Author Topic: Can a variable thermal shut off circuit be build?  (Read 4130 times)

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Offline FriedMuleTopic starter

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Re: Can a variable thermal shut off circuit be build?
« Reply #25 on: August 05, 2019, 07:04:11 am »
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
Okay 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?
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Online coppercone2

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Re: Can a variable thermal shut off circuit be build?
« Reply #26 on: August 05, 2019, 08:51:12 am »
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 breaks

 I don't recommend solid state either, get a mechanical contactor
« Last Edit: August 05, 2019, 08:52:47 am by coppercone2 »
 

Online coppercone2

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Re: Can a variable thermal shut off circuit be build?
« Reply #27 on: August 05, 2019, 08:56:13 am »
https://www.digikey.dk/products/en/relays/contactors-electromechanical/969?k=contactor

https://www.digikey.dk/products/en/sensors-transducers/temperature-sensors-thermostats-mechanical/516?k=thermostat

if 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 safe

so 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
« Last Edit: August 05, 2019, 08:58:50 am by coppercone2 »
 

Online coppercone2

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Re: Can a variable thermal shut off circuit be build?
« Reply #28 on: August 05, 2019, 09:00:13 am »
or if its a either direction latching contactor, you turn it on and then it waits to be turned off incase of failure
 

Offline FriedMuleTopic starter

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Re: Can a variable thermal shut off circuit be build?
« Reply #29 on: August 05, 2019, 10:05:17 am »
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. :-)
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Offline paulca

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Re: Can a variable thermal shut off circuit be build?
« Reply #30 on: August 05, 2019, 02:17:09 pm »
An automotive relay certainly will not be able to break 100V at 75A.

I '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.
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Online coppercone2

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Re: Can a variable thermal shut off circuit be build?
« Reply #31 on: August 05, 2019, 04:35:10 pm »
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. :-)

i 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.
« Last Edit: August 05, 2019, 04:48:15 pm by coppercone2 »
 

Offline Rick Law

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Re: Can a variable thermal shut off circuit be build?
« Reply #32 on: August 05, 2019, 06:24:54 pm »
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. :-)

i 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.
...
...

Actually, 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.
 

Online coppercone2

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Re: Can a variable thermal shut off circuit be build?
« Reply #33 on: August 05, 2019, 07:36:06 pm »
oh man I assumed the load can take it and its hooked up to something like a glo-bar light source or something

 

Offline Rick Law

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Re: Can a variable thermal shut off circuit be build?
« Reply #34 on: August 05, 2019, 08:18:11 pm »
oh man I assumed the load can take it and its hooked up to something like a glo-bar light source or something

The 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 the magnitude of potential damage is 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.
« Last Edit: August 05, 2019, 08:21:06 pm by Rick Law »
 

Online coppercone2

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Re: Can a variable thermal shut off circuit be build?
« Reply #35 on: August 05, 2019, 10:22:29 pm »
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?
« Last Edit: August 05, 2019, 10:33:02 pm by coppercone2 »
 

Online CatalinaWOW

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Re: Can a variable thermal shut off circuit be build?
« Reply #36 on: August 06, 2019, 03:01:01 am »
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?

There 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.
 

Online coppercone2

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Re: Can a variable thermal shut off circuit be build?
« Reply #37 on: August 06, 2019, 06:45:25 am »
are two screw terminals and a drawer filled with various thermostats really going to slow things down that much? its 100A

its 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.
« Last Edit: August 06, 2019, 06:56:29 am by coppercone2 »
 

Offline FriedMuleTopic starter

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Re: Can a variable thermal shut off circuit be build?
« Reply #38 on: August 06, 2019, 07:39:48 am »
the main problem I see is that your temperature sensor is running in parallel with wires carrying 100 amps.
The whole circuit is driven by 9V until the voltage regulation that are making 6V, it is only the U6 that should be "touching" the 100A

Since 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.
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Offline FriedMuleTopic starter

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Re: Can a variable thermal shut off circuit be build?
« Reply #39 on: August 06, 2019, 07:49:14 am »
are two screw terminals and a drawer filled with various thermostats really going to slow things down that much? its 100A

its 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.
The 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.
« Last Edit: August 06, 2019, 07:52:43 am by FriedMule »
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Online coppercone2

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Re: Can a variable thermal shut off circuit be build?
« Reply #40 on: August 06, 2019, 10:17:14 pm »
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
« Last Edit: August 06, 2019, 10:29:58 pm by coppercone2 »
 

Online coppercone2

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Re: Can a variable thermal shut off circuit be build?
« Reply #41 on: August 06, 2019, 10:22:07 pm »
« Last Edit: August 06, 2019, 10:30:37 pm by coppercone2 »
 

Online coppercone2

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Re: Can a variable thermal shut off circuit be build?
« Reply #42 on: August 06, 2019, 10:39:44 pm »
anyone reminded of https://en.wikipedia.org/wiki/This_Island_Earth by this thread?
 

Offline David Hess

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Re: Can a variable thermal shut off circuit be build?
« Reply #43 on: August 06, 2019, 11:13:42 pm »
anyone reminded of https://en.wikipedia.org/wiki/This_Island_Earth by this thread?

I 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.
 

Online CatalinaWOW

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Re: Can a variable thermal shut off circuit be build?
« Reply #44 on: August 07, 2019, 04:39:55 am »
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.
 

Online coppercone2

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Re: Can a variable thermal shut off circuit be build?
« Reply #45 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
« Last Edit: August 07, 2019, 05:18:27 am by coppercone2 »
 

Online CatalinaWOW

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Re: Can a variable thermal shut off circuit be build?
« Reply #46 on: August 07, 2019, 09:31:49 pm »
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

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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