Arieljo
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Controlling temperature chamber using Peltier and PWM signal with external power source

Sat Apr 27, 2019 10:22 am

Hi all!

I am planning on building a small chamber in which I want to heat up the temperature up to around 50 degrees Celcius. My idea is to use Peltier elements (with heat sink and possibly a fan?) connected to the external power source and powered fully until it reaches the desired temperature, then modulated using a PWM signal from the PWM pin of the RPi. The Peltier element that I have is 40x40 Thermoelectric Peltier 12 V 60 W (TEC1-12706), and my RPi is the 3B+. Would it be a good idea to supply external power of 12 V using 12 V Channel Relay?

I am still pretty new with combining external power to the elements connected to the RPi, but I have done a bit of research of how the channel relay works in general, so I would love to hear your comments and suggestion about this idea. Thank you!

pcmanbob
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Sat Apr 27, 2019 6:14 pm

Hi.

You can't use a relay if you intend to use pwm control because a relay can't switch that fast.

You will need to design and build a transistor based power controller, or you could used a motor driver if you can find one designed to operated at 12V at around 5A or better.
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Arieljo
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Sat Apr 27, 2019 7:56 pm

pcmanbob wrote: Hi.

You can't use a relay if you intend to use pwm control because a relay can't switch that fast.

You will need to design and build a transistor based power controller, or you could used a motor driver if you can find one designed to operated at 12V at around 5A or better.
Hi pcmanbob,

Thanks for your reply! I was researching more about the use of relays and found out that contact relays indeed do not work really well with PWM signal, as it will degrade more with such high frequency of turning on/off of the signal http://www.omron-ap.com/service_support ... /index.asp? I also read that solid state relays with DC/DC could work pretty well with PWM signal, do you think this is true?

Regarding your suggestion to use a motor driver, I think it sounds pretty good! I was looking into this L298n motor driver https://www.conrad.com/p/joy-it-1573541. Considering that one Peltier will consume a max of 12V, and there are 2 available ports for Peltier, can I assume to give ~24 V external power source to the driver? I'm sorry if my questions are too ignorant for you, as I am just starting out with working on these things.

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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Sun Apr 28, 2019 9:23 am

Arieljo wrote:
Sat Apr 27, 2019 7:56 pm
I also read that solid state relays with DC/DC could work pretty well with PWM signal, do you think this is true?
If you can find a solid state relay that will switch DC voltage, most are DC control but only switch AC output.

Regarding your suggestion to use a motor driver, I think it sounds pretty good! I was looking into this L298n motor driver https://www.conrad.com/p/joy-it-1573541. Considering that one Peltier will consume a max of 12V, and there are 2 available ports for Peltier, can I assume to give ~24 V external power source to the driver? I'm sorry if my questions are too ignorant for you, as I am just starting out with working on these things.
So an L298N will only switch 2A max per output, so with 2 outputs that's 4A which is only 48W you were talking about 60W so you would need a bigger driver board.

If you peltier works at 12V then you need to supply it with 12V, even if there are 2 then each input is still only 12V, just because you have 2 does not mean you can double the voltage.
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Arieljo
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 12:47 pm

Hi pcmanbob,

I found this DC/DC SSR which should work with 3-32 VDC INPUT. I do not really understand however what they mean by 40VDC/5A OUT, could you explain this to me?

So, my plan is to use SSR to modulate the power by PWM signal from RPi. Considering that RPi GPIO pin only outputs 3V3, and this SSR works only for Arduino, I assume that it will need 5V for the channel signal. Therefore, I will also use a bi-directional logic level converter to convert the 3V3 to 5V from GPIO pins. This is the general overview https://ibb.co/qFgDq38 for the system, would you please give me any feedback and if there is anything wrong with it! Thank you!

The SSR is https://www.grandado.com/products/colle ... ino-uno-r3
The converter logic is https://www.sparkfun.com/products/12009

pcmanbob
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 3:29 pm

The link to the SSR does not work !

But 40v/5A out would suggest it cam handle voltage up to 40V, at a current of 5A, but would need to see the info in the broken link to be sure.

