Can a variable thermal shut off circuit be build? - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: July 31, 2019, 07:33:37 pm
content: Sometimes when I do test of circuit I would like to be able to shut off the PSU / Load leads if my circuit gets to hot.Imagine a thermal sensor that are measures a components temperature and if it exceeds the temperature I select, it shall shut of, not the unit but the test leads.Like if I am testing a DIY circuit and it i.e. gets above 120F after longer time test 3-4 hours into the test.It is important that the "cut off" part is as "invisible" for the test result as posible, so it do almost not change the power, resistance or anything like that.Edit: forgot to say that we are talking about max 100V or 75A (max voltage one of my psu can deliver and max ampere an other psu unit can deliver)

author: Rick Law
author_rank: Super Contributor
timestamp: August 01, 2019, 01:27:19 am
content: Quote from: FriedMule on July 31, 2019, 07:33:37 pmUntil someone with more experience comes along and give you a better option, let me share my hobbyist experience...(Beside, I have to jump in to see what you want to do with 75Amp!!!)I do what you wrote about all the time but at 12V 2A. The same can be done by using a better relay rated 100V 75A.75A is a hell of a lot of current and that is going to be your road block. Whether you can do it or not would be decided upon if you can find a relay that size.My full size fridge takes 6.5A (@100V) only, 75A is more than 10 full size refrigerators like mine!? 75Amp (at any voltage) is still a lot for any relay to handle.You should consider controlling the PSU's power-in instead of power-out. See the last paragraph.I use a simple Arduino NANO with LM35z as temperature probe to drive a relay.- The LM35z is able to measure −55°C to 150°C. When you are doing just +C temperature, the connection is a lot easier. You can also offset the LM35z with a couple of diodes so you don't need -Vin as shown in the datasheet (page 16). The LM35z will give you 10mV/degree C for the Arduino to read.Link:http://www.ti.com/lit/ds/symlink/lm35.pdf- To "connect" the LM35z as probe, I just tape the LM35z onto what I want to measure. Typically, I am measuring a 18650 battery, so getting a good thermo-contact is not hard. You will have to work that out properly.If what you want to probe is smaller than the LM35z, you are out of luck with this method.- The Arduino NANO reads the analog port connected to the LM35z and make decisions based on input voltage. In my case, I also display the temperature on a 20x4 LCD and some times I output it back to the PC for logging.- I use the regular cheap Arduino relay module like the one discussed in this thread:Link:https://www.eevblog.com/forum/beginners/chinese-relay-module-reliability/The moduleI use has relays rated for 250V @ 10A, I am only doing 12V@2A only. Arduino output port alone doesn't have enough power to drive even those small relay modules, the module has its own +5Vin which is necessary.You will need way way way better relay modules if you are going to do 75A! You can also use the cheap module to drive another (bigger) module with the 75Amp relay. I suspect the 75 Amp relay would be your difficulty.Make sure you read that other thread and understand the reliability and issues with this cheap relay module if you end up using that to drive power-in.- Alternative is: Just relay the input side of the PSU -- if the PSU power-in doesn't exceed the "easy to obtain" relay's spec, let the relay control the power-in for the PSU rather than having the relay module handle power-out at 75Amp...Good luck there...EDIT: Forgot the links - added now. (Also added the last section suggesting relaying the PSU input instead of output)

author: GerryR
author_rank: Frequent Contributor
timestamp: August 01, 2019, 10:25:12 am
content: An automotive starter relay can handle the current (12 volt coil) or a motor contactor used in industrial applications (different control coil voltages available). Thinking about the current, sounds like your getting into the welding arena, so a welder control relay may also be a possibility.

author: Zero999
author_rank: Super Contributor
timestamp: August 01, 2019, 10:32:38 am
content: Quote from: GerryR on August 01, 2019, 10:25:12 amAn automotive relay certainly will not be able to break 100V at 75A.One thing to note is that the original poster might not be running at 75A and 100V, as they mention two power supplies, but neglect to mention the VA of them both.Quote from: FriedMule

