Heater Resistance and Power

A project log for Hakko 907 based Soldering Station

A soldering station based on the easy to source Hakko 907 soldering iron, which is a 24V 50W soldering iron with integrated thermistor.

KuroKuro 11/27/2014 at 13:183 Comments

I've measured the heater resistance and noticed that it's smaller than the resistance for the rated Voltage/Wattage.

The measured value is around 4Ohms. As the soldering iron is rated at 24V:

P = U² / R

P = 24² / 4 = 144W

There it is. The soldering iron is rated at 24V 50W, but if you just connect a 24V supply, it will probably kill itself. You need to control the power delivered to the iron.

There's no need, then, to use a 24V power supply. The unmodified 19V notebook power supply should do the trick.

I've measured the resistance of the heater while hot, to how much it changes with temperature, but it raised to 7Ohms only at 450C.

That said, I've moved the power supply project logs to a new project, and will move a little faster on this project, as I have some other projects on my backlog.


PointyOintment wrote 11/28/2014 at 19:56 point
The resistance increases when it heats up.

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Kuro wrote 11/29/2014 at 01:00 point
Yep, I know. As I said, at around 450C it was at 7Ohms.

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PointyOintment wrote 11/30/2014 at 23:25 point
Oh, good. I must have been really tired when I read that.

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