Peltier project suggestions/ideas/corrections

Thread Starter

arronar

Joined Jul 3, 2018
10
Hi out there.

I'm coming from web dev background and I'm kinda newbie on electronics world. Here I will try to explain my first "big" project and I would like to read your suggestions/ideas/corrections.

So I want to build something that might sound simple and maybe it is. I want a controller to control a Peltier element, a fan and a temperature sensor. Since I have a background on web dev, I thought to choose as my controller a raspberryPi-zero. Install linux and build a web interface that will cooperate with some python code to control the previously mentioned elements. The user will have access to the web app through a WiFi AP( access point) that RP zero will serve.

Through this web app, a user should be able to set some kind of configuration on what temperatures and for how long the Peltier should develop. For example one could configure the following:

1 - Ramp up to 65 C and stay @ 65 for 20 min
2 - Ramp up to 95 C stay @ 95 C for 10 min
3 - Ramp down to 20 C and stop

What Peltier is going to warm and cold is a small volume (around 100 to 500 microliters) of liquids.

So far through my search, I ended up to the following construction (see picture below) and the corresponding element list. As I told you I'm kinda a newbie and the following might be completely wrong. But please be patient with me :)

Here is how I imagine the whole schematics



and here is the list of the elements

#1 16V power supply
https://www.ebay.com/itm/16V-4-5A-A...03:m:myFY9yzLow0ou5zt0uEJ1Vg&var=521727474621
#2 5V 1A regulator
https://www.dimensionengineering.com/products/de-sw050
#3 Raspberry Pi / Zero W
#4 Raspberry Pi relay

https://www.adafruit.com/product/3352
#5 H-bridge
https://www.ebay.com/itm/USA-L298-L...071129?hash=item4400ac5919:g:ROUAAOSwBOtZAOAG
#6 Peltier
https://gr.rsdelivers.com/product/a...eltier-module-162w-28a-157v-30-x-30mm/4901430
#7 Temp Sensor
https://www.ebay.com/itm/5PCS-DALLA...187157?hash=item20fbe73555:g:niUAAOSwNSxVUwed
#8 Fan
https://www.ebay.com/itm/40mm-DC-5V...341761&hash=item2a711938b7:g:R3cAAOSwOyJX3zzx

As you can see I tried to use only one power supply for the whole project as also I added and an H-bridge to reverse the polarity of the Peltier.

Any idea and suggestion is welcome.
Thanks.
 

Raymond Genovese

Joined Mar 5, 2016
1,658
What is the specific size of the chamber that you are hoping to achieve the stated temperatures within - that is an important consideration.

EDIT: Yes, you did have the volume listed.
 
Last edited:

wayneh

Joined Sep 9, 2010
17,152
What Peltier is going to warm and cold is a small volume (around 100 to 500 microliters) of liquids.
It looks like you've done your research, kudos for that.

This small a volume presents some difficulties since it's not practical to immerse a probe directly into the small volume. That means you'll be measuring temperature indirectly, for instance of a thermal "block" with a well for the sample, or of a liquid bath in which the sample is immersed. The peltier will be heating and cooling that mass. Since any mass will have a heat capacity, the response to turning the peltier on or off will be lagged. In other words, you may need a PID control scheme to avoid overshoot.
 

Thread Starter

arronar

Joined Jul 3, 2018
10
Oh! You broke my heart. I read a little about PID and it confused me ☺. will it be connected between the temp sensor and the raspberry pi? As I understood it also needs to be programmed. Anyway. I ll take this into my consideration latter on. I'm thinking to built it first without the PID and see what is going to happen.

What do you think about the schematic and the elements I chose?
 

Thread Starter

arronar

Joined Jul 3, 2018
10
So As I understand this can combine the H-bridge and the relay I chose into one hat? But I see that neither of them can provide 15.7 V and 28Amps for the Peltier I mentioned above. Am I wrong?
 
Last edited:

bertus

Joined Apr 5, 2008
21,323
Hello,

In the given link I see that the peltier is 16.2 Watts and 2.8 Ampere.
Are you planning to use 10 peltier elements?

Bertus
 

Thread Starter

arronar

Joined Jul 3, 2018
10
Hahaha no. I show the link where there is no dot between 2 and 8 and I got the 28. Sorry. It was my fault.

So the second link you posted can replace only the relay hat I posted If I understood. Where does the Pi is going to connected? At S1/S2? Can you draw a simple schematic to understand it better?
 

Thread Starter

arronar

Joined Jul 3, 2018
10
So, this is going to replace my initial relay and will control the fan and the Peltier ( with the H-bridge )
Am I right?
 
I don't like your choice of a temperature sensor. This https://www.omega.com/pptst/TFD_RTD.html?pn=TFD might work.

it was more expensive to interface when I used one from -80 to 200 C. I was able to solder to it using Sn96 solder.
Generally, you use a 3 or 4 wire interface. The 3-wire interface assumes that the same voltage drop would occur in the other lead.

https://www.digikey.com/product-detail/en/adafruit-industries-llc/3328/1528-1804-ND/6562952

I've only used a really old Cambion controller that used a thermister. Peltiers are sooo slow in responding. I never used PWM either.

Also remember that a delta T of about 60 C is likely the max (check the datasheet) and you need a heat sink or source on the other side.
It really controls delta T, not T directly.

PID isn't hard.
 

Thread Starter

arronar

Joined Jul 3, 2018
10
What about the power supply I chose? Is it going to support the whole experiment or should I change it?
Also, what if I don't use any driver (like the syren) for the peltier but instead use only the H-bridge I posted initially? Is this going to work for on/off -ing the peltier?
 
Last edited:

wayneh

Joined Sep 9, 2010
17,152
What about the power supply I chose? Is it going to support the whole experiment or should I change it?
It looks adequate to me. The listing is a little confusing because it mentions a DC output but I really don't think there is a DC output - it's hard to tell. If the only output is indeed 16V AC at the rated current, it could be a problem because your peltier has a max voltage of 15.7 volts and draws less than the rated current. The voltage it sees could well be above 16V. If you use a full wave rectifier to make your own DC, that will drop the peak voltage about 1.4V but a 16V rms AC voltage works out to peaks up to 22.6V. A genuine 12V DC supply might be better and should be easy to find. That would give a better safety factor against over-powering your module. Designing around 12-14V would also allow you to potentially plug it into an automotive system.
Also, what if I don't use any driver (like the syren) for the peltier but instead use only the H-bridge I posted initially? Is this going to work for on/off -ing the peltier?
I'm not sure exactly what you're planning here. The H-bridge switches polarity, so is not on/off, it's positive or negative. If you want to turn on/off with either a thermostat or a PWM signal, that's different than changing the direction of heat flow. You may want both capabilities?
 

Thread Starter

arronar

Joined Jul 3, 2018
10
A genuine 12V DC supply might be better and should be easy to find.
But how it supposed to go from 12V to 15.7V for the Peltier

The H-bridge switches polarity, so is not on/off, it's positive or negative.
I thought that it can also work as on/off but I made a mistake. So The driver is needed for on/off while the H-bridge for the polarity change (cool/heat). This is done.

Sorry for being such noobish.
 
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