1
\$\begingroup\$

I was considering a project with a thermoelectric cooling module rated 60w and so obtained an AC power supply of output DC 12V and 4.16A. I'm very new to electronics so excuse me for the basic questions but would I have to place some sort of resistors in the circuit even though the power supply is below the 60w rating so it shouldn't exceed what the module can handle.

Also I needed to connect two 12v 0.2A fans to the circuit, but how would I wire these with the other module and what resistors would I need? Thank you in advance.

\$\endgroup\$
3
  • 1
    \$\begingroup\$ Is the output of your power supply AC or DC? The cooling module will almost certainly require DC, and will want to draw 60 watts (5 Amp) at 12 volts, so you should have a power supply capable of at least 6 Amp, to allow some power for the fans. \$\endgroup\$
    – Peter Bennett
    Apr 19, 2017 at 23:39
  • \$\begingroup\$ I believe it's a standard laptop SMPS, educated guess since I've seen a few with that exact current rating! Hamid: your title is wrong I think: your PSU has DC output, but your title implies AC. \$\endgroup\$
    – Jodes
    Apr 19, 2017 at 23:47
  • \$\begingroup\$ Sorry about the confusion, the title was incorrect, the output is DC, and thanks \$\endgroup\$
    – Hamid
    Apr 20, 2017 at 12:22

1 Answer 1

Reset to default
0
\$\begingroup\$

The fans can be connected directly to the 12v supply. This leaves 4.12-0.2-0.2= 3.72A for the cooler. So, to ensure the PSU isn't overloaded, the TEC + resistor needs to be no more than:

Resistance = Volts/ Current = 12 / 3.72 = 3.23 ohms

The cooler has a resistance of around 12*12/60 = 2.4 ohms. So the resistor needed in series with the TEC must be at least 3.23-2.4 = 0.83 ohms.

The minimum power rating for the resistor needs to be considered as well:

Say you choose a 1 ohm resistor. The total resistance of TEC + resistor = 1 + 2.4 = 3.4 ohms.

Therefore the current flowing through both is:

Current = voltage / resistance = 12 / 3.4 = 3.53 amps

So the minimum power the resistor must ba able to handle: Power = Current^2 / resistance = 3.53 x 3.53 / 1 = 12.5 watts

So in other words, you will need a particularly beefy 1 ohm resistor.

\$\endgroup\$
11
  • \$\begingroup\$ Hi Jodes, thanks for your reply. Is it essential to have a resistor in the circuit even though 1ohm sounds like a very small amount. Also would it be worth powering the fans through other means to save the wattage for the TEC considering my current power supply isn't reaching the TEC's potential of 60W as it is? \$\endgroup\$
    – Hamid
    Apr 20, 2017 at 18:33
  • \$\begingroup\$ Yes it's a low resistor, because of the high power of the cooler. Your PSU is only 50W so removing fans wouldn't help - you'd still need a resistor, although smaller and less beefy. You could run it right off a 9v PSU though, it would draw 3.75A. (incidentally, TEC'S are actually more efficient at lower powers - but move less heat). So I think you'll want to find a higher output 12V PSU \$\endgroup\$
    – Jodes
    Apr 20, 2017 at 23:47
  • \$\begingroup\$ Sorry - I didn't answer 1 question. You might be able to get away without any resistor at all - but depending on the design of the PSU, could shorten it's life - just a tiny bit, or drastically. It's hard to say. At the very least, make sure the PSU has excellent ventilation around it - this may be enough. But, all that said, you're risking fire and/or melting and/or electrocution. These things have 2+ levels of safety, and you'd be impacting that. Not recommended \$\endgroup\$
    – Jodes
    Apr 21, 2017 at 0:17
  • \$\begingroup\$ It reminds me of what a doctor told me recently... if you walk across a quiet street blindfolded, usually you'll be OK, but eventually you'll get run over. \$\endgroup\$
    – Jodes
    Apr 21, 2017 at 0:24
  • \$\begingroup\$ Your analogy with the blindfold helped put things into perspective thank you, and for all your help. My idea of removing the fans wasn't to remove the need for a resistor, but more for having all 50W go to the TEC rather than 5W going to the fan, but I don't know how much it would impact the performance. Thanks again. \$\endgroup\$
    – Hamid
    Apr 21, 2017 at 14:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.