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The irony is that the DC power supply I’m using kicks out about as much heat as the resistor does.
I’ll try this and see what happens. I hope this should cover it.
You say I need to be limiting the current from the base of the transistor and the Arduino pin. Transidtor have a flyback diode parallel to the resistor to disperse any back EMF the resistor coil generates and a pull-down resistor on the base of the transistor. The fermenter is covered by a black bag.
Am I doing something wrong? At 12V I calculate that the 4W sandbar will be dissipating all of that, which explains the rapid tranistor of magic smoke from them.
I’m rather confused by your drawing. The grounds are all common. Also good to know I can do without the diode. You haven’t included a pull-down resistor so I take it you think I don’t need one at all. I am now using a big E transistor not the datasheet for the exact part but a similar one as I thought I was putting too much power through the little transistors. So as I still wanted a heater circuit and I am lazy I bought one of these. Thanks for the schematic. You could probably cycle it with the 7v supply, add another ds18b20 easily and when it reaches max temperature, kill it and when it drops a bit turn it on it has enough thermal mass to keep things warm in between.
Should I be running it with a heatsink? Unfortunately its too big to fit under the fermenter! My problem is that I have burnt out two transistors one C and one H already and I don’t know why. Is this too low to open the transistor gate sufficiently? This is something I’m looking at improving, probably trnsistor an immersion heater, but the point I’m trying to make is that you need the heater at a much higher temperature than the datasjeet fermentation temp.
Mike has pointed out some issues and I see more. Any input will be most gratefully received. Here’s a snap of the sandbar: Hi pwillard, thanks for your input too.
I might set the relay up again tomorrow. I’ve left it running overnight and I datssheet it will still be at about 20C tomorrow morning as night temperatures are chilly.
After playing around with this for a while I gave up as the big transistor I was using had to be reallocated to another project which is working wonderfully, thanking you. I thought resistance of transistors, especially larger ones like that, was negligible.
Why does it get this hot? I can switch an LED on and off with this circuit not at 12V, obviously but when I try it with the sandbar it quickly goes up in smoke. See my drawing above At that kinda current I would start looking into mosfets to keep the heat down, after 1amp heat starts to get in the way with transistors.
switching 4W wire wound resistor with a transistor
I measured the traansistor from the basepin on the Ruggeduino and it was putting out 4. I’m trying to make a heating element from a 4W wire-wound sandbar resistor and a 12V power supply. My Ruggeduino is using temperature measurements from a DS18B20 sensor to determine when to switch a transistor controlling power to the the resistor.
The upshot of this is that switching of the heater, on or off, occurs every few minutes so it would still burn out. Here’s pics of the Arduino and the setup. For example, its now running off 6V and I’ve got it running straight off the power supply without an control.
For simplicity Transisgor haven’t put the DS18B20 in there. Because the heater is just stuck on the bench underneath the fermenter, with a little insulation around it, thermal transfer to the vessel is poor at this stage.
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