Tuesday, June 6, 2023

This Simple Trick Turns Old CFL Lights Into Awesome Induction Heaters

It's easy to do and doesn't require any special skills or knowledge, so give it a try and see how easy it is to turn an old CFL lamp into a great induction heater!

Here is a relatively simple experiment to do and really impressive, induction heating! By understanding how induction hotplates work, we have imagined a system that is certainly less powerful, but which concentrates a large amount of energy on a small piece of metal. It can therefore be heated to more than 1,000°C, which is, for example, impossible with even a gigantic wood fire! "Good video" and long live science ;-)

• Technical remarks and personal conclusions:

- Circuit one is ZVS (zero volt switching). It has the advantage of oscillating automatically from an LC circuit (coil, capacitor). The transistors come each in turn to bail out the energy lost by the LC circuit at each half-period. When one transistor is on, the other is forced off. The inductances make it possible to have a current without interruption during switching, their exact value is not very important, provided that it is higher than a few ÂµH and lower than a few mH.

- We usually see this circuit with a 12V Zener diode and a resistor between the Gate & Source terminals of the MOSFET transistor. The zener diode is used to prevent having more than 12V on the Gate of the transistor (5V is enough), we can do without it since what poses the most problem is above all the Drain voltage. The resistor is used in the event of a problem (so that the transistors are blocked), we can naturally do without it.

- The coil must be made in such a way that the turns are closest to each other to obtain the highest possible reactance in a minimum of space.

- The LC circuit must not oscillate at more than 100KHz: because of the skin effect [...] and the section used (2.5mm²), the "apparent resistance" of the coil increases too much when you exceed 100KHz, you then find yourself in critical mode of the LC circuit, the power supply risks "cutting" at a low current (10 amps instead of 18) due to immediate overconsumption. We therefore have a minimum condition on the value of the product LxC. (industrial versions use copper tubes to overcome the skin effect, it is also an opportunity to circulate a fluid inside to cool them).

- The greater the capacity, the greater the consumption without load and therefore the lower the efficiency. On the other hand, a large capacitance makes it possible to have a higher coupling which makes it possible to heat more easily small masses which only fill a small part of the coil.

- Increasing inductance allows the reverse effects of increasing capacitance, but it causes more stress. Constrained by the fact that the coil necessarily has a certain section and that it is difficult to minimize the space between two turns, the most efficient coil that can be made has a diameter close to its thickness (one turn more and the reactance is increased too little compared to the resistance that is added).

- The variation of the inductance when an object is placed in it leads to a variation in consumption, the difference in consumption (no load - in load) makes it possible to obtain an estimate of the "theoretical" efficiency increasing (apart from the losses by Joule effect in the circuit, especially the coil). In our case 83%.

- The ideal case is close to the one presented with the mass of 50g (coupling, frequency, inductance, capacitance, efficiency).

This Simple Trick Turns Old CFL Lights Into Awesome Induction Heaters

It's easy to do and doesn't require any special skills or knowledge, so give it a try and see how easy it is to turn an old CFL lamp into a great induction heater!

Here is a relatively simple experiment to do and really impressive, induction heating! By understanding how induction hotplates work, we have imagined a system that is certainly less powerful, but which concentrates a large amount of energy on a small piece of metal. It can therefore be heated to more than 1,000°C, which is, for example, impossible with even a gigantic wood fire! "Good video" and long live science ;-)

• Technical remarks and personal conclusions:

- Circuit one is ZVS (zero volt switching). It has the advantage of oscillating automatically from an LC circuit (coil, capacitor). The transistors come each in turn to bail out the energy lost by the LC circuit at each half-period. When one transistor is on, the other is forced off. The inductances make it possible to have a current without interruption during switching, their exact value is not very important, provided that it is higher than a few ÂµH and lower than a few mH.

- We usually see this circuit with a 12V Zener diode and a resistor between the Gate & Source terminals of the MOSFET transistor. The zener diode is used to prevent having more than 12V on the Gate of the transistor (5V is enough), we can do without it since what poses the most problem is above all the Drain voltage. The resistor is used in the event of a problem (so that the transistors are blocked), we can naturally do without it.

- The coil must be made in such a way that the turns are closest to each other to obtain the highest possible reactance in a minimum of space.

- The LC circuit must not oscillate at more than 100KHz: because of the skin effect [...] and the section used (2.5mm²), the "apparent resistance" of the coil increases too much when you exceed 100KHz, you then find yourself in critical mode of the LC circuit, the power supply risks "cutting" at a low current (10 amps instead of 18) due to immediate overconsumption. We therefore have a minimum condition on the value of the product LxC. (industrial versions use copper tubes to overcome the skin effect, it is also an opportunity to circulate a fluid inside to cool them).

- The greater the capacity, the greater the consumption without load and therefore the lower the efficiency. On the other hand, a large capacitance makes it possible to have a higher coupling which makes it possible to heat more easily small masses which only fill a small part of the coil.

- Increasing inductance allows the reverse effects of increasing capacitance, but it causes more stress. Constrained by the fact that the coil necessarily has a certain section and that it is difficult to minimize the space between two turns, the most efficient coil that can be made has a diameter close to its thickness (one turn more and the reactance is increased too little compared to the resistance that is added).

- The variation of the inductance when an object is placed in it leads to a variation in consumption, the difference in consumption (no load - in load) makes it possible to obtain an estimate of the "theoretical" efficiency increasing (apart from the losses by Joule effect in the circuit, especially the coil). In our case 83%.

- The ideal case is close to the one presented with the mass of 50g (coupling, frequency, inductance, capacitance, efficiency).