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btec national diploma project!!!! i neeeed help!

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New Member
hi all, as you can tell i am new to this site, i am currently studying elecrical and electronic engineering at college and i am in my third and final year, but i am currently in the process of deisgning and making a project. I have come up with the idea of using a hall effect sensor and putting it around the lead that comes out of a soldering iron, (i have measured the ac current and it about .05 amps) and connecting this to a seperate circuit incorparating a tri ac that will then be connected to a fume extractor. So basically when you turn the soldering iron on, the hall effect sensor will detect ac current this will then switch the tri ac to turn the fume extractor on, here comes my problem...

I am not 100% sure what components i am going to need and i am un certain of how to connect it up!

any help and schematic diagrams and drawings will be much appreciated!!!




New Member
Neat idea, but a soldering iron works by pulsing the electricity on and off, so the current will pulse on and off. You can hear the contacts clicking if you put your ear close to the soldering iron (not too close though). If you want your fan pulsing on and off as the soldering iron regulates, then this method will work.

Would it not be simpler to regulate the mains voltage down to 12V and drive a dc relay off this? Just a thought...
For Hall effect sensors, look at Allegro Microelectronics, although these might not measure down to 0.05A


IF you meant TRIAC by tri ac, then what you need is a simple comparator circuit where you set the point where you want it to start.

By the way, you may use a simple 12vdc fan to blow away the soldering fume. (Im using one).


New Member
well im using an oki metcal ps-800e soldering iron station, so its a serparate lead coming out of the soldering iron that can be disconnected when ever needs be so its not actually running straight off the mains! im sure i measured .05 amps i might be wrong with this, i think it might even be 3 amps!

and yes i did mean TRIAC, sorry about the confusion. the fan i am using is a 12vdc fan but it sucks the fumes instead of blows them!


New Member
You need to get yourself a breadboard, get a decent textbook that explains how TRIACs work, then try out some circuits on the breadboard until you are comfortable with how it all works. Once you've done that, you'll have a clear idea of what to do about your project. You can do all the theory you like (and the theory is necessary), but in the end, you learn by doing. Everyone else on here all learned Electronics by doing things in practice. Regardless of their qualifications.

You need to set some stuff up and try it. Then come back to us with specific problems if/when you encounter them.



Well-Known Member
It may be beneficial to use a high temperature thermistor and a small wrap round clamp on the iron to control your fume extractor. This will have the additional benefit of allowing you to draw cool air over the iron after switch off, thereby shortening the cool down time.

I would imagine the set up would be along the lines of a comparator to sense your operational window, feeding into a schmitt trigger to clean up the output from the comparator, the output of the schmitt feeds an opto-triac driver which in turn controls your triac.

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