Electronics > Projects, Designs, and Technical Stuff
Driving (AC) mosfet switch directly from MPU using GDT
Simon:
heat won't magically race up the wire. The first short length may help but after the first few 10's of mm it's not helping anymore.
I refer to my comment you quoted in your post: you don't know what you are doing. most of your loses are not resistive while the mosfet is on but during the switching that happens at twice your drive frequency. The MOSFET does not instantly go from full on to yull off or viceversa. The transition will be "resistive" and will dissipate more heat than your 50% on. As I said 1kHz is ample for what you are doing but you know everything so why bother telling you. So long as no one else dies when you burn your house down I am happy to let Darwins law take it's course.
beduino:
--- Quote from: Simon on October 26, 2019, 07:46:42 pm ---The MOSFET does not instantly go from full on to yull off or viceversa. The transition will be "resistive" and will dissipate more heat than your 50% on.
--- End quote ---
Even when it will be 100% not 50% given only to estimate this is still less than 1/4W per each mosfet in TO220 package connected to copper wires directly from drain tap, so etimated amount of additional copper in wires is ~0.018kg which means it is huge heatsink, while this thing will usualy work in room temperature below 25*C :-DMM
Experiments shows that this AC mosfet switch doesn't need any additional heat sink in this case where we have huge amount of copper in wires connected directly to mosfet taps - this is beauty of custom design, where thanks to taking into account other things than only to be competitive with low cost on the market and look for as many customers as we can, which means another constrains to lower down price including shipping, while this design do not need to hit so huge market and thanks to using mains wires in a smart way as a heat sink, it can easy fit requirements of custom design.
Probbaly you believe in too much in market electronics products, which sometimes fit into some government regulations, but sometimes you can find CE mark on things not safe at all, so sometimes it is better to know what is inside and how it works, because of it can save your ass and money when fails - easy to repair ;)
beduino:
--- Quote from: Simon on October 26, 2019, 07:46:42 pm ---heat won't magically race up the wire.
--- End quote ---
No magic there ;)
Mosfets in "bulky" TO220 package connected directly via 3mm holes tap drain to soldered copper wires >0.5mm2 lets assume 4m long we have more than 0.0178kg of copper so less than 1/4W will flow througth 2m long copper wires in room 25*C temperatures... No :-DMM neither :-BROKE needed to imagine that heat will disapear and heat will be transfered to room air :o
Simon:
--- Quote from: beduino on October 26, 2019, 08:35:09 pm ---
--- Quote from: Simon on October 26, 2019, 07:46:42 pm ---heat won't magically race up the wire.
--- End quote ---
No magic there ;)
Mosfets in "bulky" TO220 package connected directly via 3mm holes tap drain to soldered copper wires >0.5mm2 lets assume 4m long we have more than 0.0178kg of copper so less than 1/4W will flow througth 2m long copper wires in room 25*C temperatures... No :-DMM neither :-BROKE needed to imagine that heat will disapear and heat will be transfered to room air :o
--- End quote ---
I REPEAT, YOU DON'T HAVE A CLUE WHAT YOU ARE TALKING ABOUT! YOU ARE TALKING BOLLOCKS WHILST PLAYING WITH THE MAINS. THAT IS A RECEIPE FOR BAD THINGS. THIS THREAD IS A WASTE OF TIME BECAUSE YOU WON'T LISTEN. PLEASE MAKE SURE THAT NO ONE ELSE IS INVOLVED WITH YOUR EXPERIMENTS BECAUSE THE ONLY PERSON YOU SHOULD END UP KILLING IS YOURSELF.
Yes of course your rihgt, copper offers no resistance to heat and all of that plastic insulation is as conductive to heat as copper. You carry on with your delusions and don't listen to anyone! Or are you trolling us?
beduino:
--- Quote from: Simon on October 26, 2019, 09:04:46 pm ---Yes of course your rihgt, copper offers no resistance to heat and all of that plastic insulation is as conductive to heat as copper.
--- End quote ---
Plastic insulation doesn't have to be as conductive to heat as copper, since quick estimation of area around 4m long 0.5mm2 copper wire is A: 0.010 [m^2] which is equivalent to 10cm x 10cm sheet of thin insulation, so now imagine what can happen when we heat this quite big area with lets say 0.5W from one side having 25*C room air on other side? :palm:
Problem is you didn't provide any calculations to proove your claims :-DMM
I listen to people like T3sl4co1l , who provided very usefull estimation of gate current needed, so big letters with warning not needed in your posts.
BTW: I use maxima software under Linux instead of Window$ calculator, so probably that is why no smoke so far in many projects :popcorn:
Attached detailed calculation of estimation area around a few meter copper wire. Show us your calculations to proove your claims :o
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