Your level shifter may work if it can supply enough current, or you could just use a transistor or an opto isolator instead.
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Arieljo
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 3:54 pm

Thanks for the quick reply pcmanbob,

Sorry that the link doesn't work, weirdly it works for me :? . Anyway here's the link again https://www.grandado.com/products/colle ... 7654525022. In case, it still doesn't work, here's the one with 4 channels https://www.grandado.com/products/4-kan ... oor-uno-r3. The picture : https://imgur.com/a/5TQHxNI. Sorry if they are in Dutch.

The specs for the SSR are :

Brand: Shanwen
Model: Solid State Relay
Adjustable: Yes
Input source: DC
Usage: Universal usage
Model number: 1E0535
Voltage: 12v
Contact load: N
Protection function: High-low Trigger

pcmanbob
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 4:22 pm

Tried both your links site comes up for a fraction of a second then just says oops out of service ! may be they don't like visitors from the UK :lol:

even tried going to the home page same result :(

So looking at the picture you posted I think my assumptions about output were correct.
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Arieljo
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 4:40 pm

Hahaha, hopefully not :lol: :lol:

Thanks a lot for your help! I'll update you if I do have more questions :D

pcmanbob
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 5:04 pm

Well it's not my pc causing it because it's the same on my tablet .

May be some one else on the forum could try the links.
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 5:46 pm

pcmanbob wrote:
Mon Apr 29, 2019 5:04 pm
May be some one else on the forum could try the links.
Works for me. No clearer information, though.
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 5:53 pm

Just tried them, get the bad same response.

Interestingly, while it appears to be Portuguese, it seems to be on a server in Canada. When I tried https://ca.grandado.com/ I was sent to an American server, https://no.grandado.com/ and the response was
"Blocked by Content Security Policy

An error occurred during a connection to au.grandado.com.

Firefox prevented this page from loading in this way because the page has a content security policy that disallows it."

Ernst
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 6:11 pm

WARNING --- www.granado.com could be a scam site !!!

Code: Select all

S:\>wget http://www.grandado.com/products/collectie-1-st-nice-1-kanaals-ssr-solid-state-power-levert-hoge-lage-trigger-5a-12-v-relais-voor-arduino-uno-r3
--2019-04-29 20:01:20--  http://www.grandado.com/products/collectie-1-st-nice-1-kanaals-ssr-solid-state-power-levert-hoge-lage-trigger-5a-12-v-relais-voor-arduino-uno-r3
Resolving www.grandado.com... 23.227.38.64
Connecting to www.grandado.com|23.227.38.64|:80... connected.
HTTP request sent, awaiting response... 301 Moved Permanently
Location: https://www.grandado.com/products/collectie-1-st-nice-1-kanaals-ssr-solid-state-power-levert-hoge-lage-trigger-5a-12-v-relais-voor-arduino-uno-r3 [following]
--2019-04-29 20:01:20--  https://www.grandado.com/products/collectie-1-st-nice-1-kanaals-ssr-solid-state-power-levert-hoge-lage-trigger-5a-12-v-relais-voor-arduino-uno-r3
Connecting to www.grandado.com|23.227.38.64|:443... connected.
Unable to establish SSL connection.
see AbuseIPDB for more information: https://www.abuseipdb.com/check/23.227.38.64

Code: Select all

S:\>nslookup 23.227.38.64 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Name:    shops.myshopify.com
Address:  23.227.38.64
The road to insanity is paved with static ip addresses

gordon77
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 6:17 pm

I Googled the item and the alternative seems to be aliexpress, defaulting to Russian!.

Arieljo
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 6:25 pm

That doesn't sound good! :shock:
I Googled the item and the alternative seems to be aliexpress, defaulting to Russian!.
I also found a link to Aliexpress for the one with 4 channels https://www.aliexpress.com/store/produc ... Title=true. I'm not sure about the Russian part, as I was just directed to the Dutch website of Aliexpress. :?


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Imperf3kt
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 9:37 pm

Most of this topic is moot since you should never run a Peltier from PWM unless you want your efficiency to plummet through the floor (not that it's all that great to begin with)

You should drive peltiers with current!
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Gavinmc42
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Mon Apr 29, 2019 11:51 pm

Why use a Peltier?
It is only 50C, a wirewound resistor or even some nichrome wire will work better.
I use wirewound resistors and fans in a DNA PCR that cycles between 55 - 95C.

