Pid temp control

Thread Starter

Rob1974

Joined Mar 17, 2021
6
Hi appologies if this is in the wrong thread. I am building a simple furnace for melting aluminium. I intend to use a 2500w kanthal coil with a PID controller, thermo couple and solid state relay. Ive calculated the coil will pull about 10-11 amps. I want to run it off a 240v 13a supply. As i may need to shorten the coil to get it in my furnace it will probably push over 13amps. So can i fit a voltage regulator between the coil and the relay to drop the voltage if necessary. Will this work?
 

andrewmm

Joined Feb 25, 2011
1,473
with out adding a resistance externally , you can not easily drop the voltage
what you can do is chop up the AC wave form,
but an SSR does not sound right for that .

How are you goign to cut the heater ?
sorry new to this but Im used to heaters being sealed / insulated ,
 

MrChips

Joined Oct 2, 2009
23,535
I see two problems.

1) Switching 10-13A with a relay using PID is going to burn out your relay contacts very quickly.

2) Dropping the voltage at 10A with a voltage regulator is going waste a lot of energy as heat.
 

Thread Starter

Rob1974

Joined Mar 17, 2021
6
with out adding a resistance externally , you can not easily drop the voltage
what you can do is chop up the AC wave form,
but an SSR does not sound right for that .

How are you goign to cut the heater ?
sorry new to this but Im used to heaters being sealed / insulated ,
hi thanks for your reply, i am going to wire it up as per the screen shot above. i saw a youtube video using kanthal wire. It just coiled up wire with a set gauge and length to give you a certain resistance. But as i may need to cut it size i thought wiring a voltage regulator between the ssr and kanthal wire may alow me to drop the voltage to stop blowing a fuse or burning the wire out. What are your thoughts? I understand that voltage regulators do not work for ac motor speed control but with my limited electrical knowledge i thought- as ive cut the wire and increased the resistance it would draw more amps so reducing the voltage may counter this. Admittedly i dont quite understand how a voltage regulator works, i assumed it was like a dimmer switch.
Thanks again for your time.
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MrChips

Joined Oct 2, 2009
23,535
If you start with a 2500W coil and reduce its length you will have to reduce its power rating also.
Don't use a voltage regulator. Use a dimmer switch rated for 15A or greater or use a Variac® auto transformer.
 

ElectricSpidey

Joined Dec 2, 2017
1,656
240 volt 15 amp dimmers are available, but they aren't cheap.

You might just want to use the cut off length of kanthal as an external resistor and live with the wasted power.
 

Janis59

Joined Aug 21, 2017
1,332
RE:""240 volt 15 amp dimmers are available, but they aren't cheap.""
That are 15 minute circuitry having zillions of places and available for soldering even for school-pupl, just google for circuit.

BUT, my experience with powerful heaters tells some points You may use. First, any even best PID Controller, including REX provides +/-0.1...+/-0.5 C accuracy but in the fact accuracy walks around 5 C. Reason - the power is large, inertia is huge, and the conducting regime is NOT proportional but Bang-Bang thus the PID corresponds only to the realm of TIME instead of Voltage. So, the solution to earn that 0.1 C is First adjust the power NEAR to the target T, and THEN apply the SSR with PID regulator over that. In multiple ocassions I have got such accuracy (however I prefer the Sestos PID brick).

Okay, now how to adjust the power - a)external mega-resistor (unpleasant idea), b) thyristor power regulator (thus resistor, capacitor, dinistor and triac) BUT it makes 1) VERY unpleasant noise in the power mains what really created a problems in street bloke level 2) makes very harsh FORCES crushing the kanthal wire, just it brokes "without" of proper reason 3) makes triac be crushed by needle like currents, and damping ciruits is small cure, I have multiple cases where 600 A triac was broken just with a 60 A currents, because ANY OWEN !!! is serious inductive load. So, the only INDEED effective means against it is half-period driving. Just use a proper circuitry of half period steering of triac, that regime is ensured by multiple optoisolator chips, and You shall not see any faults.

