Electronics > Beginners
Can a variable thermal shut off circuit be build?
coppercone2:
do you want a noob messing with low voltage thermocouple amplifiers for a safety system on a 100A circuit?
I would not trust it as the primary no matter what I think. Its a crappy little weird welded wire made from dissimilar metals, not very rugged, the alloys suck as far as mechanical properties go.
Granted the thermostat can malfunction too, but its simple and more rugged. If they cover each other its pretty good so long you don't try to multiplex the safety interlock to save money
CatalinaWOW:
--- Quote from: coppercone2 on August 07, 2019, 05:15:20 am ---do you want a noob messing with low voltage thermocouple amplifiers for a safety system on a 100A circuit?
I would not trust it as the primary no matter what I think. Its a crappy little weird welded wire made from dissimilar metals, not very rugged, the alloys suck as far as mechanical properties go.
Granted the thermostat can malfunction too, but its simple and more rugged. If they cover each other its pretty good so long you don't try to multiplex the safety interlock to save money
--- End quote ---
Actually I don't like a thermostat on a bus bar as the primary safety system. That should also be a backup to inherent safety in the system which should include sizing of the components so they don't heat up under the "normal" 100 Amp load, proper spacing between circuits and physical barriers to prevent inadvertent contact with components. Proper and solid connections as you and others have mentioned previously. Use of non-flammable materials. And possibly fuses at appropriate points in the circuit.
The solution I proposed does not have a noob messing with thermocouple amplifiers, it is a plug and play solution. Not without pitfalls as there are goofs to be found in programming the controller. And while thermocouples are not robust structural components there are many applications that do not subject them to vibration and shock and they are well capable of withstanding many, many thermal cycles. Thermocouples also have an advantage in that they report their observations in normal operation. A failure is evident and a prudent operator will perform appropriate maintenance. The thermostat provides no such indication. You either have to assume it is still working properly, or test it periodically. Which is at best a nuisance.
In my personal experience I have had more failures with thermostats of the type suggested than I have had thermocouple failures. Fortunately both numbers are small, with three failed thermostats and one thermocouple in my memory. My sample size is far too small to meaningfully compare reliability, but I take it to mean they aren't dramatically different.
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