I found out the hard way temperature cycling a bunch of PN silicon junctions squashed between two heatsinks eventually fails.
Digital, fault protected transistors switches the fan and resistors on and off.
PWM is not really needed, PID is overkill, delays of 100-800ms are fine.

There is a lot of thermal mass in a Peltier device, it has what I call thermal lag.
A bit of nichrome wire has much less mass, stops heating fast.
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speedfixer
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Tue Apr 30, 2019 2:34 am

I'm getting ready to cool a fair size eq cabinet with Peltier. It gets hot in my garage in southern California. Lots of research.
Not not fully completed yet, but ...

1st - your layout for that SSR device is incorrect. The 3 lug side is relay supply and control. The two lug side is normal open **switch**.
Also, an SSR is not really a good choice for PWM.

Peltiers DO NOT like to be power cycled. The thermal cycling kills them fast.

One large quality name manufacturer says PWM no problem if freq is between 100 -> 200 Hz. Low freq beats them up. Higher and other issues with the junctions happen.

The Peltier you mention is the same as I am using.
They can be max about 15v. At that voltage they would be about max current, however any above about 65% of max current and the efficiency (because of internal heat across the about 2 ohms internal) doesn't make sense unless power consumed is not a factor. (This for cooling.)

That model Peltier is not designed to be a heater. The first time you try to heat anything STARTING with full current you will probably melt the solder in the chip.
You probably don't want to take that long for your chamber to heat up. You need to calculate how much heat you will need to maintain the temp you want for the size chamber you want and how fast you want it to reach that temp (ambient, total mass, object in the chamber, etc.)
I am using 7 chips to lower my cabinet about 15 degrees max - from 120F to below 105F. The cabinet is 16" x 18" x 20", all aluminum, insulated. Through the MOSFETs and PWM control - I can get only about 3.5+ amps @ 12 volts max per chip. (Yes - over 20 amp supply needed.) About right. In my case, it is maintenance of temp and not really trying to make a large temp swing fast.

Peltiers usually only make sense when size, noise, and mechanical reliability are the main factors.

david
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Arieljo
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Tue Apr 30, 2019 10:08 am

Thank you guys for all the reply! I'm still open to some ideas, so I will do a bit more research on the other ideas as well.
1st - your layout for that SSR device is incorrect. The 3 lug side is relay supply and control. The two lug side is normal open **switch**.
Isn't that what I actually show in the diagram?
3 lugs:
DC+ and - are for the external power supply and ground respectively. The channel is for the control
2 lugs:
the open switch which will open or close according to the signal given
Also, an SSR is not really a good choice for PWM.
Is there any reason why this is the case? What other alternatives do you have in mind that I can use? The thing is the research I did point out that SSR is used for many PWM projects. It seems to work reasonably well with the high frequency of the PWM signal.
That model Peltier is not designed to be a heater.
Would you mind giving me direction on how to select the proper type of Peltier for heating purposes? :) Thank you! Sorry for my many questions!

speedfixer
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Thu May 02, 2019 5:11 pm

Asking questions is how we learn. Answering them is how I find out I'm wrong, sometimes!


The three lug side supply is for control of the 'switch' on the two lug side. That is, there is no current between the three lug side and two lug side.
Power for a device on the two lug side must come from the two lug side in series. Just like a light switch.
Instead of a finger, the PI (or whatever) controls the 'switch' (two lug side) from the three lug side. Example:

https://www.fasttech.com/product/598650 ... tate-relay

I will not argue whether an SSR or MOSFET or simple transistor is better: that really is a function of your skill and intent. Or maybe what you have on hand.
And, I see some advice that Peltiers like to be PWMed at 1k -> 2k, not lower. Different manufacturer. No consensus, though.

Using a Peltier for heating is kind of exotic for a hobbyist. Yes, they can heat instead of cool.

