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Topic: What do I need to keep the temperature constant (about 200 °C)? (Read 854 times) previous topic - next topic

G_darko1624

Hi, i'm new... This is my first project and I've never done something similar before so I apologize if I will ask some trivial things but I've already done some research and nothing seems to be similar to my problem. Basically I want to keep the temperature of a simple resistance, constant at a value of about 200 °C and I wanted to ask you what do I need to do that. I have to use a thermocouple and a ssr and a generator similar to this one:

https://www.amazon.it/GW-Instek-GPS-3030D-Alimentatore-corrente/dp/B010TMF7G0/ref=sr_1_1?ie=UTF8&qid=1525351175&sr=8-1&keywords=generatore+di+corrente+laboratorio

What kind of ssr do I need? What kind of thermocouple do I need? Do I need other things? I'm asking because I do not own those things except for the generator and I can't buy useless stuff (and since I'm a noob I probably would do that without your help).
Thank you for reading this and for paying attention hope you can help me.

Paul_KD7HB

Hi, i'm new... This is my first project and I've never done something similar before so I apologize if I will ask some trivial things but I've already done some research and nothing seems to be similar to my problem. Basically I want to keep the temperature of a simple resistance, constant at a value of about 200 °C and I wanted to ask you what do I need to do that. I have to use a thermocouple and a ssr and a generator similar to this one:

https://www.amazon.it/GW-Instek-GPS-3030D-Alimentatore-corrente/dp/B010TMF7G0/ref=sr_1_1?ie=UTF8&qid=1525351175&sr=8-1&keywords=generatore+di+corrente+laboratorio

What kind of ssr do I need? What kind of thermocouple do I need? Do I need other things? I'm asking because I do not own those things except for the generator and I can't buy useless stuff (and since I'm a noob I probably would do that without your help).
Thank you for reading this and for paying attention hope you can help me.
First, if your "generator" adjustable power supply, can supply the maximum voltage and current at the same time, you are limited to 900 watts. What is the value of resistor that can dissipate 900 watts and maintain a 200C temperature? Yes, you can figure that out.

Second, a SSR is of no use to you with DC power. Use a MOSFET and a large heat sink to turn the current to the resistor on and off.

Others may have answers to the thermocouple question.

Paul

jremington

The power supply linked is 90 Watts (30V, 3A max).

What, exactly, is the "resistor"? Please describe it in detail (resistance, maximum power dissipation, etc.).

Paul_KD7HB

The power supply linked is 90 Watts (30V, 3A max).

What, exactly, is the "resistor"? Please describe it in detail (resistance, maximum power dissipation, etc.).
Only off a little! Guess I saw the 30 in the picture and thought it was amps. Just need to learn my numbers!

Wow, 200C with 90 watts. Must be a light bulb.

Paul

G_darko1624

Only off a little! Guess I saw the 30 in the picture and thought it was amps. Just need to learn my numbers!

Wow, 200C with 90 watts. Must be a light bulb.

Paul
First, if your "generator" adjustable power supply, can supply the maximum voltage and current at the same time, you are limited to 900 watts. What is the value of resistor that can dissipate 900 watts and maintain a 200C temperature? Yes, you can figure that out.

Second, a SSR is of no use to you with DC power. Use a MOSFET and a large heat sink to turn the current to the resistor on and off.

Others may have answers to the thermocouple question.

Paul
It is actually made of tungsten so i guess it's like a lightbulb if you want. I'm sorry I can't remember right now the exact resistance but I can measure it after. I've already use that power supply and it works but I have to adjust "manually" the voltage to have the right temperature so i wanted to use arduino to do that work for me. Can you please explain to me why can't I use a ssr like this for example:

https://www.amazon.it/Caiyuangg-stato-solido-ssr-10dd-DC-DC/dp/B073WPZCFF/ref=sr_1_1?ie=UTF8&qid=1525423180&sr=8-1&keywords=ssr+rel%C3%A8+dc

and why a mosfet and a large heat sink would help me with this problem.
Thank you again for answering.

Paul_KD7HB

A SSR used with DC can be turned ON by your Arduino, but cannot be turned OFF. It only goes off then the controlled voltage goes to ZERO!. AC does that once every cycle.

The MOSFET can be switched on and off by your Arduino in order to turn the DC to the wire on and off. The heat sink may or may not be required to dissipate the heat generated in the mosfet junction when a large current is controlled.

To complicate your project, the heat generated by the wire will be concentrated in the center of the wire because your connections to the tungsten wire will act as heat sinks and draw the heat away from the wire. So your connections must be as small as possible and the copper wire carrying the power to the connections  will also act as heat sinks, so they mus be as small as possible and still carry the current.

Begins to get more complicated, doesn't it? Perhaps it's time to explain what you are doing! I am sure you know the tungsten wire is extremely brittle.

Paul

Wawa

A SSR used with DC can be turned ON by your Arduino, but cannot be turned OFF.
OP posted a link to a DC SSR.
Leo..

Paul_KD7HB

OP posted a link to a DC SSR.
Leo..
I didn't look till now. Sure is. Lot of cost to switch 3 amps, but should work. My DC SSR is a plug-in, no heat sink, good for 65-75 ma.

Wonder how he plans to attach the thermocouple to the tungsten wire?

Paul

cattledog

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Wonder how he plans to attach the thermocouple to the tungsten wire?
Quote
I've already use that power supply and it works but I have to adjust "manually" the voltage to have the right temperature so i wanted to use arduino to do that work for me.
Can you please show how you sense the temperature. Switching 30vdc, 3a is the easy part of this project compared to sensing the temperature of the wire.

Quote
Basically I want to keep the temperature of a simple resistance, constant at a value of about 200 °C
Is there a varying thermal load, or is it stable? Do you set the dial on your power supply to the right place and all is good, or are you having to move it around to keep at 200C.

MarkT

A tungsten wire has a resistance that varies with temperature so you could use a measurement of
its own resistance to sense its temperature (ie measure voltage and current).

A PID loop and slow PWM using a MOSFET seems a reasonable approach - perhaps 1 to 10Hz or so
would give good control without objectionable audible buzzing.  Measuring voltage and current would
need coordinating with the PWM cycle, but at these rates that's not hard to achieve (synchronizing
with the hardware PWM would be trickier).

Be careful about over heating the wire, tungsten burns in air much more easily than alloys
designed for use as heater elements (nichrome being the main one).  I suspect 200C is OK
for tungsten.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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