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 01, 2019, 11:05:26 pm
content: Yes 75A is an insane amount og current, but nice to have, because, hmm, just nice to have. :-)The 75A is a 10V unit and I do newer think I'll use that many amps, but why not build so it can be used?I imagine some sort of turn button that when turned, changes the max temperature on a display and if the real temperature on the probe is going above, then off!My reason for wanting to "cut" the leads and not the PSU is that I have heard so many times, that: "if you want a reliable and precise result, keep the unit on for at least xx hours"

author: digsys
author_rank: Unknown
timestamp: August 02, 2019, 12:11:41 am
content: Go solid state - perfect voltage / current for parallel sets of Power FETs, say 10-20A per. Should be able to find Rdson of ~ 1mR. Control it all with 1mA. A bit more work than a simple Kilovac / Gigovac relay (used in EVs), but "cleaner" / more controlled switching.

author: ledtester
author_rank: Super Contributor
timestamp: August 02, 2019, 01:20:54 am
content: Quote from: digsys on August 02, 2019, 12:11:41 amI looked up what a 75A solid state relay costs at Mouser and was shocked.I suppose paralleling two $10 40 amp SS relays from Amazon isn't a great idea.

author: digsys
author_rank: Unknown
timestamp: August 02, 2019, 01:36:07 am
content: Quote from: ledtesterWe've used Crydoms (and others), at ~$100 ea, actually not much cheaper than a Kilovac / Gigovac proper DC mechanical relays. BUT, you can make a simple switch yourself, with parallel power FETs, IF cost is important. After all, it is just an On/Off switch.

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 02, 2019, 05:23:17 am
content: Quote from: digsys on August 02, 2019, 01:36:07 amIt is always dagerus to say that the price dos not matter, but I'd rather that it WORKS!! then save a few dollars.Since I am a noob, I'd tryed to find some circuit on the internet, but I havent found any.A circuit where a turn button changes the number in the display to maybe max 200 C and also can compare the measured temperature with the max choosen value and then shut off.What about optorelays, do they not have to handle great amount of current and voltage?

author: Rick Law
author_rank: Super Contributor
timestamp: August 02, 2019, 06:16:18 am
content: The latest reply from the OP said the75Amp is at only 10V. Out of curiosity, I did a Amazon search. At this happy voltage, automotive relay is an option. The available options are aplenty:$23.45 USD Pack of 5(store brand) relays+harnesses rated at 12V 80A/60A High Switching Capability (I have no idea why they have both 80A and 60A in the description.)https://www.amazon.com/ONLINE-LED-STORE-Switch-Harness/dp/B01NCA6CABFor a better known brand$45.50 USD Each: Bosch Automotive Relay, 12V 75Ahttps://www.amazon.com/Bosch-332-002-168-0332002168/dp/B0117FAGVOSo, one can indeed do it easily and inexpensively: Use Arduino driving a cheap relay module (5 volt coil) which in turn drive the coil for the 75Amp relay. Not exactly pretty, but works in theory to drive 75amp.* * *Actually, the LM35 makes a rather easy to use probe. Let me show off my "quick and dirty" temperature probe construct here. It was really a "quick and dirty" construct, made for "one time use" when I found my newly recovered 18650 (from a dead laptop pack) seem to be charging warmer than I like, so I want it to log the V/I/Temp/Time plus cut off at about 90 degree C.I made my own "offset circuit" before I ran into the version of LM35 datasheet with an example. So my offset circuit isn't the same as the one in the datasheet. Mine has only 1 diode offsetting the LM35's Vgnd at about 1Volt. With the 5V from the NANO, that leaves me about 4V, just high enough to run the LM35. I also made my offset board into a "daughter card" for two LM35 probes and plugs directly plug into NANO's 5V and three analog ports - a shared Vgnd of the LM35, and two V-sense for the two probes.The two LM35's has the connections with extension wires from a dead network cable then shrink-wrap into a probe.Like most "one time thing", the "one" is a repeating one. This little "one time" thing is still in use. The NANO is equipped with 2004 LCD display and a DS3231 real time clock so I can log with date/time. It is now my regular desk clock with "room" temperature display from the DS3231 module - plus two other temperatures from these two probes that I can just stick anywhere... Mostly just to see how hot my batteries are on the charger or how hot my desk-lamp is getting... The relay module is currently reassigned to another experiment.

