Help with PSU (Temp control fan, load bank, & PWM circuit)

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How did you get a day off?? Or was the 2nd the last day of extensions?
 
I wish I had the day off. I worked a full day today, well a full Saturday at least, about 8 hours, a full week day would be more like 10 hours min. I think today was the last Saturday for a while luckily...well, back to the dummy load, I got the volt meters hooked up amazingly they are spot in, so no worries there, unless my watt meter an the volt meters are both off by the same variances lol, because the numbers agree. I added an "on" LED while I was at it.
 
Ah, just as I suspected...took another reading of the op-amps to ground and they are all exactly the same now. I did three things so I don't know which one fixed it. First, I soldered the voltmeters on (maybe closing the loop on that circuit did something). Second, I soldered a few more thing onto the ground wire and the positive 12 volts PSU (volt meters, "on" LED). Third, while I was doing this I cleans up an ugly soldering job where there was a kind of big blob of solder which connected the op-amp that had the off readings to +12v and I noticed that the connection of this op-amp was only connected by this solder blob so I added a little wire I cut off a resistor and soldered that on (maybe that fixed it). Anyway, I am glad it's working. Now I just need to assemble it and put conformal coating on. Do I just paint polyurethane on EVERYTHING for conformal coating?
 
Well, I don't know, the reading are off again now, the same two, but even while the readings are off the LED volt meter still agrees with my watt meter, so I guess it doesn't really matter.
 
I think it is just noise in the measurement. Glad they agree. Temperature is ok as well?

I'm not a big fan of conformal coating. Seems like as soon as you paint it you want to change somethig. But if you do I would just do the wire side. The resistors may be to hot for the coating.

Thanks for the fun, it's been a nice project.
 
If you get time post some pictures of the finished product! Hope you sell a hundred.
 
Thanks! I will post pictures, probably even video on YouTube. I hope I sell a hundred too, thanks for the encouragement!

I just got done glueing the temperature sensor onto the copper pipe. It works amazingly well! I tested it out just to be sure it would function properly, so I cranked it up to about 25 amps and left the water turned off. Guessing I would say it was probably about 45 seconds and it got up to 86c then alarm and LED turned on and amps dropped down to 0. About 15-20 seconds later the temp was around 75-77 and alarm and light went off and current picked back up and the cycle started again. With the water on full it held about 35c at 25 amps and 24v, so 600 watts. I turned the water down to a pretty slow flow and temp went up to about 44c. This thing is really so cool! I love it!
 
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I was thinking of adding an MOV, as we talked about before, to the dummy load to protect against arc if I ever unplug it and forget it's on...but I was reading on Wikipedia that MOVs degrade over time causing a permenant short circuit and then explode. Maybe I will just take my chances that I will never forget it's on and unplug it.
 
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MOVs degrade over time causing a permenant short circuit and then explode.
Click to expand...

I think that's like... dozens of years. Or after lots and lots of trigger events. For practical use they work 100%. Otherwise why would they make devices out of them?
 
Yeah, that makes sense. I'll have to look into this more later. I have to go somewhere now. What voltage should the one I get trip at to provide adequate protection?
 
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Damn it. I was wondering why there was no activity on this thread. Turns out the forums were not sending me up dates. Good thing I decided to check in manually.

As for the MOV, a 50V unit will work. It just needs to blow at a low enough voltage to protect the FET's. If I remember right the FET's you used are not rated for more than ~70 volts, so no more than this.
 
I was looking at MOVs, i did some reading up on them but am still not really sure exactly what I need. For instance, is the 50v spec you refer to above, is that called the clamping voltage, meaning the voltage at which it shorts to ground? And what is the difference between the clamping voltage and the rated voltage. Also I don't know what joul rating I need or peak current rating or what the capacitance rating is all about, basically I don know anything lol, about these that is. Can you help me understand these, or at least point me in the right direction of some online explanation that is in plain English?
 
Here is a link to some. Use either the 5KP26A or 28A. You will need two since they are not bi-directional. Place them from +24 to ground at the load box side of the plug with the band of each in the oposite direction.. They are like a big zener diode. They turn on if the voltage goes above the breakdown voltage. There is one voltage where it is barely on (breakdown voltage) and another where it has maximum rated current flowing (maximum clamp voltage). So these two will be slightly on (5 ma. of current) at 26 and 28 volts and fully on (107 or 99 amps) at 46 or 50 volts.

https://www.electro-tech-online.com/custompdfs/2012/09/Littelfuse_TVS-Diode_5KP.pdf
 
I started putting everything together tonight but I have a problem with my fans. My power supply to the fans is 24v 1amp max rating. The fans draw .28 amps each and have a max volt rating of 24v. If I turn the power on, then plug both fans at the same time into the active power they both come on full blast and work just fine. If I plug one fan in, and only one, and then turn the power on it comes on full blast and still works just fine. But, when I plug both fans in at the same time before turning the power on, then power up, the fans just sort of click and try to come on but never do. Any clue as to what could be causing this and what I need to do to fix it?
 
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That's a bummer.

Fans often take quite a bit more current (4 or 5 times) to start than they do to run. It sounds like your power supply doesn't like to supply the current to both start up and start the fans at the same time. What is the sequence you have to turn everthing on? I forget, how big is the 12 volt supply? What parts do you have left over?
 
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