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Fabrication of an aquarium cooler/heater

Hello,

I am new here so hello everyone and thanks in advance for the ones who will be able to help me.
I am currently trying to create a bloc to cool (and also heat) an aquarium of 200L (or 53 US galls if I’m not mistaken).
The idea I have is to use Peltier modules like the TEC1-12706 in interface to: on one side a waterblock in aluminium in which the aquarium water will circulate, and on the other side of the Peltier another waterblock for heat extraction through water.

With my input, I determine that I need 125W of cooling power and 160W of heating power, that is only to maintain the temperature, so to regulate it properly I will say that I need 350W for both (heating and cooling), that’s a round value and it seems quite reasonable (any feedback on this approach would be appreciated :nerd_face:).

To cool and heat that, I am willing to use a pack of 40 Peltier modules that I will power with 2.5V and 1A. According to the datasheet I found, it would allow each one of them to drain 9W of heat (the datasheet is here: http://www.everredtronics.com/files/TEC1-12706_40,40,3.8.pdf ).
Same here, that is the first time I try to use the performances curves of a Peltier module so maybe I am mistaken, once again, if I am totally wrong, please help me :grimacing:

To drive these Peltier, I intend to use some motors drivers. They should allow me to turn them on and off and also to invert the power to cool or to warm the aquarium water.
The model I found is the DRV8838 (link : Pololu - DRV8838 Single Brushed DC Motor Driver Carrier). But because of the numbers of Peltier I use, I will need 40 of them also. As they need 2 digital input from an Arduino each of them, that’s a total of 80 DIN that I need !
Note that I do not intend to use the PWM function to preserve the Peltier module, so a straight value of 5V will be supplied instead. I read that PWM is not very appreciated by the Peltier module so I will simply turn them on and off at the 100%, with 40 modules, I can do a proper regulation without PWM.

My question is:
To reduce the numbers of DIN used by these modules, can I group them and connect several of them on only 2 PIN from the Arduino ? Is it possible to connect them by pack of 4 to the Arduino ?

On the general idea, I’m a doing this right ?

Many thanks for your time and feedback !

Regards,

Koyotwe

Hello, Koyotwe.

I am not very familiar with the Peltier modules, so I do not have much feedback to offer regarding your overall approach. In case it helps, I did a quick Google search and found some blog posts about designing Peltier module systems which seem to have some useful information.

As far as controlling your drivers, it should be fine to parallel the logic connections from your drivers to your Arduino to reduce the number of I/O pins you need. However, keep in mind you will lose the ability to independently drive the modules (i.e. they will all behave the same way).

- Patrick

Hello Patrick,

Thanks for this feedback.
If the group of modules are working the same, that’s ok. Regarding their numbers, 40, or maybe even 48, it should still be manageable to control the power to regulate. That would be 10 or 12 groups to activate/deactivate.

A pack of 4 DRV8838 connected in parallel to the same 2 pins looks reasonable to you ? Or I should try to go for a pack of 3 ?

Thanks in advance !

  • Koyotwe

Connecting the logic inputs to four DRV8838 drivers to one pair of Arduino pins should be totally fine, and it is probably okay to connect more driver logic inputs in parallel. Though there will ultimately be some limit to how many parallel connections you can make before things stop working reliably. (It is just hard to predict exactly where that threshold will be.)

- Patrick