My vote would be no overcurrent detect. What do you guys think?
Yeah, let's just use fuses I guess. That should save us from just about any problem. Though.... of the three PSU's I broke, not a single one blew it's fuse... lol.
Attached is a schematic that uses an LM35 temperature sensor to shut off the load at 100C and turn it back on at about 75C.
I have no hard objections to your thermal shut down circuit. Just minor "what if" things.
First, I like the idea of things turning off and screaming/blinking at you to telling you SOMETHING'S WRONG!!! Rather than getting stuck in a loop where you may not notice anything. I had a project that would work for a while, screw up randomly, then stop completely. It was low power so for several days I didn't even think to check the temp of the LM7805 that had no heat sink. It now has a heat sink and works 100%. Would have been a lot easier to figure out the problem if there was some obvious indicator of what was happening. Even if such before mentioned loops work to keep things from getting destroyed. Indicators are nice.
Secondly, the OP has purchased a bunch of NTC thermistors, and knows how they work for the most part. It would be less accurate, but we could use something like that for over temperature. And I agree 100% that we need some over temperature protection. Even on mine at 50 Watts it got hot as hell after only a few seconds when the water was off. And even with clear hose and a some what noisy pump, there is almost no indicator that water is flowing. Things you gota check for that are easy to forget are EXACTLY what we want safety designs installed for. Takes the human element out of it.
Third, I know nothing about the LM35 temperature sensor. It would be your thing to help the OP with that, not that I'm incapable of learning.
Also shown is an op amp to scale the current up to 5 volts = 50 amps. If we add a little voltmeter we could put in a switch to look at current, voltage and temperature.
This is good, was thinking of this too. This allows us to do a wider range of things, based off of current level. One of those little analog needle point meters, like the ones you find in old voltmeters can run off less than 5 milliamps. I have one here, it's 85 Ohms, and maxes out at 0.002A. Something like this would be quite functional as an indicator. The OP needs to make a back plate with the right markings on it. This can be done with a LASER printer and sticky back labels. With analog we don't have to make the scales exact. We can just get it close and some what even, then adjust with trimmer pots. With digital, we need a stable reference and exact maths. More complex, but cleaner and more sharp looking results.
If I take this project farther in the future, I plan on doing something like this using a PIC and a text LCD module.
Very flashy results can be had going this route. (warning!! Annoying music)