I'm interested in creating a arduino-controlled temperature regulator for a small aquarium.
So far the best (and cost-efficient) approach I have seen involves using a peltier. The cool side connects to a aluminium casing through which water is pumped, and the hot side is connected to a CPU heatsink + fan.
aluminium casing:
setup:
That takes care of the cooling side. For heating, I was thinking of using another peltier with the hot side mounted to the casing in much the same way. The cool side can just be left exposed in this case.
However this would require a separate pump and a separate peltier.
I am wondering if anyone here can think of a way to use a single peltier and a single pump to achieve both heating and cooling of water for an aquarium? Answers on a postcard....
There are lots of high current H-bridges advertised on eBay - search for VNH5019 or BTS7960. Or use this one Pololu - VNH5019 Motor Driver Carrier from Pololu.
Great, thanks again. I've looked at these h-bridge chips available on ebay and BTS7960 looks the cheapest (£12 from China). It's a little more than I was expecting to pay (about the cost of 4 peltiers!) -- before I order, is there a cheaper DIY approach or should I just take the plunge and get this?
Also, will I need an opto-coupler or similar to protect the arduino? Or is that taken care of? Thanks.
With the BTS7960 rated at 43A I guess up to 4 peltiers (10A each) can be connected.
I was looking at power supply units for such a project and it seems a DIY AC->DC will be needed. I had no problem finding bridge rectifiers rated for 50A, but where does one find 50A transformers (240v AC to 12v DC)?
The cheap DIY approach would be to use 1 or 2 relays. Preferably a DPDT relay to reverse the polarity of the drive to the H-bridge and a single mosfet to turn the power on/off (and do PWM if you want to). That way, you can use the mosfet to turn the current off before switching the relay over, to avoid arcing. But if you don't want to PWM the Peltier, then two SPST automotive relays with >10A DC contact ratings would be sufficient. You'd need to use transistors to drive the relays.
You don't need optical isolation if you use a common ground between the Arduino power supply and the Peltier power supply.
Combo:
With the BTS7960 rated at 43A I guess up to 4 peltiers (10A each) can be connected.
I wouldn't push units purchased via eBay too close to their maximum ratings. OTOH the BTS7960 drivers I found on eBay are all dual units, so you could run e.g. 2 or perhaps 3 Peltiers from each channel.
Combo:
I was looking at power supply units for such a project and it seems a DIY AC->DC will be needed. I had no problem finding bridge rectifiers rated for 50A, but where does one find 50A transformers (240v AC to 12v DC)?
Don't do that, buy a switch mode power supply instead. Search your local distributor for a suitable one. If you intend to use more than one Peltier, consider connecting 2 identical ones in series, because 24V 10A is easier to manage than 12V 20A.
Thanks this really helps. I have an old PC power supply unit which can provide 450w via 12v and 5v rails. Would that be a suitable? Are PC PSU's switch mode power supplies?
Combo:
Thanks this really helps. I have an old PC power supply unit which can provide 450w via 12v and 5v rails. Would that be a suitable? Are PC PSU's switch mode power supplies?
Yes they are. Check the current ratings of the individual outputs, which are usually written on the unit. You will probably find that the +12V output can't supply as much as 10A.
How much heating/cooling power do you think you really need?
Combined power on +3.3v and +5v rails not exceed 150w
Combined power on +12va and +12vb rails not exceed 360w.
Max continuous dc output power shall not exceed 375w.
Ok so it's 375w. Does this seem ok? It would be convenient to power both the arduino and peltier(s) from a single power source...
To start with I'd like to power one peltier but I'm thinking this could probably power two of them? I'd be happy to use more to get a faster temperature ramp (they're cheap).
Combo:
With the BTS7960 rated at 43A I guess up to 4 peltiers (10A each) can be connected.
I was looking at power supply units for such a project and it seems a DIY AC->DC will be needed. I had no problem finding bridge rectifiers rated for 50A, but where does one find 50A transformers (240v AC to 12v DC)?
They're available but cost a pretty penny. Here is a 120V to 12V@600W(50A):
Ouch, yes. Salvaging an old PSU so much more economical (assuming I can get it to switch on, been trying for a couple of hours now jumping various wires, etc).
Ouch, yes. Salvaging an old PSU so much more economical (assuming I can get it to switch on, been trying for a couple of hours now jumping various wires, etc).
Connect the green wire to one of the black wires, and it will turn on (assuming it's an standard ATX)
In some cases the PC power-supplies need a minimum load on the 5V output, but it's not often that it's an issue.
Thanks for the help. I was wondering if these BTS7960B (or similar components capable of reversing a motor) will supply the peltier with PWM or with pure DC? I've read that PWM for peltier is not ideal.
Combo:
Thanks for the help. I was wondering if these BTS7960B (or similar components capable of reversing a motor) will supply the peltier with PWM or with pure DC? I've read that PWM for peltier is not ideal.
They can supply the unit with a fixed DC voltage in either direction, or they can be used to PWM the element. See item 41 at http://www.tellurex.com/technology/peltier-faq.php regarding PWM and Peltier elements. It's true that if you want to use PWM to run the Peltier element at less than full power, then this is not as efficient as running it off steady DC at a lower voltage, unless you use a series inductor to smooth out the PWM.
Hello,
I was looking for the same project as I also need to cool a small size (25 l) aquarium to a constant 26-27 deg. c. and I would like to use a Peltier based solution + temperature ontrol loop based on Arduino.
Please let me know in case you completed the project.
Ouch, yes. Salvaging an old PSU so much more economical (assuming I can get it to switch on, been trying for a couple of hours now jumping various wires, etc).
Momentary contact the green output wire to any black (ground) output wire.