author: digsys
author_rank: Unknown
timestamp: August 02, 2019, 06:47:40 am
content: Quote from: FriedMuleNO ONE suggested that the "cheap(er) price of ~$100 reflected poor quality" !! Crydom is one of the very best solid-state manufacturers out there. I was replying to ledtesters comment = "I looked up what a 75A solid state relay costs at Mouser and was shocked".I don't know what price ledtester saw or what part he was actually looking at, or what he thought was "expensive". ~$100 is an extremely good price for that type of device !Quote from: FriedMuleThat is an "opto-relay". 100V at 75A+

author: ledtester
author_rank: Super Contributor
timestamp: August 02, 2019, 04:10:50 pm
content: Quote from: FriedMule on August 01, 2019, 11:05:26 pmThere is something to be said for using a power supply that is sized for your application. You want some headroom, but using a 75A power supply when you only need a couple of amps is foolhardy. Even if the supply has current limiting, 750W is a lot of power, and it's a good idea, especially for beginners, to limit the worst possible outcome to something that's not going to ruin your day. At the very least employ fuses that are appropriate to your application.QuoteThese things are called "temperature controllers" (and in the consumer world "thermostats") and there are a ton of ready-made bare modules available with a "dial" and display. The difficulty is finding something that will work at the temperatures you want and uses a sensor that is compatible with your application. Thermistors and thermocouples are generally used to measure the temperature of a heatsink / battery / electronic component.You might also find some pre-made modules by searching for "fan controller". I just recently bought one of these:https://www.ebay.com/itm/12V-PWM-Fan-Temperature-Speed-Controller-Module-High-Temp-Alarm-5V-Buzzer-PC-CPU/263605466941?hash=item3d601c373d:m:md_Xw7-TdWpozYJ83KekdBwHaven't had a chance to test it out though.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 02, 2019, 05:28:28 pm
content: Your supplies should have a remote turn off option which will do the job nicely. I know you have said you don't want to turn off the supplies so you can maintain a long on time on your test circuit for "stability", but when you change the load current by that amount all stability is out the window anyway. Those stability issues arise because of thermal effects primarily and when you dump the load you change the thermal environment completely.If you decide to stick with your plan as others have said temperature controllers are widely available.https://www.omega.com/en-us/search/?text=temperature+controllerThe ones in the link are pricey, but quality is assured. I am sure you can find Chineseum ones far cheaper. Then the only trick is to use the relatively low power relay (only a few hundred watts) in these things to turn off the high power contacter you need to find.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 02, 2019, 05:30:50 pm
content: Here is a link to a far cheaper modulehttps://www.amazon.com/Inkbird-Temperature-Controller-Thermostat-Itc-100VL/dp/B0148FS5FO/ref=asc_df_B0148FS5FO/?tag=hyprod-20&linkCode=df0&hvadid=167124686369&hvpos=1o3&hvnetw=g&hvrand=8827568315575995131&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033112&hvtargid=pla-304949473590&psc=1

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 02, 2019, 10:30:23 pm
content: Thanks a lot, you are all fantastic!About 75A being to much if I maybe only need a few amp. Yes that is perfectly correct and I do have some 30V 5A and other that I can use for the normal everyday use.What I am looking for, is the possibility to turn off the PSU no matter what PSU I choose to use, if it is my 30v-5A, 10V-75A, or my 100V-10A.I'll take a look on the thermostats! :-)

author: David Hess
author_rank: Super Contributor
timestamp: August 03, 2019, 03:18:32 am
content: We have used the metal can AD590 as the temperature sensor for this sort of application in the past but they are pretty expensive. The current output is easier to use.I would build a latching circuit using the temperature sensor, a reference, and an operational amplifier as a precision comparator. With proper calibration, the trip point can be set with a potentiometer and multimeter.An external temperature trip might be a useful feature to build into a power supply.

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 03, 2019, 09:24:55 am
content: Quote from: David Hess on August 03, 2019, 03:18:32 amThe dmm idea sounds great, maybe even use one of the dmm displays from Ebay?Yes and maybe in an electronic load, I am wondering on why that is not standard in the top of the range PSU / Loads.May I put an enormous strange on your genres help? :-)Could you maybe try to draw a schematic that I can start my project from?

author: David Hess
author_rank: Super Contributor
timestamp: August 03, 2019, 10:42:08 am
content: Quote from: FriedMule on August 03, 2019, 09:24:55 amThat could work but I always just connected a multimeter temporarily to set the trip point.QuoteThere is not much to draw. Filter the signal and reference voltage before the comparator. Using an operational amplifier makes this easier because of lower input bias current.When I did it, I latched the output by using the operational amplifier to trigger an SCR which pulled the output to the load disconnect down to ground and kept it that way until reset.

