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schematic

simulate this circuit – Schematic created using CircuitLab

I am trying to build a DIY BGA reflow machine. I have a very crude schematic, but the idea is run each of the 6 heating elements in parallel. Doing the math, I have found that the equivalent resistance would be around 4.88 ohms. This would leave the circuit requiring almost 25A. I want to get it below 20A so that I can run it in the house. An idea that comes to mind would be to install a 2 or 3 ohm resistor in parallel to lower the current draw below 20A. I'm not sure if I need a PSU or if I can wire straight into the 120. I also saw some other videos on the subject where they install a circuit breaker as a protection. Any advice or tips on how to build and wire this safely without burning my house down would be greatly appreciated!

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  • \$\begingroup\$ The “schematic” you drew is very hard to read. Use the CircuitLab tool built into this site. Edit the question then click on the little schematic button above the edit area. When drawing the schematic; use resistor symbols for the heater, a custom “box” symbol for the SSR, a voltage source for the power supply, and add descriptive text as needed. \$\endgroup\$
    – Kuba hasn't forgotten Monica
    Commented May 29 at 16:46
  • \$\begingroup\$ what is the purpose of the arrow heads on the lines? ... it makes a cluttered looking diagram \$\endgroup\$
    – jsotola
    Commented May 29 at 17:17
  • \$\begingroup\$ @Kuba hasn't forgotten Monica I have redone my schematic \$\endgroup\$
    – MacAttack1
    Commented May 29 at 17:58
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    \$\begingroup\$ ”install a 2 or 3 ohm resistor in parallel to lower the current draw” That would increase the power consumption, not lower it. \$\endgroup\$
    – winny
    Commented May 29 at 18:01
  • \$\begingroup\$ Why are there so many heaters? What voltage is across them? Could you simply use lower power heaters? \$\endgroup\$
    – Andrew Morton
    Commented May 29 at 18:48

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Schematic is a mess since hot seems to be connected to neutral. That aside: If you want to use less power you should use heaters that use less power, or use less heaters.

Do you really need 20 amps of heat? That's 2400 watts. Stand next to the biggest space heater you can buy in the store - imagine all that heat going into your rework machine - do you really need it all, or can you use less?

Notice that if you put a resistor in series (where it needs to be to reduce the power) the resistor becomes another heater. Which leads to another idea: placing two heaters in series instead of parallel. They will each output somewhere between a quarter and a half of the heat (depending on how much the resistance changes with temperature) as they would in parallel. Of course you'll have less heat.

If you are making your own heaters from coils of resistance wire, make the wire longer. Longer = more resistance = less heat. You might think it's the opposite, that a longer heating coil would make more heat, but it doesn't.

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