PTC Heaters – Primer – ElectroSchematics.com

Let me start by showing the inside view of the common Goodknight Gold Flash System. It is a powerful electric liquid vaporizer with flash action and an intelligent heater control system (https://www.goodknight.in/products/indoor-electric/goodknight-gold-flash-system/).

This compact AC230V mosquito repellent has two operating modes – Normal mode when there are few mosquitoes and Flash mode when there are many mosquitoes. On flash mode, the device releases flash vapors for thirty minutes for every four hours and then automatically switches back to normal mode. A green light from its bicolour LED indicator shows the normal mode while yellow color announces the flash mode. A small microcontroller is there to supervise the intelligent heater control system!

As you can see, the main part of the electric heating system, as in other similar devices, is a self-regulating heater, commonly referred to as a PTC heater. (https://en.wikipedia.org/wiki/Self-regulating_heater).

This is the reverse engineered schematic of the Goodknight Gold Flash system. It took a long time to create it, but I don’t guarantee accuracy. I include it for study, and do not intend any copyright infringements.

Let’s get into the amazing loop of PTC heaters!

How does a PTC Heater Work?

Positive temperature coefficient heaters (PTC Heaters) consist of specialized heating discs built from advanced ceramic materials. If a material exhibits a positive temperature coefficient that means as its temperature increases its resistance to current increases proportionately.

A ceramic PTC heater is made of small ceramic pieces pressed between two metal plates. The constraint compartment causes them to get a strong positive temperature coefficient effect. That means, the ceramic stones’ ambient temperature that makes up a PTC heating element has a positive temperature coefficient. As the temperature increases, the resistance increases. So, a ceramic PTC heater requires no regulating electronics, temperature sensors, overheat protection etc, because it is the material in the heater itself that regulates the temperature.

A ceramic element is constructed for a specific temperature range and maximum temperature, and it automatically compensates for lower or higher ambient temperatures. At low ambient temperature, the resistance is lower and the current higher quickly heats it. There will be more resistance to the current with higher temperatures, limiting the speed of temperature rise. So, the temperature will never exceed the set-point temperature thus decreasing the chances of overheating and circuit damage or fire.

Note that PTC ceramics can be fabricated to have different set-point temperatures at which the drastic resistance change takes place. This temperature point is the Curie Point of the PTC heater.

What are the applications of PTC Heaters?

PTC heaters are widely used in industrial, commercial, and residential applications. Since PTC heaters improve on previous heater designs to provide safe, energy-efficient heating systems for small and large applications, they are a welcome choice for applications in various domains like automotive, healthcare, food, and beverages, etc. PTC heaters play an important role in heated apparel technology (gloves, scarfs, or vests).

The Goodknight Gold Flash System is a great example of consumer application with small PTC heaters. Its electronics hold a Dual PTC Heater cartridge.

How to build your own PTC heating system?

PTC Heater is a great way to build your own portable heating systems. This session will give you quick clues to do it with commonly available inexpensive little PTC heaters.

PTC heaters come in a variety of sizes and specifications. Note that PTC Heaters come in standard voltages of 12V, 24V, 120V and 240V. Choose the one that best fits your application (don’t try to stick a square unit in a round hole, ha ha).

Below you can see a couple of PTC Heaters tailored for egg incubator applications.

A traditional electric heating system usually calls for a control circuitry to monitor and set the temperature. Luckily, applications utilizing PTC heaters may not need such consecrated control systems due to the self-regulating nature of the PTC heating elements. Even if the temperature demands a control circuitry, PTC Heaters may still be easier to handle than traditional resistance wire heaters.

Now let’s begin our experiments with easily available PTC Heaters that we can buy from most online storefronts. Such a PTC heater, made up of an aluminum shell, is unique in that it draws a limited amount of current and can achieve up to 120°C with 12VDC (see below). You can make so many amazing things with these 12V PTC Heater Plates!

Before the buy, remember all critical parameters for a PTC heater design/construction like target temperature, physical shape, applicable power source, etc.

I need to test a small PTC Heater (PTC heating element in aluminum enclosure) that has a rated voltage of 12V and temperature of 120°C. The wiring diagram is simple as you can see below.

The idea behind this first experiment is to ensure that it can then be to make a portable heater plate. Only a handful of components are required to proceed with the project.

I used my laboratory 12VDC power supply able to provide up to 5A, but the original intention is to power the finalized portable heater plate thru a 12V automotive battery. It can be used in a car by plugging it into the cigar lighter socket situated on the dashboard (https://en.wikipedia.org/wiki/Automobile_auxiliary_power_outlet).

Below you can find my 12V/120°C PTC Heater. It has a cold resistance close to 10Ω when measured with my trusty digital multimeter. Ambient temperature at that time was around 29°C.

Here are some of my quick findings and related jots:

  • I saw a high inrush current during the initial few seconds after turning on the power source
  • When testing the heater element in the air, it hits 60°C approx. in a couple of seconds
  • The heater element gets very lazy to hit its target temperature ie, it gets slower the closer it gets to the rated temperature
  • I don’t think it has much power around the target temperature (120°C) but still looks great for many applications
  • Perhaps, we need to increase the number of heater elements to quickly rise the temperature of the dreamt up portable heater plate. I should have a few more PTC Heaters in the immediate weeks to continue with this experiment
  • I carried out the rough temperature measurements with a soldering iron tip thermometer

In Closing

Just a trial run of a suboptimal setup is actually a poor means of substantiation, but more fun is waiting!

Anyway, now we know something about PTC Heaters. Later we could add the support of an entry-level microcontroller. Stay tuned.

Other odd design ideas could be car seat heaters, hair dryers, mirror defoggers, warming blankets, diffusers, cup warmers, defrosters, etc…

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