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 03, 2019, 11:11:38 am
content: Thanks a lot, I'll try to se if I can draw something that do that:-)Would you mind looking at it when / if I can draw it?

author: David Hess
author_rank: Super Contributor
timestamp: August 03, 2019, 05:17:58 pm
content: Quote from: FriedMule on August 03, 2019, 11:11:38 amJust post it. Everybody will comment on it.

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 05, 2019, 05:18:58 am
content: I have tried to make something that may work, remember I am as noob as they come! :-)My idea is that the "temp to LCD" shall connectes in some way so the display show max alloveable temperature and by switch, show the current temperature.Placeholder relay shal go to an NC 100A 100V relay

author: ledtester
author_rank: Super Contributor
timestamp: August 05, 2019, 06:32:29 am
content: Why is pin 3 of the LM358 unconnected?Temperature doesn't change that fast, so why not just use the uC to activate the relay? In pseudo-code:Code:while (1) {read LM35 using the ADCif LM35 temp > threshold temp:activate relay using a GPIO pinbreak}

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 05, 2019, 06:41:55 am
content: Quote from: ledtester on August 05, 2019, 06:32:29 amOh sorry, an error! LM358 Pin 3 -> LM35 pin 2I am not sure about your code question, uC ?

author: coppercone2
author_rank: Super Contributor
timestamp: August 05, 2019, 06:52:39 am
content: use a contactor triggered by a thermostat (heat sink the parts so you can screw a thermostat into them, it will be more fool proof then trying to make a control system based on thermocouples that is safe, thermostats and contactors are used everywhere

author: ledtester
author_rank: Super Contributor
timestamp: August 05, 2019, 07:00:28 am
content: Quote from: FriedMule on August 05, 2019, 06:41:55 amuC = microcontroller

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 05, 2019, 07:04:11 am
content: Quote from: coppercone2 on August 05, 2019, 06:52:39 amOkay thanks great advice!So an unit like this:https://www.digikey.dk/product-detail/en/sensata-crydom/PM2260D95VJ/PM2260D95VJ-ND/5699042?And then how about the thermostat? Does that go to an high temperature?Sorry but noob-alert! :-)

author: coppercone2
author_rank: Super Contributor
timestamp: August 05, 2019, 08:51:12 am
content: digikey sells thermostats that trigger at various temperatures, then you need to build a circuit which will basically open a contactor permanently when the thermostat is triggered, otherwise it goes hot cold hot cold until something breaksI don't recommend solid state either, get a mechanical contactor

author: coppercone2
author_rank: Super Contributor
timestamp: August 05, 2019, 08:56:13 am
content: https://www.digikey.dk/products/en/relays/contactors-electromechanical/969?k=contactorhttps://www.digikey.dk/products/en/sensors-transducers/temperature-sensors-thermostats-mechanical/516?k=thermostatif you find latching contactors for your voltage and current rating its better (because you just need to send it one pulse, then it latches mechanically to a open state, so you can google for a normally closed latching open contactor rated for 100A and your voltage if you want the most simple circuit that is engineered safeso as soon as the thermostat gives it juice, it opens up and stays mechanically open. otherwise you need to design a circuit (such a circuit might be a normally open contactor which is armed closed (power is flowing) and another circuit breaks current flow, such as a lower power relay which latches mechanically, if you can't find an appropriate contactor.you need to do some looking because 100A is not exactly kids stuff

author: coppercone2
author_rank: Super Contributor
timestamp: August 05, 2019, 09:00:13 am
content: or if its a either direction latching contactor, you turn it on and then it waits to be turned off incase of failure

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 05, 2019, 10:05:17 am
content: The contactor looks like a great unit and it looks like they have no problem handling high power!I do just need some way to make the max temp variable and latch, and that should my circuit almost be able to, I just need to find out the problem as showen in my circuit. :-)

author: paulca
author_rank: Super Contributor
timestamp: August 05, 2019, 02:17:09 pm
content: Quote from: Zero999 on August 01, 2019, 10:32:38 amI 'believe' an automotive starter motor using a much smaller/normal 12V relay to drive a solenoid which slams a conductor pin against the starter motor contact. It is that contact which takes the 100-400+Amps of cranking current. Obviously that solenoid is able to break the contact as well. I would expect it has a seriously beefy spring on it.I also expect this is normal in switching high currents. IE. a small relay closes to drive a solenoid/motor for a mechanical connection that takes the high current.

