| Electronics > Beginners |
| Newbie understanding joule heating |
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| Zero999:
--- Quote from: larsdenmark on August 02, 2018, 07:49:16 am ---A few points: Resistance changes with temperature so you have to take the operating temperature of the wire into account. Since you don’t know the temperature you have to perform a few experiments. If the fan fails the wire could get extremely hot and start a fire. Monitor the fan and make you don’t have any power on the heating wire when the fan doesn’t run. --- End quote --- And add a thermal fuse to protect against fire, if the controller develops a fault or the MOSFET switching the element fails short circuit. |
| rthorntn:
I'm learning a lot, thanks everyone! |
| hamster_nz:
My local hobby shop has 4m rolls of thinner nichrome wire that is about 14 ohms per meter - a meter of that over 48V would be around 100W, and would most likely glow red hot. I used to use about 900mm and a 12V supply to make a hot wire foam cutter. But it makes me think... What are you trying to do? Watts is a unit of energy, not heat, Even a few Watts can heat a well-insulated thing very hot. And 250 degrees is as hot as an oven. No hairdryer blows 250 degree air... And why 48V? Mabe just run a mains heater (of whatever sort you need) off of a 1000W DC/AC inverter? |
| rthorntn:
Thanks hamster_nz. It's more like a portable air cooker with up to a 15 minute run time. I want it to run directly off of DC, solar, maybe with something like an e-bike battery pack, and I don't care that it makes it more complicated and costly. It will be efficient and insulated but I want to be able to adjust the temperature ramp fairly accurately. |
| Eka:
--- Quote from: rstofer on August 02, 2018, 02:51:16 am ---Current is a result, not a cause. You have 48V and 4.8 Ohms so P = E2 / R or 480 Watts. There are MANY MOSFETS that can handle 10A. Most can handle MUCH more current. The problem is getting them to turn on with only logic level voltages. Vgs for full current has to be a logic level, like 5V in the case of the Arduino. Otherwise, you need a MOSFET Driver.arch for 'logic level mosfet 100A 60V' or something like that. --- End quote --- For this much current, use a MOSFET driver chip. That way the FET turns on fully and fast so little heating happens in it. |
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