Electronics 2000

My objective is to insert a PVC tube in a the (cold) mold. The heater should heat the mold to an ideal temperature to melt the tip of the PVC tube inside the mold (for a few seconds) and then the heater must switch off and the mold must be cooled down immediately by circulating water through the outer sleeve of the mold.

The mold is made with steel for experiment only. I inserted the tail of the mold in a 45w soldering iron as shown in the picture. My test was successful.

I plan to build a set-up in which I can use molds of various working sizes. I mean, the outer dimensions of the mold will remain the same only the hole diameters would vary to match various sizes of PVC tubes. The actual molds will be coated with chrome or nickle. And, if required, I can change the material of the mold to aluminum, copper or brass for better conductivity. The mold would be installed inside a cooling sleeve, which cover only the body of the mold (excluding the tail).

After testing the trial mold on a soldering iron, I planned to use a soldering gun which heats the tip more quickly.

Here is my proposed idea to quickly heat-up the mold. The transformer's secondary winding is 2/3 turns of 4 SWG solid copper wire to give 2-4volts but high amperes like 400 - 500A. The rest circuit is self-explanatory. The pictures of the mold is also attached to give you the idea of the size of the mold.

Lastly, I want to use 4 such heaters connected parallel and work at the same time.

Questions:

What kind of cables/wires should I use to connect the Transformer-Relay-Heater ?
What should be the amperage of the relay to switch on the Transformer?

Since the secondary voltage is low there are no great problems with insulation - you just need thick enough cables to carry the current. To work this out you need to measure the resistance of your heating element and use Ohms law to find the current (you'll also need to know or measure the secondary voltage). You should then be able to select some suitable cable.

Once you know the secondary current and voltage you can work out the primary current. The power (watts) on the primary and secondary side will be the same (ignoring a small loss in the transformer), and P = V * A, so if you work out P on the secondary side you can then re-arrange the equation to give A = P / V to find the primary current (V = 220). Select a fuse slightly higher than this, you may need an anti-surge one due the high inrush current of the transformer.

Thanks for your response.

Can I use solid copper wire to connect the transformer-relay-heater?

Do you think the automotive ignition relay is a good choice here?

Solid copper wire would be fine assuming it doesn't need any flexibility. I'm not familiar with automotive relays, but I would think you would be well within both the current and voltage ratings of the contacts. Not sure what the coil current would be - you'd need to check that the timer circuit could provide the required current, an possibly add a transistor to drive it if not. Remember to put diode across the relay coil to prevent back EMF damaging the timer circuitry.

Thanks for your help.

The required driving transistors, diodes and RC-snubbers are being used.

There is one more confusion, how to connect the soldering iron prongs with the solid copper wire? Do you think brass-brazing would do the job?