author: coppercone2
author_rank: Super Contributor
timestamp: August 05, 2019, 04:35:10 pm
content: Quote from: FriedMule on August 05, 2019, 10:05:17 ami recommend then making a gross overload safety with a thermostat that is way up there but fire safe, and a secondary adjustable safety that uses electronics. If you want to be really safe put them on separate contactors. or with more thought and analysis you can make a or-gate type circuit that triggers the contactor (but don't actually use transistors with the fire safety)the main problem I see is that your temperature sensor is running in parallel with wires carrying 100 amps. i have no idea what that can do to a RTD, thermistor, thermocouple or other signal, it sounds kinda bad and like it requires shielding at least, if you can have the signal for the temperature wire come in at a right angle it would be better, but I assume its basically strapped to the main cable via zip ties for the sake of not being ridiculous. The thermostat kind of gets around alot of these problems but its not adjustable or precise. Someone with high current industrial experience can tell you what to expect, I never worked with a crazy circuit that required a signal line routed in parallel with a giant conductor.But in terms of reliable function I think the contactor is basically a requirement for safety.Keep in mind the electronics control system connected to the temperature sensor can get a malfunction from spikes possibly, or just get damanged from bad manufacturing or defects or age or whatever (i.e. arcing, surges), so its highly recommended to make it a one way trip that needs a manual reset if triggered so it can't turn it self back on. Another way to do this is to trip a breaker with a contactor that shorts out the supply, like a crowbar circuit, and blows a fuse.I think the automotive stuff is more dealing with inrush survival from batteries , it sounds like you have a regulated supply that you just need to disconnect reliably.

author: Rick Law
author_rank: Super Contributor
timestamp: August 05, 2019, 06:24:54 pm
content: Quote from: coppercone2 on August 05, 2019, 04:35:10 pmActually, for real safety, you are best off using a smaller power source for smaller needs.If there is some failure, 75Amp even at mere 10V can cause quite a bit of damage.You may never get to the stage of "too hot". Way before getting hot, something else got vaporized, melt, or sparked or...750 Watt of power waiting to hurt something...Power can be use for good or evil. So give it enough power to do its job. Anything more is just increasing the potential damage.

author: coppercone2
author_rank: Super Contributor
timestamp: August 05, 2019, 07:36:06 pm
content: oh man I assumed the load can take it and its hooked up to something like a glo-bar light source or something

author: Rick Law
author_rank: Super Contributor
timestamp: August 05, 2019, 08:18:11 pm
content: Quote from: coppercone2 on August 05, 2019, 07:36:06 pmThe OP left an earlier reply that it is just "nice to have" instead of for any specific application. Nothing wrong with that, I like to have something powerful to play with too.Being a cautious person that I am (some would call me a pessimist), I worry about the price of failure before I contemplate the disposition of the fruits of success. So I rang the alarm bell to make sure themagnitude of potential damageis not overlooked. Not much there, just me having a typical pessimistic day.I sure like to have a flame thrower to play with - something like that could be kind of fun. But I surely would not use it to light my cigarette - may be once for fun but for sure not as daily use lighter.

author: coppercone2
author_rank: Super Contributor
timestamp: August 05, 2019, 10:22:29 pm
content: honestly I don't know if you should be hooking up anything 50A with alligator clips, its kind of like you need to build a proper hookup to the experiments with heavy ferrules and screw terminals and stuff.Who the hell prototypes 50A shit in the fly? It's kind of nuts.Those experiments require so much thought to run properly that maybe, its a good idea to be slowed down by having to make a special wiring fixture rather then just slap some alligator clips on it.EZ-high voltage is not a good idea either. I don't know who the hell deals with so much high current parts so quickly, a navy yard? Almost everything you hook into 100A is either gonna be really expensive, or really hot (and some what expensive), not to mention heavy, unweidly, ugly. Even a factory should have the time to do proper fixturing.and it can explode, so its a bad idea to not have it in a enclosure anyway?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 06, 2019, 03:01:01 am
content: Quote from: coppercone2 on August 05, 2019, 10:22:29 pmThere are times when it is appropriate. The power lab back at university had patch boards with various voltages of three phase current. 4/0 jumper cables. Made hooking up large motor and generator experiments easy. Also made for spectacular results on some kinds of mistakes. There is an argument for discovering these mistakes and their rather large consequences in a relatively benign environment instead of a remote field location, far from knowledgeable people, medical help and other useful items.