Syncronous zero crossing switching tech and circ is well described at https://learnabout-electronics.org/Semiconductors/thyristors_62.php
 
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Thread Starter

Rob1974

Joined Mar 17, 2021
6
Hi thanks for taking the time to reply. As i mentioned my electrical knowledge is limited so its probably a bit beyond me to wire up a triac. So ive managed to get the full length of kanthal wire in my furnaceand i am going to wire it up as per the screen shot i attached and hope for the best. I am using 2.5mm steel heat resistant catering wire to connect the ssr to the kanthal wire. I have screwed some 6mm stuf iron into the end of the kanthal coil, drilled a 6mm hole through the fire brick and am going to use a crimp connector to connect to the stud iron. Does this sound reasonable. I will wire the rest in 2.5mm flex cable.
 

Alec_t

Joined Sep 17, 2013
12,071
Slight problem with 15A dimmers, if they're the type which chops the AC waveform: the TS wants to run this from a 13A supply. Even if the average current is below 13A, peak current will be over 13A. Running things beyond their ratings is not good practice,, even if you can 'get away with it'.
 

andrewmm

Joined Feb 25, 2011
1,473
regarding cutting a coil heater,
I half thought.

If heater was designed to run at say 250v, at a set length, its resistance was designed to limit the current at that voltage.
if you cut the heater length, you are lowering its resistance,
thus with the same voltage applied, it will take more current ,

more current, is thus more wattage / heat ,
 

efital1

Joined Jun 5, 2016
1
Hi appologies if this is in the wrong thread. I am building a simple furnace for melting aluminium. I intend to use a 2500w kanthal coil with a PID controller, thermo couple and solid state relay. Ive calculated the coil will pull about 10-11 amps. I want to run it off a 240v 13a supply. As i may need to shorten the coil to get it in my furnace it will probably push over 13amps. So can i fit a voltage regulator between the coil and the relay to drop the voltage if necessary. Will this work?
Put a light bulb of 40w-100w in line to coil.
 

anniel747

Joined Oct 18, 2020
1,095
View attachment 232978hi thanks for your reply, i am going to wire it up as per the screen shot above. i saw a youtube video using kanthal wire. It just coiled up wire with a set gauge and length to give you a certain resistance. But as i may need to cut it size i thought wiring a voltage regulator between the ssr and kanthal wire may alow me to drop the voltage to stop blowing a fuse or burning the wire out. What are your thoughts? I understand that voltage regulators do not work for ac motor speed control but with my limited electrical knowledge i thought- as ive cut the wire and increased the resistance it would draw more amps so reducing the voltage may counter this. Admittedly i dont quite understand how a voltage regulator works, i assumed it was like a dimmer switch.
Thanks again for your time.
Beware of chinese junk. You better overate everything if you go with ali.
 
Hi appologies if this is in the wrong thread. I am building a simple furnace for melting aluminium. I intend to use a 2500w kanthal coil with a PID controller, thermo couple and solid state relay. Ive calculated the coil will pull about 10-11 amps. I want to run it off a 240v 13a supply. As i may need to shorten the coil to get it in my furnace it will probably push over 13amps. So can i fit a voltage regulator between the coil and the relay to drop the voltage if necessary. Will this work?
Use a phase controlled Thyristor (SCR) circuit. Might have to wind yourself one heck of a coil on the output to smooth that edge and keep it from broadcasting a brutal 60 cycle hum through everything that can receive within a hundred yards :)
https://electricalacademia.com/electronics/scr-thyristor-phase-control-circuit/
https://www.electronics-tutorials.ws/power/thyristor.html
https://www.electronics-tutorials.ws/power/thyristor-circuit.html
https://learnabout-electronics.org/Downloads/Littelfuse_App_Note_AN1003.pdf.pdf
 
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