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Topic: Peltier based aquarium cooler/heater? (Read 3 times) previous topic - next topic

Combo

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....

dc42

Yes, you can use a single Peltier device for both heating and cooling - all you need to do is reverse the current flow through it using an H-bridge.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Combo

#2
Jun 09, 2013, 11:59 pm Last Edit: Jun 10, 2013, 12:10 am by Combo Reason: 1
Awesome.  The peltier I'm looking at draws up to 10A.  Are there any h-bridge IC's that can handle that kind of draw?

Ok seems I have a lot to read about h-bridges.  If anyone can give me some pointers that would be great.  Thanks.

sonnyyu


dc42

There are lots of high current H-bridges advertised on eBay - search for VNH5019 or BTS7960. Or use this one http://www.pololu.com/catalog/product/1451 from Pololu.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Combo

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.

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)? 

dc42

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.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

dc42


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.


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.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

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?

dc42


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?
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

MisterResistor


Combo

#12
Jun 10, 2013, 09:09 pm Last Edit: Jun 10, 2013, 09:14 pm by Combo Reason: 1
The PSU says input 200-240v / 4.5A.

Output: +5V 22A max
+5V(FP) 2A max
+12VA 18A MAX

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).

afremont


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):
http://www.amazon.com/Tiella-Lighting-800AT600T-Remote-Transformer/dp/B007JY3U66
Experience, it's what you get when you were expecting something else.

Combo


They're available but cost a pretty penny.  Here is a 120V to 12V@600W(50A):
http://www.amazon.com/Tiella-Lighting-800AT600T-Remote-Transformer/dp/B007JY3U66


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).

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