author: coppercone2
author_rank: Super Contributor
timestamp: August 06, 2019, 06:45:25 am
content: are two screw terminals and a drawer filled with various thermostats really going to slow things down that much? its 100Aits hilariously lazy/'efficient' you will tire out swapping 100A components from the weight like 100 times faster then you would save time from leads.this is like, an automated probing jig of the future in some fully automated industrial robotics factory. It's hard to imagine when it would actually even make economic sense in a factory. I don't think you can even make 100A components fast enough right now to justify that, let alone find a buyer for that volume. Anything that runs at 100A right now is just ridiculous. Maybe if a full home energy storage system sold for like 150$. And even then I think osha would kill it being 100A.I am imagining a big copper block with a thermostat on it, with a eyelet for a screw terminal or pin that goes into a screw terminal or something. Its like a bus bar territory. It would basically be a bus bar with a thermostat on it that connects to other bus bars? I have NO idea.

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 06, 2019, 07:39:48 am
content: Quote from: coppercone2 on August 05, 2019, 04:35:10 pmThe whole circuit is driven by 9V until the voltage regulation that are making 6V, it is only the U6 that should be "touching" the 100ASince my knowledge is about zero, you are super welcome to change, delete or do anything with the circuit. One missing function is now that it can't tell what max temp are set to.

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 06, 2019, 07:49:14 am
content: Quote from: coppercone2 on August 06, 2019, 06:45:25 amThe thermal relay is meant to shut the test lead's power off if my test point is getting to hot, lets say that after3 minutes a component goes higher then max temperature I allow, then does the relay trigger. The same if I am testing a PSU for several hours, if the heat gets to great, it shuts everything off so nothing is starting to burn.

author: coppercone2
author_rank: Super Contributor
timestamp: August 06, 2019, 10:17:14 pm
content: what components are you using that are rated for 100 amps and dont come with a stud bolt mount?even diode bridges past 50 amps come with screw mount studs. If you have components that use screws, get a bus bar, properly attach it to a thick wire, put a thermostat into the bus bar (screw it on) and use that I guess. And put touch safety stuff.And like someone already said you might want to get 2 power supplies like the guy said, a lower current one (say a 10A one) to catch obvious failures without explosions or worry that a circuit safety will malfunction to increase your safety factor. Ramp that one slowly to 10A then ramp the big one slowly to 100A

author: coppercone2
author_rank: Super Contributor
timestamp: August 06, 2019, 10:22:07 pm
content: high power components look like this typically ********you can usehttps://www.mcmaster.com/bus-bars*find upper threshold of safety for specifiying the thermostathttps://www.alliedelec.com/product/selco/ca-85/70098628/?gclid=CjwKCAjwyqTqBRAyEiwA8K_4O7G4-PS2s0J7TDW5lLwfAPH2xlNubC6u-QXeqLo3FaUJz7ew4_1OTRoC_aoQAvD_BwE&gclsrc=aw.ds

author: coppercone2
author_rank: Super Contributor
timestamp: August 06, 2019, 10:39:44 pm
content: anyone reminded ofhttps://en.wikipedia.org/wiki/This_Island_Earthby this thread?

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2019, 11:13:42 pm
content: Quote from: coppercone2 on August 06, 2019, 10:39:44 pmI know nothing of what you are referring to. Now hand me that AB619 model condenser from Directory Electronic Service Unit 16 of Supreme Equipment so I can finish my interocitor.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 07, 2019, 04:39:55 am
content: Unfortunately the thermostats recommended in the last few posts don't meet friedmules criteria of adjustability. I like the idea of using one as a safety backup, with the thermostat selected for the highest desired temperature. Of course he could have a whole string of these with set points at temperature intervals and a multipole switch to tie the appropriate one into the circuit.The thermal controller I suggested earlier will work fine as an adjustable limit. It is a PID controller, but just set the I and D terms to zero and it becomes an on off switch at the set temperature. As mentioned in some earlier posts it is well worth putting a latch on the output so the power is not turned on again as the device cools. There are many ways to do the latching function, including latching relays, a deadman switch on mains power that is held by the normal power supply output and various electronic types. All of these, even though they may be relatively high power are merely the drive for the contactor you will need for the high current circuit.Do pay attention to all of the safety warnings, and also spend time thinking through all of the possible actions. Thinking becomes increasingly important as the danger goes up, and with you are well into welding and fire starting territory.

author: coppercone2
author_rank: Super Contributor
timestamp: August 07, 2019, 05:15:20 am
content: 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

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 07, 2019, 09:31:49 pm
content: Quote from: coppercone2 on August 07, 2019, 05:15:20 amActually 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.