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I'm building an indoor greenhouse. I have gathered a few tutorials on how to achieve what I need but on the heater I bought I can't seem to find anything that could help, and my knowledge on electricity is a bit shaky.

I'm using an ESP32 to control the sensors and valves I need and I thought that I could control this heater (https://www.ebay.com/itm/322871906747) with the ESP32 and a MOSFET. The MOSFET (IRFZ44N) is rated for 55 V and 49 A which is safely above what I need.

Upon receiving the heater I tried to test it with some Dupont cables and a PC power supply but those thin cables couldn't handle the 12 A that the heater was trying to pull, so they melted. After this little accident this got a bit real (I come from a software background where a bad day is when you crash something important but starting a fire is a whole new level).

I read that the problem was the thickness of the cables. I didn't seem to find a clear way to check how thick I needed to be to be able to handle all the amperage but I'm sure this I can figure out.

My question is: handling this kind of power on a breadboard will burn down my house won't it (because this greenhouse is supposed to take care of itself and being unattended for most of the time)?

How can I safely build it without soldering (I have shaky hands and zero soldering skills)?

I'm planning to use a PC power supply for everything but I have no idea what resistors and/or diodes I would need to keep the usage of this heater safe. (I have ordered 1N4001 diodes and 0.25 W 1 kΩ resistors for other sensors and valves, but for this I don't think it will do (some reading materials for understanding this are welcomed).

Lastly: connecting thick cables to the MOSFET seems wrong (for lack of a better word). I bought some Dupont connectors; I was thinking on using these with the thicker cables on the breadboard, but now I have no idea how to connect them.

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  • \$\begingroup\$ Soldering is pretty important for a permanent project like this.... I guess you could use a breadboard, but it's probably not the best idea, since it's only for prototyping... Your best bet would be to create a schematic (shouldn't be too complex if the heater is the only function of the circuit) then give it to someone else who has some experience with soldering. I'm not sure whether the breadboard will handle the power safely or not, but with an application like this, it's not a very good idea. \$\endgroup\$
    – skillz21
    Commented May 4, 2018 at 3:21
  • \$\begingroup\$ For your wire problem, here's a pretty decent wire gauge to current capacity chart: powerstream.com/Wire_Size.htm (look at the "maximum amps for chassis wiring" column). As for connecting the wires, don't use dupont connectors. Use crimp terminals (example: allelectronics.com/category/196/crimp-terminals/1.html). The male/female variety (not the ring variety) go together quite firmly and will handle the required wire size and current. \$\endgroup\$
    – Los Frijoles
    Commented May 4, 2018 at 6:10
  • \$\begingroup\$ The longer your heat cables the thicker they need to be since it is low voltage and resistance produces voltage drop and heat. Consider 14 or 16 AWG houshold wiring for short runs \$\endgroup\$
    – D.A.S.
    Commented May 4, 2018 at 7:13
  • \$\begingroup\$ You shouldn't fiddle around with 12A current on a breadboard, or at all - in case you don't have a sufficient electronics background. That being said, consider using a relay instead of a MOSFET. It means that you get galvanic isolation between your brittle home-made electronics and the 12A :) And you wouldn't have to worry as much about cooling. \$\endgroup\$
    – Lundin
    Commented Mar 12, 2020 at 7:34

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It is not possible to determine if your project "will burn down your house" with the information you have provided, but it is very unlikely. Your fireplace gets hotter and it has not burned your house!

At any rate, you are not using that much power (250 Watts, max.), but you must keep it contained and away from flammable materials, off course!

If you can't solder, you can use crimps and terminal strips!

An example of how to determine the wire size needed. Assume the heater voltage is 25V and the current required is 10A (250W), this means the heater's resistance is 2.5 ohms. In order for the wire to "not melt," it should have less that .25 ohms (1/10th). You now look at a chart that shows the ampacity of cables with a give length and diameter, and a resistance of less than .25 ohms.

I would guess that a 3 foot length of 10 AWG should do the job. Don't forget to heat-sink your FET.

Mount a terminal strip to your PCB, connect thick cables to terminal strip via screws. PCB should have thick lands plating under the terminal strip that connect with mounting screws.

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  • \$\begingroup\$ Relative resistance is useless; the heater is far better at dissipating heat than the wire. OP needs to look up ampacity tables for wire to see what it can handle. \$\endgroup\$
    – SomeoneSomewhereSupportsMonica
    Commented May 13, 2018 at 9:06

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