This Simple Trick Turns Old CFL Lamps Into Stunning Induction Heaters

• This is a relatively simple and truly impressive experiment to do: induction heating! By understanding how induction hotplates work, we imagined a system that is certainly less powerful, but which concentrates a large quantity of energy on a small piece of metal. We can therefore heat it 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 a ZVS (zero volt switching). It has the advantage of automatically oscillating from an LC circuit (coil, capacitor). The transistors each take turns replenishing the energy lost by the LC circuit at each half-period. When one transistor is on, the other is forced not to be on. The inductors allow for a current without interruption during switching, their exact value is not very important, provided that it is greater than a few ÂµH and less 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 constructed so that the turns are as close to each other as possible to obtain the highest possible reactance in the minimum amount 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 we exceed 100KHz, we then find ourselves in critical mode of the LC circuit, the power supply risks "cutting off" at a low current (10 amps instead of 18) because of 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, this is also an opportunity to circulate a fluid inside to cool them).

- The greater the capacity, the more the empty consumption increases and therefore the lower the efficiency. On the other hand, a large capacity allows for a higher coupling, which makes it easier to heat small masses which only fill a small part of the coil.

- Increasing inductance allows the opposite effects of increasing capacitance, but this causes more stress. Content of 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 more turn and we increase the reactance too little compared to the resistance that we add).

- The variation in inductance when an object is placed in it causes a variation in consumption, the difference in consumption (unloaded - under load) makes it possible to obtain an estimate of the increased "theoretical" efficiency (apart from losses by joule effect in the circuit, notably the coil). In our case 83%.

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

This Simple Trick Turns Old CFL Lamps Into Stunning Induction Heaters

• This is a relatively simple and truly impressive experiment to do: induction heating! By understanding how induction hotplates work, we imagined a system that is certainly less powerful, but which concentrates a large quantity of energy on a small piece of metal. We can therefore heat it 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 a ZVS (zero volt switching). It has the advantage of automatically oscillating from an LC circuit (coil, capacitor). The transistors each take turns replenishing the energy lost by the LC circuit at each half-period. When one transistor is on, the other is forced not to be on. The inductors allow for a current without interruption during switching, their exact value is not very important, provided that it is greater than a few ÂµH and less 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 constructed so that the turns are as close to each other as possible to obtain the highest possible reactance in the minimum amount 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 we exceed 100KHz, we then find ourselves in critical mode of the LC circuit, the power supply risks "cutting off" at a low current (10 amps instead of 18) because of 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, this is also an opportunity to circulate a fluid inside to cool them).

- The greater the capacity, the more the empty consumption increases and therefore the lower the efficiency. On the other hand, a large capacity allows for a higher coupling, which makes it easier to heat small masses which only fill a small part of the coil.

- Increasing inductance allows the opposite effects of increasing capacitance, but this causes more stress. Content of 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 more turn and we increase the reactance too little compared to the resistance that we add).

- The variation in inductance when an object is placed in it causes a variation in consumption, the difference in consumption (unloaded - under load) makes it possible to obtain an estimate of the increased "theoretical" efficiency (apart from losses by joule effect in the circuit, notably the coil). In our case 83%.

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

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