These TEC1-12706 and others easily and cheaply available are rated to survive only to about 80C: easy to exceed if you don't have good control. Those designed for heating are much more expensive and typically rated to 200C. Your TARGET temp isn't that high, but your device can easily exceed the 80C if trying to pump out a lot of heat fast.

Reality is: getting something hot is cheap and easy. So many ways to do that. That particular TEC1-12706 just isn't going to give you enough heat quick enough unless your chamber is really small, not very massive, well-insulated, in an ambient close to where you want the target temperature. A light bulb would probably be better.

My best suggestion: look at the thermo tape solutions used by 3D printer beds as easy to build/design/control examples.

At place to start looking for information about Peltiers (though dated):

http://www.peltier-info.com/info.html

A quick look on Amazon does not have any Peltier HEATERS, just cooling modules. (Though there are many that put 'heater' in their description.)
As I say, the point about using these cooling chips to heat are that they will not survive high heat.
If you want to heat something gently and well controlled, perfect. But as the main heat source, almost anything else would be faster and cheaper.

david
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ptimlin
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Thu May 02, 2019 5:25 pm

Arieljo wrote:
Tue Apr 30, 2019 10:08 am
Would you mind giving me direction on how to select the proper type of Peltier for heating purposes? :) Thank you! Sorry for my many questions!
As others have mentioned, if you only need to heat and not cool, then a peltier is an overly complicated way to do it. Just use heating elements instead. There are a bunch of ways to do it from (as mentioned above) nichrome wires (what you typically see in a kitchen toaster, power resistors, flat adhesive sticker type heaters, or heck, you could even use incandescent light bulbs to create heat if having the inside of the chamber lit up isn't an issue. Then you only need to monitor the temperature to regulate the heating elements.

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Imperf3kt
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Thu May 02, 2019 10:36 pm

speedfixer wrote:
Thu May 02, 2019 5:11 pm
A quick look on Amazon does not have any Peltier HEATERS, just cooling modules. (Though there are many that put 'heater' in their description.)
Amazon and other online retailers of a similar nature are useless information resources.
Try a manufacturer instead. After finding a model you like, you can then search for it on Amazon etc, with a better description of what you are actually buying.

Here's a good example.
https://tecteg.com
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Gavinmc42
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Sat May 04, 2019 9:24 am

I found out the hard way there are two types of standard old tech Peltiers, ones with soldered junctions for temps up to about 80C, others can go to 150C. Those 80C ones don't last long when heated and cooled between 55 and 95C, 10,000 of times ;)

The heat goes both ways, just reverse the voltage, hot side cools down, cold side heats up.

Now we have the new types coming out that go much higher, like those TEG ones
Mainly for power harvesting for IoT micropower sensors etc.

An expensive way to heat when Ni-chrome wire works up to 1400C.
Heating wire can get hot spots which can burn out, so by having a low duty cycle those hottest spots cool down fastest.
This reduces the failures and spreads the heat from the hot part of the wire to the colder parts, useful for nichrome hot wire cutters etc.
The duty cycle needs to be low enough to allow the heat to travel from hot to cold.

Stainless steel fishing leader wire can be used too for hot wire cutters.
Is does not stretch as much when heated but has lower resistance and so needs more current.
Have not used it as a heater except for foam cutting.
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Arieljo
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Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Sat May 04, 2019 3:16 pm

Hi Gavinmc42,

Thanks for your suggestion, and the others too! I have briefly looked into using Nichrome wires, but we discussed that it would be a bit dangerous for us to implement, as this test chamber is going to be running for several months at a time, and the risk of it burning the test chamber does not seem to be worth it. I have actually made the first prototype with a Peltier plate in a small chamber box and it was able to reach about 40 degrees Celcius on the test chamber environment, but it broke down afterward.

The problem seems to be as you mentioned the type of Peltier that I use, as well as the size heat sink that I used. I put one heatsink with about the same size (heat sink size is a bit bigger) as the Peltier on the hot side with a fan attached, and small heat sink on the cold side without a fan. A bigger heat sink with fans for both of the faces could be used to avoid thermal runaway, at least that is what I think is happening. Another thing I could do if this still does not work is to find higher temperature Peltier as you mentioned.

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