have to use more temperature and maybe an electric heater is more powerfull.

High resistance is a relative term Any resistor gives off heat. P(Watts) = I^2(R). The trick is to find a material whose Resistance is such the material won't melt at a specific voltage while dissipating a given amount of power.
Ni-Chrome is one such material.

I take note. Thanks



So, to start, I will use a peltier junction and I will use a regulated DC power source to regulate the temperature of the peltier junction. A question is... If a potentiometer can change the Voltage, then.. what kind of electrical component can regulate the amperage?

A thermostat is use to increase or decrease the temperature of the wire, so its function is to control de amount of amperes that can flow to the wire?

Update #1
Instead of using a variable power supply to regulate the temperature, can I use a Pulsed DC source with PWM, to regulate the temperature produced by the peltier plate?

 

[kpatz]

Instead of using a variable power supply to regulate the temperature, can I use a Pulsed DC source with PWM, to regulate the temperature produced by the peltier plate?

You don't need a variable power supply or PWM. Thermostats work by cycling power to the element. When the element is cool, the thermostat switch closes, turning on the current, and the element heats up. When the thermostat (which is near or touching the element so that it heats up as well) reaches its set temperature, the switch opens, shutting off the current to the element, which then starts to cool. When it cools to below the set temperature, the element switches back on, and this cycle repeats (well, I suppose it could be a really low frequency PWM done in a low-tech fashion). You could do something similar with a microcontroller with A/D and a thermistor (digital temperature control), or even a thermistor and a comparator (use a pot as a temperature control). Have the circuit control a relay that turns the element on and off.

If you have an electric oven in your kitchen, you probably have seen it works in this fashion, and you can hear the thermostat click on and off as it switches.

 

[Reloadron]

Update #1
Instead of using a variable power supply to regulate the temperature, can I use a Pulsed DC source with PWM, to regulate the temperature produced by the peltier plate?

Sparky, we have beat this to death. Over a few different threads we have looked at heating elements and temperature control in detail. That includes the use of a Peltier element including the use of an H-Bridge incorporated with a Peltier element for temperature control.

We have covered countless heating elements as well as many means to accurately control temperature. Somewhere in all of that info spanning several threads is a wealth of information. There really isn't much else that can be said about it. I don't know what else to suggest.

Ron

 

[KeepItSimpleStupid]

The type of control/heating element is selected based in part, by thermal mass and temperature variation.

You can't use a 1000 W heater to heat 10 mL of water to 80 F (+- 1 degree), for example. A 1000 W heater won't heat a swimming pool either.

A bi-metalic strip (on off control) and a 50-75 W heater is perfectly happy regulating the temperature of a 10 gallon aquarium. The desired temp is between 72 and 80 F

Peltier is good for about a delta T of about 60 C if I remember. I would have to check my design book. PWM is a good way to regulate a Peltier block.

We beat thins thing to death without knowing what you want to control, with what accuracy, what material is acceptable to measure the temperature, how much etc.

Most hot plates are just a bimetalic strip and an on/off thermostat. The heating element is under the plate. This doesn't mean, you can't separate the heater and replace the temperature controller with a much more expensive unit and still have, for instance the magnetic stirring capability.

Temperaure control of liquids, could mean I want to heat the ocean to 100 degrees Centegrade. That borders absurdity, yes, but so does 10 mL of water to 80 deg F with a 1000 W heater.

 

[Sparky_s]

Sparky, we have beat this to death. Over a few different threads we have looked at heating elements and temperature control in detail. That includes the use of a Peltier element including the use of an H-Bridge incorporated with a Peltier element for temperature control.

We have covered countless heating elements as well as many means to accurately control temperature. Somewhere in all of that info spanning several threads is a wealth of information. There really isn't much else that can be said about it. I don't know what else to suggest.

Ron

I really appreciate your answers and the answers of the other users.
I will take a look more deeply into this forum looking for the info.
Thank you very much.