What kind of load does an electric heater have? (inductive, resistive) - Page 1
Forum section: electronics / beginners

author: diegoterc3
author_rank: Regular Contributor
timestamp: September 07, 2014, 06:40:16 pm
content: Hello,I have an electric heater that has 2 heating elements that look like a flourecent bulb, but I've seen that most electric heaters have a resistive heating element so I am a little confused.I would like to know what kind of load is it, and how to calculate its values if possible. The oven is this one:http://www.soloelectro.net/products/12367-nex-eo-900/Thank you in advance.

author: Simon
author_rank: Unknown
timestamp: September 07, 2014, 06:47:54 pm
content: Heating will always be resistive as it is resistance that turns electricity into heat, inductance just stores electricity as a magnetic flux and makes no heat other than in it's resistive windings.A resistive heating element will have some inductance but this is an unavoidable by product of the fact that most elements are a coil of highly resistive wire and the inductance can be mostly ignored.

author: SeanB
author_rank: Super Contributor
timestamp: September 07, 2014, 07:17:55 pm
content: Those elements are a resistive coil inside a quartz glass tube, and are pretty much a really big power resistor. Typically each tube is around 300W to 1000W in power, depending on the length of the resistive element and it's thickness inside the tube. The thinner ones are higher resistance and thus lower power. They are designed to run with the quartz glass at around 500C-800C or so, which is a red glow, so it heats both by direct radiation and by convection in the air.

author: IanB
author_rank: Super Contributor
timestamp: September 07, 2014, 07:29:20 pm
content: Quote from: diegoterc3 on September 07, 2014, 06:40:16 pmIf it's a 700 W oven and it has two heating elements, then each element will be 350 W.Assuming a mains voltage of 220 V then the current is found by dividing the voltage into the power, so it's 350/220 = 1.6 A per element, 3.2 A in total.The resistance of each element when operating will be 220/1.6 = 138 ohms. However, the resistance when cold will be less and the initial current will be higher until the element warms up.

author: coppice
author_rank: Super Contributor
timestamp: September 08, 2014, 12:22:34 am
content: The characteristics of a heater like that, or an incandescent light bulb, are kind of funky. The device is a resistor, but the temperature changes a lot through each 50Hz or 60Hz mains cycle. This leads to substantial resistance changes through each mains cycle. The result is considerable THD. If you apply a nice pure mains sine wave and measure the current waveform you may see 10% to 15% THD. If you try the same thing with a typical water heater you will see very little THD. The much more effective cooling in a typical water heater results in much smaller temperature cycles, and the load is close to a simple resistor with a hint of inductance, and a smidgeon of capacitance to ground.

author: diegoterc3
author_rank: Regular Contributor
timestamp: September 09, 2014, 11:22:10 pm
content: Thank you everyone for your answers I have a better understading of the device and how to control it.

author: PepeK
author_rank: Regular Contributor
timestamp: September 10, 2014, 02:52:37 pm
content: It has a pure resistive nature and capacitance / inductance can be ignored for 50 Hz mains frequency. For high frequencies - it will be more complicated case.